U.S. patent application number 16/203090 was filed with the patent office on 2019-05-30 for membrane heat and mass exchanger and methods of manufacture.
This patent application is currently assigned to Oregon State University. The applicant listed for this patent is Oregon State University. Invention is credited to Paul D. ARMATIS, Brian M. FRONK, Steven KAWULA, Brian K. PAUL, Chuankai SONG, Hailei WANG.
Application Number | 20190162429 16/203090 |
Document ID | / |
Family ID | 66632220 |
Filed Date | 2019-05-30 |
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United States Patent
Application |
20190162429 |
Kind Code |
A1 |
ARMATIS; Paul D. ; et
al. |
May 30, 2019 |
MEMBRANE HEAT AND MASS EXCHANGER AND METHODS OF MANUFACTURE
Abstract
A heat and mass exchange (HMX) device comprising a plurality of
membranes arranged in a stack. Adjacent membranes are separated
from one another by an airflow channel Each membrane of the stack
comprises an array of integrated support structures that extend
into the airflow channel and to the second membrane. The support
structures comprise an adhesive material that is bonded to each
membrane. The support structures divide the airflow channels into
subchannels.
Inventors: |
ARMATIS; Paul D.;
(Corvallis, OR) ; PAUL; Brian K.; (Corvallis,
OR) ; WANG; Hailei; (Corvallis, OR) ; FRONK;
Brian M.; (Corvallis, OR) ; KAWULA; Steven;
(Corvallis, OR) ; SONG; Chuankai; (Corvallis,
OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Oregon State University |
Corvallis |
OR |
US |
|
|
Assignee: |
Oregon State University
Corvallis
OR
|
Family ID: |
66632220 |
Appl. No.: |
16/203090 |
Filed: |
November 28, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62591400 |
Nov 28, 2017 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28F 21/066 20130101;
F28F 2275/025 20130101; F28D 21/0015 20130101; F24F 3/147 20130101;
F28D 9/0062 20130101; F28F 2245/02 20130101 |
International
Class: |
F24F 3/147 20060101
F24F003/147 |
Goverment Interests
GOVERNMENT SUPPORT
[0002] This invention was made with government support under Award
No. DE-SC0006224, awarded by the United States Department of
Energy. The government has certain rights in the invention.
Claims
1. A heat and mass exchange (HMX) device, comprising: a plurality
of membranes arranged in a stack, wherein: adjacent ones of the
plurality of membranes are separated by an airflow channel; the
plurality of membranes comprise at least a first membrane and a
second membrane over the first membrane; the first membrane
comprises an array of support structures integrated on the first
membrane; and the array of support structures each comprises an
adhesive material that is bonded to the first membrane and extends
to the second membrane.
2. The heat and mass exchange device of claim 1, wherein the ones
of the array of support structures are bonded to the second
membrane by adhesive bonds.
3. The heat and mass exchange device of claim 1, wherein: the ones
of the plurality of membranes are elongated along a main axis and
comprise a first header portion at a first end and a second header
portion at a second end, the first header portion and the second
header portion each have two non-parallel sides extending to a
vertex, wherein the membrane has an elongated hexagonal shape; and
the first header portion comprises a first array of fins oriented
along a secondary axis that is non-parallel to the main axis, and
the second header portion comprises a second array of fins oriented
along the secondary axis.
4. The heat and mass exchange device of claim 1, wherein the ones
of the plurality of membranes comprise silica-filled polyethylene,
silica-filled polyvinyl chloride, silica-filled PEEK, or
perfluorosulfonic acid, and has a thickness ranging between 20 and
30 microns.
5. The heat and mass exchange device of claim 1, wherein the
adhesive material is any one of a silicone, an epoxy resin a
urethane resin, a polyester resin, a silyl-terminated polyether
resin, or an acrylic resin.
6. The heat and mass exchange device of claim 1, wherein the array
of support structures is an array of strip fins, wherein ones of
the array of strip fins are substantially parallel to one another
and have a longitudinal span that extends along a length of the
membrane, a transverse span that extends in a direction that
extends along a width of the membrane, and a z-height that is
approximately equal to the z-height of the first or the second
airflow channels.
7. The heat and mass exchange device of claim 6, wherein the
airflow channel is divided into two or more subchannels, wherein
each one of the two or more subchannels is between a a pair of
adjacent ones of the array of strip fins, wherein the pair of
adjacent ones of the array of strip fins are sidewalls of each one
of the two or more subchannels.
8. The heat and mass exchange device of claim 7, wherein the two
more subchannels have a hydraulic diameter between 2 mm and 3
mm.
9. The heat and mass exchange device of claim 6, wherein ones of
the array of strip fins have a ratio of the longitudinal span to
the transverse span that is at least 100:1, and a ratio of the
z-height to the transverse span that is between 1:1 and 2:1.
10. The heat and mass exchange device of claim 6, wherein the ones
of the array of strip fins have a z-height of 4 mm or less.
11. The heat and mass exchange device of claim 6, wherein adjacent
ones of the array of strip fins are separated from one another by a
first distance that is one-tenth or less of the width of the
membrane.
12. The heat and mass exchange device of claim 6, wherein the ones
of the array of strip fins comprise one or more curved
portions.
13. The heat and mass exchange device of claim 1, wherein the array
of support structures is an array of pillars, wherein ones of the
array of pillars each have a first transverse span extending along
the membrane in the x- directions and a second transverse span
extending along the membrane in the y-direction, and a z-height
extending above the membrane, and wherein the z-height of the
pillars is approximately the same as the z-height of the first or
the second airflow channel.
14. The heat and mass exchange device of claim 13, wherein the
first and second transverse spans are substantially equal, and the
ones of the array of pillars each have a ratio of z-height to width
that ranges from 1:1 and 2:1, and a ratio of length-to-width that
ranges from 1:1 to 20:1.
15. The heat and mass exchange device of claim 13, wherein at least
a portion of the ones of the array of pillars have a length
extending along a first direction and a width extending along
second direction that is orthogonal to the first direction, wherein
the length is greater that the width.
16. An energy recovery ventilation (ERV) system comprising: a
housing; a heat and mass exchange (HMX) device contained within the
housing, the HMX device comprising: a plurality of membranes
arranged in a stack, wherein: adjacent ones of the plurality of
membranes are separated by an airflow channel; the plurality of
membranes comprise at least a first membrane and a second membrane
over the first membrane; the first membrane comprises an array of
support structures integrated on the first membrane; and the array
of support structures each comprises an adhesive material that is
bonded to the first membrane and extends to the second membrane;
and an air circulation system coupled to the HMX device such that
air is circulated in a first direction through a first subarray of
airflow channels, and in a second direction through a second
subarray of airflow channels, wherein the first subarray is
interleaved with the second subarray.
17. The ERV system of claim 16, wherein the array of support
structures is an array of strip fins, wherein the array of strip
fins has a z-height that is approximately equal to the z-height of
the first or the second airflow channels; adjacent ones of the
array of fins are sidewalls of a subchannel such that a first array
of subchannels is within the first airflow channel and a second
array of subchannels is within the second airflow channel; or the
array of support structures is an array of pillars, wherein the
array of pillars has a z-height that is approximately equal to the
z-height of the first or the second airflow channels and the first
direction is opposite the second direction such that air is
circulated through the HMX in a counterflow configuration, or the
first direction is orthogonal to the second direction such that the
air is circulated through the HMX in a cross-flow
configuration.
18. A method for making a heat and mass exchange device,
comprising: receiving a heat and mass exchange (HMX) core stack,
wherein the HMX core stack comprises a first membrane on the top of
the core stack, the first membrane has a first surface over a
second surface, the second surface bonded to a first layer of an
adhesive material; depositing a second layer of the adhesive
material in a support structure array pattern on the first surface
to form a plurality of support structures on the first surface; and
stacking a second membrane over the first membrane, wherein a third
surface of the second membrane is opposite the first surface and is
tacked onto the second layer of adhesive material, and the second
membrane is at a first z-height over the first membrane.
19. The method of claim 18, wherein depositing the adhesive
material comprises: dispensing the second layer of the adhesive
material from a nozzle over the first surface, wherein the nozzle
is translated relative to the first surface to dispense the
adhesive material in a pattern; or dispensing the second layer of
an adhesive material from the nozzle, wherein the wherein the
nozzle is translated relative to the first surface in a first
direction to deposit the adhesive material in a pattern; and
dispensing a third layer of the adhesive material from the nozzle
over the second layer of the adhesive, wherein the nozzle is
translated relative to the first surface in a second direction
opposite the first direction.
20. The method of claim 18, wherein stacking a second membrane over
the first membrane comprises tacking the second membrane to the
second layer of adhesive material and raising the second membrane
to a second height over the first membrane and holding the position
of the second membrane over the first membrane for a time period,
wherein the adhesive material is stretched over the first membrane,
and wherein a height of the second layer of adhesive material over
the first membrane is increased and a height-to-width aspect ratio
is 1:1 or greater.
Description
CROSS-REFERENCE TO PRIORITY DOCUMENTS
[0001] This U.S. Patent Application claims the benefit of priority
under 35 U.S.C. 119(e) of U.S. Provisional Application No.
62/591,400, filed on Nov. 28, 2017.
BACKGROUND
[0003] A large amount of thermal energy is wasted when conditioned
air in buildings is exhausted to the environment in order to meet
ventilation requirements. Building ventilation systems may expend a
good deal of energy to heat, cool, humidify or dehumidify a volume
of fresh air taken in from the outside. Without any way to recover
at least some of this energy, it is lost when the conditioned air
is exhausted to the outside. Several technologies have been
developed to recover some of the energy before the conditioned air
is exhausted to the outside. Among these are Energy Recovery
Ventilators (ERVs), which have recently been developed. ERVs
exchange sensible heat and moisture between incoming fresh air and
outgoing exhaust air. The exchange may be accomplished by
countercurrent and cross-flow energy and mass exchange techniques
through ERV cores comprising multiple membrane stacks. Market
penetration of ERV devices has been hampered by high manufacturing
costs and relatively low volumetric efficiency. A more advanced
airflow architecture and method of manufacture of ERVs needs to be
developed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The embodiments of the disclosure will be understood more
fully from the detailed description given below and from the
accompanying drawings of various embodiments of the disclosure,
which, however, should not be taken to limit the disclosure to the
specific embodiments, but are for explanation and understanding
only.
[0005] FIG. 1 illustrates a plan view in the x-y plane of a heat
and mass exchanger (HMX) membrane unit having integrated strip fin
ribbing support structures, according to some embodiments of the
disclosure.
