U.S. patent application number 14/068005 was filed with the patent office on 2014-05-01 for high-thermal conductivity adsorbents for rapid absorption of heat pulses and a pressure-cascade burst desorption system using the same.
This patent application is currently assigned to Government of the United States as Represented by the Secretary of the Air Force. The applicant listed for this patent is Government of the United States as Represented by the Secretary of the Air Force. Invention is credited to Ajit Roy, Patrick J. Shamberger.
Application Number | 20140116640 14/068005 |
Document ID | / |
Family ID | 50545892 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140116640 |
Kind Code |
A1 |
Shamberger; Patrick J. ; et
al. |
May 1, 2014 |
HIGH-THERMAL CONDUCTIVITY ADSORBENTS FOR RAPID ABSORPTION OF HEAT
PULSES AND A PRESSURE-CASCADE BURST DESORPTION SYSTEM USING THE
SAME
Abstract
A composite adsorbent and heat burst desorption system using the
same. The composite adsorbent material includes a backbone and a
filler. The backbone comprises a first material having a high
thermal conductivity and a plurality of pore. The filler, within
the pores of the backbone, comprises a second material having a
large specific surface area.
Inventors: |
Shamberger; Patrick J.;
(Centerville, OH) ; Roy; Ajit; (Beavercreek,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Government of the United States as Represented by the Secretary of
the Air Force |
Wright-Patterson AFB |
OH |
US |
|
|
Assignee: |
Government of the United States as
Represented by the Secretary of the Air Force
Wright-Patterson AFB
OH
|
Family ID: |
50545892 |
Appl. No.: |
14/068005 |
Filed: |
October 31, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61720416 |
Oct 31, 2012 |
|
|
|
Current U.S.
Class: |
165/4 ;
165/10 |
Current CPC
Class: |
F28D 20/003 20130101;
B01J 20/02 20130101; F28D 17/02 20130101; B01J 20/28047 20130101;
Y02E 60/142 20130101; B01J 20/205 20130101; B01J 20/20 20130101;
Y02E 60/14 20130101; B01J 20/28066 20130101 |
Class at
Publication: |
165/4 ;
165/10 |
International
Class: |
F28D 17/02 20060101
F28D017/02; F28D 17/04 20060101 F28D017/04 |
Goverment Interests
RIGHTS OF THE GOVERNMENT
[0002] The invention described herein may be manufactured and used
by or for the Government of the United States for all governmental
purposes without the payment of any royalty.
Claims
1. A composite adsorbent comprising: a backbone comprising a first
material having a high thermal conductivity and having a plurality
of pores therein; and a filler within pores of the plurality of the
backbone and comprising a second material having a large specific
surface area.
2. The composite adsorbent of claim 1, wherein the thermal
conductivity of the first material comprising the backbone is
greater than about 20 W/mK.
3. The composite adsorbent of claim 1, wherein the specific surface
area of the second material comprising the filler is greater than
about 1000 m.sup.2/g.
4. The composite adsorbent of claim 1, wherein the first material
comprising the backbone is a graphitic foam, an aluminum foam, a
copper foam, a three-dimensional network of carbon nanotubes, a
three-dimensional network of multi-walled carbon nanotubes, a
three-dimensional network of metallic or semiconducting nanowires,
grapheme, or a combination thereof.
5. The composite adsorbent of claim 1, wherein the second material
comprising the filler is an aerogel or a cryogel.
6. The composite adsorbent of claim 1, wherein a surface of the
first material comprising the backbone, a surface of the second
material comprising the filler, or both is chemically modified.
7. The composite adsorbent of claim 6, wherein the chemical
modification includes introduction of a polar ionic species.
8. The composite adsorbent of claim 1, wherein the second material
comprising the filler comprises exfoliated outer layer of the first
material comprising the backbone.
