U.S. patent application number 13/511196 was filed with the patent office on 2012-11-08 for thermal energy storage.
Invention is credited to David H. Bank, Kalyan Sehanobish, Andrey N. Soukhojak.
Application Number | 20120279679 13/511196 |
Document ID | / |
Family ID | 44320106 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120279679 |
Kind Code |
A1 |
Soukhojak; Andrey N. ; et
al. |
November 8, 2012 |
THERMAL ENERGY STORAGE
Abstract
The invention is directed at articles and devices for thermal
energy storage, and for process of storing energy using these
articles and devices. The articles comprise a capsular structure 10
having one or more sealed spaces 14, wherein the sealed spaces
encapsulate one or more thermal energy storage materials 26:
wherein the capsular structure has one or more fluid passages 16
which are sufficiently large to allow a heat transfer fluid to flow
through the one or more fluid passages; and when a heat transfer
fluid contacts the capsular structure 10 the thermal energy storage
material 26 is Isolated from the heal transfer fluid. The devices
include two or more articles arranged so that a fluid, such as a
heat transfer fluid, may flow through the fluid passage 16 of an
article before or after flowing through a space between two of the
articles.
Inventors: |
Soukhojak; Andrey N.;
(Midland, MI) ; Bank; David H.; (Midland, MI)
; Sehanobish; Kalyan; (Rochester, MI) |
Family ID: |
44320106 |
Appl. No.: |
13/511196 |
Filed: |
January 27, 2011 |
PCT Filed: |
January 27, 2011 |
PCT NO: |
PCT/US11/22662 |
371 Date: |
May 22, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61299565 |
Jan 29, 2010 |
|
|
|
Current U.S.
Class: |
165/10 |
Current CPC
Class: |
B60K 2001/008 20130101;
B60H 1/00492 20130101; F28D 2020/0008 20130101; F28D 20/026
20130101; Y02E 60/14 20130101; B60K 11/02 20130101; F28D 20/02
20130101; F28D 2020/0021 20130101; Y02E 60/145 20130101 |
Class at
Publication: |
165/10 |
International
Class: |
F28D 17/00 20060101
F28D017/00 |
Claims
1. An article comprising a capsular structure having one or more
sealed spaces wherein the sealed spaces encapsulate one or more
thermal energy storage materials; wherein the capsular structure
has one or more fluid passages which are sufficiently large to
allow a heat transfer fluid to flow through the one or more fluid
passages, and when a heat transfer fluid contacts the capsular
structure the thermal energy storage material is isolated from the
heat transfer fluid.
2. The article of claim 1, wherein the capsular structure includes
two sheets capable of encapsulating the thermal energy storage
material, the sheets having an outer periphery and each sheet being
sealingly attached at least along the outer periphery to each other
and/or to one or more additional sub-structures and forming the one
or more sealed spaces therebetween containing the thermal energy
storage materials.
3. The article of claim 2, wherein the sheets are sealingly
attached to each other along the outer periphery and along the
periphery of its opening.
4. The article of claim 1, wherein the capsular structure has a top
surface and an outer periphery; wherein the top surface includes
two or more grooves each extending from the fluid passage to the
outer periphery and each providing fluid connection between the
passage and the outer periphery.
5. The article of claim 1, wherein the capsular structure has a
first outer surface and a second outer surface, the capsular
structure has a thickness defined by the average separation between
the first outer surface and the second outer surface; wherein the
capsular structure is sufficiently thin so that heat can be quickly
transferred out of the one or more sealed spaces; the thermal
energy storage material is a phase change material having a solid
to liquid transition temperature greater than about 30.degree. C.
and less than about 350.degree. C.; and the one or more sealed
spaces have a total interior volume, at a temperature of about
25.degree. C., and the sealed spaces contains a total volume of
thermal energy storage material, at a temperature of about
25.degree. C., wherein the ratio of the total volume of thermal
energy storage material to the total interior volume is at least
about 0.50; so that the article can store a large amount of thermal
energy.
6. The article of claim 5, wherein the fluid passage is near the
geometric center of the first outer surface.
7. The article of claim 1, wherein the article includes 3 or more
sealed spaces.
8. The article of claim 1, wherein the outer periphery of the
article includes one or more indents, so that when a stack of the
articles are placed in a hollow cylinder a heat transfer fluid can
flow through the space formed by the indents; the thickness of the
article is less than about 1 cm, the article has a dimension
greater than about 5 cm; and a surface of the article includes one
or more protrusions so that when a plurality of the articles are
stacked there will be a space between the articles for the flow of
a heat transfer fluid.
9-26. (canceled)
Description
CLAIM OF BENEFIT OF FILING DATE
[0001] The present application claims the benefit of the filing
date of U.S. Provisional Application Ser. No. 61/299,565, filed
Jan. 29, 2010, which is hereby incorporated by reference for al
purposes.
FIELD OF THE INVENTION
[0002] The present invention relates to thermal energy storage
using a thermal energy storage material and to the packaging of the
thermal energy storage material to allow for both efficient heat
storage and efficient heat transfer.
BACKGROUND OF THE INVENTION
[0003] Industry in general has been actively seeking a novel
approach to capture and store waste heat efficiently such that it
can be utilized at a more opportune time. Further, the desire to
achieve energy storage in a compact space demands the development
of novel materials that are capable of storing high energy content
per unit weight and unit volume. Areas of potential application of
breakthrough technology include transportation, solar energy,
industrial manufacturing processes as well as municipal and/or
commercial building heating.
[0004] Regarding the transportation industry, it is well known that
internal combustion engines operate inefficiently. Sources of this
inefficiency include heat lost via exhaust, cooling, radiant heat
and mechanical losses from the system. It is estimated that more
than 30% of the fuel energy supplied to an internal combustion
engine (internal combustion engine) is lost to the environment via
engine exhaust.
[0005] It is well known that during a "cold start" internal
combustion engines operate at substantially lower efficiency,
generate more emissions, or both, because combustion is occurring
at a non-optimum temperature and the internal combustion engine
needs to perform extra work against friction due to high viscosity
of cold lubricant. This problem is even more important for hybrid
electric vehicles in which the internal combustion engine operates
intermittently thereby prolonging the cold start conditions, and/or
causing a plurality of occurrences of cold start conditions during
a single period of operating the vehicle. To help solve this
problem, original equipment manufacturers are looking for a
solution capable of efficient storage and release of waste heat.
The basic idea is to recover and store waste heat during normal
vehicle operation followed by controlled release of this heat at a
later time thereby reducing or minimizing the duration and
frequency of the cold start condition and ultimately improving
internal combustion engine efficiency, reducing emissions, or
both.
[0006] To be a practical solution, the energy density and the
thermal power density requirements for a thermal energy storage
system are extremely high. Applicants have previously filed 1) U.S.
patent application Ser. No. 12/389,416 entitled "Thermal Energy
Storage Materials" and filed on Feb. 20, 2009; 2) U.S. patent
application Ser. No. 12/389,598 entitled "Heat Storage Devices" and
filed on Feb. 20, 2009, and 3) PCT Application No. PCT/US09/67823
entitled "Heat Transfer Systems Utilizing Thermal Energy Storage
Materials" and filed on Dec. 14, 2009. These previous applications
are herein incorporated by reference in their entirety.
[0007] There are known heat storage devices and exhaust heat
recovery devices in the prior art. However, in order to provide a
long term (e.g., greater than about 6 hour) heat storage
capability, they generally occupy a large volume, require pumping
of a large volume of heat transfer fluid, require a relatively
large pump to overcome the hydraulic resistance, and the like.
Therefore, there is a need for a heat storage system which can
offer an unprecedented combination of high energy density, high
power density, long heat retention time, light weight, low
hydraulic resistance for heat transfer fluid flow, of any
combination thereof.
SUMMARY OF THE INVENTION
[0008] One aspect of the invention is an article comprising a
capsular structure having one or more sealed spaces, wherein the
sealed spaces encapsulate one or more thermal energy storage
materials; wherein the capsular structure has one or more fluid
passages which are sufficiently large to allow a heat transfer
fluid to flow through the one or more fluid passages; and when a
heat transfer fluid contacts the capsular structure the thermal
energy storage material is isolated from the heat transfer
fluid.
[0009] Another aspect of the invention is a device including a
container and a plurality of the articles having a fluid passage
and containing the thermal energy storage material, such as a
plurality of articles described herein, wherein the plurality of
articles are stacked so that the fluid passages are aligned
axially.
[0010] A process related aspect of the invention is a method for
removing heat from a heat storage device, such as a device
described herein wherein the process includes a step of flowing a
heat transfer fluid through the device. Preferably, the process
includes flowing a heat transfer fluid having an initial
temperature through an inlet of the device; flowing the heat
transfer fluid through an axial flow path so the heat transfer
fluid can be divided into e plurality of radial flow paths; flowing
the heat transfer fluid through a radial flow path so that it can
remove heat from the thermal energy storage material, wherein the
thermal energy storage material has a temperature greater than the
initial temperature of the heat transfer fluid; flowing the heat
transfer fluid through a different axial flow path so that a
plurality of radial flow paths can recombine; flowing the heat
transfer fluid having an exit temperature through an outlet of the
device; wherein the heat transfer fluid exit temperature is greater
than the initial temperature of the heat transfer fluid.
[0011] Another process related aspect of the invention is a method
for preparing or assembling an article including cutting an opening
in a base sheet, embossing a base sheet so that it has one or more
troughs, filling one or more troughs with a thermal energy storage
material, cutting an opening in a cover sheet, and sealingly
attaching the cover sheet at least along an outer periphery and an
opening periphery to the base sheet so that an article having one
or more sealed spaces containing the thermal energy storage
material is formed.
[0012] Yet another aspect of the invention is a system including a
heat storage device, such as a heat storage device described
herein, and a heat transfer fluid, wherein the heat transfer fluid
is in thermal communication with the thermal energy storage
material in a sealed space (e.g., a sealed space of an article in
the heat storage device).
[0013] The articles, devices, systems and processes of the present
invention advantageously are capable of containing a high
concentration of thermal energy storage material so that a large
amount of thermal energy can be stored (e.g., having a high energy
density), are capable of having a high surface area between the
heat transfer fluid and the article containing the thermal energy
storage material so that heat can be quickly transferred into
and/or out of the thermal energy storage material (e.g., having a
high power density, preferably greater than about 8 kW/L), are
capable of having multiple flow paths that have similar or equal
hydraulic resistance so that heat is uniformly transferred to
and/or transferred from different regions; have a rotational
symmetry so that they may be arranged easily; have a structure that
is strong and durable; have a high heat storage density so that
they can be used in applications requiring compact designs, light
weight components, or both; have lower hydraulic resistance for a
heat transfer fluid flow (for example, a pressure drop of less than
about 1.5 kPa at a heat transfer fluid pumping rate of about 10
liters/min) so that the pumping requirements for the heat transfer
fluid are reduced, or an combination thereof.
BRIEF DESCRIPTION OF THE FIGURES
[0014] The present invention is further described in the detailed
description which follows, in reference to the noted plurality of
drawings by way of non-limiting examples of embodiments of the
present invention, in which like reference numerals represent
similar parts throughout the several views of the drawings, and
wherein:
[0015] FIG. 1A is a drawing of an illustrative article having one
more sealed compartments and a fluid passage.
[0016] FIG. 1B is a drawing of an illustrative article having a
plurality of segments each containing one or more sealed
compartments. The segments are arranged so that the article has a
fluid passage.
[0017] FIG. 2A is a drawing of an illustrative article having a
sealed compartment and a fluid passage.
[0018] FIG. 2B is a drawing of an illustrative cover sheet having a
fluid passage that may be employed in the article.
[0019] FIG. 2C is a cross-section of an illustrative article, such
as the article illustrated in FIG. 2A.
[0020] FIG. 2D is cross-section of an illustrative embossed base
sheet that may be employed in an article.
[0021] FIG. 3A is a side view of two illustrative adjacent segments
that may be employed in an article. The segments may have an edge
that generally mate.
[0022] FIG. 3B is a side view of two illustrative adjacent segments
that may be employed in an article. The segments may have an edge
that generally mate.
[0023] FIG. 4 is a side view of adjacent segments that mate along
their edges when one of the segments is shifted so that the
adjacent segments bottom surfaces of the segments are on different
parallel planes.
[0024] FIG. 5A is a drawing of an illustrative embossed base sheet
having a plurality of troughs that may be used in an article having
a plurality of sealed compartments containing thermal energy
storage material.
[0025] FIG. 5B is a drawing of an illustrative portion of the
embossed sheet of FIG. 5.
[0026] FIG. 5C shows an illustrative stack of articles having
corresponding fluid passages.
[0027] FIG. 6A is a drawing of an illustrative article having one
or more surfaces containing a plurality of grooves extending from
the opening to the outer periphery.
[0028] FIG. 6B is a drawing showing the interface between a bottom
surface of a first article and the top surface of a second article
when the two surfaces each have a plurality of curved grooves.
[0029] FIG. 6C is a drawing of two segments of an illustrative
article.
[0030] FIG. 6D is a side view of a stack of the segments of FIG.
6.
[0031] FIG. 7 is a top view drawing of an illustrative article
having a top surface that is non-circular and/or has an opening
that is non-circular.
[0032] FIG. 8 shows a cross-section of an illustrative heat storage
device including a stack of articles in a container.
[0033] FIG. 9 is another cross-section of an illustrative heat
storage device including a stack of articles in a container.
[0034] FIG. 10 is a schematic drawing showing illustrative features
of a thermal energy storage system.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0035] In the following detailed description, the specific
embodiments of the present invention are described in connection
with its preferred embodiments. However, to the extent that the
following description is specific to a particular embodiment or a
particular use of the present techniques, it is intended to be
illustrative only and merely provides a concise description of the
exemplary embodiments. Accordingly, the invention is not limited to
the specific embodiments described below, but rather; the invention
includes all alternatives, modifications, and equivalents falling
within the true scope of the appended claims.
[0036] As will be seen from the teachings herein, the present
invention provides unique articles, devices, systems, and process
for storing thermal energy and/or transferring stored thermal
energy to a fluid. For example, the articles and devices for
storing thermal energy of the present invention are more efficient
at storing thermal energy, allow for transferring thermal energy
more uniformly, allow for transferring thermal energy with a
smaller pressure drop of the heat transfer fluid, or any
combination thereof.
[0037] Various aspects of the invention are predicated on an
article including a capsular structure having one or more sealed
spaces (i.e., capsules) and one or more thermal energy storage
materials that are encapsulated in the one or more sealed spaces of
the capsular structure so that the thermal energy storage material
cannot flow out of the capsular structure or otherwise be removed
from the capsular structure. The capsular structure has a novel
geometry that includes one or more fluid passages that are
sufficiently large so that the capsular structure is capable of
allowing a fluid (e.g., a heat transfer fluid) to flow through the
fluid passage. The thermal energy storage materials are
sufficiently encapsulated in one or more of the sealed spaces so
that when the heat transfer fluid contacts the capsular structure,
the thermal energy storage material is isolated from the fluid.
Other aspects of the invention include novel arrangements including
a plurality of the articles, novel devices including one or more of
the articles, novel processes for manufacturing the article, and
novel processes for using one or more of the articles. By employing
the novel article, it is possible to assemble devices capable of
storing a large quantity of thermal energy, capable of rapidly
transferring thermal energy into or out of the thermal energy
storage material, capable of being compact, capable of being light
weight, capable of having a low pressure drop of a heat transfer
fluid, or any combination thereof.