[0006] FIG. 2 illustrates a plan view in the x-y plane of a HMX
membrane unit having integrated elongated pillar support
structures, according to some embodiments of the disclosure.
[0007] FIG. 3A illustrates a plan view in the x-y plane of a HMX
membrane unit having integrated circular pillar support structures
in a rectangular array, according to some embodiments of the
disclosure.
[0008] FIG. 3B illustrates a plan view in the x-y plane of a HMX
membrane unit having integrated circular pillar support structures
in a hexagonal array, according to some embodiments of the
disclosure.
[0009] FIG. 4 illustrates a plan view in the x-y plane of a HMX
membrane unit having serpentine fin rib support structures,
according to some embodiments of the disclosure.
[0010] FIG. 5 illustrates a partially exploded oblique view of a
HMX core assembly comprising a stack of HMX membrane units,
according to some embodiments of the disclosure.
[0011] FIG. 6 illustrates a flow chart summarizing an exemplary
method for making a HMX core assembly, according to some
embodiments of the disclosure.
[0012] FIGS. 7A-F illustrate a succession of key operations of an
exemplary method to a HMX core assembly, according to some
embodiments of the disclosure.
[0013] FIG. 8 illustrates a flow chart summarizing an alternative
method for making a HMX core assembly, according to some
embodiments of the disclosure.
[0014] FIGS. 9A-9I illustrate a succession of key operations of an
alternate exemplary method for making a HMX core assembly,
according to some embodiments of the disclosure.
DETAILED DESCRIPTION
[0015] Described herein is a parallel membrane gas-to-gas heat and
mass exchanger (HMX) device core for energy recovery ventilation
(ERV) systems comprising multiple membranes having integrated
support structures. The HMX core of an ERV system generally
comprises a stack of parallel hydrophilic membranes, each separated
by an airflow channel. The stack of airflow channels in the HMX may
be arranged in a counter-flow or crossflow configuration.
[0016] Embodiments of the disclosed HMX membrane core comprises
multiple HMX membranes having integrated support structures. The
HMX membrane laminates exhibit low heat and mass transport
resistance, in part due to their small thickness (e.g., a thickness
less than 30 microns), and in part due to the hydrophilic membrane
material exhibiting high selectivity to water transport. Support
structures in the form of strip fins and/or pillars are
incorporated onto the membrane material to enhance the rigidity of
the membrane material that by itself is too thin to be
self-supporting. Such membranes do not have sufficient rigidity as
a stand-alone membrane to hold a specified shape without a
scaffolding comprising a frame, ribbing or other types of support
structure. The integrated structures permit the otherwise flaccid
membranes to be self-supporting. When formed into a HMX core stack,
an ensemble of the disclosed HMX membranes enable a high-efficiency
and high-capacity heat and mass exchange in countercurrent,
quasi-cross-flow (described below) or cross-flow configurations
without the need for separate channeled spacers or frames. This
allows for more compact form factors of the HMX cores.
[0017] To improve heat and mass transport in ERV systems, rigid
membranes, which are generally thick (e.g., thicknesses greater
than 50 microns) and have relatively high mass and heat transfer
resistance, may be pleated or corrugated. Thin membranes (e.g.,
membranes having less than 30 microns in thickness) lack the
rigidity to hold pleated folds or corrugations. One objective of
pleating and corrugation of membranes is to increase membrane
surface while maintaining a specified footprint. The increase in
surface area helps to reduce mass and heat transfer resistance of
the membrane, but the increase in surface area may be 100% or less,
while the thickness of the membrane may be the principle
contribution to transport resistance. Another objective of pleating
and corrugation of the membrane is to increase convective transport
of heat and mass from an airstream to the membrane by inducing some
turbulence near the membrane surface. Thinner membranes may remain
flat, without pleats or corrugations, and yet have much lower mass
and heat transfer resistance in comparison to more rigid membranes
without enhancement of convective transport within the airflow
channel.
[0018] Rigid membranes that can form stand-alone structures on
their own, such as pleated or corrugated membranes, may be
substantially thicker or have fiber materials that tend to impede
mass transfer. In some instances, pleated membranes comprise a
fibrous paper or paper-like material that can be folded. Membranes
having sufficient rigidity for maintaining a shape may also exhibit
higher resistance to mass and heat transport.
[0019] In addition, reduction of the hydraulic diameter of the air
channels (e.g., the space between membranes in a HMX core stack)
has been incorporated into HMX designs to increase convective
transfer from airstreams to the membranes. The reduction of the
hydraulic diameter of airflow channels is generally done by
decreasing the vertical spacing between membranes bounding the
channels. Both methods have proven effective, but at the cost of
high pressure drop across the HMX core stack. One operational
objective of ERV installations in a building is a maximum allowable
pressure drop (.DELTA.P) of 300 Pa (Pascals; e.g., approximately
0.05 psi). To meet this criterion, cores must have very low flow
resistance within the airflow channels that are the spaces between
membranes in an HMX core stack.
[0020] A criterion of the membrane is that it prevents mixing of
airstreams on opposite sides of the membrane. Only diffusive
transport processes are therefore permitted, and mass transport is
generally limited to water vapor while excluding air (e.g.,
nitrogen and oxygen) and other organic and inorganic species. Water
vapor carries latent heat that can be exploited for cooling and
heating purposes. Sensible heat transfer is by conduction through
the membrane.
[0021] To enable sufficient diffusive mass transport, the mass
transport of water through the membrane must be highly efficient to
allow sufficient mass in the form of water vapor to be exchanged
across the membrane, to the exclusion of air and other gases. In
particular, undesirable species in the air exhaust stream may be
prevented from entering the outside air intake stream. Hydrophilic
polymer membranes less than 30 microns in thickness are most
efficient for this purpose. However, membranes having such small
thicknesses are difficult to handle, and in general do not possess
the requisite mechanical properties that make them amenable for
employment in HMX core stacks as self-supporting structures. An
important constraint is flexure or deflection in the membrane
caused by pressure differentials in the airflow path between
airflow channels on opposite sides of the membrane. Membrane
deflection is especially prevalent in counter-flow configurations.
Flexure must be limited to only a few percent of the vertical space
in the airflow channel above the membrane, otherwise the hydraulic
diameter of the flow channel is reduced and the flow resistance
increases, increasing the pressure drop .DELTA.P. Thin membranes
that are not self-supporting will deflect under pressure
differentials across the membrane, and may increase .DELTA.P.
[0022] One objective is to reduce size and costs of ERV units.
High-efficiency HMX membranes may enable a smaller footprint for
some described embodiments of the disclosed HMX cores as compared
to conventional HMX cores, permitting embodiments of the disclosed
HMX core to fit within a compact space such as a building wall
cavity as part of a building ERV system. The smaller footprint may
be a smaller length-to-width aspect ratio of the HMX core,
permitting the HMX core to be more easily integrated into the
building envelope for new construction or retrofit purposes. As an
example, some embodiments of the HMX core as disclosed may fit
within cavities of walls of commercial buildings in North America,
where wall thicknesses are generally 8-10 inches.
[0023] Membrane properties such as selectivity and low heat and
mass transfer resistance are determinant for the development of
compact, high capacity HMX cores. Many membrane types are available
that meet these requirements, and are relatively inexpensive.
Membrane cost may not be a limiting factor in achieving cost
effectiveness goals of high capacity HMX cores. High-capacity
membrane-based HMX cores that are currently on the market have
associated high costs due to complex manufacturing and assembly
procedures. In some cases, the assembly of membrane layer stacks as
HMX cores requires a number of manual steps, including assembly of
HMX core stacks with support frames that may be separately formed
and may or may not be bonded to membrane laminates. Rigid membranes
are generally employed for stack assembly to reduce or avoid
handling difficulties often encountered with thin membranes.
Consequently, these cores must be dimensionally large in comparison
to the disclosed HMX cores to meet the same performance.
[0024] To address the problem of high manufacturing costs, a
manufacturing method is disclosed herein that circumvents many of
the manual manipulations of the membrane that are currently
practiced to produce and assemble HMX membrane stack units or
elements. The disclosed method embodiments comprise forming support
structures that are directly integrated with the individual HMX
membranes. The manufacturing process can be fully automated. Some
embodiments of the disclosed manufacturing process comprise
dispensing an adhesive material over one or both surfaces of a
suitable membrane material. At a pre-process stage, the membrane
material may be pre-cut to desired dimensions and shapes.
Alternatively, the membrane material may be meted out as a
continuous strip from a roller, then laser cut to produce
individual membranes after structures have been formed.
[0025] In some embodiments, an adhesive material is dispensed from
a nozzle to form beads of adhesive material as lines or pillars in
a programmed pattern on the membrane surface. To accomplish this,
the membrane may be fixed on a computer-controlled moving X-Y
table, with the nozzle stationary. The table may also move in the
z-direction so that the nozzle height above the membrane may be
adjusted. Alternatively, the membrane may be stationary and the
nozzle moves over the membrane to dispense the adhesive in a
pre-programmed x-y pattern under computer control. The nozzle may
also move in the z-direction to adjust the nozzle height over the
membrane. In alternative embodiments, the adhesive material is
sprayed or printed through a stencil. A roller applicator method
may be used in this embodiment to print the adhesive onto the
stencil, facilitating thickness adjustment of the uncured adhesive
material.
[0026] The adhesive material may be dispensed as a paste or in a
high-viscosity semi-liquid state, and is partially cured at this
stage. To form support structures of a desired height above the
membrane surface, more than a single layer of the adhesive may be
applied. The height is important to create a flow channel with a
minimal height for sufficient airflow without significant pressure
drop (e.g., not exceeding 300 Pa). Attention is also paid to the
lateral dimension of the structure, so as to minimize coverage of
the active membrane surface. To minimize the lateral dimension of
the structure, the adhesive is dispensed in layers. As dispensed, a
bead of adhesive may have a circular cross-sectional
height-to-lateral dimension ratio of 1:1, due to the bead holding
its substantially circular cross-sectional shape. As an example,
the bead is approximately 1 mm in cross-sectional diameter. During
curing, the first layer of adhesive material may collapse by some
flow, producing a structure having an aspect ratio of less than
1:1, often as low as 0.6:1 or lower. With such low aspect ratios,
multiple layers of adhesive may need to be dispensed over each
other to achieve a target structure height. As a greater amount of
adhesive would need to be dispensed, incurring longer and more
expensive process times and/or loss of active membrane surface.
