HYBRID ADSORBER HEAT EXCHANGING DEVICE AND METHOD OF MANUFACTURE
FIELD OF THE INVENTION
The present invention relates to hybrid adsorber heat exchanging devices,
such as heat exchanger systems. The systems of the invention are useful in
5 environments where adsorbate is required to be temporarily or periodically stored
and released. In particular, the present invention relates to adsorbent based heat
exchanger systems for adsorption cooling, heat pump and desalination applications.
The present invention also provides a method for the manufacture of such hybrid
adsorber heat exchanging devices, and applications of such heat exchanging device.
10 BACKGROUND OF THE INVENTION
The concerns of environmental pollution and primary energy consumption
issues call for the rapid development of environmentally benign energy conservative
technologies. Among them, thermally powered adsorption systems are considered
as one the key technologies as these systems can recover and reuse low-
15 temperature waste heat sources which otherwise will be purged to the ambient.
There is a recognized need to replace existing mechanically or electrically
driven vapour compression based systems used for chilling or refrigeration purposes.
Such systems typically use gases such as hydrofluoro carbons. It is now recognised
that there is a need to replace the use of such materials in view of the deleterious
20 effect they have on the environment.
One of the mechanisms used to replace conventional vapour compression
based systems is to use heat exchangers which utilise adsorbent beds in order to
ensure mass transfer as well as heat transfer.
~ds'orbenmt aterials are classified according to their properties into physical
25 adsorbents, chemical adsorbents, and composite adsorbents. Physical adsorbents
are materials that have differing pore sizes. Typical of this category are mesoporous
silicates, zeolites, metaluminophosphates, porous carbons and metal organic
frameworks. ~ e s o ~ o r o usislic ates include materials such as synthetic amorphous
silica gel which consists of a rigid and continuous net of colloidal silica connected to
30 small grains of hydrated SO4. Porous carbons include activated carbons obtained by I
I
gasifying char with an oxidising agent. Zeolites include crystalline microporous I
HY etc. The advantages of zeolite or zeolite based materials are their diversity of
uses, and their susceptibility to modification dependent on the purpose of use.
Metal organic frameworks are a new generation of materials which are microporous,
have high porosity, uniform pore size and have well defined adsorption sites and
5 large surface area. These frameworks typically comprise of organic linkers which
connect metal centres.
Chemical adsorbents comprise substances used in chemisorption. These
include metal chlorides such as calcium chloride, barium chloride, strontium chloride
etc., salt and metal hydrides such as lithium hydride, calcium hydride, high
10 polymerised hydrides of covalent nature, and non-metal molecular hydrides, and
metal oxides.
Composite adsorbents include combinations of chemical and physical
adsorbents such as combinations of metal chloride and activated carbon fibres,
expanded graphite, silica gel, or zeolite. Composite adsorbents provide an advantage
15 in enhancement of performance of physical adsorbents without incurring the effect
of chemical adsorbents such as swelling, poor conductivity, or agglomeration.
PRIOR ART
Several different heat exchange mechanisms have been postulated in the art
as replacement for conventional vapour compression based refrigeration systems.
20 Some of these are discussed below for the purpose of reference.
A two-bed adsorbent based cooling system comprises of separated heat
exchangers. Essentially, this mechanism comprises of four main parts, two reactors
which function as adsorbey or desorber depending on the operating mode, an
evaporator and a condenser. The reactors are packed with adsorbent material to
25 adsorb or desorb the adsorbate during the adsorption or desorption processes. The
flow of the medium is regulated using refrigerant valves.
One alternative to the two bed adsorption cooling system is a system that
uses an integrated adsorption mechanism. This usually comprises two units, wherein
each,unit is provided with an adsorbent bed, an evaporator and a condenser. The
30 heat exchange cycle in this device comprises of two modes - evaporation triggered
adsorption which is known as adsorption/evaporation mode and desorption resulted
-- ---- ----
E L l E E I l E . 5 - C W . y - h f! --k>>.B SF' cde - -
C - F - ---- --.a. -=rB-TBr-----.--rCn--,z-&-~d
condensation which is known as desorption/condensation mode. Control valves are
provided to control the flow of secondary fluid to each unit.
Another alternative mechanism involves a three bed adsorption system. This
consists of three reactors in addition to the condenser and the evaporator. A three
5 bed heat exchange system enables continuous evaporation. This mechanism has
four operational modes - preheating, desorption, pre-cooling and adsorption.
