U.S. patent application number 16/099120 was filed with the patent office on 2019-05-16 for water storage tank with passive enhanced thermal energy management and resistance.
This patent application is currently assigned to FLEXCON INDUSTRIES, INC.. The applicant listed for this patent is FLEXCON INDUSTRIES, INC.. Invention is credited to Thomas W. Wideman.
Application Number | 20190145631 16/099120 |
Document ID | / |
Family ID | 60203340 |
Filed Date | 2019-05-16 |
United States Patent
Application |
20190145631 |
Kind Code |
A1 |
Wideman; Thomas W. |
May 16, 2019 |
WATER STORAGE TANK WITH PASSIVE ENHANCED THERMAL ENERGY MANAGEMENT
AND RESISTANCE
Abstract
A water storage tank with passive enhanced thermal energy
management is provided. The tank is formed of substantially
cylindrical central section comprising a majority of the length
along its axis and a dome-shaped section at each end, A first
system of managing energy management includes providing insulation
covering all or most of the tank in order to prevent heat flow
energy leaving the tank. The strength of the insulation, is varied
such that one end of the tank has less insulativity than the other
end of the tank. Preferably change occurs gradually along the axial
length of the tank. The second system for providing passive energy
management is using insulation formed of a material that has a
glass phase change temperature at or near the temperature of the
water when it enters the tank. In order for the temperature of the
water in the tank to change from the initial temperature it must
first cause the insulation to make that glass phase change in order
to either heat up or cool down from its initial temperature point.
By varying the mass or thickness of the glass phase insulation
along the axial length of the tank the amount of passive energy
resistance to change varies thereby causing desired convection
currents that serve to maintain a constant temperature within the
tank thereby slowing any change of temperature at minimum cost.
Inventors: |
Wideman; Thomas W.; (Milton,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FLEXCON INDUSTRIES, INC. |
Randolph |
MA |
US |
|
|
Assignee: |
FLEXCON INDUSTRIES, INC.
Randolph
MA
|
Family ID: |
60203340 |
Appl. No.: |
16/099120 |
Filed: |
May 5, 2017 |
PCT Filed: |
May 5, 2017 |
PCT NO: |
PCT/US17/31366 |
371 Date: |
November 5, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62332875 |
May 6, 2016 |
|
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Current U.S.
Class: |
122/13.01 |
Current CPC
Class: |
F28D 20/0034 20130101;
F28F 2270/00 20130101; F24D 3/1016 20130101 |
International
Class: |
F24D 3/10 20060101
F24D003/10; F28D 20/00 20060101 F28D020/00 |
Claims
1. A double diaphragm tank with passive thermal management for the
storage of water at temperatures up to 150.degree. C., while
avoiding the use of active heating or cooling means, the tank
comprising a central, substantially cylindrical housing section 1,
joined at two circumferential locations 2 and 22 to an upper and a
lower dome-shaped housing sections, and within the tank housing
sections, and secured to the inner circumferential surface of the
cylindrical housing section is a rigid diaphragm, and a flexible
diaphragm, the upper circumferential rim of the rigid diaphragm
being secured to the inner surface of the central housing section
and the flexible diaphragm being sealingly secured to the upper
rim, and circumferentially, internally of the rigid diaphragm, by a
removable circumferential clip; and an insulation layer surrounding
the housing sections; there being operatively connected to the
bottom of the tank, and extending through the bottom of the rigid
diaphragm, a water inlet pipe; and operatively connected to and
extending through the top of the tank is a pressure relief valve;
the improvement comprising, varying the insulative effectiveness of
the insulation layer, axially along the central housing section 1,
so that the either the upper or lower dome-shaped housing sections
are covered with a less effective insulation layer, so as to create
an internal temperature gradient in any water held in the tank, so
as to create convective mixing currents in such water within the
tank, when the water is at a temperature different from the ambient
temperature exterior of the tank.
2. The double diaphragm tank of claim 1, wherein the insulative
effectiveness of the insulation layer is varied by providing a
sealed insulation and varying the width of the air gaps within
portions of the insulation layer.