[0027] To circumvent this problem, maintenance of larger
height-to-lateral dimension (e.g., width or diameter) aspect ratio
adhesive beads may be achieved by dispensing a first bead layer of
a suitable adhesive, then allowing some adhesive bond formation to
take place with the membrane, but not curing the adhesive. In this
way, the adhesive structure (e.g., bead) remains tacky, but has
enough body so as to maintain its initial shape, having a
height-to-lateral dimension aspect ratio of 1:1 (or more). The
dispensing nozzle may be displaced vertically (in the z-direction)
relative to the membrane and a second layer of the adhesive may be
dispensed directly over the first layer. In some embodiments, the
second bead is dispensed in the opposite direction relative to the
first bead. At this point, the first layer may be hardened enough
to support the second layer without losing its initial shape and
height-to-width aspect ratio, yet having enough tack for adhesive
bonds with a second layer.
[0028] According to some embodiments, the second layer as dispensed
may not be as thick as the first layer, allowing a total
height-to-width aspect ratio ranging from 1:1 to 2:1. In this
manner, a target height may be achieved with the minimal number of
dispensed layers of adhesive, saving manufacturing time and costs.
At the same time, the coverage of active membrane surface is
minimal. The second layer may be bonded with a second adjacent
membrane, sealing the intermembrane airflow channel The
membrane-integrated support structures formed according to the
described embodiments disclosed herein provide mechanical support
for the compliant membranes, form flow paths within the airflow
channels, and seal the airflow channels to prevent leakage of air
in and out of the airflow channels and produce rigid HMX core
stacks that do not require external framework or other support
mechanisms.
[0029] In an alternative method, a HMX core stack is received in
process, where the HMX core stack is partially complete. The HMX
core stack has a top membrane that has no adhesive material on the
top surface of the membrane. A layer of adhesive material is
deposited in a pattern of beads on the surface of the top membrane.
The pattern of beads is an array of nascent support structures that
may be dispensed from a nozzle or deposited by through a stencil. A
blank membrane that is mounted on a movable platen is tacked down
over the adhesive layer, which is firm but tacky, forming adhesive
bonds with the blank membrane. The blank membrane is raised upward,
pulling the adhesive layer upward with it due to tensile forces,
stretching the material vertically. The height of the adhesive
layer over the top membrane is increased in this way, while the
width of the beads decrease as material is pulled upward. The
height-to-width aspect ratio may be increased in this manner to
values of 1:1 or greater.
[0030] Here, the term "integrated" generally refers to a structure
or multiple structures formed directly on a substrate and bonded to
it. As part of this definition, the bonding of the structure(s) to
the substrate is generally part of the formation process. The
formation process comprises depositing an adhesive material on a
membrane surface, where the membrane is the substrate.
[0031] Here, the term "adhesive bond" may have several definitions.
In one definition, an adhesive bond may be defined as chemical
bonding between the reactive molecular groups at the interface
between the structure(s) and the substrate. Reactive groups in the
uncured adhesive material that is deposited on the membrane to form
the structures by internal cross-linking, may also form chemical
linkages to the substrate during the curing process, chemically
bonding the structure(s) to the substrate. In another definition,
an adhesive bond may be defined as a physical bond, such as formed
by van der Waals forces established between the structure(s) and
the substrate. In a further definition, an adhesive bond may be
defined as a mechanical bond formed by infiltration of the material
of the structure(s) into microscopic pores or between microscopic
irregularities at the interface between the structure(s) and the
substrate. According to the embodiments disclosed herein, the
integrated support structures described above are directly formed
on a membrane material and bonded to it by any of the adhesion
mechanisms just described. Accordingly, the integrated structures
comprise an adhesive material that is cured to form solid or
semi-solid structures that are directly bonded to the membrane
substrate without an intermediary of a second adhesive substance at
the interface of the integrated support structures and the membrane
substrate.
[0032] Here, the term "adhesive" generally means a substance that
is expressly employed for the purposes of forming chemical bond
linkages or physical bonds (e.g., van der Waals bonds, hydrogen
bonds) between the substance and a substrate, for binding objects
together. The substance is formulated and marketed, if sold
commercially, as a glue, a sealant, an adhesive or a cement,
according to standard definitions. The substance is generally
obtained in a precursor, a pre-bond state that may be characterized
as "resinous", which may be further characterized as a viscous
liquid. Some examples of an adhesive are so-called hot glues, where
the adhesive is a thermoplastic resin procured as a solid material
a room temperature. The thermoplastic resin is then melted and
applied in a molten state to one or more substrates. In the molten
state, the "hot glue" material is tacky and adheres to many types
of substances. Chemical (e.g., reactive) or physical (e.g., van der
Waals) bonds are formed between the substrate(s) and the hot
adhesive. The hot adhesive hardens upon cooling, and bonds to the
substrate(s). The hot adhesive may be a thermoplastic material.
This type of adhesive may be particularly suitable for adhering to
non-polar surfaces (e.g., having low surface energy) of many
plastics by van der Waal forces, as the resin itself may be
non-polar thermoset plastic.
[0033] An adhesive may form bonds to substrates by chemical
reaction, and polymerize internally by similar reactions between
reactive groups on nearby polymer chains, forming a hardened or
cured material that is chemically bonded to the substrate. By
chemical bonding, it is understood that chemical linkages are
established between the polymer backbone of polymers in the
adhesive and reactive groups at the substrate surface. For example,
ester linkages may be formed between surface hydroxyl groups and
carboxylic groups on the polymer chains of the adhesive by a
condensation reaction. For silicone-based adhesives, bonds may also
be formed between silanol groups and available surface-bound
hydroxyl groups on the substrate. Ether linkages, y bonds may be
formed by the Such adhesives comprise reactive molecular precursors
that are oligomeric and polymeric chains having pendant reactive
groups that remain stable in the absence of moisture, air (oxygen)
elevated temperatures and/or light (e.g., ultraviolet light). A
solvent may be present as well in the material to reduce viscosity
and exclude moisture and air. Catalysts may also be included in the
formulation that promote cross-linking or polymerization of the
precursor molecules when the in the pendant adhesive is exposed to
moisture, air, heat and/or light. In the pre-cure state, the
adhesive is often sticky or tacky, meaning it forms bonds with
solid substrates
[0034] When curing, the precursor molecules may undergo reactions
that grow the polymer chains and/or crosslink them, causing the
liquid adhesive precursor to "harden" into a highly viscous glassy
substance, or one that at least partially crystallizes into
crystalline domains. The adhesive may harden to form a thermoset
plastic, which cannot melt into a liquid once set. Other adhesives
may contain a non-chemically reactive polymeric materials dissolved
in a solvent, such as emulsion and polymer dispersion adhesives,
where curing involves evaporation of the solvent (e.g., drying),
causing the polymeric molecules to lock together in the absence of
the solvent, forming an amorphous (glassy) solid polymer, a
polycrystalline solid or a solid comprising combination of the two
states. In other examples, the polymeric material comprises an
elastomer, and forms an elastic solid when dry. Some adhesives,
such as epoxies are resins that are mixed with a hardener, which
cross-links the resin during the curing process to form a thermoset
solid plastic. The curing takes place at room temperature, but may
be accelerated at elevated temperatures. Epoxies comprise polymer
chains that are replete with polar groups such as hydroxyls, ether
linkages, secondary and tertiary amino and imino groups, which give
the adhesive power, forming hydrogen bonds or van der Waals bonds
with a substrate.
[0035] As a result of the curing process, the adhesive "hardens",
meaning that the adhesive solidifies or becomes a semi-solid that
is chemically or physically bonded to the substrate(s). The
solidified adhesive may remain amorphous, being glass-like, or form
crystalline domains, having properties of polycrystalline solids.
Some adhesives, such as epoxies, harden into a thermoset plastic
material. Some adhesives, such as silicones and so-called rubber
cement, comprise elastomeric molecules and retain elastic,
rubber-like properties. The precursor molecules may comprise
relatively low molecular-weight polymer chains that have pendant
bonds, such as, but not limited to, epoxide groups, carboxylic acid
group, amino groups, imino groups, sulfhydryl groups, hydroxyl
groups, acrylate groups and undergo further polymerization and
cross-linking to other polymer chains. The adhesive power of the
material may be due to similar reactions with surface groups on a
substrate, or by formation of strong van der Waals forces or
hydrogen bonds at the interface between the adhesive and the
substrate.
[0036] Adhesives are characterized as having an "open" time and a
cure time. The open time is the time the adhesive remains pliable
in the pre-cured state. The adhesive may be in a liquid state
having a sufficient viscosity to retain a shape when extruded from
a nozzle and resist flowing during the open time. Some adhesives
may be molded or otherwise shaped while in the open state.
[0037] For purposes of description of the disclosed embodiments and
the views shown in the figures, the vertical orientation is in the
z-direction and it is understood that recitations of "top",
"bottom", "above" and "below" refer to relative positions in the
z-dimension with the usual meaning. However, it is understood that
embodiments are not necessarily limited to the orientations or
configurations illustrated in the figure.
[0038] The terms "substantially," "close," "approximately," "near,"
and "about," generally refer to being within +/-10% of a target
value (unless specifically specified). Unless otherwise specified
the use of the ordinal adjectives "first," "second," and "third,"
etc., to describe a common object, merely indicate that different
instances of like objects are being referred to, and are not
intended to imply that the objects so described must be in a given
sequence, either temporally, spatially, in ranking or in any other
manner.
[0039] For the purposes of the present disclosure, phrases "A
and/or B" and "A or B" mean (A), (B), or (A and B). For the
purposes of the present disclosure, the phrase "A, B, and/or C"
means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and
C).
[0040] Views labeled "cross-sectional", "profile", "plan", and
"oblique" correspond to orthogonal planes within a cartesian
coordinate system. Thus, cross-sectional and profile views are
taken in the x-z plane, plan views are taken in the x-y plane, and
isometric views are taken in a 3-dimensional cartesian coordinate
system (x-y-z). Where appropriate, drawings are labeled with axes
to indicate the orientation of the figure.
[0041] FIG. 1 illustrates a plan view in the x-y plane of HMX
membrane unit 100 having integrated fin ribbing support structures
102, according to some embodiments of the disclosure.