Multistage systems are also available which are used to utilise low
temperature heat sources. These systems operate at temperatures that are not
suitable for a two bed adsorption cooling system.
10 As discussed above, an adsorption cooling system can effectively utilize lowgrade
waste heat or solar thermal energy of temperature typically below 100°C and
can produce effective cooling energy. Thermally driven adsorption cooling cycle does
not require any electricity to drive the cycle and it is environmentally friendly as. it
utilizes natural refrigerants or alternative to HFC based refrigerants. Moreover, this
15 system requires a lesser level of maintenance and is also free from moving parts.
However, the main drawbacks of the low-temperature thermally powered
adsorption cooling system are its poor performance in terms of specific cooling
capacity and coefficient of performance and relatively larger footprint as opposed to
conventional vapour compression cycle.
20 Adsorption heat exchangers typically comprise a heat exchanger structure
which is used for supplying and discharging thermal energy and which is in a thermal
contact with a sorben't material which uses a phase change of an adsorbate working
medium for binding and releasing latent heat. Heat is released through the
condensation of a vaporous working medium. Conversely, the thermal energy
25 supplied via the heat exchanger structure can be used for the renewed vaporization
of the adsorbate.
Solids materials are mostly used for performing the phase change of the
adsorbate, which are so-called sorbent or adsorbent materials. A characteristic for
such sorbent materials are their open-pore structure with a high ratio of surface to
30 volume. The inner cavities in these materials have molecular magnitude dimensions.
The effect of the sorbent materials is based on adsorbing foreign atoms and foreign
are clays such as bentonite, silica gel or zeolites. Water is usually used as the working
, .
medium for these sorbent materials since it has a high heat of condensation and is
also easy to use.
Adsorption based heat exchange systems are driven by the adsorption and
desorption of an adsorbate vapour by a porous solid adsorbent. In contrast to
conventional vapour-compression cooling systems which are driven by a mechanical
compressor, no electrical energy is needed to drive the adsorption cycle. The basic
cycle involves an adsorption phase and a desorption phase. In the adsorption phase,
10 the refrigerant vapour is adsorbed by the adsorbent substance resulting in the
release of heat. In the desorption phase, heat is applied to the adsorbent causing
desorption of the refrigerant. The heat transferred during these processes is
conveyed by a heat exchanger between the adsorbent and a heat transfer fluid (e.g.
water or methanol or a water-glycol mixture) or an external environment. The
15 adsorption and desorption processes occur in conjunction with evaporation and
condensation of refrigerant in an evaporatorlcondenser. The adsorption of the
gaseous refrigerant lowers the vapour pressure, promoting evaporation of the liquid
refrigerant in 'the evaporator. During this evaporation, heat is extracted from an
environment to be cooled, resulting in refrigeration. By supplying heat to the
20 adsorbent via the heat exchanger, the adsorbed refrigerant is released into the
vapour phase, thus regenerating the adsorbent material for the next adsorption
cycle. The resulting gaseous adsorbate passes to a condenser where heat rejection
to the environment takes place. As in conventional vapour-compression cooling, the
liquid refrigerant is passed through a control device (e.g. an expansion valve) back
25 into the evaporator, and the cycle can then be repeated.
When an adsorption heat exchanger is supplied with thermal energy from the
outside, e.g. by having a heat carrier liquid flow through the same, the heat flowing
in from the outside needs to be transferred effectively to the porous sorbent
material in order to release the adsorbed working medium situated in the same. In
30 the opposite case, the release of thermal energy, which means an energy flow
direction out of the adsorption heat exchanger, the thermal energy released as a
~
, , " : ' k,: I$.-, e-k;, 'k., - 2 g.,$ 'g. g' '$. 3; "' 'c
---LCli:-.CIZ.--I(r --2 7-
. - -. . --
result o f f ~ ~ 6 ~ d ~ n 3 ~ 3 f ~ t l ~ ~ f i 0 ~ 1 7 i h ~ ~ ~ ~
needs to be transported from the adsorption heat exchanger to the outside. Since
known porous sorbent materials show adverse thermal conductivity, adsorption
heat exchangers are usually produced as a combination of a heat exchanger
structure with high thermal conductivity and the porous sorbent material that is
5 used for binding and releasing the working medium. The heat exchanger structures
mostly consist of metallic materials such as copper, aluminum or stainless steel, as
well as other materials with a high thermal conductivity such as ceramic materials,
carbon materials, carbon fiber reinforced plastic (CFRP) materials and certain plastic
materials.