Capsular Structure
[0038] The capsular structure generally has a dimension in one
direction (i.e., a thickness) that is smaller than the dimensions
in the other directions. The capsular structure has one or more
openings (i.e., fluid passages), preferably in the smaller
direction of the capsular structure.
Opening/Fluid Passage
[0039] The capsular structure has one or more fluid passages.
Preferably the capsular structure has one fluid passage. The one or
more fluid passages may allow a fluid, such as a heat transfer
fluid to flow through the article without contacting the thermal
energy storage material. The fluid passage (e.g., the
cross-sectional area of the fluid passage) preferably is
sufficiently large so that the heat transfer fluid can flow through
it with minimal loss in pressure. The fluid passage preferably is
near or includes the geometric center of the capsular structure. As
described hereinafter, an fluid passage that is near or includes
the geometric center of the capsule may allow the article to be
employed in a device that is characterized generally as a
Tichelmann system.
[0040] The fluid passage may be of any cross-sectional shape that
facilitates passage of fluid through the capsular structure.
Without limitation, the fluid passage may have an axial direction
and a cross-section of the fluid passage with a plane normal to the
axial direction may be generally circular, generally polygonal, or
generally oval shaped. Preferably, the fluid passage has a
generally cylindrical shape. For example the fluid passage may have
an axial direction and the cross-section of the fluid passage with
a plane normal to the axial direction may be generally
circular.
[0041] The length of the fluid passage may be any length that
allows for efficient heat transfer and preferably is the thickness
of the capsular structure. The size of the fluid passage is a
measure of the diameter of the fluid passage (e.g., for an fluid
passage having a generally cylindrical shape) or twice the shortest
distance from the center of the opening to a surface of the
capsular structure. The size of the fluid passage is preferably
greater than about 0.1 mm, more preferably greater than about 0.5
mm, even more preferably greater than about 1 mm, and most
preferably greater than about 2 mm so that a fluid can flow through
the opening. The size of the fluid passage may be sufficiently
small so that the fluid passage does not occupy a large volume of
space (e.g., that could otherwise be occupied by a thermal energy
storage material). Preferably the fluid passage has a size less
than about 20 mm. For example, the fluid passage may a generally
circular cross-section with a radius that is preferably less than
about 10 mm.
[0042] It will be appreciated that a capsular structure having one
or more sealed spaces and a fluid passage may be formed from a
single component having a fluid passage such as shown by reference
number 16, such as shown in the article 10 illustrated in FIG. 1A,
or by assembling and/or arranging a plurality of segments 2 which
together provide generally the same shape, such as the capsular
structure 10' illustrated in FIG. 1B. As such, a layer of capsules,
including one or more sealed spaces, may be provided by a single
segment or by a plurality of segments 2. A capsular structure may
advantageously be provided by a plurality of segments so that the
stresses in the structure (hoop stresses, or otherwise) are reduced
or eliminated. A capsular structure may advantageously be provided
by a plurality of segments so that a failure (e.g., a leak or
puncture) of a sealed space results in a reduced loss of thermal
energy storage material. If the capsular structure is formed by a
plurality of segments, the number of segments may be two or more
three or more, about four or more, or about six or more. The number
of segments preferably is about 100 or less, more preferably about
30 or less, and most preferably about 10 or less. It will be
appreciated that more than 100 segments may be employed when the
capsular structure is large (e.g., greater than about 500 mm in one
or more directions), or when the thermal energy storage material in
the capsular structure is desired to be compartmentalized into 100
or more sealed spaces. A segment of a capsular structure, such as
the segment 2 of a capsular structure 10 illustrated in FIG. 1B,
may have a top surface and a bottom surface that forms a portion of
the top surface 4 and bottom surface 6 of the capsular structure. A
segment of a capsular structure, such as the segment 2 of a
capsular structure 10 illustrated in FIG. 1B, may have an edge
surface that becomes a portion of the outer edge surface 8 of the
capsular structure. A segment of a capsular structure, such as the
segment 2 of a capsular structure 10 illustrated in FIG. 1B, may
have an edge surface that forms a portion of the opening of the
capsular structure. A segment of a capsular structure, such as a
segment 2 of a capsular structure 10 illustrated in FIG. 1B, may
have one or more edges (e.g., two edges) that each mate with an
edge of an adjacent segment.
[0043] Two or more segments of a capsular structure (e.g., two
segments that share a common edge), or even all of the segments,
may include the same thermal energy storage material or may include
two or more different thermal energy storage materials. Preferably
the segments in a capsular structure include a plurality of
segments having the same thermal energy storage material. More
preferably, all of the segments in the capsular structure have the
same thermal energy storage material.
[0044] A pair of adjacent segments may have the same shape, volume,
or both, or may have different shape, volume, or both. Preferably
the capsular structure includes adjacent segments having generally
the same volume. Preferably, the capsular structure includes
adjacent segments generally having the same thickness. More
preferably, the capsular structure includes adjacent segments
generally having the same shape and size. Most preferably, the
capsular structure includes, consists essentially of, or consists
of adjacent segments having the same shape, size, and volume.
[0045] When a capsular structure includes two or more segments, it
may be necessary to arrange the segments so that fluid flow between
the edges of adjacent segments is reduced, minimized, or even
eliminated. It will be appreciated that if adjacent segments are
separated by a gap, a fluid (e.g., a heat transfer fluid) may flow
radially between the opening and the exterior periphery of the
capsular structure and thus decrease the heat transfer along the
top and bottom surfaces of the capsular structure. In various
embodiments of the invention, adjacent segments in a capsular
structure may be shaped and/or arranged with mating edges so that
the flow of heat transfer fluid between the adjacent segments is
reduced, minimized, or eliminated. Preferably the adjacent segments
have edges that generally mate.
[0046] The shape of the capsular structure and/or article may be
defined by the packaging space and may be oddly shaped. The article
may include a cover sheet (i.e., a cover sheet) having a top
surface and a generally opposing base sheet having a bottom
surface. The cover sheet (e.g., the top surface of the cover
sheet), the base sheet (e.g., the bottom surface of the base
sheet), or both, may have a portion that is (or may be) generally
flat (e.g., have a generally planar surface), generally arcuate, or
any combination thereof. Preferably the base sheet and/or the
bottom surface of the base sheet includes a generally arcuate
portion or is generally arcuate, and the top surface of the article
is generally planar (e.g., the cover sheet is generally flat).
[0047] The cover sheet and the base sheet both include one or more
openings. The cover sheet and the base sheet are arranged so that
at least one opening of the cover sheet overlaps at least one
opening of the base sheet. As such, the cover sheet and the base
sheet have one or more corresponding openings. The cover sheet has
an outer periphery in the regions furthest from the center of the
cover sheet. The cover sheet has one or more opening peripheries in
the region of the cover sheet near an opening (preferably near the
center) of the cover sheet. The base sheet has an outer periphery
in a region far from the center of the base sheet and an opening
periphery near the opening (preferably near the center) of the base
sheet. Each of the cover sheet and the base sheet may be sealingly
attached to each other or to one or more other optional
sub-structures (such as an outer ring) along the respective outer
peripheries of the sheets, for forming one or more sealed spaces
therebetween. Each of the cover sheet and the base sheet may be
sealingly attached to each other or to one or more other optional
sub-structures (such as an inner ring) along the respective opening
peripheries of the sheets, for forming one or more sealed spaces
therebetween. Preferably the cover sheet and the base sheet are
sealingly attached to each other along their respective outer
peripheries, along at least one of their respective corresponding
opening peripheries, or both. Most preferably the cover sheet and
the base sheet are sealingly attached to each other both along
their respective outer peripheries and along at least one of their
respective corresponding opening peripheries. It will be
appreciated that the cover sheet and the base sheet may also be
sealingly attached to each other or to one or more other optional
sub-structures along one or more additional regions (other than
their peripheries) so that a plurality of sealed spaces are
formed.
[0048] The capsular structure may optionally include one or more
sub-structures that when sealingly attached to a base sheet and a
cover sheet forms one or more sealed spaces. The one or more
sub-structure may be employed to form one or more walls that
separates one or more sealed spaces from a heat transfer fluid. For
example, the capsular structure may include an outer ring that
provides a wall to isolate one or more sealed spaces from a heat
transfer fluid along one or more side surfaces of the capsular
structure. As another example, the capsular structure may include
an inner ring that provides a wall to isolate one or more sealed
spaces along at least a portion of the fluid passage through the
capsular structure. If employed, the inner ring may have any
geometry capable of being sealingly attached to an opening
periphery of the base sheet, an opening periphery of the cover
sheet and preferably both. Preferably the inner cross-section of
the inner ring has a similar size and shape as the opening of the
cover sheet, the base sheet, or both. If employed, the outer ring
may have any geometry that can be sealingly attached to the outer
periphery of the base sheet, the outer periphery of the cover sheet
and preferably both. Preferably the outer cross-section of the ring
has a similar size and shape as the outer circumference of the
cover sheet, the base sheet, or both. The one or more
sub-structures may be employed to form one or more walls that
separates or provides a fluid isolation between two or more sealed
spaces. For example, the one or more sub-structures may include one
or more generally radial walls, one or more generally cylindrical
walls, and the like. As another example, the one or more
sub-structures may include a honeycomb or other open cell
structure, such as described in paragraph 0084 of U.S. Patent
Application Publication No. 2009-0250189 by Bank et al., published
on Oct. 8, 2009, incorporated herein by reference. The wall
thickness of the one or more sub-structures (e.g., inner ring,
outer ring, or open cell structure) should be sufficiently thick to
contain the thermal energy storage material, to support the
structure, or both. The wall thickness of the one or more
sub-structures preferably is greater than about 1 .mu.m, and more
preferably greater than about 10 .mu.m. The wall thickness of the
one or more sub-structures (e.g., inner ring, outer ring, or open
cell structure) should be sufficiently thin so that a large portion
of the volume and/or weight of the article can be the thermal
energy storage material The wall thickness of the one or more
sub-structures preferably is less than about 5 mm, more preferably
less than about 1 mm, and most preferably less than about 0.2
mm.
[0049] The thickness of the capsular structure is defined by the
average separation between the top surface of the article (e.g.,
the top surface of the cover sheet) and the bottom surface of the
article (e.g., the bottom surface of the base sheet). The article
may have a geometry so that heat can be rapidly provided from a
fluid to thermal energy storage material and/or rapidly removed
from the thermal energy storage material to a fluid. For example,
the article may be relatively thin (e.g., compared with the length
or diameter of the article). Preferably, the thickness of the
article is less than about 80 mm, more preferably less than about
20 mm, even more preferably less than about 10 mm and most
preferably less than about 5 mm. The thickness of the article
preferably is greater than about 0.5 mm, more preferably greater
than about 1 mm.
[0050] The longest dimension of the article (e.g., the length or
diameter of the article) is typically much greater than the
thickness of the article so that the article can both have a large
volume (e.g., for containing a large volume of thermal energy
storage material), and a large surface area (e.g., for rapid
transfer of thermal energy). The longest dimension of the article
preferably is greater than about 30, more preferably greater than
about 50 mm and most preferably greater than about 100 mm. The
longest dimension is defined by the use, and can be any length that
meets the need for heat storage, heat transfer, or both, a
particular use. The longest dimension of the article typically is
less than about 2 m (i.e., 2,000 mm), however articles having
longest dimension greater than about 2 m may also be employed.
[0051] The article may have one or more side surfaces. For example
the article may have one or more side surfaces that are nonplanar.
The article may have a single side surface that is generally
arcuate, generally nonplanar, generally continuous, or any
combination thereof. Preferably the one or more side surfaces are
generally equidistant from a center of the article so that the
article can be placed in a container having a generally cylindrical
cavity with a cavity diameter that is only slightly larger than the
average diameter of the article. When the ratio of the cavity
diameter to the average diameter of the article is low, a large
amount of the cavity is occupied by the article. For example, the
ratio of the cavity diameter to the average diameter of the article
may be less than about 1.8, preferably less than about 1.2, more
preferably less than about 1.1, and most preferably less than about
1.05. It will be appreciated that the ratio of the cavity diameter
to the average diameter of the article is typically at least about
1.0 (e.g., at least about 1.001).
[0052] A large portion of the volume of the capsular structure is
the encapsulated volume (i.e. the volume of the one or more sealed
spaces) so that the article can contain a relatively large amount
of the thermal energy storage material. The total volume of the one
or more sealed spaces of the article is preferably at least about
50 volume percent, more preferably at least about 80 volume
percent, even more preferably at least about 85 volume percent and
most preferably 90 volume percent based on the total volume of the
article. The total volume of the one or more sealed spaces of the
article is typically less than about 99.9 volume percent based on
the total volume of the article. The remaining volume, not occupied
by the thermal energy storage material, may include or consist
substantially entirely of the capsular structure, void spaces
(e.g., containing one or more gases), one or more structures for
improving the heat transfer between the thermal energy storage
material and the capsular structure, or any combination thereof.
Structures for improving heat transfer between the thermal energy
storage material and the capsular structure include any structure
formed of a material having a relatively high thermal conductivity
(e.g., relative to the thermal energy storage material) that is
capable of increases the rate of heat flow from the thermal energy
storage material to a heat transfer fluid. Suitable structures for
improving the rate of heat flow include fins, wire mesh,
protrusions into the sealed space, and the like.
[0053] The article preferably is easy to stack with other identical
shaped articles, or other articles having a generally mating
surface. For example, two articles to be stacked may have opposing
surfaces that are generally mating surfaces so that when stacked,
the two articles nest together. It will be appreciated that one
approach for stacking articles so that they easily nest together is
to select a shape (e.g., a shape of an arcuate surface, a shape of
the sealed spaces, or both) having a rotational symmetry of a high
order. The rotational symmetry may be about an axis in the stacking
direction (e.g., an axis through the fluid passage of the capsular
structure). The order of the rotational symmetry typically
describes the number of distinct rotations between the two surfaces
being stacked together in which they will nest together. The order
of the rotational symmetry of the article, the base sheet (e.g.,
the arcuate surface, of the, base sheet), or both, preferably is at
least 2, more preferably at least 3, even more preferably at least
5, and most preferably at least 7.