3. The double diaphragm tank of claim 1, wherein the insulative
effectiveness of the insulation layer is varied by changing the
thickness of the insulation layer.
4. The double diaphragm tank of claim 1, extending vertically,
wherein the insulative effectiveness of the insulation layer is
varied such that the Kvalue of the insulation layer in one of the
upper or lower dome sections is at least 10% greater than the
insulation in the rest of the tank, intended to create convective
currents in water in the tank to improve temperature distribution
in the water and to prevent fouling of the internal surfaces of the
tank.
5. A double diaphragm tank with passive thermal management for the
storage of water at temperatures up to 250.degree. F., while
avoiding the use of active heating or cooling means, the tank
comprising a central, substantially cylindrical housing section 1,
joined at two circumferential locations 2 and 22 to an upper and a
lower dome-shaped housing sections, and within the tank housing
sections, and secured to the inner circumferential surface of the
cylindrical housing section is a rigid diaphragm, and a flexible
diaphragm, the upper circumferential rim of the rigid diaphragm
being secured to the inner surface of the central housing section
and the flexible diaphragm being sealingly secured to the upper
rim, and circumferentially internally of, the rigid diaphragm by a
removable circumferential clip; and an insulation layer surrounding
the housing sections; there being operatively connected to the
bottom of the tank and extending through the bottom of the rigid
diaphragm is a water inlet pipe, and operatively connected to and
extending through the top of the tank is a pressure relief valve;
the improvement comprising securing to the housing sections a layer
of insulating material having a glass transition temperature not
greater than the desired temperature of the water in the tank, in
order to maintain the temperature of the tank near the glass
transition temperature.
6. The double diaphragm tank of claim 4, wherein the insulative
effectiveness of the insulation layer is varied by varying the
quantity of the glass phase transition material within the
insulation layer.
7. The double diaphragm tank of claim 4, wherein the insulative
effectiveness of the insulation layer is varied by varying the
thickness of the glass phase transition material within the
insulation layer.
8. The double diaphragm tank of claim 4, wherein the insulative
effectiveness of the insulation layer is varied by varying the
spacing of the glass phase transition material insulation layer
from the surface of the tank shell.
Description
BACKGROUND OF THE INVENTION
[0001] Tanks used for the storage of elevated temperature water,
such as hydronic heating, hot water expansion, buffer tanks, and
geothermal heating tanks, are required to maintain a temperature
differential with the outside environment, and in some cases, a
temperature gradient within the tank itself. The approach to
maintaining temperature, or temperature gradient, has typically
been to either insulate the tank as a whole, or actively heat or
cool the tank, or a combination of both. Previous approaches to the
design of these tanks, including the materials of construction for
fluid barriers, pressure reinforcement, and insulation, have
provided largely uniform properties around the tank, not taking
advantage of differences in thermal properties of these materials
to optimize the performance of the tank. Meanwhile, active heating
and cooling has the disadvantage of consuming additional energy,
usually in the form of electricity, natural gas, or other fossil
fuels. Therefore, there is a need for novel hot water storage tanks
that take advantage of differences in the thermal properties of the
materials of construction to provide enhancements in passive
thermal management.
GENERAL DESCRIPTION OF THE INVENTION
[0002] The present invention provides an efficient, inexpensive
passive means to provide a double diaphragm water tank, capable of
providing the desired temperature maintenance. In accordance with
one preferred aspect of the present invention, there is provided a
double diaphragm holding tank with passive thermal management for
the storage of water at temperatures up to 250.degree. F. This
invention avoids the use of more costly active heating or cooling
means. Preferably, the tank comprises a central, elongated,
substantially cylindrical housing section 1, joined at two
circumferential end locations 2 and 22 to an upper and a lower
dome-shaped housing end-sections. Within the tank housing sections,
and secured to the inner circumferential surface of the cylindrical
housing section is a flexible diaphragm and, preferably, a rigid
diaphragm. The flexible diaphragm is preferably secured to the
upper circumferential rim of the rigid diaphragm, which in this
preferred embodiment is secured to the inner surface of the central
housing section and the flexible diaphragm is sealingly secured to
the upper rim, and circumferentially internally of, the rigid
diaphragm by a removable circumferential clip. This invention
provides an insulation layer surrounding the housing sections,
which is preferably formed on the elongated central tank section
and at least closely adjacent the dome sections, if present.