[0042] HMX membrane unit 100 comprises membrane 101 and an array of
multiple integrated strip fins 102 extending across the face of
membrane 101 in the x-direction of the figure. In some embodiments,
membrane 101 has a thickness ranging between 20 microns and 30
microns. In some embodiments, strip fins 102 have a height (not
shown) ranging between 1 mm and 4 mm, and a thickness t.sub.1
ranging between 1 mm and 2 mm Strip fins 102 provide sidewalls for
subchannels 103 to direct airflow when HMX membrane unit 100 is
employed in a HMX core stack. The orientation of strip fins 102 and
associated subchannels 103 defines the direction of length L of HMX
membrane unit 100 extending in the x-direction of the figure, where
the width W of HMX membrane unit 100 extends in the y-direction of
the figure. In some embodiments, the length-to-width (L/W) aspect
ratio of HMX membrane unit 100 is 2:1 or greater. In some
embodiments, HMX membrane unit 100 has an overall length L ranging
between 500 mm and 1000 mm. In some embodiments, the overall width
W ranges between 150 mm and 200 mm In some embodiments, subchannels
103 have a width d ranging between 3 mm and 7 mm. In general, width
d is one tenth or less of the width of HMX membrane unit 100,
allowing an array comprising 10 or more subchannels 103 to fit in
an HMX membrane unit 100. The cross-sectional area ranges between 3
mm.sup.2 and 20 mm.sup.2. In some embodiments, the hydraulic
diameter d.sub.h of subchannels 103, where d.sub.h is defined as
four times the cross-sectional area A divided by the
cross-sectional perimeter P (d.sub.h=4A/P) ranges between
approximately 1.5 mm and 4.0 mm In some embodiments, HMX membrane
unit comprises between 30 to 70 subchannels 103.
[0043] According to some embodiments, HMX membrane unit 100 is
hexagonal in shape, as shown in FIG. 1. Triangular-shaped headers
104 and 105 extend from the rectangular main body 106 of HMX
membrane unit 100 at the left and right ends, respectively. Headers
104 and 105 comprise strip fins 107 that are oriented at an angle
relative to the strip fins 102 in main body 106. In the illustrated
embodiment, strip fins 107 are oriented at approximately a
45.degree. angle to strip fins 102. It will be understood that
other suitable relative orientations may be employed for strip fins
107. In some embodiments, strip fins 107 have the same
cross-sectional dimensions of strip fins 102. Headers 104 and 105
are interchangeably airflow introduction and exhaust portions of
HMX membrane unit 100.
[0044] The triangular shape of headers 104 and 105 permits stacking
of HMX membrane units with alternate header orientations, so that
quasi-cross flow HMX core stack configurations (described below)
may be obtained, where intake and exhaust air streams may both be
couple to the HMX core stack on the same end, as described below.
Strip fins 107 serve to direct air flow to or away from main body
106 though associated subchannels 108, while permitting some heat
and mass exchange to take place within headers 104 and 105 before
or after the bulk of the heat and mass transport occurs in main
body 106. This is explained below and shown for quasi-cross flow
HMX core stack configurations.
[0045] In alternate embodiments, HMX membrane unit 100 is
rectangular in shape, as described below. The rectangular shape is
commonly employed in cross-flow HMX core stack configurations.
[0046] Membrane 101 comprises a hydrophilic membrane material
including, but not limited to, silica-filled polyethylene,
silica-filled polyvinyl chloride, silica-filled polyethylene ethyl
ketone (PEEK), paper and cellulosic materials, or perfluorosulfonic
acid. In some embodiments, membrane 101 exhibits a diffusivity
D.sub.m for water ranging between 2.times.10.sup.7 m.sup.2s.sup.-1
and 4.times.10.sup.7 m.sup.2s.sup.-1 at room temperature. In some
embodiments, membrane 101 has a heat condutivity ranging between
0.05 and 0.10 W/mK. Strip fins 102 and 107 are formed from an
adhesive material by process embodiments described below.
[0047] In some embodiments, strip fins 102 and 107 comprise a
substantially polymerized adhesive material homogeneously
distributed within the interior of the structures and at the
surface, including, but not limited to, silicone resins, epoxy
resins, polyimide resins, urethane resins, cyanoacrylate resins,
acrylate resins. Any suitable adhesive material having a suitable
cure time at room temperature and cure temperature below the glass
transition temperature of membrane 101 may be employed. Suitable
adhesive materials may be a paste or a gel-like material that
exhibits a high viscosity as a freshly deposited bead of adhesive
(e.g., a bead or line of the adhesive extruded from a nozzle) on a
substrate. In some embodiments, the adhesive material has a
viscosity or a degree of internal bonding such that the bead does
not flow under its own weight (e.g., does not slump) and retains
its extruded form until cured.
[0048] According to some embodiments, strip fins 102 and 107 are
directly integrated with membrane 101 by formation of the
structures from adhesive material deposited and cured on membrane
101 as the substrate. The method of manufactured of HMX membrane
unit 100 described below gives details of the integration process.
Structurally, the transition from membrane material to bulk
material composition of strip fins 102 and 107 at the membrane
interface is substantially sharp (e.g., no intervening layer of a
material is present at the interface). This is shown by the inset
of FIG. 1, where a small section of HMX membrane unit 100 is taken
along the y-axis in an x-z plane indicted by the dashed line
cutting across the lower-most strip fin 102 within the small
circle. The section is shown magnified in the inset, where the x-z
coordinate axes indicate the section is in the x-z plane. The inset
shows that strip fin 102 is interfaced directly with and bonded to
membrane 101 by adhesive bonds as described above, with no
intervening layer of material between strip fin 102 and membrane
101.
[0049] The adhesive bonds may be chemical bonds formed between
strip fin 102 and membrane 101 by native reactive groups of the
adhesive material comprised by strip fin 102 and reactive groups
native to the membrane material comprised by membrane 101 (e.g.,
surface hydroxyl groups, amino groups, oxo groups, carboxylic acid
groups, etc.). In some embodiments, the adhesive bonds are physical
bonds such as van der Waals interactions, as described above. This
type of bond may be formed by electrostatic interaction between
polar groups on polymer chains native to the adhesive material
comprised by strip fins 102 electrostatically and polar groups on
polymer chains native to the membrane material comprised by
membrane 101.
[0050] In some embodiments, physical bonds may be formed by
infiltration of the adhesive material comprised by strip fins 102
into pores in membrane 101.
[0051] FIG. 2 illustrates a plan view in the x-y plane of HMX
membrane unit 200 having integrated elongated pillar support
structures 201, according to some embodiments of the
disclosure.
[0052] HMX membrane unit 200 comprises elongated pillars 201
integrated onto membrane 101. The overall description of HMX
membrane unit 100 is generally applicable to HMX membrane unit 200,
with some exceptions. In some embodiments, elongated pillars 201
have a similar height-to-width aspect ratio to that of strip fins
102 shown in FIG. 1, ranging between 1:1 and 2:1. Elongated pillars
201 have a length p extending in the x-direction in the figure, and
a width t.sub.2 extending in the y-direction of the figure. In some
embodiments, width t.sub.2 of elongated pillars 201 is the same as
for the width t.sub.1 for strip fins 101. In some embodiments,
elongated pillars 201 have length-to-width ratio (p/t.sub.1)
ranging between 2:1 and 20:1. Elongated pillars 201 are separated
from each other along the x-direction by gaps 202. In some
embodiments, the ratio of the length of elongated pillars 201 to
the length of gaps 202 ranges from approximately 1:1 to 10:1. While
the elongated pillar structure provides complex flow paths for
airflow within HMX membrane unit 200 with no well-defined
subchannels (e.g., no delineated flow channels as are subchannels
103 in FIG. 1). Air may flow along subchannels (not specified)
longitudinally along elongated pillars 201, or transversely between
longitudinal flow paths. In some embodiments, the height of
elongated pillars 201 (not shown) is between 1 mm and 4 mm. The
hydraulic diameter of HMX membrane unit 200 is substantially the
same as the hydraulic diameter for HMX membrane unit 100, ranging
between approximately 1.5 and 4 mm.
[0053] HMX membrane unit 200 comprises header portions 104 and 105
extending from main body 106 of membrane 101, comprising strip fins
107 integrated onto the membrane material forming headers 104 and
105, providing sidewalls for subchannels 108. In some embodiments,
the general description of headers 104 and 105 given for HMX
membrane unit 100 is applicable to HMX membrane unit 200. Headers
104 and 105 perform the same or a similar function as was described
above for HMX membrane unit 100. Principally, headers 104 and 105
may provide conduits in the form of subchannels 108 for introducing
intake air and removing exhaust air from main body 106 at opposite
ends of membrane 101.
[0054] Elongated pillars 201 are integrated directly on membrane
101, as described above for strip fins 102 in HMX membrane unit
100.
[0055] FIG. 3A illustrates a plan view in the x-y plane of HMX
membrane unit 300a having integrated circular pillar support
structures 301 in a rectangular array, according to some
embodiments of the disclosure.
[0056] HMX membrane unit 300a comprises circular pillars 301
configured in a rectangular or square array, integrated onto
membrane 101. Spacing between circular pillars 301 extends in the
x-dimension and the y-dimension. In some embodiments, x-spacing
p.sub.2 and y-spacing p.sub.3 range between 2 mm and 4 mm. In some
embodiments, p.sub.2 is substantially equivalent to p.sub.3,
yielding a square array. In alternative embodiments, p.sub.2 and
p.sub.3 are not equal, yielding a rectangular array. In some
embodiments, circular pillars 301 have a height (not shown) ranging
between 1 mm and 4 mm. In some embodiments, circular pillars 301
have a diameter ranging between 0.5 mm and 2 mm.
[0057] Headers 104 and 105 introduce and remove airstreams from
main body 106 of membrane 101. Strip fins 107 are integrated onto
the membrane base of headers 104 and 105, providing airflow
subchannels 108 between strip fins 107, which are sidewalls for
subchannels 108. The flow paths for introduced air within the main
airflow channel in which circular pillars 301 are distributed are
random, as indicated by the arrows in the gaps between circular
pillars 301. Primary flow vectors are in the x- and y-directions,
entering flow orifices between circular pillars 301 having widths
of p.sub.2 or p.sub.3, and height h. A hydraulic diameter may be
defined as {4.times.h.times.p.sub.2(3)}/{(2.times.p.sub.2(3))+2h},
where h is the pillar height. p.sub.2 and p.sub.3 are
interchangeable, as indicated by the parentheses in the subscript
of p. In some embodiments, the hydraulic diameter ranges between
approximately 1.5 and 4.
[0058] The general description of HMX membrane unit 100 is
applicable to HMX membrane unit 300a. Headers 104 and 105 extend
from both ends of membrane 101, and comprise integrated strip fins
107, dividing subchannels 108. The triangular shape of headers 104
and 105 serves to provide separate flow paths for intake air and
exhaust air on the same side of a HMX core (shown in FIG. 5).
[0059] When multiple HMX membrane units 300a are assembled in
stack, circular pillars 301 extend from membrane 101 to a second
membrane (not shown). In some embodiments, circular pillars are
bonded to the second membrane, forming a seal. In some embodiments,
the height of circular pillars 301 is the height of the main
airflow channel between membranes. Multiple HMX membrane units 300a
may be bonded together, forming a rigid HMX and sturdy core stack
comprising high-performance membranes (e.g., membrane 101). Main
airflow channels are formed between stacked HMX membrane units
300a, having circular pillar (e.g., circular pillars 301) as inner
integrated support structures.