[0054] In one particularly preferred embodiment of the invention,
adjacent layers (e.g., adjacent capsular structures) do not nest
together. For example, a top surface of a first layer (e.g., of a
first capsular structure) may be in contact with a bottom surface
of a second layer (e.g., of a second capsular structure). The
contacting top surface, bottom surface, or both may have one or
more radial grooves or radial channels (i.e., a groove or channel
that has a radial component (i.e., the orientation of at least a
portion of the groove or channel includes a projection onto the
radial direction), and preferably extends from the center opening
to the outer periphery of the capsular structure) that allows for a
heat transfer fluid to flow between the two surfaces. For example,
the cover sheet of the first layer and the base sheet of the second
layer may have a straight groove or channel that extends in a
straight line form the opening to the outer periphery. In addition
to having a radial component, a groove or channel may have a
tangential component (i.e., the orientation of at least a portion
of the groove or channel includes a projection onto the tangential
direction). For example, a groove or channel may have a spiral
shape that includes both a radial component and a tangential
component. Two sheets in contact may have tangential components
that are different (e.g., having different directions and/or
different magnitudes) or the same. Tangential components of
adjacent sheets may be arranged so that the fluid flowing between
the adjacent sheets at least partially mixes. Advantageously, one
sheet may have grooves or channels with a tangential component in
the clockwise direction and the adjacent sheet may have grooves or
channels with a tangential component in the counterclockwise
direction, so that the fluid flowing between the two layers at
least partially mixes when grooves intersect (e.g., when two
streams of fluid flowing in the grooves of two adjacent capsular
structures come into direct contact for less than their entire flow
paths). FIG. 6A is a schematic drawing of a capsular structure 10
having a plurality of radial grooves 15 that extend between the
opening of the structure 16 and the exterior periphery 19 of the
structure. With reference to FIG. 6A, the grooves 15 may have one
or any combination of the following features: be curved, the
grooves may be curved so that they have a tangential component, the
grooves may be uniformly spaced, adjacent grooves may have the same
length, the grooves may have a spiral shape, and adjacent grooves
may provide flow paths having the same hydraulic resistance. FIG.
6B is a schematic drawing showing the contact between a portion of
a base sheet 30 of a first capsular structure and a portion of a
cover sheet 28 of a second capsular structure. The two contacting
surfaces may have generally different shapes or the same general
shape, such as illustrated in FIG. 6B. As illustrated in FIG. 6B,
the grooves of the contacting surfaces may have one or more
intersections. As illustrated in FIG. 6B, the grooves of the first
contacting surface may have a tangential portion and the grooves of
the second contacting surface may have a tangential portion in an
opposing direction relative to the first contacting surface. If
grooves or channels are employed for providing a flow path, one or
more surfaces may have any number of grooves or channels.
Preferably, the number of grooves or channels in the capsular
structure is sufficiently high and sufficiently distributed so that
heat transfer fluid flowing between two layers (e.g., between two
surfaces) can divided into a plurality of flow paths for
efficiently removing heat. Adjacent flow paths may be the same or
different. Preferably two or more flow paths (e.g., all of the flow
paths) have generally the same length, generally the same hydraulic
resistance, or both.
[0055] The capsular structure, such as the capsular structure
illustrated in FIG. 6A, may have an opening 16, preferably at or
near the geometric center of the capsular structure. The capsular
structure includes one or more sealed spaces. The capsular
structure may include a single sealed space, such as illustrated in
FIG. 6A. The capsular structure may be generally thin and include a
top surface 18, a bottom surface 20 an surface 22 near the exterior
periphery 19 and an edge surface 24 near the opening. The capsular
structure may include one or more features on the top surface, the
bottom surface, or both that provides a flow path for a fluid to
flow in at least a radial direction (e.g., when a plurality of
capsular structures are stacked). Such a feature preferably extends
from an opening periphery 21 of the capsular structure to an outer
periphery 19 of the capsular structure. Such a feature may provide
a flow direction that is generally arcuate, generally linear, or
have regions that are linear and regions that are straight. As
illustrated in FIG. 6A, the flow path may be provided by one or
more channels or grooves that extend from the center periphery to
the outer periphery. The grooves or channels in the top surface or
bottom surface of the capsular structure may be distributed over
the surface, so that each flow path (when a plurality of capsular
structures are stacked) has generally the same hydraulic
resistance. As illustrated in FIG. 6A, the grooves or channels may
have a curvature such that the flow path has a tangential component
in addition to the radial component. Such a curvature may be
advantageous in preventing adjacent capsular structures from
nesting together when identical capsular structures are stacked.
For example, as illustrated in FIG. 6A, the capsular structure may
be prepared by joining together a cover sheet and a base sheet
having generally the same shape, and both having a plurality of
curved grooves. When joined, the curved grooves in the top surface
and the bottom surface are curved in opposite directions (when
viewed from the top surface). As illustrated in FIG. 6A, the cover
sheet and the base sheet may be sealed along the opening periphery
and along the outer periphery, so that a sealed space is
formed.
[0056] FIG. 6C, is a schematic drawing showing two adjacent
segments 2 that form a portion of a capsular structure. As
illustrated in FIG. 6C, each segment may include two sheets that
are sealingly attached along a periphery of the segment. The
location of the attachment may be on an edge surface 9. As
illustrated in FIG. 6C, each segment may include one or more sealed
spaces. Although no individual segment may have an opening, the
segments may be arranged edgewise so that a capsular structure
including an opening is formed. As illustrated in FIG. 6D, edges 9
of adjacent segments may mate when one segment is translated by a
fraction of the thickness (e.g., half the thickness) relative to
the adjacent segment.
[0057] The top surface of the capsular structure may be generally
circular in shape, such as the top surfaces illustrated in FIGS. 1A
and 6A. Other shapes for the top surface of the capsular structure
are possible and may even be desirable. For example, the capsular
structure may be employed in a heat storage device that is required
to fit in a tight space, such as under the hood or under the floor
of a vehicle. Although a cylindrical shape may be advantageous for
reducing surface area other more elongated, or boxy shapes may be
advantageous for fitting into a available space. It will be
appreciated according to the teachings herein that the generally
circular shaped surfaces of the capsular structure may
advantageously be replaced with shapes that are not circular. As
such, the capsular structure may have a top surface and/or a bottom
surface having a generally oval shape, a generally rectangular
shape, a generally square shape, a generally irregular shape, or
any combination thereof. For example, the top surface and/or the
bottom surface of the capillary structure may have a generally
rectangular shape with rounded corners. FIG. 7 is a drawing showing
illustrative features of a surface of a capsular structure. As
illustrated in FIG. 7, the profile of the periphery of the top
surface and the bottom surface of the capsular structure may have
an elongated shape. For example the profile (of the outer
periphery) of the top surface and the bottom surface may have a
generally rectangular shape, a generally square shape, or a
generally oval shape). It will be appreciated that the profile of
the opening in the top surface may be any shape. The profile of the
opening in the top surface and the profile of the outer periphery
of the top surface may have shapes that are similar (but different
size) or may have shapes that are different (such as a generally
circular opening and a noncircular outer periphery). As illustrated
in FIG. 7, the profile of the opening and the profile of the outer
periphery may have the same shape, such as a generally oval
shape.
[0058] The article preferably has a capsular structure that is
difficult to bend. For example, the capsular structure may be free
of a cross-section in which a cover sheet and a base sheet are in
contact throughout most or even all of a length of the
cross-section (such as a diameter of the capsular structure). There
are venous approaches that may be employed for assuring that the
capsular structure will be difficult to bend, including selecting
an arrangement of the capsules so that the order of rotational
symmetry is not an even number, selecting an arrangement of the
capsules so that there is no rotational symmetry, selecting an
arrangement of capsules including two or more rings of capsules
(such as concentric rings) that are rotated relative to each other
so that every radial section includes at least one sealed space, or
any combination thereof. It will be appreciated that other
geometries and other means may be employed to make the capsular
article resistant to bending. For example, the materials for the
capsular structure may be chosen to be generally stiff, the
structure may include one or more ribs (e.g., in a tangential
direction), and the like.
[0059] All of the thermal energy storage material of the article
may be in a single sealed space. Preferably the thermal energy
storage material of the article is divided between a plurality of
sealed spaces so that if a sealed space is punctured or otherwise
leaks, only a portion of the thermal energy storage material can be
removed. As such, the number of sealed spaces in the article (e.g.,
sealed spaces that contain thermal energy storage material) is
preferably at least 2, more preferably at least 3, and even more
preferably at least about 5. The upper limit on the number of
sealed spaces is practicalilty and for a particular application is
defined by the need of the application. Nevertheless, the number of
sealed spaces in the article typically is less than 1,000. However,
it will be appreciated that very large articles may have 1,000 or
more sealed spaces. For the same reasons, the volume fraction of
the thermal energy storage material that is found in any single
sealed compartment preferably is less than about 55%, more
preferably less than about 38%, even more preferably less than
about 29%, and most preferably less than about 21%, based on the
total volume of the thermal energy storage material in the article.
Typically a sealed space includes at least 0.1 volume % of the
thermal energy storage material in the article. However, it will be
appreciated that the article may include one or more sealed spaces
that are substantially or even entirely free of the thermal energy
storage material.
[0060] The sealed spaces may optionally be arranged in a plurality
of concentric rings, including an innermost ring (e.g., a ring
closest to the opening periphery) and an outermost ring (e.g., a
ring closest to the outer periphery), each containing one or more
sealed spaces. The sealed spaces in one ring may have a generally
repeating pattern. For example, each sealed space or each groups of
2, 3, 4 or more sealed spaces in a ring may have generally the same
shape and size. The number of sealed spaces in each ring may be the
same or different. Preferably the outermost ring has more sealed
spaces than the innermost ring, the average length of the sealed
spaces of the outermost ring is less than the average length of the
sealed spaces of the innermost ring (where the average length is
measured in the radial direction from the opening to the outer
periphery), or both, so that the volume variation between the
sealed spaces of the outermost ring and the innermost ring is
reduced.
[0061] As discussed hereinafter, the article may be placed in a
container having a generally cylindrical shaped cavity, such as a
(levity that is only slightly greater in dimension than the longest
dimension of the article. For example, the diameter of the cavity
of the container may be only slightly larger than the diameter of
the capsular structure of the article. The diameter of the cavity
should be sufficiently large so that the article can be inserted
into the cavity. When the article (or a stack of the articles) is
placed in the container, it may be desirable for a fluid to be
capable of flowing between the outer periphery of the article and
an interior wall of the container. This can be achieved by
designing the relationship of the interior of the container and the
shape of the article to create and maintain fluid flow paths. Any
means of creating such fluid flow paths may be used. As such, the
article may optionally have one or more indents along its periphery
(e.g., the cover sheet and the base sheet may have one or more
corresponding indents along their respective outer peripheries) so
that a space is formed for flowing a heat transfer fluid.
Alternatively, or in addition, the cavity of the container may have
a surface with one or more grooves for flowing a fluid between the
outer periphery of the article and the surface of the container. As
another example, the diameter of the article may be sufficiently
small in relation to the diameter of the interior of the cavity so
that a fluid can flow along the entire outer periphery of the
article. For example, the article may have one or more indents or
the container may have one or more grooves, for each sealed space
in the outermost ring of sealed spaces. An indent or a groove may
have any shape, such as a polygonal shape, an arcuate shape, a
wedge shape, and the like, provided it has a sufficient size to
allow for the heat transfer fluid to flow. If employed, the
smallest dimension of the indents and/or grooves is typically at
least about 0.1 mm). It will be appreciated that a combination of
two or more means of creating a fluid flow path may be used. For
example, the article may have one or more indents along its outer
periphery and the article may have a sufficiently small diameter so
that fluid can flow along its entire outer periphery when placed in
a cavity.
[0062] The base sheet may optionally have one or more protrusions,
so that when the article is stacked with another article having a
surface that generally mates with the base sheet, the two articles
only partially nest. As such the one or more protrusions may
function as a spacer to separate the generally mating surfaces so
that a fluid (e.g., a heat transfer fluid) can flow between the
mating surfaces. Stacking of articles and other spacing means are
discussed hereinafter. If employed, the protrusions preferably
cover only a small portion of the surface are of the base sheet so
that the one or more protrusions do not substantially interfere
with the flow of the fluid. The height of the protrusions may be
selected to define the height (e.g., the average height) of the
flow path between the two generally mating surfaces. The cover
sheet preferably is free of such protrusions and has an outer
surface that is generally flat so that two articles can be arranged
with their over sheets in can contact generally over their entire
top surfaces.
Thermal Energy Storage Material
[0063] Without limitation, suitable thermal energy storage
materials for the heat storage device include materials that are
capable of exhibiting a relatively high density of thermal energy
as sensible heat, latent heat, or preferably both. The thermal
energy storage material is preferably compatible with the operating
temperature range of the heat storage device. For example the
thermal energy storage material is preferably a solid at the lower
operating temperature of the heat storage device, is at least
partially a liquid (e.g., entirely a liquid) at the maximum
operating temperature of the heat storage device, does not
significantly degrade or decompose at the maximum operating
temperature of the device, or any combination thereof. The thermal
energy storage material preferably does riot significantly degrade
or decompose when heated to the maximum operating temperature of
the device for about 1,000 hours or more, or even for about 10,000
hours or more.
[0064] The thermal energy storage material may be a phase change
material having a solid to liquid transition temperature. The solid
to liquid transition temperature of the thermal energy storage
material may be a liquidus temperature, a melting temperature, or a
eutectic temperature. The solid to liquid transition temperature
should be sufficiently high so that when the thermal energy storage
material is at least partially or even substantially entirely in a
liquid state enough energy is stored to heat the one or more
objects to be hosted to a desired temperature. The solid to liquid
transition temperature should be sufficiently low so that the heat
transfer fluid, the one or more objects to be heated, or both, are
not heated to a temperature at which it may degrade. As such the
desired temperature of the solid to liquid transition temperature
may depend on the object to be heated and the method of
transferring the heat. For example, in an application that
transfers the stored heat to an engine (e.g., an internal
combustion engine) using a glycol/water heat transfer fluid, the
maximum solid to liquid transition temperature may be the
temperature at which the heat transfer fluid degrades. As another
example, the stored heat may be transferred to an electrochemical
cell of a battery using a heat transfer fluid where the heat
transfer fluid has a high degradation temperature, and the maximum
solid to liquid temperature may be determined by the temperature at
which the electrochemical cell degrades or otherwise fail. The
solid to liquid transition temperature may be greater than about
30.degree. C., preferably greater than about 35.degree. C., more
preferably greater than about 40.degree. C., even more preferably
greater than about 45.degree. C., and most preferably greater than
about 50.degree. C. The thermal energy storage material may have a
solid to liquid transition temperature less than about 400.degree.
C., preferably less than about 350.degree. C., more preferably less
than about 200.degree. C., even more preferably less than about
250.degree. C., and most preferably less than about 200.degree. C.
It will be appreciated that depending on the application, the solid
to liquid transition temperature may be from about 30.degree. C. to
about 100.degree. C., from about 50.degree. C. to about 150.degree.
C., from about 100.degree. C. to about 200.degree. C., from about
150.degree. C. to about 250.degree. C., from about 175.degree. C.
to about 400.degree. C., from about 200.degree. C. to about
375.degree. C., from about 225.degree. C. to about 400.degree. C.,
or from about 200.degree. C. to about 300.degree. C.
[0065] For some applications, such as transportation related
applications, it may desirable for the thermal energy material to
efficiently store energy in a small space. As such, the thermal
energy storage material may have a high heat of fusion density
(expressed in units of megajoules per liter), defined by the
product of the heat of fusion (expressed in megajoules per
kilogram) and the density (measured at about 25.degree. C. and
expressed in units of kilograms per liter). The thermal energy
storage material may have a heat of fusion density greater than
about 0.1 MJ/liter, preferably greater than about 0.2 MJ/liter,
more preferably greater than about 0.4 MJ/liter, and most
preferably greater than about 0.6 MJ/liter. Typically, the thermal
energy storage material has a heat of fusion density less than
about 5 MJ/liter. However, thermal energy storage materials having
a higher heat of fusion density may also be employed.
[0066] For some applications, such as transportation related
applications, it may be desirable for the thermal energy storage
material to be light weight. For example, the thermal energy
storage material may have a density (measured at about 25.degree.