Operatively connected to the bottom of the tank and extending
through the bottom of the rigid diaphragm, if present, is a water
inlet pipe, and operatively connected to and extending through the
top of the tank is a pressure relief valve and nipple.
[0003] This invention provides a varying insulative effectiveness
of the insulation layer along the length of at least the central
elongated section, so that either the upper or lower dome-shaped
housing section is covered with a less effective insulation layer,
so that an internal temperature gradient is formed in the water,
and thus to create convective mixing currents in water within the
tank, when the water is at a temperature different from the
temperature exterior of the tank. This can be accomplished by
varying the thickness of the insulation along its length, or to
otherwise change the effectiveness of the insulation, such as by
changing its nature.
[0004] Another novel aspect of this invention is the use of an
insulative material that has a glass phase transition temperature
(t.sub.g) of about the incoming temperature of the water in the
tank, or preferably slightly lower. This temperature is commonly up
to about 250.degree. C. Generally, the insulation material should
be tailored to the intended use of the tank, i.e., for holding cool
water at room temperature or lower, or to hold hot water, as may be
used for a hot water tank in the home or commercial building or
factory.
[0005] Further, the desired variability of the insulative
effectiveness can be achieved by selecting insulation material
having a t.sub.g near the desired temperature of the water in the
tank.
[0006] The insulative effectiveness of material selected for its
t.sub.g may also be varied by varying the thickness of the glass
phase insulation, or by reducing the percentage of that material in
the total insulation, along the axial length of the tank, or even
by varying the nature of the insulation material, so as to reduce
the t.sub.g of material forming the insulation along the length of
the tank, to thereby create different temperatures along the length
of the tank, so as to create the desired convection currents.
[0007] The glass phase transition temperature can also be useful
when it is desired to merely increase the time of maintaining a
constant temperature as compared with using the usual selection of
material having a higher t.sub.g. glass phase transition
temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic cross-section of an elevated
temperature water tank according to an embodiment of the invention,
representing the tank charged with air pressure and the space below
the flexible diaphragm being not charged of water; and
[0009] FIG. 1B is an expanded view of the schematic cross-section
of the diaphragm tank in FIG. 1.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
[0010] FIG. 1 is a cross section of a double diaphragm tank 11 with
passive thermal management.
[0011] The upper portion of inside the tank, outside of the rigid
diaphragm 31, and flexible diaphragm 32, is charged with air
through the nipple 9, and lower portion, between rigid diaphragm 31
and flexible diaphragm 32, may be charged with water. The tank
comprises a central, substantially cylindrical housing section 1,
joined at two circumferential joint locations 2 and 22 to
dome-shaped housing sections 5 and 6, respectively. The overall
tank 11, preferably forms a substantially isotensoidal shape. The
dome-shaped section 5 further comprises an air valve and nipple 9,
which allows one area of the tank to be charged with air or gas.
The lower dome-shaped section 6 further comprises a threaded
connection 10 through which water can flow, via pipe 110, which
extends to the bottom of the rigid diaphragm 31; through a
water-tight seal the pipe 110 can discharges water into the volume
between the two diaphragms 31,32. The condition of the flexible
diaphragm 32, when the volume is filled with water is shown by the
dashed line A, in FIG. 1.
[0012] The three housing sections 1, 5, and 6 are further
reinforced with a pressure barrier, 41, and an insulation layer 42,
and an outer shell, 43, substantially surrounding the pressure
barrier 41, with openings for an inlet/outlet line 10 and for the
pressure relief valve 9, and any other fittings or valve. Although
the insulation layer 42 is shown as a rectangular box surrounding
the tank, the insulation layer 42 is actually formed adjacent to at
least the cylindrical central section 1, as shown in FIG. 1B.