[0060] FIG. 3B illustrates a plan view in the x-y plane of HMX
membrane unit 300b having integrated circular pillar support
structures 301 in a hexagonal array, according to some embodiments
of the disclosure.
[0061] HMX membrane unit 300b comprises circular pillars 301
configured in a hexagonal array, integrated onto membrane 101.
Spacing between circular pillars 301 extends in the x-dimension and
in a diagonal direction, indicated by the dashed lines. In some
embodiments, x-spacing p.sub.4 and vertical (y) spacing p.sub.5
range between 2 mm and 4 mm. In some embodiments, circular pillars
301 have a height (not shown) ranging between 1 mm and 4 mm. In
some embodiments, circular pillars 301 have a diameter ranging
between 0.5 mm and 2 mm.
[0062] Similar to the description for HMX membrane unit 300b,
headers 104 and 105 introduce and remove airstreams from main body
106 of membrane 101. Strip fins 107 are integrated onto the
membrane base of headers 104 and 105, providing airflow subchannels
108 between strip fins 107, which are sidewalls for subchannels
108. The flow paths for introduced air within the main airflow
channel in which circular pillars 301 are distributed are random,
as indicated by the arrows in the gaps between circular pillars
301. The arrows indicate various flow paths that the air streams
can take. Primary flow vectors, indicated by the arrows entering
header 105 and the bent arrows drawn in main body 106, are in the
x- and diagonal directions, entering flow orifices between circular
pillars 301 having widths of p.sub.4 or distance
.alpha.=p.sub.5/cos .theta., where .theta. is the angle of the
diagonal, and height h. A hydraulic diameter may be defined for any
of the flow paths as the distances between circular pillars 301 and
the height h of circular pillars 301 may be substantially constant.
The flow path hydraulic diameter d.sub.h may be defined as
{4.times.h.times.p.sub.4(.alpha.)}/{(2.times.p.sub.4(.alpha.))+2h},
where h is the pillar height. p.sub.4 and .alpha. are
interchangeable, as indicated by the parentheses in the subscript
of p. In some embodiments, the hydraulic diameter of the flow
ranges between approximately 1.5 and 4, depending on the values for
p.sub.4, .alpha. and h.
[0063] The flow paths may be substantially random, as shown by the
arrows within main body 106. Airstreams entering from header 105
encounter circular pillars 301 where the airstreams may be
deflected laterally, then begin to split into multiple paths. This
is indicated by the arrows drawn in the main body 106. The multiple
paths may exhibit a level of tortuosity relative to straight flow
paths (e.g., subchannels 103 shown in FIG. 1), increasing the
effective path length and contact surface. As a consequence,
individual airstreams may follow longer flow paths across main body
106.
[0064] The longer flow path generally increases heat and mass
exchange along a longer strip of active membrane surface relative
to what would be available along a straight flow path for the same
length of main body 106. Some increased pressure drop may occur
relative to straight and unobstructed flow paths as a result of the
increased path length, and the deflection caused by circular
pillars. In some embodiments, the hydraulic diameter of the random
flow paths is the same as for straight flow paths (e.g.,
subchannels 103 shown in FIG. 1).
[0065] FIG. 4 illustrates a plan view in the x-y plane of HMX
membrane unit 400 having serpentine fin rib support structures 401,
according to some embodiments of the disclosure.
[0066] HMX membrane unit 400 comprises serpentine (curved) strip
fins 401 extending laterally across main body 106 of membrane 101.
Stipfin ribs 401 provide are integrated onto membrane 101, and
divide the main airflow channel over membrane 101 into curved
subchannels 402. In some embodiments, strip fins 401 have a
z-height ranging between 1 mm and 4 mm, extending over membrane
101. In some embodiments, the height of the main airflow channel
over membrane 101 (e.g., between membrane 101 and the membrane
floor of an adjacent HMX membrane unit 400 in a HMX core stack (not
shown)) is substantially equal to the z-height of curved strip fins
401. Curved strip fins 401 have a width extending generally in the
y-direction of the figure, ranging between 1 mm and 2 mm. In some
embodiments, strip fins 401 have a height-to-width aspect ratio
ranging between 1:1 and 2:1. In some embodiments, strip fins 401
comprise an adhesive material, such as, but not limited to,
silicones, epoxy resins or acrylate resins. The adhesive material
is bonded to membrane 101 by adhesive bonds that are formed during
manufacture, as described below.
[0067] In the illustrated embodiment, curved strip fins 401
comprise three curved segments. In some embodiments, curved strip
fins 401 are S-shaped, comprising two alternately curved segments.
In alternative embodiments curved strip fins 401 comprise four or
more curved segments. It will be appreciated by persons skilled in
the art that the greater the number and curvature of the curved
segments, the greater the length of the airflow path along
subchannels 402. The curvature increases the flow path length of
subchannels 402 for a given lateral extent relative to straight
subchannels (e.g., subchannels 103 shown in FIG. 1). As for HMX
membrane units 300a and 300b, more contact surface area is thus
provided for heat and mass exchange within curved subchannels 402
without necessitating an increase in the length of membrane
101.
[0068] In some embodiments, the overall dimensions and material
compositions described for HMX membrane unit 100 are generally
applicable to HMX membrane unit 400. Trangular-shaped headers 104
and 105 extend from the ends of membrane 101
[0069] FIG. 5 illustrates a partially exploded oblique view of HMX
core assembly 500 comprising a stack of HMX membrane units 100,
according to some embodiments of the disclosure.
[0070] In the illustrated embodiment, HMX core assembly 500
comprises multiple HMX membrane units 100 (shown individually in
the exploded view) assembled into a stack extending in the
z-direction of the figure. Integrated support structures (e.g.,
strip fins 102) extend between HMX membrane units, and have
adhesive bond joints with the base membrane (e.g., membrane 101) of
the HMX membrane unit, and with the base membrane of an adjacent
HMX membrane unit within the core stack. The space between each
pair of adjacent base membranes is a main flow channel (e.g., main
flow channels 501). It will be appreciated that any of the
embodiments of HMX membrane units (e.g., HMX membrane units 200,
300a, 300b and 400) described above may be substituted for HMX
membrane units 100. In some embodiments, overall dimensions for HMX
core assembly comprise a length extending in the x-direction of the
figure ranging between 500 mm and 1000 mm, a width extending in the
y-direction of the figure ranging between 150 mm and 200 mm, and a
height extending in the z-direction of the figure ranging between
750 mm and 1250 mm. In some embodiments, HMX core assembly
comprises between 700 and 1000 HMX membrane units 100.
[0071] Individual HMX membrane units are bonded though the
integrated support structures (e.g., strip fins 101) extending from
the base HMX membrane (e.g., membrane 101) of one HMX membrane unit
to the base membrane of an adjacent HMX membrane unit within the
core stack. The support structures (e.g., strip fins 102) comprise
an adhesive material, and may be bonded to both base membranes by
adhesive bond joints formed during assembly of the HMX core
stack.
[0072] HMX core assembly 500 comprises multiple HMX membrane units
that are structurally coupled to each other by the integrated
support structures on each HMX membrane unit. The compounded
adhesive bond joints between support structures and adjacent
membranes within HMX core assembly 500 produce a rigid stand-alone
assembly of HMX membrane units that does not require an external
frame or clamping mechanism to hold the membrane units together.
The integrated support structures provide the rigidity for each
membrane unit and permit the employment of non-rigid,
high-performance mass and heat exchange membranes as the base
membranes (e.g., membrane 101) for each HMX membrane unit. In the
assembly, HMX membrane units 100 are stacked so that headers 104
alternate with headers 105 on each side of HMX core stack 500.
[0073] Bold dark arrows drawn in FIG. 5 indicate exemplary airflow
streams that pass internally within HMX core assembly 500, through
subchannels 103 of each individual HMX membrane unit. The arrows
external to HMX membrane units 100 show the delivery of intake air,
generally from the outside, into headers 104, and the exit of the
exhaust stream from headers 105. In the illustrated embodiment,
adjacent HMX units 100 are stacked such that headers 104 alternate
with headers 105 on each side of HMX core assembly 500. HMX
membrane units 100a and 100c have overlapping headers 104 on a
first side of HMX core stack 500, with header 105 on HMX membrane
unit 100b sandwiched in between.
[0074] Referring to HMX membrane units 100a and 100c, intake air
directed substantially along the y-direction below the plane of the
figure enters headers 104 on the left side of HMX membrane units
100a and 100c and flows along the membrane in the x-direction to
headers 105 on the right side, exiting HMX core assembly 500, where
the exhaust stream is directed above the plane of the figure aimed
substantially along the x- and y-directions of the figure.
[0075] Referring to HMX membrane unit 100b, intake air directed
substantially along the x and y directions below the plane or the
figure enters header 104 on the right side of the membrane. Air
flows along the membrane in the opposite direction relative to air
flow in the channels above HMX membrane units 100a and 100c. A
countercurrent flow is then established between HMX membrane units
100b and 100a within the main body portions of membrane 101 (e.g.,
main body 106 shown in FIG. 1), and HMX units 100band 100c. Between
vertically alternating headers 104 and 105, a crossflow is
established as strip fins 107 in the alternating header regions may
be substantially orthogonal to each other or are rotated from each
other by an acute or obtuse angle close to 90.degree.. In some
embodiments, the flow configuration of HMX core assembly 500 is a
quasi-crossflow configuration, as the flow path configuration above
and below each membrane 101 results in a partial crossflow within
the header portions and a partial countercurrent flow within the
main body (e.g., main body 106) portions of membrane 101.
[0076] The alternate orientation of strip fins 107 for each
adjacent HMX membrane unit 100 permits opposing airflow streams to
be directed in orthogonal or quasi-orthogonal directions on each
side of the core. For headers 104 providing air intake along
subchannels between strip fins 107, rotated strip fins 107 on
interleaved headers 105 block introduction of intake air into the
exhaust outlets, so that an intake ERV duct may be coupled to the
inlet sides of HMX core assembly 500 and not introduce intake air
into the exhaust. This detail is shown in a magnified view in the
inset of FIG. 5. Each side receives an intake stream and exhausts
an output stream, where the intake and output streams may be
collected in separate ducts in the ERV system.