C.) less than about 5 g/cm.sup.3, preferably less than about 4
g/cm.sup.3, more preferably less than about 3.5 g/cm.sup.3, and
most preferably less than about 3 g/cm.sup.3. The lower limit on
density is practicality. The thermal energy storage material may
have a density (measured at about 25.degree. C.) greater than about
0.6 g/cm.sup.3, preferably greater than about 1.2 g/cm.sup.3, and
more preferably greater than about 1.7 g/cm.sup.3.
[0067] The sealed spaces may contain any art known thermal energy
storage material. Examples of thermal energy storage materials that
may be employed in the thermal energy storage material compartments
include the materials described in Atul Sharma, V. V. Tyagi, C. R.
Chen, D. Buddhi, "Review thermal energy storage with phase change
materials and applications", Renewable and Sustainable Energy
Reviews 13 (2009) 318-345. and in Belen Zalba, Jose Ma Marin, Luisa
F. Cabeza, Harald Mehling, "Review on thermal energy storage with
phase change: materials, heat transfer analysis and applications",
Applied Thermal Engineering 23 (2003) 251-283, both incorporated
herein by reference in their entirety. Other examples of suitable
thermal energy storage materials that may be employed in the heat
transfer device include the thermal energy storage materials
described in U.S. patent application Ser. No. 12/389,416 entitled
"Thermal Energy Storage Materials" and filed on Feb. 20, 2009; and
U.S. patent application Ser. No. 12/389,598 entitled "Heat Storage
Devices" and filed on Feb. 20, 2009.
[0068] The thermal energy storage material may include an organic
material, an inorganic material or a mixture of an organic and an
inorganic material that exhibits the solid to liquid transition
temperature, the heat of fusion density density, or both, described
hereinbefore. Organic compounds that may be employed include
paraffins and non-paraffinic organic materials, such as a fatty
acid. Inorganic materials that may be employed include salt
hydrates and metallics. The thermal energy storage material may be
a compound or a mixture (e.g., a eutectic mixture) having a solid
to liquid transition at generally a single temperature. The thermal
energy storage material may be a compound or a mixture having a
solid to liquid transition over a range of temperatures (e.g., a
range of greater than about 3.degree. C., or greater than about
5.degree. C.).
[0069] Without limitation, suitable non-paraffinic organic
materials for use as a thermal energy storage material include
acids, alcohols, aldehydes, amides, organic salts, mixtures thereof
and combinations thereof. By way of example, the non-paraffinic
organic materials that may be used alone or as a mixture include
polyethylene glycol, capric acid, eladic acid, lauric acid,
pentadecanoic acid, tristearin, myristic acid, palmatic acid,
stearic acid, acetamide, methyl fumarate, formic acid, caprilic
acid, glycerin, D-lactic acid, methyl palmitate, camphenilone,
docasyl bromide, caprylone, phenol, heptadecanone,
1-cyclohexylooctadecane, 4-heptadacanone, p-joluidine, cyanamide,
methyl eicosanate, 3-heptadecanone, 2-heptadecanone, hydrocinnamic,
cetyl alcohol, nepthylamine, camphene, o-nitroaniline,
9-heptadecanone, thymol, methyl behenate, diphenyl amine,
p-dichlorobenzene, oxolate, hypophosphoric, o-xylene dichloride,
chloroacetic, nitro naphthalene, trimytristin, heptaudecanoic, bees
wax, glyolic acid, glycolic acid, p-bromophenol, azobenzene,
acrylic acid, dinto toluent, phenylacetic acid, thiosinamine,
bromcamphor, durene, benzylamine, methyl brombrenzoate, alpha
napthol, glautaric acid, p-xylene dichloride, catechol, quinone,
acetanilide, succinic anhydride, benzoic acid, stibene, benzamide,
or any combination thereof.
[0070] Without limitation, the thermal energy storage material may
include one or more inorganic salts selected from the group
consisting of nitrates, nitrites, bromides, chlorides, other
halides, sulfates, sulfides, phophates, phosphites, hydroxides,
carboxides, bromates, mixtures thereof, and combinations thereof.
By way of example, the thermal energy storage material may include,
or consist substantially of K.sub.2HPO.sub.4.6 H.sub.2O,
FeBr.sub.3.6H.sub.2O, Mn(NO.sub.3).sub.2.6 H.sub.2O,
FeBr.sub.3.sub.3.6 H.sub.2O, CaCl.sub.2.12 H.sub.2O, LiNO.sub.3.2
H.sub.2O, LiNO.sub.3.3 H.sub.2O, Na.sub.2CO.sub.3.10 H.sub.2O,
Na.sub.2SO.sub.4.10 H.sub.2O, KFe(SO.sub.3).sub.2.12 H.sub.2O,
CaBr.sub.2.6 H.sub.2O, LiBr.sub.2.2 H.sub.2O, Zn(NO.sub.3).sub.2.6
H.sub.2O, FeCl.sub.3.6 H.sub.2O, Mn(NO.sub.3).sub.2.4 H.sub.2O,
Na.sub.2HPO.sub.4.12 H.sub.2O, CoSO.sub.4.7 H.sub.2O, KF.2
H.sub.2O, Mgl.sub.2.8 H.sub.2O, Cal.sub.2.6 H.sub.2O,
K.sub.2HPO.sub.4.7 H.sub.2O, Zn(NO.sub.3).sub.2.4 H.sub.2O,
Mg(NO.sub.3).4 H.sub.2O, Ca(NO.sub.3).4 4 H.sub.2O,
Fe(NO.sub.3).sub.2.9 H.sub.2O, Na.sub.2SiO.sub.3.4 H.sub.2O,
K.sub.2HPO.sub.4.3 H.sub.2O, Na.sub.2S.sub.2O.sub.3.5 H.sub.2O,
MgSO.sub.4.7 H.sub.2O, Ca(NO.sub.3).sub.2.3 H.sub.2O,
Zn(NO.sub.3).sub.2.2 H.sub.2O, FeCl.sub.3.2 H.sub.2O,
Ni(NO.sub.3).sub.2.6 H.sub.2O, MnCl.sub.2.4 H.sub.2O, MgCl.sub.2.4
H.sub.2O, CH.sub.cCOONa.3 H.sub.2O, Fe(NO.sub.3).sub.2.6 H.sub.2O,
NaAl(SO.sub.4).sub.2.10 H.sub.2O, NaOH.H.sub.2O,
Na.sub.3PO.sub.4.12 H.sub.2O, LiCH.sub.3COO.2 H.sub.2O,
Al(NO.sub.3).sub.2.9 H.sub.2O, Ba(OH).sub.2.8 H.sub.2O,
Mg(NO.sub.3).sub.2.6 H.sub.2O, KAI (SO.sub.4).sub.2.12 H.sub.2O,
MgCl.sub.2.6 H.sub.2O, or any combination thereof. It will be
appreciated that inorganic salts having higher or lower
concentrations of water may be used.
[0071] The thermal energy storage material may include or may even
consist essentially of or consist of) at least one first metal
containing material, and more preferably a combination of the at
least one first metal containing material and at least second metal
containing material. The first metal containing material, the
second metal containing material, or both, may be a substantially
pure metal, an alloy such as one including a substantially pure
metal and one or more additional alloying ingredients (e.g., one or
more other metals), an intermetallic, a metal compound (e.g., a
salt, an oxide or otherwise), or any combination thereof. One
preferred approach is to employ one or more metal containing
materials as part of a metal compound; a more preferred approach is
to employ a mixture of at least two metal compounds. By way of
example, a suitable metal compound may be selected from oxides,
hydroxides, compounds including nitrogen and oxygen (e.g.,
nitrates, nitrites or both), halides, or any combination thereof.
It is possible that ternary, quaternary or other multiple component
material systems may be employed also. The thermal energy storage
materials herein may be mixtures of two or more materials that
exhibit a eutectic.
[0072] The volume of the thermal energy storage material in the one
or more sealed spaces of the article is sufficiently high so that
the article can store a large amount of thermal energy. The ratio
of the volume of the thermal energy storage material contained in
the article to the total volume of the one or more sealed spaces,
the ratio of the volume of the thermal energy storage material to
the total volume of the article, or both (the volumes measured at a
temperature of about 25.degree. C., or at a temperature at which
the thermal energy storage material is a liquid) preferably is
greater than about 0.5, more preferably greater than about 0.7, and
most preferably greater than about 0.9. The ratio of the volume of
the thermal energy storage material contained in the article to the
total volume of the one or more sealed spaces, the ratio of the
volume of the thermal energy storage material to the total volume
of the article, or both (the volumes measured at a temperature of
about 25.degree. C., or at a temperature at which the thermal
energy storage material is a liquid) is typically less than about
1.0, and more typically less than about 0.995.
[0073] The sealed space may include a volume that contains a gas,
such air, N.sub.2, or an inert gas such as He, Ar, and the like, so
that the thermal energy storage material can expand when heated.
For example, the sealed space may have a region that is free of
thermal energy storage material at a temperature of about
25.degree. C., so that upon heating the thermal energy storage
material above its liquidus temperature, the thermal energy storage
material can expand without forming a hole in the cover sheet or
base sheet or causing one or more sheets to delaminate. The volume
of a sealed space that is free of thermal energy storage material
(e.g., the volume of the sealed space that contains a gas) at
25.degree. C., may be at least about 0.5%, preferably at least
about 1%, and most preferably at least about 1.5%, based on the
total interior volume of the sealed space.
[0074] FIG. 2A is a drawing that illustrates features of an article
10 that includes a capsular structure having a single sealed space
(i.e., a single capsule). The capsular structure includes a cover
sheet 28 having an opening 29 and a base sheet 30 having an opening
31. The opening of the cover sheet 29 and the opening of the base
sheet 31 overlap each other (e.g., completely overlap) and are thus
corresponding openings. The cover sheet 28 and the base sheet are
sealingly attached to an outer ring 32. As illustrated, the outer
periphery of the cover sheet 28, the outer periphery of the base
sheet, or preferably both may be sealingly attached to the outer
ring 32. The cover sheet has a top surface 18 that is an exterior
surface of the article 10, and an opposing surface that is
generally on the interior of the article 10. The base sheet has a
bottom surface 20 that is generally an exterior surface of the
article 10, and an opposing surface that is generally on the
interior of the article. The capsular structure may also have an
inner ring 34 that is sealingly attached to an opening periphery of
the cover sheet 28, an opening periphery of the base sheet 30 or
preferably both. As illustrated, the outer ring 32 may have a
generally cylindrically shaped outer surface and a generally
cylindrically shaped inner surface, the inner ring 34 may have a
generally cylindrically shaped outer surface and a generally
cylindrically shaped inner surface, the cover sheet 28 (e.g., the
top surface 18 of the cover sheet) may have a generally circular
shape, the base sheet 30 (e.g., the bottom surface of the base
sheet) may have a generally circular shaped circumference, or any
combination thereof. One of any combination of the following
openings may have a generally cylindrical shape: the fluid passage
of the article 16, the opening of the cover sheet 29, and the
opening of the base sheet 31. It will be appreciated that a
cross-section of an opening may have a different shape, such as a
polygonal shape, or a different arcuate shape (e.g., an oval
shape).
[0075] As illustrated in FIG. 2A, the article 10 may have have a
single side surface 22 that is generally arcuate, generally
nonplanar, and generally continuous. Such a side surface may be
generally equidistant from the center of the article so that the
article can be placed in a container having a generally cylindrical
cavity with a cavity diameter that is only slightly larger than the
average diameter of the article.
[0076] An illustrative cover sheet 28 having an opening 29 for use
in the article, is shown in FIG. 2B. It will be appreciated that
the opening in the cover sheet may be formed prior to, during, or
after attaching (e.g., sealingly attaching) the cover sheet to one
or more other sheets or one or more other sub-structures. The cover
sheet may have an outer periphery 19 that is generally circular, an
inner or opening periphery 21 that is generally circular, or both.
The cover sheet 28 may have a bottom surface 38 that is generally
flat and an opposing top surface 18 that is generally flat. The
cover sheet 28, may be formed from one or more encapsulant
materials 12. As illustrated in FIG. 2B, the outer periphery 19 of
the cover sheet 28 may include a region 23 on the bottom surface 38
of the cover sheet 28, near the outer perimeter of the cover sheet.
Referring to FIGS. 2A and 2B, the base sheet 28 may be sealingly
attached along the region 23 of the outer periphery 19 on the
bottom surface 38. The encapsulant material for the top surface 18
preferably is a material that resists corrosion when in contact
with the heat transfer fluid. The encapsulant material for the
bottom surface 38 preferably is a material that resists corrosion
when in contact with the thermal energy storage material. The
encapsulant material for the top surface 18 and the bottom surface
38 may be the same material or different materials. The top surface
18, except for the opening 29 may have a generally circular shape.
The thickness of the rover sheet 28, as measured by the distance
between the top surface 18 and the bottom surface 38 of the cover
sheet may be generally uniform. The standard deviation of the
thickness of the cover sheet 28 is preferably less than about 15%,
more preferably less than about 10%, and most preferably less than
about 3% of the average thickness of the cover sheet.
[0077] FIG. 2C illustrates a cross-section of the article 10 of
FIG. 2A, taken perpendicular to the top surface 18 of the cover
sheet 28. As illustrated in FIG. 2C, the article may have one or
more sealed spaces 14 that includes thermal energy storage material
26. The sealed space may include an unfilled volume 27, i.e., a
volume contains a gas. The unfilled volume 27 may allow for the
thermal energy storage material to expand when it is heated, such
as when the temperature of the thermal energy storage material
increases, when the thermal energy storage material undergoes a
solid to liquid phase transition, or both. The cover sheet, the
base sheet, the outer ring, the inner ring, or any combination
thereof preferably includes one or more encapsulant materials that
resists corrosion when contacted with the thermal energy storage
material (e.g., on an interior surface), one or more encapsulant
materials that resist corrosion when contacted by a heat transfer
fluid, (e.g., on an exterior surface), or both. The cover sheet,
the base sheet, the outer ring, the inner ring, or any combination
thereof most preferably include or consist substantially entirely
of the same one or more encapsulant materials. The cover sheet 28
and the base sheet 30 are both sealingly attached along both their
outer peripheries 19 and their opening peripheries 21 for forming
the one or more sealed spaces 14.
[0078] FIG. 2D, illustrates a formed sheet 40 that may be employed
as a base sheet for the article. The formed sheet may be embossed
or otherwise formed so that it is generally arcuate and/or has a
plurality of walls. The formed sheet has a trough region 43 that is
capable of holding or containing a liquid. The formed sheet also
has an opening 46, so that a fluid can flow through the formed
sheet. The formed sheet preferably also has one or more generally
flat regions such as one or more lip regions 44 that may be
attached to a generally flat cover sheet such as a cover sheet
described in FIG. 2B). The one or more lip regions 44 preferably
are coplanar. The formed sheet 40 is not a generally flat sheet.
For example, the formed sheet 40 may have a bottom well that
includes a top surface 41 and a generally opposing bottom surface
42. The formed sheet may have a side all extending from the bottom
wall. The side wall may include a side surface 49 that is generally
arcuate. The formed sheet 40 may have an opening wall extending
from an interior periphery of the bottom wall. The opening wall may
have an opening surface 48 that is generally arcuate and partially
or totally defines the fluid passage through the article. The
formed sheet has an outer periphery 45 and an opening periphery 47.