[0013] In certain embodiments, the tank sections and housing
sections 1, 5, 6 and rigid diaphragm 31, may be independently, or
together formed of non-metallic materials, selected from the group
including thermoplastic polymers, thermoset polymers, whether
plastic or elastomeric, natural rubbers, or multilayer materials
comprising the same.
[0014] In certain embodiments, the tank segments and housing
sections 1, 5, 6 and rigid diaphragm 31 may be formed of materials
selected from a group of thermoplastics including polyolefins,
polyethylene, polypropylene, polybutylene, nylon, PVC, CPVC,
ionomers, fluoropolymers, copolymers, crosslinked polyolefins such
as crosslinked polyethylene (PEX, PEX-a. PEX-b, PEX-c or XLPE), or
multilayer structures comprising the same. The individual items
forming the above-described tank: housing sections 1, 5, 6 and
rigid diaphragm 3 may also include a "tie-layer". A "tie layer" is
usually one or a combination of two or more mutually compatible
materials that form a bonding layer between two mutually
incompatible materials. Tie layers may include, for example, a
thermoplastic material that provides adhesion to two adjacent
materials, most often through melt processing or chemical
reactions; modified acrylic acid, or anhydride grafted polymers or
those similar to but not limited to DuPont's Bynel, Nucrel, and
Fusabond grades, or those described and referenced, as further
examples, in U.S. Pat. Nos. 8,076,000, 7,807,013 and 7,285,333. The
melting point or melt index of the tie layer may be selected so
that the tie-layer can be post-processed without substantially
melting or flowing other non-metallics in the structure.
[0015] In some embodiments, housing sections 1, 5, 6 and rigid
diaphragm 31 may be filled polymers or comprise solids such as but
not limited to particles or flakes of polymers or minerals
including glass, talc, carbon and graphite; chopped fibers,
discontinuous fibers, short or long fibers, or continuous fibers of
polymers or minerals including glass or carbon; nanocomposites;
clays; or other fibers, particles, flakes or hollow microspheres.
In some embodiments, housing sections 1, 5, 6 and rigid diaphragm
31 are independently or together metals, such as but not limited to
steels, stainless steels, aluminum, or the like. In some cases, 5
and 6 may further comprise fittings or valves, including those made
of metals or non-metals, including but not limited to threaded
fittings, compression fittings, bulkhead fittings, quick-disconnect
fittings, clip or crimp fittings, air valves, ball valves, needle
valves or the like. In some cases, housing sections 5 and 6 may
provide surfaces on which to make additional connections through
processes including but not limited to stick welding, butt welding,
spin welding, friction stir welding, ultrasonic welding, induction
welding, solvent welding, RF/microwave processing, resistance-based
fusion, adhesives, tie layers, or the like. These fittings, valves,
or other surfaces may be connected by means known to those skilled
in the art to additional system components including, but not
limited to, heaters, filters, pumps, pipes, tanks, or hoses.
[0016] In certain preferred embodiments, housing sections 1, 5, 6
and rigid diaphragm 31 are polypropylene, ethylene-polypropylene
copolymers, and glass particle or glass fiber-filled polypropylene
and ethylene-polypropylene copolymers. The ethylene-propylene
copolymers may be block copolymers. The melting point and melt
index of housing sections 1, 5, 6 and rigid diaphragm 31 may be
tailored to improve the assembly and processing of the tank. In
certain embodiments, the outer surface of housing sections 1, 5, 6
and rigid diaphragm 31 may be independently or together surface
modified by high energy treatments including ion implantation,
plasma, corona or arc, to improve adhesion to adjacent materials.