[0077] The large pseudo three-dimensional arrows external to HMX
core assembly 500 indicate collective air streams flowing into each
side of the core from ERV intake ducts (not shown) and out of each
side of the core to ERV exhaust ducts (not shown). Arrows labeled
"outside air intake" and "inside air exhaust to outside" indicate
airstreams entering HMX core assembly 500 from an intake ERV duct
(not shown) coupled to main channels 501 through headers 104 on the
right side of the core, and exiting into an exhaust duct leading
from main channels 501 through headers 105 on the right side of the
core. The ERV ducts (not shown) may be oriented orthogonally or
quasi-orthogonally to each other to couple to the right side of HMX
core assembly 500, allowing separation of duct work and mitigating
mixing of the two air streams.
[0078] The arrow labeled "outside air exhaust to inside" indicates
collective flow of conditioned outside air exiting HMX core
assembly into a duct leading to the interior of a building from
left-side headers 105, and exhausting the conditioned air therein.
Not shown is building air entering left-side headers 104 for
recovering energy by HMX core assembly 500 from interior air by
heat/mass (e.g., mass in the form of water vapor) countercurrent or
quasi-cross flow exchange across HMX membrane units 100.
[0079] As mentioned above, subchannels 103 provide flow multiple
parallel ducts for the airflow, allowing the bulk airstreams divide
upon entry into the core and may increase velocity across the
membrane relative to the bulk velocity of the air delivered to HMX
core assembly 500 by the ERV system. As an example, the ERV system
may deliver an air flow rate of 300 cubic feet per minute (CFM),
divided into 704 main channels 501, each comprising 23 subchannels
301, each having a width of approximately 6 mm and a height of
approximately 1.2 mm. An increase in flow velocity of the air over
the membrane reduces the boundary layer thickness, increasing
convective mass and heat transport to the membrane from the bulk
airstream passing above. Subchannels 103 also may be extended by
folding of strip fins 102, or by multiple flow paths introduced by
pillars to increase the effective flow path length, as described
above for HMX membrane units 300 and 400, allowing greater contact
surface for heat and mass exchange within the same overall membrane
size.
[0080] The ability to employ high-performance (e.g., low mass and
heat transfer resistance) membranes increase overall heat and mass
exchange efficiency of the core with very low pressure drop (e.g.,
a .DELTA.P of 300 Pa or less), permit a reduction of the overall
dimensions of HMX core assembly 500 relative to some currently
available HMX cores and offer a more compact HMX core for ERV
systems. In addition, a simplified assembly process where manual
assembly operations are supplanted by automated operations, as
described below, permits lower manufacturing costs to be associated
with HMX core assembly 500.
[0081] FIG. 6 illustrates a flow chart of an exemplary method for
making HMX core assembly 500, according to some embodiments of the
disclosure. The set of operations described below is an illustrated
embodiment of the method for making an HMX core assembly according
to the embodiments described herein. It will be appreciated that
other embodiments of the method that have some variations of the
particular operations may be substituted for operations described
below.
[0082] At operation 601, a first HMX membrane is received for
processing into a HMX membrane unit (e.g., HMX membrane unit 100)
and assembled into a HMX core assembly (e.g., HMX core assembly
500). In some embodiments, the HMX membrane is precut to a
specified shape, such as, but not limited to, a hexagonal shape as
shown in FIGS. 1-5, or a rectangle (e.g., a square shape). In some
embodiments, the HMX membrane is supplied on a roller system, where
membrane material is fed across an adhesive application station.
For the latter, the membrane may be cut in a subsequent operation
by a laser cutting operation or a similar cutting operation.
[0083] The HMX membrane may be placed in the workspace of a
dispensing station. The dispensing station may comprise a movable
nozzle, where the nozzle may be displaced at least vertically (in
the z-direction). A pre-cut HMX membrane may be secured to a
motorized X-Y stage, where the X-Y stage is computer controlled,
using computer numerical control (CNC) techniques.
[0084] At operation 602, a first layer of adhesive is dispensed
from the nozzle in a pattern over the membrane. As an example, a
strip fin (e.g., strip fin 102) is formed in this and succeeding
operations. The adhesive, described above, is dispensed as a paste
or a viscous liquid as a continuous bead line as a base layer for
the strip fin. The bead may be a line of adhesive that is dispensed
from the nozzle while the nozzle is displaced in the x and
y-directions along a particular direction. Alternatively, the
membrane may be moved on the X-Y table relative to the nozzle,
which is held stationary. The beads of adhesive may form tack bonds
with the HMX membrane immediately upon contact. The adhesive
material may be chosen such that it begins to gradually cure on
contact with the air. The length of cure time may be tailored to
allow some degree of solidification, but remaining tacky for a
specified number of minutes. At the same time, adhesive bonds are
formed with the HMX membrane.
[0085] In some embodiments, the beads have a roughly circular cross
section. The bead may hold its shape if the adhesive cures
internally to an extent where the adhesive does not flow, while
remaining tacky on the surface.
[0086] At operation 603, a second bead of adhesive is dispensed
over the first bead. The operation may be described as a "writing"
of the bead onto the HMX membrane, as the nozzle dispenses the
adhesive similarly to a pen dispensing ink over paper. This
operation relies on the degree of cross-linking of the adhesive in
the first bead allowing the first bead to hold its shape without
flowing or deforming under the weight of the second bead. In some
embodiments, the second bead is applied in a direction opposite of
the first bead. The dispensing head may travel back to a starting
position while dispensing the second bead over the first bead. The
reversal of the dispensing path may compensate gradually increasing
flow of adhesive from the nozzle as the deposition progresses from
beginning to the end of the nozzle travel. The bead may be less
thick at the beginning and thickest at the end. Commencement of the
dispensing of the second bead at the end of the first bead may
allow for an even height of the feature, as more adhesive is
deposited at the end of the travel, or where deposition of the
second bead finishes at the beginning of the first bead.
[0087] As the bead is dispensed, its cross-section may be
approximately circular, having a height-to-width aspect ratio of
approximately 1:1. An adhesive may be chosen that begins to harden
on contact with air as mentioned above, so that the first and
second beads do not flatten due to flow under gravity to the extent
that the height-to-width aspect ratio significantly reduces to
values less than 0.9:1. At the same time, the surface of the bead
remains tacky to form adhesive bonds with an overlying bead as well
as the underlying HMX membrane. In this way, the structure is built
up by two (or more) layers. In some embodiments, the overall
height-to-width aspect ratio of the support structure ranges from
1:1 to 2:1. In some embodiments, the overall height-to-width aspect
ratio of the support structure (e.g., strip fin 102 or pillar 301)
is approximately 1.2:1. To produce an overall aspect ratio of less
than 2:1, the thickness of the second bead as dispensed may be less
than the thickness of the first layer. The nozzle diameter or the
flow rate of the adhesive may be adjusted to produce a desired bead
thickness.
[0088] The writing process may be performed at room temperature in
ordinary air. In the writing process, each single line (e.g., a
strip fin) or pillar is produced at a time. After depositing a
single support structure, the nozzle is displaced laterally over
the HMX membrane and the next structure is deposited. During this
time, the adhesive may continue to slowly cure and still remain
tacky at the surface. Adhesives requiring a thermal treatment at
elevated temperatures for a final cure are suitable for the writing
operation, as they may solidify internally to a large extent
relatively slowly at room temperature, but remain tacky enough for
the amount of time needed to complete assembling the HMX core
assembly.
[0089] As an alternative to the dispensing/writing operation, in
some embodiments, a stencil having openings configured in the
intended pattern for the support structures is overlaid on the
membrane and adhesive is applied by a spraying tool or is applied
by a roller. Employment of a stencil may require more than one
layer of adhesive to be applied. The nascent structures formed in
the openings of the stencil may cure rapidly enough to partially
solidify within an allotted time, for example within 5 minutes or
less, before additional layers are applied. The particular details
of firmness, tackiness and aspect ratio described earlier may apply
to the employment of the stencil for simultaneous application of
the adhesive.
[0090] Layer thicknesses may range from approximately 0.5 mm to 2
or 3 mm. The target height of the support structure may require
application of multiple layers of adhesive to build up the
structures to the desired height. For each layer, the deposition
process (e.g., writing or through-stencil application) is repeated
until the desired height of the structures are reached.
[0091] At operation 604, an optional partial cure is performed to
solidify the nascent support structures further than its state of
crosslinking in operation 603. The cure step may comprise a thermal
treatment at an elevated temperature. In alternative embodiments, a
photocure may be performed. Alternatively, a cured adhesive may be
activated to a pre-cure stage exhibiting surface tackiness or
adhesion, where surface crosslink bonds are re-opened. Restoring
adhesive power to the surface of the support structure permits
attachment of a second HMX membrane that may be overlaid on the
tacky but firm support structure. Activation of adhesion at the
surface may comprise chemical treatments with organic solvents or
acidic/basic solutions to rupture bonds (e.g., by hydrolysis). In
some embodiments, the chemical treatments are performed at
temperatures above room temperature.
[0092] At this stage in the process, the support structures have
been developed to a desired amount of firmness and surface tack. In
some embodiments, the HMX membrane is part of a roll and not cut to
the desired shape at this stage. After completion of the pattern of
support structures, the portion of the membrane roll is conveyed to
a cutting station downstream, and the HMX membrane unit (e.g., HMX
membrane unit 100) is cut to shape. At this stage, the HMX membrane
unit is completed. The completed HMX membrane unit may be
transferred to a subsequent station by a robotic mechanism, or
manually, for core stack assembly. In some embodiments, the HMX
membrane had been precut before deposition of the support
structures. The completed HMX membrane unit comprising the precut
HMX membrane may be left in place in the adhesive deposition tool,
and a second HMX membrane overlaid in a subsequent operation for
formation of the next HMX membrane unit, as described in the
following paragraphs.
[0093] At operation 605, the core stack build-up assembly process
takes place. In some embodiments, a second HMX membrane (e.g.,
membrane 101) is aligned to and placed over the completed HMX
membrane unit while in the adhesive deposition tool. The transfer
and placement operation may be performed by a robotic arm or tool
that carries the membrane in a taut state, similar to a
pick-and-place operation. The HMX membrane may be carried on a
carrier frame over which it is stretched. In some embodiments, the
second HMX membrane is pressed against the underlying support
structures to ensure that the membrane makes sufficient contact
with all of the underlying support structures.