The outer periphery 45, the opening periphery 47, or preferably
both are lip regions 44. It will be appreciated that the formed
sheet may include a transition region connecting the bottom wall
and the side wall, or the bottom wall and side wall may be combined
into one arcuate wall. It will be appreciated that the formed sheet
may include a transition region connecting the bottom wall and the
opening wall, or the bottom wall and opening wall may be combined
into one arcuate wall.
[0079] As described hereinbefore, the capsular structure may
include a plurality of segments that are arranged to form the
capsular structure having one or more sealed spaces and one or more
fluid passages. FIGS. 3A, 3B, and 4 are illustrative side views of
adjacent segments of capsular structures. As illustrated in FIGS.
3A, 3B and 4, adjacent segments may have mating edges 9 (i.e.,
edges surfaces that generally mate). The segments may mate when the
adjacent segments are arranged in a coplanar orientation, such as
shown by segments 2', 2'' in FIGS. 3A and 3B, where surfaces 4' and
6' of the two segments are generally coplanar. The edges of
adjacent segments may mate when the two adjacent segment are
shifted, so that their top and bottom surfaces 4' and 6' are not
coplanar. For example, the one segment may be shifted by half the
thickness of the segment 2''', as illustrated in FIG. 4. As such,
the mating edge 9 of a first segment may mate with portions of the
edges of two stacked segments that are both adjacent to the first
segment. As illustrated in FIG. 4, one stack of segments may
include one or more (e.g., two) fractional segments 3, such as a
fractional segment having half the height of the other segments
2'''.
[0080] It will be appreciated that some or all of the troughs of
the formed sheet 40' may be partially or substantially entirely
filled with a thermal energy storage material, and a generally flat
cover sheet (such as described in FIG. 2B) can be placed over the
troughs so that the cover sheet generally contacts the lip region.
The cover sheet may be sealingly attached to the formed sheet in
some or even all of the lip regions for forming a plurality of
sealed spaces containing the thermal energy storage material. As
shown in FIG. 5A and 5B, the formed sheet 40' may have a pattern of
troughs so that the bottom surface 41' of a first formed sheet 40
is generally a mating surface of a bottom surface 41' of an
identical second formed sheet 40'. As such, two articles made using
the formed sheet 40' are capable of being stacked with their bottom
surfaces 41' opposing each other so that the two articles will at
least partially nest.
[0081] FIG. 5B is a schematic drawing of a portion of a formed
sheet 40' (e.g., a base sheet) that may be employed in an article
having a plurality of sealed spaces. The formed sheet has an
opening 46 near the center of the sheet, which may be a generally
circular opening. FIG. 5B shows only 1/4 of the formed sheet and
thus only 1/4 of the opening is shown. FIG. 5B shows the bottom
surface 41' of the formed sheet 40'. The formed sheet has a
plurality of trough regions 43' and a plurality of lip regions 44'.
The trough regions 43' may be arranged in a plurality of rings of
troughs 50. As illustrated, the formed sheet may have an innermost
ring of troughs 50' and an outermost ring of troughs 50''. The
formed sheet may also have one or more additional rings of troughs
50''', between the innermost and the outermost rings of troughs
50', 50''. As illustrated in FIG. 5B, some or all of the troughs in
a ring, or even some or all of the troughs in different rings may
have about the same shape, about the same volume, or even be
substantially congruent. It will be appreciated that the number of
troughs in the innermost ring of troughs may be more than, less
than or the same as the number of troughs in the outermost ring of
troughs. Preferably, the number of troughs in the innermost ring of
the formed sheet 40' is less than the number of troughs in the
outermost ring, as illustrated in FIG. 5B. Some, or preferably all
of the troughs regions 43' have a lip region 44' around the trough
region. As such, a trough region 43' may be separated by the other
trough regions by a lip region 44'. The formed sheet 40; has an
outer periphery 45'. As illustrated in FIG. 5B, the formed sheet
may have one or more indents 51 near the outer periphery 45. The
one or more indents may be used for flow channels or flow paths
along the outer periphery. Preferably the outer perimeter of the
bottom surface of the formed sheet has a generally circular shape
(excluding the optional one or more indents). As illustrated in
FIG. 5B, the outer periphery, the inner periphery, and preferably
both, may be lip regions 44'.
[0082] FIG. 5A shows an illustrative relationship between a
capsular structure 10' (e.g., a formed sheet 40' of a capsular
structure) and a container 68. The container 68 may have an inner
wall 60, an outer wall 62, an insulating layer 64, or any
combination thereof. With reference to FIG. 5A, the container 68
may have, an insulating layer 64 interposed between two walls, 60,
62. The inner wall 60 of the container has a larger diameter than
the diameter of the formed sheet so that the formed sheet can fit
within the container. A flow path between the periphery of the
sheet and the inside wall of the container may include one or more
indents 51 in the formed sheet 40', a gap 52 formed by the
differences in the sizes (e.g., the diameters) of the formed sheet
40' and the cavity of the container, one or more grooves 53 in an
inside wall 60 of the container, or any combination thereof.
Stack of Articles
[0083] The articles containing he thermal energy storage material
preferably are capable of being stacked either with other identical
articles or with a second article having a generally mating surface
(such as a generally mating base sheet). The articles are stacked
in axial layers with a space between adjacent axial layers so that
a heat transfer fluid can flow between the axial layers. An axial
layer will generally contain one, two or more article. An axial
layer (e.g., each axial layer) preferably contains one or two
articles. For example, an axial layer may have two articles that
are in contact on a surface, such as a base surface or a cover
surface, so that a fluid cannot generally flow between the two
articles). As such, some of the articles (e.g., each article except
the articles at an end of a stack) may have a first surface (e.g.,
a base surface) that is generally in complete contact with a
surface of a first adjacent article so that a fluid cannot flow
along the first surface, and a second surface that is separated
from a second adjacent article (e.g., having an opposing surface
that is generally a mating surface with the second surface) so that
a fluid can flow along some, most, or even all of the second
surface. The separation between two adjacent axial layers may be
due to any art known spacing means. By way of example, suitable
spacing means include one or more protrusions on a surface of at
least one of the articles, a spacer material between, the two
layers, a capillary structure between two layers, or any
combination thereof. Preferably the second surface of the article
has a generally arcuate shape and the article partially nests with
the second adjacent article. The spacing between two articles that
partially nest preferably is generally constant (except for the
protrusions or other spacers that cause the adjacent articles to be
separated). It will be appreciated that the stacking of the
articles may include a step of rotating an axial layer (e.g.,
rotating an article), or otherwise arranging it so that the axial
layer at least partially nests with an adjacent axial layer. The
flow of a fluid between two opposing surfaces of two adjacent axial
layers will generally be in a radial direction and may be described
as a generally radial flow. Each pair of axial layers that are
spaced apart will have a radial flow path. The stack of articles
will typically have a plurality of radial flow paths (e.g., 2, 3,
or more). Two or more (e.g., each radial flow path may have the
same flow length, the same thickness, the same crass-sectional
shape, or any combination thereof. For example, two or more (e.g.,
all) of the radial flow paths may be congruent. It will be
appreciated that if the opening (i.e., fluid passage) is at the
center of the article, the radial flow path may be generally
symmetric, irrespective of the flow direction.
[0084] When stacked (e.g., in a stack containing 3, 4 or more
articles), the articles preferably each have at least one opening
that corresponds with an opening from each of the other articles
(except possibly an article at one end of the stack), so that a
portion of a fluid can flow from a first article in the stack to a
last article in the stack by flowing through each of the
corresponding openings of the articles interposed between the first
and last article without flowing between adjacent articles (i.e.,
without a generally radial flow). The flow through the openings
will generally be in an axial direction and may be described as a
generally axial flow.
[0085] As described above, the stack of articles may define a
central axial flow path (e.g., through the central axis formed by
the openings of the articles) and one or more radial flow paths
that are generally perpendicular to the central axial flow
path.
[0086] The stack of articles will generally be tightly packed
(e.g., except for the radial flow paths) so that the stack of
articles is compact and contains a large amount of thermal energy
storage material. As such, the radial flow path has a height (in
the direction between the adjacent articles), e.g., an average
height, that is generally small. The height of the radial flow path
preferably is less than about 15 mm, more preferably less than
about 5 mm, even more preferably less than about 2 mm, even more
preferably less than about 1 mm, and most preferably less than
about 0.5 mm. The height of the radial flow path typically is large
enough so that the fluid can flow through the path. Typically the
height (e.g., the average height) of the radial flow path is
greater than about 0.001 mm (e.g., greater than about 0.01 mm).
[0087] FIG. 5C illustrates an aspect the invention that includes a
plurality of articles 10', each having one or more sealed spaces 14
for containing a thermal energy storage material. The articles 10'
may include a formed sheet 40'' having a generally arcuate surface
41''. The surface 41'' of one article may generally mate with the
surface of a second article. The articles may be arranged so that
adjacent articles partially nest together. The articles illustrated
in FIG. 5C have a rotational symmetry of order 8 and thus can be
rotated in 8 different positions so that they will partially nest.
It will be appreciated that articles with a higher or a lower order
of symmetry may be employed. As illustrated in FIG. 5C, the
articles may have a generally circular cross-section. The outer
periphery of each article may have a plurality of indents 51 that
are large enough to allow for a fluid flow. The articles 10' may
have sealed spaces 14 arranged in one or more concentric rings of
sealed spaces. Each article 10' may have a fluid passage 46'
generally near the center of the article so that when the articles
are stacked (e.g., stacked in an axial direction), an axial flow
path 84' is formed. The axial flow path 84' preferably includes a
fluid passage 46' of each article 10'.
Heat Storage Device
[0088] The articles (e.g., a stack of articles) described herein
may be employed in a heat storage device. The heat storage device
may include a container or other housing having one or more
orifices for flowing a heat transfer fluid into the container and
one or more orifices for flowing a heat transfer fluid out of the
container. The heat storage device has one or more heat transfer
fluid compartments. Preferably, the heat storage device includes a
single heat transfer fluid compartment. A heat transfer fluid
compartment may include or consist substantially of a contiguous
space in the container between the inlet and the outlet, where the
heat transfer fluid can flow. The containers preferably is at least
partially insulated so that heat losses from the container to the
ambient may be reduced or minimized.
[0089] The heat storage device may be designed so that it contains
a large concentration of thermal energy storage material, so that
it can transfer thermal energy between a heat transfer fluid and
the thermal energy storage material rapidly and/or uniformly, so
that it is generally compact, so that it can store heat for a long
time, or any combination thereof.
[0090] The inside of the container of the heat storage device may
have any shape capable of holding a stack of articles. Preferably,
the shape of the inside of the container is such that the stack of
articles occupies a large portion of the interior volume of the
container. The ratio of the total volume of thermal energy storage
material (e.g., measured at about 25.degree. C.) contained in the
sealed spaces of the articles in the container to the total
interior volume of the container (e.g., at a temperature of about
25.degree. C.) may be greater than about 0.3, preferably greater
than about 0.5, more preferably greater than about 0.6, even more
preferably greater than about 0.7, and most preferably greater than
about 0.8. The upper limit on the volume of thermal energy storage
material in the container is the need for space for a heat transfer
fluid that contacts the articles for transferring thermal energy.
The ratio of the total volume of thermal energy storage material
(e.g., measured at about 25.degree. C.) contained in the sealed
spaces of the articles in the container to the total interior
volume of the container (e.g., at a temperature of about 25.degree.
C.) may be less than about 0.99, preferably less than about
0.95.
Heat Transfer Fluid Compartment/Flow Path
[0091] The heat storage device has a heat transfer fluid
compartment for flowing a capable of containing a heat transfer
fluid as it circulates through the device. The heat transfer fluid
compartment preferably is connected to one or more orifices (e.g.
one or more inlets) for flowing a heat transfer into the heat
transfer fluid compartment. The heat transfer fluid compartment
preferably is connected to one or more orifices (e.g., one or more
outlets) for flowing a heat transfer out of the heat transfer fluid
compartment. The heat transfer fluid compartment may be a space at
least partially defined by one or more heat transfer fluid
compartment walls, a space at least partially defined by one or
more articles, a space at least partially defined by a housing or
container of the heat storage device, or any combination
thereof.
[0092] The heat transfer fluid compartment defines the flow path of
a heat transfer fluid through the heat storage device. The heat
transfer fluid compartment includes a generally axial flow path
through the openings of the stack of articles. The heat transfer
fluid compartment includes a generally radial flow path between two
adjacent articles. It will be appreciated that the radial flow may
be an inward flow from an outer periphery to the opening of an
article, or an outward flow from an opening to the outer periphery
of an article. The heat transfer fluid compartment includes a flow
path having a generally axial component (and optionally a
tangential component) between an outer periphery of the article and
a wall of the container. Preferably the combined radial flow paths
have a relatively high hydraulic resistance. For example, the
combined radial flow paths has a hydraulic resistance that is
greater than (more preferably at least two times greater than) the
hydraulic resistance of the central axial flow path, the outer
axial flow path, or both.
[0093] The heat transfer fluid compartment preferably has
sufficient thermal communication with the sealed spaces containing
the thermal energy storage material so that it can remove heat or
provide heat to the thermal energy storage material. The heat
transfer fluid compartment preferably is in direct thermal
communication with one or more (or more preferably all) of the
sealed spaces. A direct thermal communication can be any path of
shortest distance between a sealed space and a portion of the heat
transfer fluid compartment that is free of a material having low
thermal conductivity. Low thermal conductivity materials include
materials having a thermal conductivity less than about 100 W/(mk),
preferably less than about 10 W/(mk), and more preferably less than
about 3 W/(mK). For example, the heat transfer fluid or the heat
transfer fluid compartment may contact a wall of one or more (or
preferably all) of the sealed, or be separated from the sealed
spaces substantially or entirely by materials having high thermal
conductivity (e.g., greater than about 5 W/(mK), greater than about
12 W/(mK), or greater than about 110 W/(mK).
[0094] The heat transfer fluid compartment preferably is in direct
thermal communication with one or more (or more preferably all) of
the sealed spaces in the heat storage device. A direct thermal
communication can be any path of shortest distance between a
thermal energy storage compartment and a portion of the heat
transfer fluid compartment that is free of a material having low
thermal conductivity. For example, the heat transfer fluid or the
heat transfer fluid compartment may contact a wall of one or more
(or preferably all) of the sealed paces (such as a base sheet or a
cover sheet), or be separated from the sealed spaces substantially
or entirely by materials having high thermal conductivity (e.g.,
greater than about 5 V/(mK), greater than about 12 W/(mk), or
greater than about 110 W/(mK). It will be appreciated that a very
thin layer (e.g., less than about 0.1 mm, preferably less than
about 0.01 mm, and more preferably less than about 0.001 mm) of a
material having a low thermal conductivity may be between the heat
transfer fluid compartment and a thermal energy storage material
compartment without appreciably affecting the heat transfer.
[0095] The size and shape of the sealed spaces and/or articles may
be chosen to maximize the transfer of heat to and from the phase
change material contained in the capsules. The average thickness of
the article may be relatively short so that the heat can quickly
escape from the center of the sealed space. The average thickness
of the article, sealed space, or both may be less than about 100
mm, preferably less than about 30 mm, more preferably less than
about 10 mm, even more preferably less than about 5 mm, and most
preferably less than about 3 mm. The average thickness of the
article, the sealed space, or both, may be greater than about 0.1
mm, preferably greater than about 0.5 mm, more preferably greater
than about 0.8 mm, and most preferably greater than 1.0 mm.