9. A heat burst desorption system for absorbing rapid heat bursts
from a heat load, the system comprising: an adsorbent bed
containing an adsorbent; an adsorbate supply containing an
adsorbate, the adsorbate configured to adsorb onto a surface of the
adsorbent with a large heat of adsorption; a first heat transfer
path thermally coupling the adsorbent bed to the heat load; and a
second heat transfer path thermally coupling the adsorbent supply
to a cooling loop, wherein the system is operable in an absorption
mode and recharge mode: (i) when the system is in the absorption
mode, the adsorbent bed is fluidically coupled to an exhaust such
that adsorbate desorbs from surface of the adsorbent and vented
when heat is transferred on the first heat transfer path, and (ii)
when the system is in the recharge mode, the adsorbent bed is
fluidically coupled to the adsorbate supply such that adsorbate
adsorbs onto the surface of the adsorbent and heat is transferred
on the second heat transfer path.
10. A method of absorbing rapid heat bursts from a heat load, the
method comprising: decompressing an adsorbent bed comprising an
adsorbent when heat is generated by the heat load; and recharging
the adsorbent bed with an adsorbate when heat generation ceases,
the adsorbate configured to adsorb onto a surface of the
adsorbent.
11. The method of claim 10, wherein the adsorbent is the composite
adsorbent of claim 1.
12. The method of claim 10, wherein heat generated while recharging
the adsorbent bed is rejected from the adsorbent bed.
13. The method of claim 12, wherein the rejected heat is
transferred to a cooling loop.
14. A composite adsorbent comprising: a thermally-conductive
backbone comprising a first material having a plurality of pores
therein; and a filler within pores of the plurality of the backbone
and comprising a second material having a large specific surface
area.
15. The composite adsorbent of claim 14, wherein a thermal
conductivity of the first material comprising the backbone is
greater than about 20 W/mK.
16. The composite adsorbent of claim 14, wherein the specific
surface area of the second material comprising the filler is
greater than about 1000 m.sup.2/g.
17-21. (canceled)
Description
[0001] Pursuant to 37 C.F.R. .sctn.1.78(a)(4), this application
claims the benefit of and priority to prior filed co-pending
Provisional Application Ser. No. 61/720,416, filed Oct. 31, 2012,
which is expressly incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The present invention relates generally to the rapid
absorption of heat pulses and, more particularly, to adsorbents and
systems for rapid absorption of heat pulses.
BACKGROUND OF THE INVENTION
[0004] Technological advances in electronics, avionics, and
automotive industries are often accompanied by a further need for
energy storage. However, the energetic needs of these platforms
often result in high thermal output. At times, the thermal output
may include large bursts of heat (ranging from about 100 kW to
about 1 MW) over a relatively short period of time (about 10
seconds to about 100 seconds). Conventional systems of managing the
heat produced by these platforms have included micro- and
meso-porous materials (e.g., activated carbons, zeolites, silica,
and alumina gels) having large specific surface areas (ranging from
about 1000 m.sup.2/g to about 2000 m.sup.2/g). However, some of
these materials (zeolites and silica gels) have poor thermal
conductivity due to low intrinsic thermal conductivity or poor
consolidation of powders.
[0005] Certain gases and vapors (e.g., NH.sub.3, CO.sub.2, MeOH,
and H.sub.2O), known and used as adsorbates, adsorb onto solid
adsorbents, such as the micro- and meso-porous materials with large
heats of adsorption. Exemplary heats of desorption, on an
adsorbate-mass basis, are shown below in Table 1. However, these
systems (solid/vapor desorption systems) have conventionally been
used as refrigerators or heat pumps that function on a continuous,
low instantaneous, cooling power basis. Therefore, these
conventional systems have not been suitable for use in adequately
adsorbing rapid bursts of heat, particularly over the lifetime of
the platform.