[0094] As mentioned above, the support structures on the underlying
HMX membrane unit remain tacky enough to form adhesive bonds with
the second HMX membrane. Sufficient bond formation between the
underlying structures and the second HMX membrane is necessary to
seal the second membrane to the underlying support structures. As
an example, subchannels (e.g., subchannels 103 shown in FIG. 1) are
separated from one another by strip fin sidewalls (e.g., strip fins
101 shown in FIG. 1) that are integrated with both the first HMX
membrane and the overlying second HMX membrane. The integration of
the support structures with the HMX membranes is performed by the
adhesive bonding of the support structures to the HMX membrane
material. Accordingly, the strip fin sidewalls seal the passageways
so that airstreams flowing within the subchannels do not mix. In
embodiments where the support structures are pillar structures
(e.g., elongated pillars 201 shown in FIG. 2 or circular pillars
301 shown in FIGS. 3A and 3B), the pillar structures are integrated
to both first and second HMX membranes by formation of adhesive
bonds with both membranes. At this stage, the support structures
are still partially cured, and may remain tacky. Final curing and
solidification of the structures may be carried out in a subsequent
operation.
[0095] Once in place over the first HMX membrane unit, the second
HMX membrane is ready for processing into a second HMX membrane
unit with its own set of support structures. In some embodiments,
the process flow cycles back to operation 602 and repeats the
operations to operation 605, as indicated in FIG. 6. The process
cycle may be repeated a prescribed number of times to build up the
HMX core stack. In some embodiments, the process cycle is repeated
between 700 and 1000 times.
[0096] At operation 606, the core stack build-up process is
complete (e.g., as HMX core assembly 500). In some embodiments, a
final curing operation is performed by thermal treatment at
elevated temperatures (e.g., at 50.degree. C. or higher). The
thermal treatment may be performed in an oven. The curing
temperature may be selected to be under the glass transition
temperature of the HMX membrane material. A cure time may be
adjusted to cure the support structures to a specified rigidity,
where the cure time is selected so that the cured structure does
not plastically deform more than approximately 2% to maintain the
desired shape and dimensions of the structures, particularly the
height and lateral dimensions (e.g., the width or diameter). After
the final cure, the HMX core stack is complete.
[0097] FIGS. 7A-F illustrate a succession of key operations of an
exemplary method to manufacture HMX core assembly 500, according to
some embodiments of the disclosure.
[0098] In the operation depicted in FIG. 7A, nozzle 700 is
translated over HMX membrane 101 in a first direction along the
x-axis (e.g., toward the right side of the figure) to dispense
first adhesive bead 701 as a strip fin line (e.g., strip fin 102
shown in FIG. 1) on the surface of HMX membrane 101. Nozzle 700 is
positioned over HMX membrane 101 at a z-height that is optimized to
dispense first adhesive bead 701 at a prescribed speed of
translation (e.g., 250 mm/s) that permits approximately predictable
dimensions along the length of first adhesive bead 701 in the x-
and z-dimensions. In some embodiments, first adhesive bead 701 is
thicker at the end of the write run that at the beginning.
[0099] Nozzle 700 may be mounted on a movable arm that is capable
of displacement in the x- and z-directions, and translated with HMX
membrane 101 held stationary during the write operation. In some
embodiments, Nozzle 700 may be held stationary while HMX membrane
101 is translated on an X-Y table under nozzle 700. Nozzle 700 may
be displaced in the z-direction by a movable arm on the dispensing
tool, or by displacement of HMX membrane 101 on an X-Y-Z table. As
an example, nozzle 700 may be displaced relative to membrane 101 at
250 mm/sec.
[0100] In the operation depicted in FIG. 7B, the writing (e.g.,
dispensing) of first adhesive bead 701 is complete. Nozzle 700 is
positioned above the end portion. In some embodiments, nozzle 700
is displaced to a higher position (in the z-direction) over the end
of first adhesive bead 701. In some embodiments, a delay or hold
time is imposed between write runs to allow first adhesive bead to
set or partially cure to a point where it is firm (e.g., still
deformable under sufficient strain) but tacky (e.g., still able to
form adhesive bonds). In some embodiments, multiple nozzles are
employed. In some embodiments, the width of adhesive bead 701 is
approximately 0.5 mm as deposited.
[0101] In the operation depicted in FIG. 7C, nozzle 700 is
translated in the reverse direction over first adhesive bead 701 to
write second adhesive bead 702 directly over first adhesive bead
701. In some embodiments, the speed of translation of nozzle 700
(relative to HMX membrane 101) to write second adhesive bead 702 is
substantially the same as the first write operation to form first
adhesive bead 701.
[0102] In some embodiments, the amount of adhesive to form second
adhesive bead 702 is less than the amount used for formation of
first adhesive bead 701. In general, a lesser amount of adhesive to
for the second layer may be necessary to control the height
dimension or the height-to-lateral dimension (e.g., width or
diameter) aspect ratio of the support structure. As an example, a
desired aspect ratio may be 1.2:1. To achieve the target aspect
ratio, the amount of adhesive dispensed to form second adhesive
bead 702 may be 50% to 80% less than the amount of adhesive
dispensed to form first adhesive bead 701.
[0103] In the operation depicted in FIG. 7D, the writing of second
adhesive bead 702 is complete. A delay or hold time may be imposed
to allow second adhesive bead 702 to set or partially cure to a
point where it is firm (e.g., still deformable under sufficient
strain) but tacky (e.g., still able to form adhesive bonds). At
this stage, formation of strip fin 102 is complete and integrated
onto HMX membrane 101. The write operations depicted in FIGS. 7A
through 7C may be repeated a number of times (e.g., 20-40 times) on
HMX membrane 101 to complete an array of strip fins 102, as shown
in FIG. 1. After completion of the strip fin array, comprising
strip fins 102 and 107 (not shown), HMX membrane unit 100 is
completed. In some embodiments, multiple nozzles are employed in
parallel to reduce the duration of the write operations.
[0104] In the operation depicted in FIG. 7E, the assembly process
to make HMX core assembly 500 is shown where multiple HMX membrane
units 100a and 100b are stacked. The stacking process may be
performed by a robotic arm. Some details of this procedure are
described above in the discussion relating to FIG. 6. As an
example, HMX membrane unit 100b is aligned over HMX membrane unit
100a and lowered to make contact between strip fins 102 on HMX
membrane unit 100a and HMX membrane 101 of HMX membrane unit 100b.
Tack bonds may be formed between strip fins 102 and overlying HMX
membrane material to seal strip fins 102 to the overlying HMX
membrane.
[0105] In the operation depicted in FIG. 7F, a representative
portion of an assembled HMX core assembly 500 comprising a stack of
multiple HMX membrane units 100 is shown. The core stack is
mechanically bonded together by the adhesive bonds between strip
fins 102 between each sheet of HMX membrane 101, forming a rigid
unit without the aid of an external framework or mechanical
supports. Main airflow channels 501 are formed in the space between
HMX membrane units 100 and extend above and below the plane of the
figure, in the y-direction. The height of main airflow channels 501
is determined the z-height of strip fins 102, which also form the
sidewalls of the subchannel array (e.g., subchannels 301 in FIG. 1)
extending along the x- and y-directions.
[0106] FIG. 8 illustrates flow chart 800 summarizing an alternative
method for making HMX core assembly 500, according to some
embodiments of the disclosure. It will be appreciated that other
embodiments of the method that have some variations of the
particular operations may be substituted for operations described
below.
[0107] At operation 801, an in-process HMX core stack (e.g., HMX
core assembly 500) is received for further processing. The HMX core
stack may comprise a platen holding a single blank HMX membrane, or
it may comprise multiple pre-assembled HMX membrane units (e.g.,
HMX membrane units 100) assembled together into an unfinished core
stack. It will be understood that by "unfinished" refers to a core
stack having fewer than the target number of HMX membrane units
assembled together and is still in-process. The core stack has a
top HMX membrane that is blank, meaning that it does not have any
adhesive material deposited over it. The assembly process comprises
multiple bonding cycles, each bonding cycle producing a HMX
membrane unit addition to the HMX core stack.
[0108] At operation 802, an adhesive is deposited over the top HMX
membrane to from an array of integrated support structures.
Suitable adhesive materials that may be deposited over the HMX
membrane have been described in detail above. A criterion of the
adhesive is that it non-slumping, meaning it does not flow under
its own weight during the open time (e.g., in the pre-cured state),
maintaining its as-deposited shape.
[0109] In some embodiments, the deposition process is a
nozzle-dispensing process as described above, and shown in FIGS.
7A-7F. In this process, beads of adhesive are extruded through the
nozzle. The dispensed bead may hold its shape substantially
as-extruded. In contrast to the multi-layer dispense process
described earlier, a single layer of adhesive may be deposited over
the blank HMX membrane. In alternate embodiments, the adhesive is
applied through a stencil as a deposition mask. Here, the adhesive
may be deposited by a roller over a stencil having a through-mask
pattern of openings delineating the support structure array. The
width of elongated structures (e.g., strip fins 102 or elongated
pillars 201) as defined by the stencil mask may be wider than the
target dimension.
[0110] At operation 803, a blank and unattached HMX membrane is
mounted on a platen. The blank HMX membrane may be precut to the
intended dimensions and shape. In some embodiments, the HMX
membrane is cut to a hexagonal shape, as shown in FIGS. 1-4. The
platen may comprise a vacuum mounting system, or a vacuum chuck.
The vacuum firmly holds the HMX membrane, which is highly
compliant, on a flat surface. The membrane may be mounted on the
platen in a taut manner such that there are no wrinkles.
[0111] In some embodiments, the platen may be part of or entirely
an end effector (e.g., the manipulating mechanism of a robot arm)
of a robotic arm capable of motion in three dimensions. In
alternate embodiments, the platen may be an end effector of a
linear actuator capable only of motion along a single axis, for
example, vertical motion in the z-direction.
[0112] At operation 804, the platen may be rotated to face the
blank HMX membrane downward, or opposite the top membrane having
the freshly deposited patterned adhesive layer on the HMX core
stack. The platen is then lowered by vertical displacement in the
z-direction to tack the blank membrane on the patterned adhesive
layer on the top HMX membrane of the core stack. The platen motion
may be controlled in such a way that the contact pressure is
adjusted so that no gaps exist between the adhesive beads and the
HMX membrane. The adhesive beads may be firm, but not solid enough
to resist significant strain, where the adhesive may deform
plastically. Adhesive bonding takes place between the blank HMX
membrane and the adhesive beads, and the blank HMX membrane is
tacked down on the patterned adhesive layer.
[0113] At operation 805, the platen is raised by upward motion in
the z-direction by several tens or hundreds of microns over the
as-deposited height of the adhesive bead. At the same time, the
membrane remains bonded to the adhesive, and is pulled upward,
stretching and elongating the adhesive beads in the z-direction
beyond the elastic limit. The adhesive forces may be strong enough
to remain intact during the stretching process. According to some
embodiments, the platen is raised a distance that substantially
goes beyond the elastic deformation limit of the adhesive material
in the uncured state.