[0096] The articles preferably have a relatively high surface area
to volume ratio so at the area of contact with the heat transfer
fluid is relatively high. For example, the article may have a
surface that maximizes the contact with a heat transfer fluid
compartment, the article may have a geometry that maximizes the
transfer of heat between the capsule and the heat transfer fluid
compartment, or both. The ratio of the total surface area of the
interface between the heat transfer fluid compartment and the
articles in the heat storage device to the total volume of the
thermal energy storage material in the heat storage device may be
greater than about 0.02 mm.sup.-1, preferably greater than about
0.05 mm.sup.-1, more preferably greater than about 0.1 mm.sup.-1,
even more preferably greater than about 0.2 mm.sup.-1, and most
preferably greater than about 0.3 mm.sup.-1.
Container Housing
[0097] The heat storage device has a container for containing the
stack of articles. The stack of articles may be contained in one or
more cavities of the container. Suitable containers have one or
more orifices (e.g., one or more inlets) for flowing a heat
transfer fluid into the cavity of the container and one or more
orifices (e.g., one or more outlets) for flowing a heat transfer
fluid out of the cavity of the container. The inlet and the outlet
may be on the same side or on different sides (e.g., opposing
sides) of the heat storage device. Other than the orifices, the
container preferably is sealed or constructed so that a fluid
flowing through the container does not leak out of the container,
so that a fluid flowing through the container may have a pressure
greater than ambient pressure, or both.
[0098] The container may have any shape. Preferably, the container
has a shape that can be filled with a large amount of thermal
energy storage material in the (e.g., in the sealed spaces of the
stack of articles) so that the heat storage device can store a
large quantity of heat. Without limitation, the container and/or
the cavity of the container may have a cross-section (e.g.,
perpendicular to the direction of stacking) that is generally
circular, generally oval-shaped, generally rectangular, generally
square-shaped, or have a different generally polygonal shape. In a
particularly preferred embodiment, the container has a generally
cylindrical shape, the cavity of the container has a generally
cylindrical shape, or both. For example, the container of the heat
storage device may have a generally cylindrical shaped inner
surface, a generally cylindrical shaped outer surface, or both. A
cylindrical shaped cavity may allow for efficient packing of
articles having a generally circular cross-section in the cavity.
By way of example, a generally cylindrically shaped articles has a
generally circular cross-section. A cylindrical shaped article, a
cylindrical shaped cavity, or both, may allow for efficient
insulation of the heat storage device. Typically, the container may
be characterized by a height in the direction of stacking of
articles (i.e., the axial direction) and an average length (e.g., a
diameter) in the direction perpendicular to the stacking direction.
For example, a cylindrically shaped container may be characterized
by a height and a diameter. The height to length (e.g. diameter)
ratio of the container may be less than about 20, preferably less
than about 5, more preferably less than about 3, and most
preferably less than about 2. The height to length ratio (e.g., the
height to diameter ratio) of the container may be greater than
about 0.05, preferably greater than about 0.2, more preferably
greater than at 0.33, even more preferably greater than about 0.5,
and most preferably greater than about 0.6. The cavity of the
container may be characterized by a height in the direction of
stacking of the articles and an average length (e.g., a diameter)
in the direction perpendicular to the stacking direction. Most
preferably, the interior of the container has a generally
cylindrical shaped cavity, characterised by a cavity diameter, a
cavity height, and an axial center. The interior of the container
may have a generally arcuate wall (having an arcuate surface) that
is parallel to the axial direction of the cavity. As previously
discussed, the arcuate surface preferably has a generally circular
cross-section. The container may be employed to house a stack of
the articles. The stack of articles is preferably arranged so that
there is a central axial flow path (e.g., through fluid passages of
a plurality of cavities) at or near the axial center of the cavity
of the container. The outer periphery of the articles may include
one or more indents, the interior wall of the container may have
one or more grooves (preferably in an axial direction, or a
direction having an axial component), the articles may have a
length or diameter less than the cavity length or diameter, or any
combination thereof, so that a heat transfer fluid can flow in an
axial direction between the outer peripheries of the articles and
the interior axial surface of the container. Such a flow may be
described as an outer axial flow. The stack of articles preferably
is arranged in the container so the the distance between the outer
periphery of the articles and the arcuate interior surface of the
container is generally uniform for different regions of an article
and for different articles (except for any indents in the article
or grooves in the wall of the container).
[0099] The heat storage device may be used in applications that
require storing heat for long periods of time, storing heat in a
generally cold environment (e.g., an environment having a
temperature less than about 0.degree. C., or even less than about
-30.degree. C.), or both. Preferably the heat stored in the heat
storage device is slowly lost to the environment Therefore some
form of insulation is preferably used in the present invention. The
better the insulation of the system is, the longer is the storage
time.
[0100] Any known form of insulation which reduces the rate of heat
loss by the heat storage device may be utilized. For example, any
insulation as disclosed in U.S. Pat. No. 6,689,751, incorporated
herein of its entirety by reference, may be employed. The heat
storage device preferably is (thermally) insulated container, such
that it is insulated on one or more surfaces. Preferably, some or
all surfaces that are exposed to ambient or exterior will have an
adjoining insulator, The insulating material may function by
reducing the convection heat loss, reducing the, radiant heat loss,
reducing the conductive heat loss, or any combination. Preferably,
the insulation may be through the use of an insulator material or
structure that preferably has relatively low thermal conduction.
The insulation may be obtained through the use of a gap between
opposing spaced walls. The gap may be occupied by a gaseous medium,
such as an air space, or possibly may even be an evacuated space
(e.g., by use of a Dewar vessel), a material or structure having
low thermal conductivity, a material or structure having low heat
emissivity, a material or structure having low convection, or any
combination thereof. Without limitation, the insulation may contain
ceramic insulation (such as quartz or glass insulation), polymeric
insulation, or any combination thereof. The insulation may be in a
fibrous form, a foam form, a densified layer, a coating or any
combination thereof. The insulation may be in the form of a woven
material, a knit material, a nonwoven material, or a combination
thereof. The heat transfer device may be insulated using a Dewar
vessel, and more specifically a vessel that includes, generally
opposing walls configured for defining an internal storage cavity,
and a wall cavity between the opposing walls, which wall cavity is
evacuated below atmospheric pressure. The walls may further utilize
a reflective surface coating (e.g., a minor surface) to minimize
radiant heat losses.
[0101] Preferably, a vacuum insulation around the heat storage
device and or the heat storage system is provided. More preferably,
a vacuum insulation as disclosed in U.S. Pat. No. 6,889,751,
incorporated by reference herein in its entirety, is provided.
Compaction Means
[0102] The heat storage device may optionally include one or more
compaction means to a stack of articles so that the spacing between
layers is generally maintained. The compaction means may be any
means capable of applying a compressive force to the stack of
articles. The compressive force should be sufficiently high so that
two articles do not rotate relative to each other, do not move
axially relative to each other, or both. The compressive force may
be sufficiently low so that an article is not permanently deformed,
cracked, or both. Preferred means of compaction will allow for some
changes in the thickness of the articles as the temperature of the
thermal energy storage material changes, as the thermal energy
storage material changes between a solid and a liquid phase, or
both. By way of example, the one or more means of compaction may
include one or more springs above the stack of articles, one or
more springs below the slack of articles, or both. Without
limitation, a means of compaction such as a spring, may be employed
to reduce or minimize the change in the thickness of a radial flow
path between two adjacent articles when the thermal energy storage
material is heated, undergoes a phase transition (such as a solid
to liquid transition) or both.
[0103] The heat storage device may have a plurality of flow paths
for the flow of a heat transfer fluid through the device. Each flow
path preferably includes at least one radial flow between two
adjacent articles. Preferably two or more (e.g., each) of the flow
paths through the heat storage device has a similar total length, a
similar total hydraulic resistance, or both. For example, two or
more (e.g., each of the flow paths may generally be characterized
as a Tichelmann system. An orifice of the heat storage device may
be connected to the openings of the stack of articles by a tube or
other means so that the heat transfer fluid must flow through the
axial path formed by the openings of the stack of articles.
Typically a tube connecting an orifice to the axial flow path
formed by the openings of the articles will extend to either one of
the first (e.g., the first) article in a stack of articles or one
of the last (e.g., the last) articles in a stack of articles. The
device may include one or more seals or plates (e.g., at the top
and/or bottom of the stack of articles) so that a heat transfer
fluid flowing from an inlet to an outlet must flow through a radial
flow path. A seal may include an opening for allowing a tube to
connect an orifice to the opening of the stack of articles. A seal
may be used to block the flow of the fluid at an end of an axial
flow path along the openings of the stack of articles, to block the
flow of a fluid at an end of an axial flow path along a periphery
of the stack of articles, or both.
[0104] Method for Making the Capsular Structure
[0105] The capsular structure and the articles containing the
thermal energy storage material may be formed using any method that
provides for the encapsulation of the thermal energy storage
material. Without limitation, the process may employ one or any
combination of the following: cutting or punching an opening (e.g.,
a hole) through a cover sheet, cutting or punching an opening
(e.g., a hole) through a base sheet (e.g., a thin sheet such as a
foil), forming (e.g., thermoforming, stamping, embossing or
otherwise deforming) a base sheet to define a pattern in the sheet
including at least one depression or trough region, forming a base
sheet to define a pattern in the sheet including one or more lip
regions and one or more trough regions, cutting or punching an
outer periphery (e.g., a generally circular outer periphery) on a
be sheet, cutting or punching an outer periphery (e.g., a generally
circular outer periphery) on a cover sheet, filling a trough (e.g.,
a trough formed from the base sheet) with a thermal energy storage
material, covering a trough (e.g., a filled trough) with a cover
sheet, sealingly attaching a cover sheet (e.g., to a base sheet) so
that one or more sealed spaces containing thermal energy storage
material are formed, sealingly attaching a base sheet along an
outer periphery, sealingly attaching a base sheet along an opening
periphery, sealingly attaching a cover sheet (e.g., to a base
sheet) along an opening periphery, or sealingly attaching a cover
sheet (e.g., to a base sheet) along an outer periphery. The process
of forming the article preferably includes a step of stamping,
embossing, or thermoforming a base sheet. The process of forming
the article may employ one or more of the process steps for
producing a capsule described in U.S. patent application Ser. No.
12/389,598 entitled "Heat Storage Devices" and filed on Feb. 20,
2009. The method for forming the article may optionally include one
or any combination of the following: sealingly attaching a base
sheet to one or more substructures such as an inner ring, an outer
ring, or both; sealingly attaching a cover sheet to one or more
substructures such as an inner ring, an outer ring, or both; or
cutting, stamping or punching one or more indents along the outer
periphery of a base sheet and/or a cover sheet.
[0106] According to the teachings herein, the capsular structure
(or a segment of the capsular structure) may be formed by a process
including sealingly attaching two sheets about their periphery.
Preferably at least one of the sheets is embossed, stamped, or
otherwise formed so that it is capable of holding a liquid. More
preferably both sheets are embossed, stamped or otherwise formed.
For example the capsular structure, or a segment thereof, may be
formed by a process including one or more of the following steps:
partially joining only a portion of an outer periphery of a first
sheet to a second sheet so that a space between the two sheets can
be filled with a thermal energy storage material; filling at least
a portion of the space between the two sheets with a thermal energy
storage material; and joining the remainder of the sheets so that a
sealed space including thermal energy storage material is formed.
One or more of these steps may be repeated to provide a structure
including a plurality of sealed spaces.
[0107] Suitable sheets for encapsulating the thermal energy storage
material include thin metal sheets (e.g., metal foil) that are
durable, corrosion resistant, or both, so that the sheet is capable
of containing the thermal energy storage material, preferably
without leakage. The metal sheets may be capable of functioning in
a vehicle environment with repeated thermal cycling for more than 1
year and preferably more than 5 years. The metal sheet may
otherwise have a substantially inert outer surface that contacts
the thermal energy storage material in operation. The outer surface
of the metal sheet that contacts the thermal energy storage
material should include or consist essentially of one or more
materials that do not significantly react with, corrode, or both,
when contacted with the thermal energy storage material. Without
limitation, exemplary metal sheets that may be employed include
metal sheets having at least one layer of brass, copper, aluminum,
nickel-iron alloy, bronze, titanium, stainless steel or the like.
The sheet may be a generally noble metal or it may be one that
includes a metal which has an oxide layer (e.g., a native oxide
layer or an oxide layer which may be formed on a surface). One
exemplary metal sheet is an aluminum foil which comprises a layer
of aluminum or an aluminum containing alloy (e.g. an aluminum alloy
containing greater than 50 weight percent aluminum, preferably
greater than 90 weight percent aluminum). Another exemplary metal
sheet is stainless steel. Suitable stainless steels include
austenitic stainless steel, ferritic stainless steel or martensitic
stainless steel. Without limitation, the stainless steel may
include chromium at a concentration greater than about 10 weight
percent, preferably greater than about 13 weight percent, more
preferably greater than about 15 weight percent, and most
preferably greater than about 17 weight percent. The stainless
steel may include carbon at a concentration less than about 0.30
weight percent, preferably less than about 0.15 weight percent,
more preferably less than about 0.12 weight percent, and most
preferably less than about 0.10 weight percent. For example,
stainless steel 304 (SAE designation) containing 19 weight percent
chromium and about 0.08 weight percent carbon. Suitable stainless
steels also include molybdenum containing stainless steels such as
316 (SAE designation). The metal sheet may have any art known
coating that may reduce or eliminate the corrosion of the metal
sheet.
[0108] The metal sheet has a thickness sufficiently high so that
holes or cracks are not formed when forming the sheet, when filling
the capsules with thermal energy storage material, during use of
the capsules, or any combination thereof. For applications such as
transportation, the metal sheet preferably is relatively thin so
that the weight of the heat storage device is not greatly increased
by the metal sheet. Suitable thicknesses of the metal sheet may be
greater than about 10 .mu.m, preferably greater than about 20
.mu.m, and more preferably greater than about 50 .mu.m. The metal
foil may have a thickness less than about 3 mm, preferably less
than 1 mm, and more preferably less than 0.5 mm (e.g., less than
about 0.25 mm).
[0109] FIG. 8 illustrates a cross-section of an exemplary heat
storage device 80 having a plurality of articles 10'', and 10'''
each laving thermal energy storage material 26 encapsulated in a
plurality of sealed spaces 14. The articles are arranged in an
insulated container 82 which may have a generally cylindrical
shape. The device includes an article 10'' having a first adjacent
article 10'''(a) and a second adjacent article 10'''(b), The
article 10'' and its first adjacent article 10'''(a) may be
arranged with the top surfaces (i.e., exterior surfaces) of their
respective flat cover sheets generally in contact. The article 10''
and the second adjacent article 10'''(b) may have generally mating
surfaces (e.g., the exterior surfaces of their respective base
sheets may be generally mating surfaces) and may be arranged so
that they partially nest together. A spacer (not shown) may be used
to maintain a distance between the article 10'' and its second
adjacent article 10'''(b) so that a heat transfer fluid can flow
through a radial flow path 83 in a generally radial direction
between the two articles, 10'' and 10'''(b). The space between the
article 10'' and the second adjacent article 10'''(b) is part of
the heat transfer fluid compartment. As illustrated in FIG. 8, each
article may have a surface (e.g., a surface of the base sheet) that
is in contact with the heat transfer fluid compartment so that the
heat transfer fluid can be in direct contact with each article and
preferably each seated space. As illustrated in FIG. 8, each radial
flow path 83 may have the same length, the same cross-section, or
even may be congruent. Each article has an opening near its center.