The inner surface of housing sections 1, 5, 6 and rigid diaphragm
31, and flexible diaphragm 32, can also be modified to change
properties, such as, but not limited to, chemical resistance,
permeability, and wettability by water. Treatments may include but
not limited to fluorination or the technologies employed by NBD
Nano, or by metallization through chemical vapor deposition or the
like. In certain preferred embodiments, polypropylene,
polypropylene copolymers, glass filled polypropylene and glass
filled polypropylene copolymers are treated by a flame to improve
adhesion to adjacent layers. In some preferred embodiments, housing
sections 1, 5, 6 and rigid diaphragm 31, and flexible diaphragm 32
may include antimicrobials, including antifungals, antivirals, or
antibiotics, or comprise silver. In other preferred embodiments,
housing sections 1, 5, 6 and rigid diaphragm 31, and flexible
diaphragm 32 contain antioxidants and stabilizers.
[0017] The flexible diaphragm 32 may be comprised of a polymer,
elastomer, rubber, RTV, or thermoplastic, or multiple layers
comprising the same. In certain preferred embodiments, the
diaphragm 32 comprises butyl rubber or EPDM. In other embodiments,
the diaphragm may be filled with solids such as but not limited to
particles or flakes of polymers or minerals including glass, talc,
carbon and graphite; chopped fibers, discontinuous fibers, short or
long fibers, or continuous fibers of polymers or minerals including
glass or carbon; nanocomposites; clays; or other fibers, particles,
flakes or hollow microspheres; or woven or non-woven fabrics; to
improve the thermomechanical properties or decrease permeability of
gases through the membrane. In some embodiments, these multiple
layers of the diaphragm are bonded, but the layers may also be
non-bonded. In certain embodiments, the layers include a thin
higher modulus layer supported by a thicker, lower modulus layer.
The high modulus layer may be selected from chemically resistant
polymers, or polymers preferred for contact with potable water,
such as polypropylene, polyethylene, polybutylene, or the like. The
low modulus layer may be selected for different properties, such as
durability, toughness, and low cost, protected from contact with
the potable water by the high modulus layer.
[0018] The flexible diaphragm 32 may also comprise features to
reduce the tendency of the diaphragm to wear or become fatigued in
service, or protect it from abrasion or cutting by adjacent
structures such as a clinch ring. In some cases, the flexible
diaphragm 32 may be of substantially non-uniform thickness or
modulus. The non-uniform thickness or modulus may be controlled
across the surface to reduce the tendency for the diaphragm to rub
against itself, against other structures, abrade or tear. The
flexible diaphragm 32 can also be substantially folded, in an
accordion, serpentine, or wavy shape. These shapes may allow for
more compact or rigid diaphragms to be used, while still allowing
extension in service without localized strains exceeding the limits
of the materials. The diaphragm may be further molded or installed
in the shape or orientation that it is most often in service to
reduce the in-situ strains or abrasion.
[0019] The flexible diaphragm 32 can be sealably joined at the
peripheral edge to the rigid diaphragm 31, by methods known to
those skilled in the art. Such sealable joints can be formed using,
for example, adhesives, solvent bonding, stick welding, butt
welding, spin welding, friction stir welding, induction welding,
RF/microwave processing, resistance-based fusion, tie layers, or
the like, with or without additional sealants. In certain preferred
embodiments, the connection of the peripheral edges of diaphragms
31 and 32 may also be made by the application of a rigid clinch
ring 3. Such a clinch ring 3 can be comprised of metal or non-metal
and provides a clamping force by means known to those skilled in
the art, such as but not limited to crimping, snap coupling,
fasteners, adhesives, melt processing, thermoforming or the like.
The connection between clinch ring 3, the flexible diaphragm 32 and
the rigid diaphragm 31 is accomplished by the use of features or
structures that improve the connection and seal such as lips,
dimples, ridges, knobs, integral rings, including multiple
rings.
[0020] In certain preferred embodiments, the flexible diaphragm 32
may extend over both sides of the rigid diaphragm 31 and/or be
gripped between the surfaces of a u-shaped clinch ring 3, i.e., a
preferably elastic ring with a u-shaped cross-section. In some
cases, the clinch ring 3 may have a contour that controls the
radius of curvature of the diaphragm and protects the diaphragm
from contacting any sharp edges.