[0114] In some embodiments, the distance above the top HMX membrane
to which the platen is raised is substantially the target height of
the final structure after curing. At the same time, the width of
the bead may decease as material is pulled upward. In some
embodiments, the adhesive bead is plastically deformed and assumes
the new dimensions of at the height and width as a result of the
stretching process. According to some embodiments, the adhesive is
firm enough as a result of partial curing at room temperature, to
retain the shape assumed by the plastic deformation. As an example,
the adhesive bead may be stretched a distance above the
as-deposited adhesive beads to attain a height-to-width aspect
ratio between 1:1 and 2:1 (e.g., the aspect ratio is adjusted to
1.2:1). When this operation is completed, the HMX membrane and
integrated structures form a HMX membrane unit (e.g., HMX membrane
unit 101)
[0115] At operation 806, the blank HMX membrane is released from
the platen. The blank HMX membrane is tacked to the top adhesive
layer and raised to the target height. To release the membrane, the
vacuum may interrupted if a vacuum chuck or vacuum mounting system
is employed. Once released, the blank membrane is the top HMX
membrane of the in-process core stack. The platen is available to
retrieve another blank membrane to add to the core stack by
repeating the bonding cycle as described in operations 802-806. As
indicated in FIG. 8, the process cycles back to operation 802.
[0116] At operation 807, the core stack is complete. By being
complete, it is meant that the target number of HMX membrane units
have been assembled in the core stack build-up cycle comprising
operations 802-806. The entire core stack may be cured at an
elevated temperature, as described for operation 606 in FIG. 6.
[0117] FIGS. 9A-9I illustrate a succession of key operations of an
alternate exemplary method for making HMX core assembly 500,
according to some embodiments of the disclosure.
[0118] In the operation depicted in FIG. 9A, an in-process HMX core
assembly 500, where the core stack is unfinished. The target number
of HMX membrane units 100 has not yet been attained. Multiple HMX
membrane units 100 are tack-bonded together in a stack that is
built up by the operations in the exemplary manufacturing process
described in the following paragraphs. At any stage of completion,
the in-process HMX core stack is capped by top HMX membrane 900,
which is tacked onto the adhesive layer of the lower HMX membrane
unit produced in the previous bonding cycle. There are no
structures integrated over top HMX membrane 900 at this stage. The
operations are part of a cyclic bonding process to manufacture the
HMX core stack (e.g., HMX core assembly 500) by a build-up method.
Each bonding cycle produces a HMX membrane unit 100.
[0119] In the operation depicted in FIG. 9B, adhesive bead 901 is
dispensed from nozzle 902, which is positioned at a z-height above
top membrane 900 and translated over it along the x-direction in
the figure. The adhesive bead 901 is extruded from the nozzle and
has an as-deposited z-height and width as the nozzle travels along
the membrane. When deposited on the membrane, adhesive bead 901 may
have an approximately circular cross section. In some embodiments,
multiple nozzles may be employed in parallel. As described above,
suitable adhesives are non-slumping, in that the adhesive material
does not flow under gravity after deposition, substantially
retaining its as-deposited shape until it cures. In some
embodiments, the width of adhesive bead 901 is approximately 0.5 mm
as deposited.
[0120] The deposition of adhesive bead 901 may be performed by a
similar method described for FIGS. 7A and 7B. In some embodiments,
nozzle 902 translates while HMX core assembly 500 remains
stationary. In some embodiments, HMX core assembly 500 is mounted
on an x-y table and translated while nozzle 902 remains stationary.
The relative motion of nozzle 902 relative to top HMX membrane 900
may be computer controlled (e.g., by CNC operation) to follow coded
write commands to produce a pattern of structures created by
multiple beads of similar or different lengths and orientations. As
an example, nozzle 902 is translated at a speed of approximately
250 mm/sec relative to HMX membrane 900.
[0121] In the operation depicted in FIG. 9C, the writing of bead
901 is completed. As an example, bead 901 is written to form a
strip fin 102. An array of strip fins 102 may be created in this
manner by displacement of nozzle 902 in the y-direction of the
figure and repeating the x-translation. The adhesive remains firm
but tacky, holding its shape. At the same time, adhesive bead 901
forms adhesive bonds with top HMX membrane 900.
[0122] In the operation depicted in FIG. 9D, blank membrane 903 is
mounted on platen 904. In some embodiments, platen 904 is an end
effector of a robotic arm (not shown). In some embodiments, platen
904 is attached to a linear actuator that translates in the
z-direction of the figure. In some embodiments, blank membrane 903
is held by vacuum on platen 904, where a blank membrane 903 is
sucked onto a mesh that is incorporated into platen 904. In
alternate embodiments, blank membrane 903 is held onto platen 904
by a mechanical clamping mechanism.
[0123] In the operation depicted in FIG. 9E, platen 904 is aligned
over HMX core assembly 500 and lowered to tack blank membrane 903
onto adhesive bead 901. In FIG. 9E, adhesive bead 901 represents an
entire array of nascent support structures written onto top HMX
membrane 900 in FIGS. 9B and 9C. In the operation depicted in FIG.
9F, blank membrane 903 makes contact with adhesive bead 901.
Adhesive bonds begins to form and hold it onto the nascent support
structure. During the attachment of blank membrane 903 to adhesive
bead 901, platen 904 remains attached to blank membrane 903.
[0124] In the operation depicted in FIG. 9G, platen 904 is
translated upward in the z-direction by distance .DELTA.h, which
may be tens or hundreds of microns. In some embodiments, .DELTA.h
is larger than the elastic limit of the adhesive material, and the
material undergoes plastic deformation. During this operation,
vacuum may hold blank membrane 903 onto platen 904, if a vacuum
chuck is employed. Membrane 903 moves upward with platen 904,
pulling the top portion of adhesive bead 901 upward with it by
tensile force as adhesive bonds between bead 901 and blank membrane
903 are strong enough to remain attached to the surfaces of blank
membrane 903 above and top membrane 900 below.
[0125] The dimensions of adhesive bead 901 are stretched by the
tensile forces imposed during this operation, where adhesive bead
901 attains a new z-height that is greater than the initial
as-deposited z-height. Adhesive bead 901 undergoes plastic
deformation during this stretching operation. In some embodiments,
platen 904 is held at the raised position for a prescribed period
of time to allow plastic deformation to occur. During the hold
time, the polymer chains may relax into the stretched
configuration, and lose their propensity to recoil back into the
original shape as elastic strain is exceeded.
[0126] At the same time, the width of adhesive bead 901 may
decrease as tensile forces lift material from the sidewalls of
adhesive bead 901 to build up the z-height. The height-to-width
aspect ratio may be adjusted in this manner to values between 1:1
and 2:1. As an example, the height-to-width aspect ratio of the
nascent strip fin structure may be 1.2:1. The aspect ratio may be
important to ensure sufficient height of the airflow channels
(e.g., airflow channels 501) to maintain small pressure drop (e.g.,
less than 300 Pa) across the airflow channels, while at the same
time limiting coverage of the active membrane surface by the
structure to ensure high efficiency of heat and mass transfer
across the HMX membranes.
[0127] In the operation depicted in FIG. 9H, formation of the new
HMX membrane unit 100 is completed on the core stack. Adhesive bead
901 is now strip fin 102, having a target z-height and aspect
ratio. Blank membrane 903 is now top membrane 900. In the operation
depicted in FIG. 9I, the bonding cycle is complete. Platen 904 is
released from top membrane 900 and raised upward in the
z-direction. HMX core assembly 500 has an additional HMX membrane
unit 100 and a top membrane 900 ready to undergo a new bonding
cycle in the operations of FIGS. 9A-9I. The bonding cycles may be
repeated until HMX core assembly 500 comprises a target number of
HMX membrane units 100. In some embodiments, the core stack
comprises between 500 and 100 units.
[0128] Subsequent to the completion of the core stack assembly, HMX
core assembly 500 may undergo a thermal treatment at elevated
temperatures to cure the adhesive material. The curing operation
may be performed to solidify the support structures and strengthen
the adhesive bonds to membranes above and below the airflow
channels (e.g., airflow channels 501) in the core stack. A cure
time may be adjusted to cure the support structures to a specified
rigidity, where the cure time is selected so that the cured
structure does not plastically deform more than approximately 2% to
maintain the desired shape and dimensions of the structures,
particularly the height and lateral dimensions (e.g., the width or
diameter). After the final cure, the HMX core stack is
complete.
[0129] Reference in the specification to "an embodiment," "one
embodiment," "some embodiments," or "other embodiments" means that
a particular feature, structure, or characteristic described in
connection with the embodiments is included in at least some
embodiments, but not necessarily all embodiments. The various
appearances of "an embodiment," "one embodiment," or "some
embodiments" are not necessarily all referring to the same
embodiments. If the specification states a component, feature,
structure, or characteristic "may," "might," or "could" be
included, that particular component, feature, structure, or
characteristic is not required to be included. If the specification
or claim refers to "a" or "an" element, that does not mean there is
only one of the elements. If the specification or claims refer to
"an additional" element, that does not preclude there being more
than one of the additional element.
[0130] Furthermore, the particular features, structures, functions,
or characteristics may be combined in any suitable manner in one or
more embodiments. For example, a first embodiment may be combined
with a second embodiment anywhere the particular features,
structures, functions, or characteristics associated with the two
embodiments are not mutually exclusive.
[0131] While the disclosure has been described in conjunction with
specific embodiments thereof, many alternatives, modifications and
variations of such embodiments will be apparent to those of
ordinary skill in the art in light of the foregoing description.
The embodiments of the disclosure are intended to embrace all such
alternatives, modifications, and variations as to fall within the
broad scope of the appended claims.
[0132] In addition, well known power/ground connections to
integrated circuit (IC) chips and other components may or may not
be shown within the presented figures, for simplicity of
illustration and discussion, and so as not to obscure the
disclosure. Further, arrangements may be shown in block diagram
form in order to avoid obscuring the disclosure, and also in view
of the fact that specifics with respect to implementation of such
block diagram arrangements are highly dependent upon the platform
within which the present disclosure is to be implemented (i.e.,
such specifics should be well within purview of one skilled in the
art). Where specific details (e.g., circuits) are set forth in
order to describe example embodiments of the disclosure, it should
be apparent to one skilled in the art that the disclosure can be
practiced without, or with variation of, these specific details.
The description is thus to be regarded as illustrative instead of
limiting.
[0133] An abstract is provided that will allow the reader to
ascertain the nature and gist of the technical disclosure. The
abstract is submitted with the understanding that it will not be
used to limit the scope or meaning of the claims. The following
claims are hereby incorporated into the detailed description, with
each claim standing on its own as a separate embodiment.
* * * * *