The openings are also part of the heat transfer fluid compartment.
The articles 10'' and 10''' are arranged so that their openings
form a central axial flow path 84. The space between the outer
periphery of the articles 10'' and 10''' and the interior surface
of the container 85 is also part of the heat transfer fluid
compartment and forms an outer axial flow path 86. The heat storage
device has a first orifice 87 that is in fluid connection with the
central axial flow path 84. The heat storage device may have a
first seal or plate 88 that separates the first orifice 87 from the
outer axial flow path 86. The container 82 has a second orifice 89
which may be on the same side of the container as the first orifice
87, or on a different side of the container, as illustrated in FIG.
8. The heat storage device may have a second seal 90 that separates
the second orifice 89 from the central axial flow path. The first
seal, the second seal, or both may prevent a fluid from flowing
between the two axial flow paths 84 and 86, without flowing through
a radial flow path 83. With reference to FIG. 8, a fluid flowing
between the first orifice 87 and the second orifice 89 must flow
through a portion of the central axial to path 84, and through a
portion of the outer axial flow path 86. The heat transfer fluid
must also flow through one of the radial flow paths 83 between
flowing through the two axial flow paths 84, 86. The sizes of the
two axial flow paths preferably are selected so that the
hydrodynamic resistance of the fluid is generally constant
regardless of which radial flow path a portion of the fluid takes.
As such, the flow of the heat transfer fluid through the heat
storage device is preferably a Tichelmann system The container 82
preferably is insulated. For example, the container may have an
inner wall 91 and an outer wall 92 and the space between the two
walls 93 may be evacuated. The device may also have one or more
springs, such as one or more compression springs 94, that exerts a
compressive force on the stack of articles.
[0110] FIG. 9 illustrates a heat storage device 80' having two
orifices 87' and 89' on one side of the container. Such a device
may employ as tube 95 that is connected to the first orifice 87'
for flowing the fluid between the first orifice and a region 96 of
the central axial flow path 84' furthest from the first orifice.
With reference to FIG. 9, the first seal 88' and the second seal
90' may be employed to prevent a fluid from flowing from the first
orifice 87' to the second orifice 89' without first flowing through
a radial flow path 83. Again, by selecting the sizes fare the two
axial flow paths 86 and 84', the heat storage device 80' of FIG. 9
may be characterized as a Tichelmann system.
Heat Storage System
[0111] The heat storage device may be used in a heat storage system
that employs one or more heat transfer fluids for transferring heat
into the heat storage device, for transferring heat out of the heat
storage device, or both.
Heat Transfer Fluid/Working Fluid
[0112] The heat transfer fluid used to transfer heat into and/or
out of the thermal energy storage material may be any liquid or gas
so that the fluid flows (e.g., without solidifying) through the
heat storage device and the other components (e.g., a heat
providing component, one or more connecting tubes or lines, a heat
removing component, or any combination thereof) through which it
circulates when it is cold. The heat transfer fluid may be any art
known heat transfer fluid or coolant that is capable of
transferring heat at the temperatures employed in the heat storage
device. The heat transfer fluid may be a liquid or a gas.
Preferably, the heat transfer fluid is capable of flowing at the
lowest operating temperature that it may be exposed to during use
(e.g., the lowest expected ambient temperature). For example, the
heat transfer fluid may be a liquid or gas at a pressure of about 1
atmosphere pressure and a temperature of about 25.degree. C.,
preferably about 0.degree. C., more preferably -20.degree. C., and
most preferably at about -40.degree. C. Without limitation, a
preferred heat transfer fluid for heating and/or cooling the one or
more electrochemical cells is a liquid at about 40.degree. C.
[0113] The heat transfer fluid should be capable of transporting a
large quantity of thermal energy, typically as sensible heat.
Suitable heat transfer fluids may have a specific heat (measured
for example at about 25.degree. C.) of at least about 1 J/gK,
preferably at least about 2 J/gK, even more preferably at least
about 2.5 J/gK, and most preferably at least about 3 J/gK.
Preferably the heat transfer fluid is a liquid. For example, any
art known engine coolant may be employed as the heat transfer
fluid. The system preferably employ a single heat transfer fluid
for transferring heat into the thermal energy storage material in
the heat storage device and for removing heat from the thermal
energy storage material in the heat storage device. Alternatively,
the system may employ a first heat transfer fluid for transferring
heat to the thermal energy storage material and a second heat
transfer fluid for removing heat from the thermal energy storage
material. In a system including a first heat transfer fluid and a
second heat transfer fluid, the first heat transfer fluid flows
through a first heat transfer fluid compartment and the second heat
transfer fluid flows through a second heat transfer fluid
compartment, wherein the heat transfer fluid compartments are
generally separated by a relatively low thermal conductivity
material, such as the thermal energy storage material. For example,
at least 20%, at least 50%, or at least about 80%, of the surface
area of the first heat transfer fluid compartment may contact or be
surfaces of articles containing the thermal energy storage
material. This contrasts with a heat exchanger in which two heat
transfer fluids are in relatively good thermal communication.
[0114] Without limitation, heat transfer fluids which may be used
alone or as a mixture include heat transfer fluids known to those
skilled in the art and preferably includes fluids containing water,
one or more alkylene glycols, one or more polyalkylene glycols, one
or more oils, one or more refrigerants, one or more alcohols, one
or more betaines, or any combination thereof. The heat transfer
fluid may include (e.g., in addition to or in lieu of the
aforementioned fluids) or consist essentially of a working fluid
such as one described hereinafter. Suitable oils which may be
employed include natural oils, synthetic oils, or combinations
thereof. For example, the heat transfer fluid may contain or
consist substantially (e.g., at least 80 percent by weight, at
least 90 percent by weight, or at least 95 percent by weight) of
mineral oil, caster oil, silicone oil, fluorocarbon oil, or any
combination thereof.
[0115] A particularly preferred heat transfer fluid includes or
consists essentially of one or more alkylene glycols. Without
limitation, preferable alkylene glycols include from about 1 to
about 8 alkylene oxy groups. For example the alkylene glycol may
include alkylene oxy groups containing from about 1 to about 6
carbon atoms. The alkylene oxy groups in a alkylene glycol molecule
may be the same or may be different. Optionally, the alkylene
glycol may include a mixture of different alkylene glycols each
containing different alkylene oxy groups or different ratios of
alkylene oxy groups. Preferred alkylene oxy groups include ethylene
oxide, propylene oxide, and butylene oxide. Optionally, the
alkylene glycol may be substituted. For example the alkylene glycol
may be substituted with one or two alkyl groups, such as one or two
alkyl groups containing about 1 to about 6 carbon atoms. As such
the alkylene glycol may include or consist essentially of one or
more alkylene glycol monoalkyl ethers, one or more alkylene glycol
dialkyl ethers, or combinations thereof. The all glycol may also
include a polyalkylene glycol. Particularly preferred alkylene
glycols include ethylene glycols, diethylene glycol, propylene
glycol, and butylene glycol. Any of the above glycols may be used
alone or as a mixture. For example, the glycol may be employed as a
mixture with water. Particularly preferred heat transfer fluids
include mixtures consisting substantially (e.g., at least 80 weight
percent, at least 90 weight percent or at least 96 weight percent
based on the total weight of the heat transfer fluid) or entirely
of a mixture of a glycol and water. The concentration of water in
the mixture preferably is greater than about 5 weight percent, more
preferably greater than about 10 weight percent, even more
preferably greater than about 15 weight percent, and most
preferably greater than about 20 percent, based on the total weight
of the heat transfer fluid. The concentration water in the mixture
is preferably less than about 95 weight percent, more preferably
less than about 90 weight percent, even more preferably less than
about 85 weight percent, and most preferably less than about 80
weight percent. The concentration of glycol in the mixture
preferably is greater than about 5 weight percent, more preferably
greater than about 10 weight percent, even more preferably greater
than about 15 weight percent, and most preferably greater than
about 20 percent based on the total weight of the heat transfer
fluid. The concentration of glycol in the mixture is preferably
less than about 95 weight percent, more preferably less than about
90 weight percent, even more preferably less than about 85 weight
percent, and most preferably less than about 80 weight percent.
[0116] Optionally, the heat transfer fluid may include or consist
substantially entirely of a working fluid. For example, the system
may include a working fluid that flows through the heat storage
device where it is heated and evaporates and then to one or more
components (such as a component to be heated f where the working
fluid condenses, As such, the heat storage device may function as
an evaporator for the working fluid and a component to be heated
may function as a condenser for the working fluid. If a working
fluid is employed, the heat provided to the condenser preferably
includes the heat of vaporization of the working fluid. The system
may include a cold line for returning the working fluid to heat
storage device, and a heat line for removing working fluid from the
heat storage device. The cold line and the heat line preferably are
capable of containing the working fluid without leaking as it is
flows through a loop. When the heat storage device (e.g., the
thermal energy storage material in the heat storage device) is at a
temperature sufficient to cause the combined vapor pressure of all
components of the working fluid to exceed about 1 atmosphere and a
valve is opened to allow the flow of the working fluid, the working
fluid may be a) pumped by a capillary structure; b) at least
partially vaporized; c) at least partially transported to the
condenser; and d) at least partially condenses in the condenser, so
that heat is removed from the heat storage device. As such the
system may optionally include a capillary pumped loop.
Working Fluids
[0117] The working fluids may be any fluid that can partially or
completely evaporate (transition from a liquid to a gaseous state)
in the heat storage device when the thermal energy storage material
is at or above its liquidus temperature. Suitable working fluids
e.g., for the capillary pumped loop) include pure substances and
mixtures having one or any combination of the following
characteristics: a good chemical stability at the maximum thermal
energy storage system temperature, a low viscosity (e.g., less than
about 100 mPas), good wetting of the capillary structure (e.g.,
good wick wetting), chemical compatibility with (e.g., the working
fluid causes low corrosion of) the materials of the capillary
pumped loop (such as the container material, the materials employed
to encapsulate the thermal energy storage material, the materials
of the vapor and liquid lines, and the like), a temperature
dependent vapor pressure that is conducive to both evaporator and
the condenser temperatures, a high volumetric latent heat of
vaporization (e.g., the product of the latent heat of fusion and
the density of the working fluid at about 25.degree. C. in units of
megajoules per liter may be greater than about 4 MJ/liter), a
freezing point less than or equal to the freezing point of the heat
transfer fluid of the condenser (e.g., a freezing point less than
or equal to the freezing point of antifreeze), or a freezing point
less than or equal to about -40.degree. C. For example, the
equilibrium state of the working fluid may be at least 90 percent
liquid at a temperature of -40.degree. C. and a pressure of 1
atmosphere.
[0118] Without limitation, exemplary working fluids may include or
consist essentially of one or more alcohols, one or more ketones,
one or more hydrocarbons, a fluorocarbon, a hydrofluorocarbon
(e.g., an art known hydrofluorocarbon refrigerant, such as an art
known hydrofluorocarbon automotive refrigerant), water, ammonia, or
any combination thereof.
[0119] The vapor pressure of the working fluid should be high
enough in the evaporator so that a vapor stream is produced that is
sufficient to pump the working fluid. Preferably, the vapor
pressure of the working fluid should be high enough in the
evaporator so that a vapor stream is produced that is sufficient to
carry the desired thermal power measured in watts from the
evaporator to the condenser. The vapor pressure of the working
fluid in the evaporator preferably is sufficiently low so that the
capillary pumped loop does not leak and does not rupture.
[0120] The wetting of the working fluid to the capillary structure
may be characterized by a contact angle of the working fluid on the
material of the capillary structure. Preferably, the contact angle
is less than about 80.degree., more preferably less than about
70.degree., even more preferably less than about 60.degree., and
most preferably less than about 55.degree..
[0121] The working fluid preferably condenses at moderate pressures
at temperatures below about 90.degree. C. For example, the working
fluid may condense at about 90.degree. C. at a pressure less than
about 2 MPa, preferably less than about 0.8 MPa, more preferably
less than about 0.3 MPa, even more preferably less than about 0.2
MPa, and most preferably less than about 0.1 MPa.
[0122] The working fluid preferably can flow at very low
temperatures. For example, the working fluid may be exposed to very
low ambient temperatures and preferably is capable of flowing from
the condenser to the heat storage device at a temperature of about
0.degree. C., preferably about -10.degree. C., more preferably
about -25.degree. C., even more preferably about -40.degree. C.,
and most preferably about -60.degree. C. The working fluid
preferably is in a gas state when it is at a temperature of the
fully charged heat storage device. For example, the working fluid
may have a boiling point at 1 atmosphere less than the phase
transition temperature of the thermal energy storage material in
the heat storage device, preferably at least 20.degree. C. less
than the phase transition temperature of the thermal energy storage
material, and more preferably at least 40.degree. C. less than the
phase transition temperature of the thermal energy storage
material. In various aspects of the invention, it may be desirable
for the working fluid to have a boiling point at 1 atmosphere (or
the temperature at which the combined vapor pressure of all of the
components of the working fluid is equal to 1 atmosphere may be)
greater than about 30.degree. C., preferably greater than about
35.degree. C., more preferably greater than about 50.degree. C.,
even more preferably greater than about 60.degree. C., and most
preferably greater than about 70.degree. C. (e.g., so that the
working fluid is a liquid at ambient conditions). In various
aspects of the invention, the boiling point at 1 atmosphere of the
working fluid may be (or the temperature at which the combined
vapor pressure of all of the components of the working fluid is
equal to 1 atmosphere may be) less than about 180.degree. C.,
preferably less than about 150.degree. C., more preferably less
than about 120.degree. C., and most preferably less than about
95.degree. C.
[0123] A particularly preferred working fluid includes or consists
substantially of water and ammonia. For example the combined
concentration of water and ammonia in the working fluid may be at
least about 80 weight percent, more preferably at least about 90
weight percent, and most preferably at least about 95 weight
percent based on the total weight of the working fluid) water and
ammonia. The concentration of ammonia may be sufficient to keep the
boiling point of the working fluid below the boiling point of water
(e.g., at least 10.degree. C. below the boiling point of water).
The concentration of ammonia may be greater than about 2 weight
percent, preferably greater than about 10 weight percent, more
preferably greater than about 15 weight percent and most preferably
greater than about 18 weight percent based on the total weight of
the working fluid. The concentration of ammonia may be less than
about 80 weight percent, preferably Less than about 60 weight
percent, more preferably less than about 40 weight percent and most
preferably less than about 30 weight percent based on the total
weight of the working fluid. The concentration of water in the
working fluid may be greater than about 20 weight percent,
preferably greater than about 40 weight percent, more preferably
greater than about 60 weight percent and most preferably greater
than about 70 weight percent based on the total weight of the
working fluid. The concentration of water in the working fluid may
be less than about 98 weight percent, preferably less than about 95
weight percent, more preferably less than about 90 weight percent,
even more preferably less than about 85 weight percent, and most
preferably less than about 82 weight percent based on the total
weight of the working fluid. For example a solution of about 21
weight percent ammonia and about 79 weight percent water has a
liquidus point of about -40.degree. C. and the upper limit of a
boiling range at 1 atmosphere of less than about 100.degree. C.