TABLE-US-00001 TABLE 1 .DELTA.H.sub.adsorption in Adsorbent
Adsorbate [MJ/kg.sub.adsorbate] Silica gel CH.sub.3OH 1.0-1.5
H.sub.2O 2.8 Activated alumina H.sub.2O 3.0 Zeolites H.sub.2O
3.3-4.2 NH.sub.3 4.0-6.0 CO.sub.2 0.8-1.0 CH.sub.3OH 2.3-2.6
Activated carbon C.sub.2H.sub.4 0.4-1.2 C.sub.4H.sub.10 0.3
CH.sub.2F.sub.2 0.4 NH.sub.3 2.0-2.7 H.sub.2O 2.3-2.6 CH.sub.3OH
1.8-2.0 C.sub.2H.sub.5OH 1.2-1.4
[0006] Other conventional approaches to thermal management have
incorporated macroporous foams (e.g., graphitic, aluminum, and
copper foams), having high effective thermal conductivities
(ranging from about 20 W/mK to about 200 W/mK). Yet, macroporous
foams are incapable of adsorbing large quantities of adsorbates due
to low specific surface areas (ranging from about 10 m.sup.2/g to
about 100 m.sup.2/g).
[0007] Thus, there remains a need for large high-thermal
conductivity adsorbents, particularly for use in systems configured
to manage large thermal loads and accommodate short periods of
rapid cooling. Furthermore, and in particularly for uses with
respect to deployed military platforms, new devices are needed that
are light weight, compact, low cost, low maintenance, and safe to
operate (with respect to toxicity, flammability, and
reactivity).
SUMMARY OF THE INVENTION
[0008] The present invention overcomes the foregoing problems and
other shortcomings, drawbacks, and challenges of conventional heat
adsorption materials and systems. While the invention will be
described in connection with certain embodiments, it will be
understood that the invention is not limited to these embodiments.
To the contrary, this invention includes all alternatives,
modifications, and equivalents as may be included within the spirit
and scope of the present invention.
[0009] According to one embodiment of the present invention, a
composite adsorbent includes a backbone and a filler. The backbone
comprises a first material having a high thermal conductivity and a
plurality of pore. The filler, within the pores of the backbone,
comprises a second material having a large specific surface
area.
[0010] Another embodiment of the present invention is directed to a
heat burst desorption system for absorbing rapid heat bursts from a
heat load. The system includes an adsorbent bed containing an
adsorbent and an adsorbate supply containing an adsorbate. The
adsorbate is configured to adsorb onto the surface of the adsorbent
with a large heat of adsorption. The system operates in an
absorption mode and a recharge mode. In the absorption mode, when
heat is transferred from the heat load to the adsorbent bed, the
adsorbent bed is fluidically coupled to an exhaust such that
adsorbate desorbs from surface of the adsorbent and is vented. In
the recharge mode, heat is rejected from the system along a second
transfer path, the adsorbent bed is fluidically coupled to the
adsorbate supply such that adsorbate adsorbs onto the surface of
the adsorbent.
[0011] According to still another embodiment of the present
invention, a method of absorbing rapid heat bursts from a heat load
includes decompressing an adsorbent bed, containing an adsorbent,
when heat is generated. When heat generation cases, the adsorbent
bed is recharged with an adsorbate, which is configured to adsorb
onto a surface of the adsorbent.
[0012] Yet another embodiment of the present invention is directed
to a composite adsorbent having a thermally-conductive backbone and
a filler. The backbone includes a first material having plurality
of pore therein and the filler is within those pores. A second
material, comprising the filler, has a large specific surface
area.
[0013] In accordance with another embodiment of the present
invention, an adsorbent includes a plurality of
thermally-conductive elements. Elements of the plurality interface
with other elements of the plurality to form a three-dimensional
network. The elements may include carbon nanotubes, multi-wall
carbon nanotubes, metallic nanowires, semiconducting nanowires,
graphene, or a combination thereof.
[0014] An embodiment of the present invention includes a composite
adsorbent having a backbone and a filler. A first material, which
comprises the backbone, includes a plurality of pores therein and a
thermal conductivity greater than about 20 W/mK. A second material,
which comprises the filler, has a specific surface area greater
than about 1000 m.sup.2/g.