[0021] In some embodiments, housing sections 1, 5, 6 may be further
reinforced by the pressure barrier 41 to increase the pressure
carrying capabilities of the expansion tank. This reinforcement may
comprise glass (including but not limited to borosilicate, e-, s-,
and cr-glass), basalt, quartz, carbon or other inorganic or mineral
fibers. The reinforcement may also comprise organic or inorganic
polymer fibers such as but not limited to polyester, nylon,
polypropylene, aramid, Kevlar, Nomex, PPS or carbon. These fibers
or fillers may be continuous or discontinuous fibers, chopped,
non-wovens or random oriented mat, or may be in the form of fiber
tapes. The reinforcing materials may be in a thermoset or
thermoplastic matrix, or present without a matrix. In certain
preferred embodiments, the reinforcement is a fiberglass-reinforced
epoxy. The reinforcement of pressure vessels by, for example,
filament winding is well known to those skilled in the art. In some
cases, the reinforcement is a metal such as but not limited to
steels, stainless steels, aluminum or the like.
[0022] In certain embodiments, the tank does not include a rigid or
flexible diaphragm, but is rather largely filled with water. In
other preferred embodiments, there may be additional ports into the
tank, including through the wall of the cylinder 1 and the pressure
barrier 41. In certain embodiments, dome 5 may include additional
features that encourage mixing or turbulent flow, or in some cases,
laminar flow. In other embodiments additional features or plumbing
may extend from fitting 10 into the water chamber to control flow
of water within the tank.
[0023] In some embodiments, housing sections 1, 5, 6 with or
without rigid diaphragm 31 and flexible diaphragm 32, and with or
without pressure barrier 41, can be further insulated with
insulation layer 42. The insulation layer 42 may be material with a
low K value, including continuous or discontinuous fiber
insulation, pulverized or aerated materials, flakes, or chopped
materials that are poured or blown into an outer shell 43, or may
be wet blown onto the surface with or without the use of binders or
adhesives. The insulation layer 42 may also be a flexible, rigid,
or semi-rigid foam. Although the insulation layer 42 and outer
shell 43 are diagrammatically shown as a rectangle, they are
preferably formed concentric with the pressure barrier 41. The foam
may be comprised of polymers, thermosets, elastomers, ceramics, or
the like. The foam may further comprise air, CO2, or blowing agents
including hydrofluorocarbons. The foam may be formed by pouring a
foaming material, such as a two-part expanding foam urethane, into
the 43. Alternatively, preformed foam can be wrapped around the
tank or joined as sections such as in a "clam shell". Some foams,
including flexible, semi-rigid, heat formable, or kerfed may be
wrapped around the tank. In some preferred embodiments, there is a
small gap between the pressure barrier 41 and the insulation layer
42.
[0024] The outer shell 43 can be comprised of metal or non-metals,
including thermoplastics or thermosets. It may be formed as a
continuous shell by means such as but not limited to extrusion or
rotomolding or it may be applied as a wrap. The wrap may be joined
by overlap joints, but welds, seam welds, or mechanical fasteners;
the mechanical fasteners may further engage the insulation layer
42. Outer shell 43 may also have the tendency to shrink by either
induced stress from the fabrication process, application of
additional heat (such as heat shrink), or by the elasticity of
outer shell 43. In a preferred embodiment, there is a small gap
between the outer shell 43 and the insulation 42. Insulation layer
42 may be non-uniform around the tank. In one preferred embodiment,
there is extra insulation on the top of the tank, and less or no
insulation at the bottom. The pressure barrier 41, insulation layer
42 and outer shell 43 may also include barrier layers, such as
plastic or elastomeric moisture barriers, thermally reflective
foils, metallized layers, or the like. In one preferred embodiment,
insulation layer 42 and outer shell 43 may each independently have
a reflective lining 50, such as shown in FIG. 1B.
[0025] All of these materials and design elements are well known to
those skilled in the art and are common in the industry. The novel
invention, disclosed herein, is the use of novel passive designs to
enhance the thermal management without the use of active heating or
cooling, specifically for applications where the temperatures
exceed about 65.degree. C.