This solution may be stored (e.g., as a liquid) in a
non-pressurized container at room temperature.
[0124] Preferably the working fluid has a combined vapor pressure
of all of its components equal to 1 atmosphere at one temperature
from about 0.degree. C. to about 250.degree. C.
[0125] The working fluid is capable of efficiently transferring
thermal energy from the heat storage device so that the amount of
working fluid needed to remove an amount of heat from the heat
storage device is relatively small (e.g., compared to a device that
uses a heat transfer fluid that is not a working fluid to remove
the heat). Preferably a large portion of the heat transferred by
the working fluid is transferred in the form of heat vaporization.
The volume of working fluid, the flow rate of the working fluid, or
both, may be relatively low in the thermal energy storage compared
to a system that employs a heat transfer fluid that is not a
working fluid and has the same initial power. The flow rate of the
working fluid the working fluid in the liquid state flowing into
the heat storage device) per liter of the container of the heat
storage device may be less than about 5 liters/min, preferably less
than about 2 liters/min, more preferably less than about 1
liter/min, even more preferably less than about 0.5 liters/min, and
most preferably less than about 0.1 liters/ min. The ratio of the
volume of the working fluid in the system to the total volume in
the container of the heat storage device, or to the volume of the
thermal energy storage material in the heat storage device should
be sufficiently low so that the total weight of the system is not
excessively impacted by the weight of the working fluid. The ratio
of the volume of the working fluid in the system (e.g., in the
capillary pumped loop) to the total volume of the container (i.e.,
the volume inside the container) of the heat storage device (or
even the ratio of the volume of the working fluid in the system to
the volume of the thermal energy storage material in the heat
storage device) may be less than about 20; preferably less than 10,
more preferably less than about 4, even more preferably less than
about 2, and most preferably less than about 1.
[0126] As described above, the working fluid may transfer some of
the thermal energy in the form of heat of heat of vaporization. The
working fluid preferably has a high heat of vaporization so that
the amount of heat that can be transferred is high. Suitable
working fluids for the heat storage device may have a heat of
vaporization greater than about 200 kJ mole, preferably greater
than about 500 kJ/mole, more preferably greater than about 750
kJ/mole, even more preferably greater than about 1000 kJ/mole, and
most preferably greater than about 1200 kJ/mole.
[0127] In applications where the temperature of the working fluid
may be less than 0.degree. C., the working fluid preferably is not
water (e.g., so that the working fluid does not freeze, cause a
rupture, or both).
[0128] It will be appreciated that the materials that contact with
the working fluid may be resistant to corrosion from the working
fluid. For example, any one or all of the surfaces of the heat
storage device or the heat storage system that may come in contact
with the working fluid (e.g., the interior of the working fluid
vapor line, the interior of the working fluid liquid line, the
surfaces of the heat transfer fluid compartment of the heat storage
device, the interior surfaces of one or more valves, the surface of
a working fluid compartment in the condenser, the interior surface
of a working fluid reservoir, and the like) may be made of
stainless steel.
[0129] It will be appreciated that any of the working fluids or
heat transfer fluids employed in the thermal energy storage system
described herein may include an additives package. Such additive
packages are well known to those skilled in the art and are adapted
to fit the system in which the device of the invention may be
utilized. For example the additives package may include a
stabilizer, a corrosion inhibitor, a lubricant, an extreme pressure
additive, or any combination thereof.
Optional Heater
[0130] The heat storage system may optionally include one or more
heaters. The heater may be any heater that is capable of increasing
the temperature of the thermal energy storage material in the heat
storage device to a temperature above its transition temperature.
The heater may be any heater that converts energy (e.g., electrical
energy, mechanical energy, chemical energy, or any combination
thereof) into heat (i.e., thermal energy). The one or more heaters
may be one or more electric heaters. The one or more heaters may be
employed to heat some or all of the thermal energy storage in the
heat storage device. Preferably the system includes one or more
heaters that are in thermal communication with a heat storage
device. For example, the system may include one or more heaters
within the insulation of a heat storage device. An electric heater
may employ electricity from one or more electrochemical cells, from
an external source, or both. For example, when a vehicle is plugged
into an outlet connected to a stationary object, the heat storage
device may be maintained at a temperature above the liquidus
temperature of the thermal energy storage material in the heat
storage device using the electricity form an external source. When
the vehicle is not plugged into an outlet connected to a stationary
object, the heat storage device may be maintained at a temperature
above the liquidus temperature of the thermal energy storage
material in the heat storage device using electricity generated
from an electrochemical cell.
[0131] The heat storage device may be used in a process for heating
one or more components. The process may include flowing a heat
transfer fluid through the heat transfer device. The step of
flowing a heat transfer fluid through the heat storage device may
include flowing a heat transfer fluid having an initial temperature
through an inlet of the device; flowing the heat transfer fluid
through an axial flow path so the heat transfer fluid can be
divided into a plurality of radial flow paths; flowing the heat
transfer fluid through a radial flow path so that it can remove
heat from the thermal energy storage material, wherein the thermal
energy storage material has a temperature greater than the initial
temperature of the heat transfer fluid; flowing the heat transfer
fluid through a different axial flow path so that a plurality of
radial flow paths can recombine; flowing the heat transfer fluid
having an exit temperature through an outlet of the device; or any
combination thereof. Preferably the heat transfer fluid exit
temperature is greater than the initial temperature of the heat
transfer fluid. The process for heating one or more components may
employ a flow path through the heat storage device including one of
a selection of radial flow path and two axial flow paths, the flow
path having a total flow length, wherein the total flow length is
generally constant for the different radial flow paths.
[0132] The heat storage device and/or the heat storage system may
characterized as having a relatively high power (e.g., as measured
during the initial 30 or 60 seconds of heating) so that it can
rapidly heat a component, such as an internal combustion engine.
The heat storage device and/or the heat storage system may be
characterized by an average power greater than about 5 watts,
preferably greater than about 10 watts, more preferably greater
than about 15 watts, and most preferably greater than about 20
watts.
[0133] The heat storage device and/or the heat storage system may
be characterized as having a relatively high power density, so that
it can hold a large quantity of thermal energy in a relatively
small compartment. For example, the heat storage device and/or the
heat storage system may be characterized as having a power density
greater than about 4 kW/L, preferably greater than about 8 kW/L,
more preferably greater than about 10 kW/L, and most preferably
greater than about 12 kW/L.
[0134] The heat storage device and/or the heat storage system may
be characterized as having a relatively low pressure drop of the
heat transfer fluid (measured at a heat transfer fluid flow rate of
about 10 L/ min). For example, the heat storage device and/or the
heat storage system may be characterized as having a heat transfer
fluid pressure drop less than about 2.0 kPa, preferably less than
about 1.5 kPa, more preferably less than about 1.2 kPa, and most
preferably less than about 1.0 kPa.
[0135] By way of example, the thermal energy storage system may be
employed in a transportation vehicle (e.g., an automotive vehicle)
for storing energy from an engine exhaust gas. When the engine
produces exhaust gas, a bypass valve may either direct the flow of
the gas through the heat storage device so that the heat storage
device is charged, or through a bypass line to prevent the heat
storage device from overheating. When the engine is shut down, e.g.
during a period when the vehicle is parked, a substantial portion
of the heat stored in the heat storage device may be retained for a
long time (e.g., due to vacuum insulation surrounding the heat
storage device). Preferably at least 50% of the thermal energy
storage material in the heat storage device remains in a liquid
state after the vehicle has been parked for 16 hours at an ambient
temperature of about -40.degree. C. If the vehicle is parked for a
long enough time (e.g., at least two or three hours) for the engine
to cool down substantially (e.g., so that the difference in
temperature between the engine and the ambient is less than about
20.degree. C.), the heat stored in the heat storage device may be
discharged into the cold engine or other heat recipient indirectly
by flowing a heat transfer fluid (such as the engine coolant)
through the heat exchanger that includes the condenser for the
working fluid. The working fluid is circulated in a capillary
pumped loop using the capillary structure inside the heat storage
device where the working fluid is vaporized. The heat from the
working fluid is transferred to the engine coolant in the heat
exchanger. By employing the heat storage device, heat that
otherwise would be wasted may be captured during a previous trip to
mitigate cold start and/or provide instant cockpit heating.
[0136] A thermal energy storage system for storing heat, such as
heat from an vehicle exhaust may include some or all of the
features illustrated in FIG. 10. The thermal energy storage system
100 includes the heat storage device 101. The thermal energy
storage system may include a heat exchanger or condenser 102 having
a first inlet 117 for a first heat transfer fluid 107 and a first
outlet 117 for the first heat transfer fluid. The thermal energy
storage system 100 may have a tube (e.g., a line) 113 connecting
the first heat transfer fluid inlet 111 of the heat exchanger 102
to the first heat transfer fluid outlet of the heat storage device
101. The thermal energy storage system 100 may have a tube 109
connecting the first heat transfer fluid outlet 117 of the heat
exchanger 102 to the first heat transfer fluid inlet of the heat
storage device 101. The first heat transfer fluid 107 flows through
a first heat transfer fluid compartment of the heat storage device
101. The first heat transfer fluid may flow through a first heat
transfer fluid compartment of the heat exchanger 102. The first
heat transfer fluid may be a working fluid, the line from the heat
storage device 101 to the heat exchanger 102 may be a vapor line,
the heat exchanger 102 may be a condenser for the working fluid,
and the first heat transfer fluid compartments may be working fluid
compartments. As such, the thermal energy storage system 100 may
contain a capillary pumped loop including the working fluid
compartment in the heat storage device, a working fluid compartment
in the condenser, the working fluid vapor tube 109, and the working
fluid liquid tube 113. The thermal energy storage system also
includes one or more heat transfer fluid or working fluid
reservoirs 110. When used in a capillary pumped loop, the reservoir
110 preferably has a fill level that is higher in elevation than
the working fluid inlet of the heat storage device 101 and lower
than the elevation of the working fluid outlet 117 of the
condenser, the working fluid inlet 111 of the condenser, or both.
The thermal energy storage system 100 may include a valve 118 to
regulate the flow of the first heat transfer fluid in the tube 113
connecting the heat storage device 101 and the heat exchanger 102.
For example, the valve 118 may be used to prevent the heat transfer
fluid from circulating when the heat storage device is charging and
when the heat storage device is storing heat. The valve 118 may be
opened when it is desired to discharge heat from the heat storage
device. Referring again to FIG. 10, the thermal energy storage
system may includes a heat transfer fluid inlet line 108 and a heat
transfer fluid outlet line 106, for flowing second heat transfer
fluid into and out of the heat storage device 101. The thermal
energy storage system may also have a heat transfer fluid bypass
line 105 and a diverter valve (e.g., a bypass valve) 104 to divert
some or all of the second heat transfer fluid to the bypass line
105 (e.g., when the heat storage device is fully charged, or when
the temperature of the second heat transfer fluid is below a
temperature of the thermal energy storage material in the heat
storage device 101). The thermal energy storage system may also
include a cold line 116 for providing another heat transfer fluid
into the heat exchanger, and a heat line 116 for removing the
heated heat transfer fluid from the heat exchanger 102. The cold
line 116 and heat line 115 are part of a heat transfer fluid loop
114. The heat transfer fluid loop 114 may contains an engine
coolant. The heat transfer fluid loop 114 may be connected to an
internal combustion engine 103. As such, the thermal energy storage
system 100, may heat an internal combustion engine 103 with the
energy stored in the heat storage device 101.
[0137] The transfer of heat using the working fluid may begin by
opening the working fluid valve (i.e., the discharge valve). The
sealed working fluid reservoir connected to the loop via an
additional liquid line serves to accommodate changes in the working
fluid liquid volume inside the loop without substantial pressure
changes. Once sufficient or all useful heat is transferred from the
heat storage device, the discharge valve may close. The remaining
working fluid in the heat storage device may evaporate (e.g., from
heat remaining in the heat storage device or when the heat storage
device begins to charge) and then condenses in the condenser. As
the heat storage device becomes evacuated of the working fluid, the
liquid level of the working fluid level may change (e.g.,
rise).
[0138] The heat storage device may optionally be a cross-flow heat
exchanger (i.e., having a flow direction for the working fluid and
a perpendicular flow direction for the flow of the exhaust gas).
For example, during operation, the heat storage device may include
three chambers occupied by 1) exhaust gas; 2) stagnant phase change
material (e.g., inside capsules, such as a blisters pack); and 3)
working fluid. All three chambers are kept separate by thin walls
made of an appropriate material, preferably stainless steel.
Exhaust gas may flow between the surfaces (e.g., the curved
surfaces) of the capsules of phase change material inside blisters,
and the working fluid may flow between different surfaces (e.g.,
flat surfaces) of the capsules of phase change material inside
blisters in a direction that is generally perpendicular to the
exhaust gas flow direction. The liquid working fluid entering its
chamber preferably wets a capillary structure (e.g., a metal wick)
and gets transported up against the combined forces of gravity and
vapor pressure by the capillary forces acting upon the working
fluid liquid menisci formed inside the capillaries. This flow is
sustained by continuous evaporation of the liquid using the heat
drawn from the phase change material inside blisters. The vapor of
working fluid leaves the capillary structure and escapes to the top
of the device via vapor channels which may be interdigitated
between columns of the capillary structure squeezed between the
surfaces (e.g., the flat surfaces) of the capsules of phase change
material inside blisters. The vapor of working fluid flows into the
condenser where it transfers its heat of vaporization and sensible
heat to the cold coolant and becomes liquid again to return to the
heat storage device and continue its circulation in the loop, being
pumped only by the capillary forces existing inside the capillary
structure (e.g., metal wick) that is partially impregnated by
liquid working fluid. All columns of the capillary structure may be
connected to a common porous base. Such a porous base may be
employed to distribute the liquid working fluid entering from the
bottom of the device to the different columns.
[0139] Furthermore, the present invention may be used in
combination with additional elements/components/steps. For example,
absorption or adsorption cycle refrigeration system for air
conditioning may be used as the heat recipient instead of or in
addition to the cold coolant (e.g., the condenser may serve also as
an evaporator for the refrigerant circulating inside an air
conditioner's fluid loop). In another application, a steady-state
waste heat recovery system using a heat engine, e.g. a Rankine
cycle, can be constructed so that it uses the same or different
capillary pumped loop working fluid and adds a mechanical power
generating turbine to the vapor line between the heat storage
device and the condenser, (e.g., to overcome high vapor pressure
upstream from the turbine), and/or adds a liquid pump to the liquid
line between the condenser and heat storage device. The above
turbine can convert a part of the captured from the exhaust gas
waste heat into useful mechanical or electrical work and thus
improve the overall fuel efficiency of the vehicle.
[0140] While the present invention may be susceptible to various
modifications and alternative forms, the exemplary embodiments
discussed above have been shown by way of example. However, it
should again be understood that the invention is not intended to be
limited to the particular embodiments disclosed herein. Indeed, the
present techniques of the invention are to cover all modifications,
equivalents, and alternative falling within the spirit and scope of
the invention as defined by the following appended claims.
* * * * *