[0015] The above and other objects and advantages of the present
invention shall be made apparent from the accompanying drawings and
the descriptions thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the present invention and, together with a general description of
the invention given above, and the detailed description of the
embodiments given below, serve to explain the principles of the
present invention.
[0017] FIG. 1 is a flowchart illustrating methods of forming a
composite adsorbent in accordance with two embodiments of the
present invention.
[0018] FIG. 2 is a schematic representation of one method shown in
FIG. 1.
[0019] FIG. 3 is a schematic representation of one method shown in
FIG. 1.
[0020] FIG. 4 is a schematic representation of a three-dimensional
composite adsorbent in accordance with another embodiment of the
present invention.
[0021] FIG. 5 is a diagrammatic view of a burst desorption system
in accordance with one embodiment of the present invention.
[0022] FIGS. 5A and 5B illustrate operation of the burst desorption
system during an absorption mode and a recharging mode,
respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Turning now to the figures, and in particular to FIGS. 1-3,
methods for building composite, high-thermal conductivity
adsorbents in accordance with embodiments of the present invention
are described. A first method, as shown in the flowchart 10 of FIG.
1, begins with selection of a material comprising a porous backbone
12 (Block 14) for a desired composite adsorbent 16. The material is
generally porous (illustrated as pores 18) and may be selected, at
least in part, on (1) the thermal conductivity characteristics of
the material and (2) the desired degree of heat pulse absorption.
Graphitic foams, such as commercially-available POCOFoam and
Koppers KFOAM, described in detail in U.S. Pat. No. 6,033,506, the
disclosure of which is incorporated herein by reference in its
entirety, have a thermal conductivity, low bulk density, and a
connected open network of pores with tunable diameters.
[0024] In Block 20 of the flowchart 10, an outermost layer of the
material comprising the backbone 12 is exfoliated and fills pores
18 of the backbone 12. One method of exfoliation, according to one
exemplary embodiment, places the porous backbone 12 into an acidic
bath such that ionic solvent may intercalate into the pores 18. The
intercalating species (illustrated as intercalating solvent 22) may
include, for example, SO.sub.4, NO.sub.3, or other like ionic
groups. With the intercalating solvent 22 permeated throughout the
backbone 12, the backbone 12 may then be rapidly heated such that
outermost layers exfoliate from the backbone 12 and reside within
the pores 18 as exfoliate filler 24.
[0025] If desired, the backbone 12 and/or the exfoliate filler 24
may be surface treated so as to further tune adsorbate-adsorbent
interaction within the composite adsorbent 16 (Block 26). For
instance, polar ionic species (e.g., acidic functional groups,
nitrates, and sulfates) may be added to change the polarity of the
adsorbent surface of the backbone 12. Additionally, or
alternatively, liquid, vapor, or plasma treatments may be used to
further modify the adsorbent surface of the backbone 12 or of the
filler 24.
[0026] A second method of forming a composite adsorbent 28, also
shown in the flowchart of FIG. 1, begins with selection of a first
material comprising the porous backbone 12. Again, the backbone 12
is generally porous (illustrated as pores 18) (Block 14). According
to the instant embodiment, the pores 18 are filled with a second
material differing from the material comprising the backbone 12.
One such method of incorporating the second material, i.e., a
filler 30, into the pores 18 includes submerging the backbone 12
into a solution 32 containing one or more sol-gel initiators, for
example, an aqueous resorcinol-formaldehyde solution (Block
34).
[0027] As residual solution is evaporated from the backbone 12,
whether by supercritical or freeze drying, an aerogel or cryogel 30
forms, respectively, within the pores 18 (Block 36). If necessary,
or desired, a reactive gas species may be directed through the
filler 30 to develop a desired distribution of porosity (Block 38).