Smart Mixing
[0026] In one embodiment of Smart Mixing, a tank shown in FIG. 1 is
capable of operating from -40.degree. F. to a maximum temperature
150-250.degree. F. The tank comprises a dome 5, fiber reinforcement
41, insulation layer 42, and outer shell 43, that independently or
together produce a K value that is at least 10% higher through the
dome 5, than the rest of the shell, or more preferably at least 25%
higher. This decreased insulation at the top of the tank changes
the near-field temperature of the fluid inside. The temperature
differential between the top surface of the tank and the rest of
the fluid in the tank has been found to induce convective currents,
which stir the fluids, improving the temperature distribution as
well as cleaning the surfaces from fouling, all without any
additional added forces, stirrers, or heaters. Similarly, the Smart
Mixing tank can have a lower dome 6, fiber reinforcement, bottom
insulation, or other features which produce a K value that is
10%-25% lower than the rest of the shell, causing near-field
temperature inversion, increasing convection within the tank and
stirring the sediment from the bottom of the tank, without the need
for additional moving parts or energy inputs.
[0027] In another embodiment of Smart Mixing, a multi-layer
composite tank is capable of operating from -40.degree. F. to a
maximum temperature 150-250.degree. F. The inner surfaces of
housing sections 1, 5, 6 are manufactured with internal upsets.
These upsets, or small baffles, may be as large as 0.1'' or as
small as 0.05'', protruding into the inside of the tank, such that
when fluids are moving within the tank, either from bulk or from
convective currents, the flow is disrupted and the increase in
turbulence improves the mixing within the tank and cleaning of
surfaces without the need for additional moving parts or energy
inputs.
Smart Strain Relief
[0028] In another embodiment of the improved passive thermal
management, a tank shown in FIG. 1 is capable of operating from
-40.degree. F. to a maximum temperature 150-250.degree. F., and is
fitted with additional ports through the side wall. Ports or
openings that penetrate the outer wall of the tank, especially
through housing section 1 and pressure barrier 41, are well
understood to be weak points in the structure of the tank, and the
location of stress risers. These areas of weakness and enhanced
stress are further exacerbated by temperature differentials with
the outside environment. In this embodiment, metal is incorporated
in and around ports. This serves to draw temperature from the tank,
into the ports, and moderate the temperature transition between the
tank and the outside environment and reduce thermal stress on the
sensitive joint structures, without the need for additional fiber
reinforcement.
Phase Transition Materials
[0029] In another embodiment of the novel passive, integrated
thermal management of the present invention, a multi-layer
composite tank shown in FIG. 1 is capable of operating from as low
as -40.degree. F. to a maximum temperature 150-250.degree. F. and
the thermal management is imparted to said tank through the use of
selected phase transition materials as insulators. Phase transition
materials may include thermoplastics or thermosets that have a
glass transition temperature within the operating window of said
tank, preferably at or below the initial inlet temperature of the
water entering the tank. These phase transition materials are used
to maintain the stored water temperature near the phase transition
for longer than if the phase transition was outside, especially far
above, the water temperature.
[0030] Examples of polymers that could be used to prepare
insulation are shown in the several listed in Table 1, below,
together with their glass phase transition temperatures (t.sub.g).
There are many well-known texts providing the transition
temperatures of available synthetic polymers as well as natural
materials.
TABLE-US-00001 TABLE I Tg Polymer (Glass Transition Temperature)
Nylon 6/6 50.degree. to 60.degree. C. Polycarbonate 140.degree. to
150.degree. C. Polyethelene Terephthalate (PET) 70.degree. to
80.degree. C. Polymethyl Methacrylate (PMMA) 85.degree. to
105.degree. C. Polyphenylene Sulfide 85.degree. to 95.degree. C.
Polystyrene 90.degree. to 110.degree. C. Polytetrafluoroethylene
(PTFE) 120.degree. to 130.degree. C. Polyeurethane (Thermoplastic)
120.degree. to 160.degree. C. Polyvinyl Alcohol 80.degree. to
90.degree. C. Polyvinyl Chloride (PVC) 65.degree. to 85.degree.