And, as described previously with respect to the composite
adsorbent 16 of FIG. 2, the composite adsorbent 28 and/or
aerogel/cryogel filler 30 may be surface treated (Block 26), if
desired or necessary.
[0028] In some instances, high thermal conductivity may be required
to extend in three dimensions. A three-dimensional adsorbent 40
suitable for such uses and according to one embodiment of the
present invention is shown and described with respect to FIG. 4.
The illustrative three-dimensional adsorbent 40 comprises a
three-dimensional network of connected, high-thermal conductivity
of elements 42 configured to form a dense mesh (on the order of
10.sup.8 interfaces/m to 10.sup.9 interfaces/m).
[0029] Each element 42 may be a carbon nanotubes (CNTs), a
multi-wall CNT, a metallic or semiconducting nanowire, graphene, or
other 2D structured material. The three-dimensional adsorbent forms
a three-dimensional network to transmit heat over a large volume
while providing a porous-like structure between adjacent ones of
the elements 42. The illustrative structure permits significant
adsorption of adsorbate species without restricting the flow of
adsorbate molecules, the necessity of which is described in greater
detail below.
[0030] One approach of synthesizing embodiments of the
three-dimensional adsorbents 40 may include template-assisted
growth from graphene. In this approach, two-dimensional graphene is
grown on all outer surfaces of a connected network of metal, e.g.,
Ni, after which the metal is dissolved to leave the residual,
covalently bonded CNT network.
[0031] While the three-dimensional adsorbent 40 may have large
inherent thermal conductivity, the high interfacial density may
suggest to those of ordinary skill in the art that the effective
conductivity of the three-dimensional adsorbent 40 will be
dominated by thermal interfacial resistance at nodes 44 formed at
the intersection of connected individual elements 42. Small
interfacial thermal resistance is likely to require strong bonding
forces at the nodes 44 (e.g., covalent, ionic, or metallic bonds),
which minimize the scattering of photons at those interfaces.
Mechanisms to promote these nodes 44 may include introduction of
metallic nanoparticles (which act as hubs connecting multiple
tubes/wires), covalent bonding between individual elements (e.g.,
branching, covalently bonded CNT structures), or other similar
mechanisms. Large specific surface areas of the three-dimensional
adsorbent 40 may be derived from the large intrinsic specific
surface areas of individual elements 42. Given that very little
area is consumed by the nodes 44, the three-dimensional adsorbent
40 will, for the large part, maintain the specific surface area of
the individual elements 42, which maximizes the area for gas or
vapor molecules to adsorb to the adsorbent.
[0032] Composite materials, as described in the various embodiments
of the present invention herein, are light-weight and have a
high-thermally conductive. Generally, the high-dielectric porous
backbone provides the desired high thermal conductivity while
filler materials provide a large surface area, which promotes
adsorbate interaction. By minimizing the thermal interfacial
resistance between the backbone and the filler, heat transfer
through the composite material is highly efficient.
[0033] The composite materials, according to the various
embodiments of the present invention, may be utilized in improving
systems configured to quickly absorb bursts of heat. That is, these
composite materials, when used with suitable gas or vapor
adsorbates, rapidly absorb large pulses of heat. In that regard,
and with reference now to FIG. 5, a burst desorption system 50 is
shown and described in accordance with one embodiment of the
present invention. The burst desorption system 50 includes a
supply, illustrated as a tank 52, containing pressurized adsorbate
54, which may be selected, for example, from the listing provided
in Table 1 above. The total volume of the tank 52 may be selected
so as to compensate for the dissipation of heat required by the
particular heat load 56 over the lifetime of the heat load 56 while
a maximum pressure within the tank 52 is limited by safety
considerations.
[0034] The fraction of the adsorbate to be used during system
operation is determined by minimum and operating pressures.
Exemplary pressures for the adsorbate tank 52 may range from about
50 bar to 100 bar; however, these pressure ranges are not
considered to be limiting. Ideally, the adsorbate may be stored in
the liquid phase to minimize the overall volume of the system.