C.
Ranges of temperatures are often shown due to the fact that such
values are often dependent upon the particular molecular weight of
the polymer, its method of manufacture and many factors well-known
to the polymer chemists who prepare such materials. The novelty of
the present invention does not reside in the method of making the
polymers, but rather in the novel way in which they are being used
to maintain temperatures of stored water, especially hot water.
Other polymers may be used for purposes of this invention without
departing from its scope. The listed Tg is usually some middle
point within the range over which the polymer transitions from a
softer state to a rigid glass. Therefore, it should be understood
that the phase change effect on temperature may linger over a range
of dropping temperatures.
Air Gap Inducers
[0031] In one embodiment of integrated passive thermal management,
a multi-layer composite tank in FIG. 1 is capable of operating from
-40.degree. F. to a maximum temperature 150-250.degree. F. Novel
features imparted into the wall of housing section 1, pressure
barrier 41, insulation layer 42, and outer shell 43 intentionally
provide spacing between the two layers. In one preferred
embodiment, the tank includes air gap inducers 51. These stand-offs
are designed to create small, air filled spaces between pressure
barrier 41 and insulation layer 42, and between insulation layer 42
and outer shell 43. In one exemplary embodiment, these stand-off
inducers decreased the heat loss from the tank by 20%. In another
embodiment multiple air gaps are used. These air gaps can be
individually selected between the rigid diaphragm 31 and dome 6;
housing sections 1, 5, 6 and the pressure barrier 41; the pressure
barrier 41 and the insulation layer 42; and the insulation layer 42
and the outer shell 43.
[0032] These air gap inducers have been found to maintain the
temperature of the tank for 2.times. longer without the need for
additional heat input. In one preferred embodiment, the air gap is
greater at the top than at the bottom to optimize temperature
striation, ideally suited for applications such as solar hot water
storage tanks.
[0033] In another embodiment, the air gap between surfaces is
controlled by changing the internal pressure or modulus of the
materials of construction during the curing of the matrix of
pressure barrier 41. In a preferred embodiment, the modulus of the
housing sections 1, 5, 6, is decreased by 5% or more through the
use of temperature and the internal air pressure is increased by at
least 10%. By increasing the air pressure inside the tank, and
decreasing the modulus of the inner layers, the gap between layers
can be reduced to less than 0.01 which has been found to be optimal
for passive thermal management.
[0034] In another embodiment, the thermal management of the tank
controlled by tailoring the amount of thermoset matrix, or fiber
volume fraction, in the tank. In one preferred embodiment, the
matrix is an epoxy, the fibers are glass, and the relative
concentration of the epoxy is lower on the top of the tank than on
the bottom. In another preferred embodiment, the amount of epoxy is
below the amount theoretically needed to fill the spaces between
the fibers resulting in extremely small voids which help serve to
insulate the tanks and retain heat.
[0035] In another embodiment, a small air gap is provided to said
tank by reducing the bonding between the housing sections 1, 5, 6
to the pressure reinforcement at joints 2 and 22. This reduces the
heat loss at this location, increasing the temperature and reducing
the modulus at joints 2 and 22 to improve the ductility and
toughness in this high stress location. This air gap is most
effective if maintained at roughly 1'' wide and less than 0.05''
h.
[0036] In some preferred embodiments, the rigid and flexible
diaphragms 31 and 32, domes 5, 6, or the cylinder 1, may include
layers that serve to reduce heat transfer, including reflective
layers, such as metalized layers, or may be light in color to
reduce the amount of radiative heat loss.
Smart Susceptors
[0037] In one embodiment of integrated thermal management, a
multi-layer composite tank is capable of operating from -40.degree.
F. to a maximum temperature 150-250.degree. F. A susceptor such as
carbon, graphite, or metal is added to housing sections 1, 5, 6 so
that it may be heated from an external energy source such as
induction, RF, or microwave, without significantly heating the
insulation or fiber reinforcement. In another embodiment, ports in
and out of the tank comprise metals which may be heated by said
external power supplies.
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