[0035] The adsorbate tank 52 is fluidically coupled to an adsorbent
bed 58 containing a composite adsorbent 60 according to embodiments
of the present invention. The adsorbent bed 58 is operable over a
range of pressures, for example, pressures ranging from about 10
bar to 50 bar, or, as necessary, to atmospheric pressure; however,
these pressure ranges are not considered to be limiting. In any
event, the adsorbent bed 58 may generally be under a lower pressure
after discharge and a higher pressure after recharged, as provided
in detail below. In some embodiments, the adsorbent bed 58 may not
be pressured over the condensation pressure of the adsorbent 60 as
depressurization may lead to rapid expansion within the adsorbent
bed 58, which is likely to irreversibly damage the adsorbent 60.
Furthermore, the maximum pressure of the adsorbent bed 58 may be
intrinsically linked to the minimum pressure of the storage tank
52, as the storage tank 52 is maintained at a higher pressure than
the adsorbent bed 58 in order to effectively recharge the adsorbent
60.
[0036] In use, the system 50 is operable in an absorption mode,
during which heat is absorbed from the heat load 56, and in a
recharge mode, during which the system 50 prepares for subsequent
heat absorption by transferring absorbed heat to a cooling loop 62
of, for example, a fuel tank (not shown). More specifically, and in
the absorption mode illustrated in FIG. 5A, heat is transferred
from the heat load 56 to the adsorbent 60 of the adsorbent bed 58.
Resultantly, the adsorbent bed 58 decompresses, causing some
quantity of adsorbate 54 to desorb from the surface of the
adsorbent 60, which dissipates a certain quantity of heat. The
quantity of heat is related to the product of the quantity of
adsorbate 54 desorbed and the specific heat of desorption. Further
dissipation of heat may occur by the expansion of adsorbate while
being exhausted via valve 64. The ordinarily-skilled artisan would
readily appreciate that without such an open system, heat may be
generated when the adsorbate 54 is recondensed or adsorbed.
[0037] Between heat burst generations, the system 50 is operated in
a recharging mode to prepare for a subsequently generated heat
burst. In that regard, the exhaust valve 64 is closed so that the
adsorbent bed 58 may be re-pressurized from the adsorbate tank 52
via valve 66. Because adsorption is essentially the inverse process
to desorption, some quantity of heat may be generated at the
adsorbent bed 58, which must be rejected for the adsorption process
to continue. However, generated heat is offset by the quantity of
heat consumed by evaporating and/or decompressing adsorbate 54 from
the tank 52. If the net effect is heat generation, the heat may be
dissipated by some other element on the platform, including, for
example, the cooling loop 62 of a fuel tank (not shown) or to the
ambient environment by way of an air-heat exchanger. However, the
rate of available heat rejection may limit the duty cycle of the
system 50.
[0038] The skilled artisan will, with the benefit of the disclosure
provided herein, note the particular benefit of a pressure cascade
to store adsorbate gas/vapor, to control adsorption/desorption, and
to regulate venting of the adsorbate 54.
[0039] The heat burst desorption system described according to the
embodiments of the present invention herein may be configured to
manage large thermal loads (about 100 kW to about 1 MW) with a
rapid response time (less than about 1 second). Recharging
capabilities are possible with a duty cycle of about 5% to about
50%, and, generally, the systems may be operational for extended
periods of time, for example, missions ranging from 100 sec to
10,000 sec.
[0040] While the present invention has been illustrated by a
description of various embodiments, and while these embodiments
have been described in some detail, they are not intended to
restrict or in any way limit the scope of the appended claims to
such detail. Additional advantages and modifications will readily
appear to those skilled in the art. The various features of the
invention may be used alone or in any combination depending on the
needs and preferences of the user. This has been a description of
the present invention, along with methods of practicing the present
invention as currently known. However, the invention itself should
only be defined by the appended claims.
* * * * *