10 Heat exchangers comprise cavities for allowing direct flow with a heat carrier
medium which usually does not come into direct contact with the sorbent material.
The heat exchanger structure comes into thermal contact with the sorbent material.
In the simplest of cases this occurs in the form of bulk material, with the sorbent
material being mostly present in the form of powder or by mixture with a binder in
15 the form of pellets.
Thermally powered adsorption chillers have been proposed for space cooling
applications. These chillers are virtually free of moving parts, except for the On/Off
operation of the refrigerant valves that separately connect the adsorbent beds to
the evaporator and condenser. Therefore these systems are highly reliable and
20 require almost no maintenance. Adsorption chillers are also capable of being
miniaturized, since adsorption of refrigerant into and desorption of refrigerant from
the solid porous adsorbent are primarily surface, rather than bulk processes.
As seen above several methods are postulated in the art for heat exchange
mechanisms. Some of the references are briefly discussed below.
2 5 US Patent 8,053,032 explains a method for production of a heat exchanger
substrate wherein a zeolite layer is deposited/produced on the substrate surface by
direct crystallization. However, there is no reference or teaching in this patent
towards any hybridization techniques.
US Patent 8,590,153 discloses an adsorption heat exchanger where an
30 adhesive layer/coating is formed on the heat exchanger structure and the exchanger
is then dipped into sorbent material to ensure adhesion thereof. The method of
..p.., .,. Q: A+;.. i ,i:s :f :.. &,.' $ , ; - . ; &' , &, , : f; "" L'-' &
= = = = = = - ~ P V ~ - 7 - ~ - c r ~ . C c~ati~=esse~rrt~lly=mmpr~ses=~e-"~f-a-fi~~~hed=manwfactwred=heat-exC-h~ariger-whi~-
is thereafter coated with the sorbent material, by a process of dipping. As will be
appreciated, this method may have the limitations of unevenness of coating
thickness, agglomeration of porous solid material in certain portions leading to
uneven coating and thereby in itself adversely impacting performance.
5 US Patent Publication 2010/0136326 discloses a method by which a layer
composite comprising of a metal support substrate and a silicate layer is obtained by
coating the substrate surface with the silicate layer obtained through solvothermal
synthesis. There is no disclosure in this publication of any attempts to hybridise heat
exchange mechanisms, or attempt to improve kinetic performance of the heat
10 exchanger without compromising on adsorbent volume or heat exchanger footprint.
US Patent Publication 2011/0183836 unveils an aluminium containing
substrate for a heat exchanger. A microporous layer of aluminium phosphate zeolite
is applied to the substrate, inter alia other layers. The publication again focuses on
increasing the number of layers forming the coating on the substrate, wherein at
15 least one layer is ALP04, and does not provide any information or guidance towards
attempts to increase kinetic performance of heat exchangers through hybridization
techniques.
US Patent Publication 2012/0216563 discloses a heat exchanger wherein a
porous material is provided in contact with the tubular portion of the exchanger in
20 order to allow vapour to pass through. The material is a fibrous material. However,
there is again no disclosure or guidance on whether this is useful for improving
performance kinetics or whether additional hybridization techniques can be used.
US Patent Publication 2013/0014538 discloses a sub-assembly for an
adsorption chiller. The sub-assembly is provided with an adsorption component
I
25 including a multiplicity of plates which are arranged in a stack. The refrigerant sides I
of adjacent pairs of the plates in the stack define refrigerant passages and an ! adsorbent material is provided within these passages. However, there is no
disclosure orguidance therein .on whether this arrangement contributes or provides
any improvement in performance kinetics.
30 JP Patent Publication No. 2011-240256 discloses an adsorbent block which is 1
provided with a plurality of activated carbon fibers. These fibers are all directed in
@,..g&,$:p..& ,$,&, z,.. M $! 6.. .& - S;.k,. $-' :r;.k: '..t.& " g:. #A " --'-dm e'i - -
- - - - : 3 ~ - - ~ - ~ ~ 8 ~ h e ~ ~ m ~ d i r e a i o ~ ~ c . y l i n c k I C c a I ~ ~ e ~ I ~ s h e e t - i s ~ p r o v i d e - d ~ c o v e - r i n g - i h ~ - ~
circumference of the activated fibers, in a manner such that the axial direction. This
is obtained by covering the fibers with the cylindrical metal sheet and then
unidirectionally rolling out and cutting the sheet. However, there is no disclosure or
guidance therein on whether this arrangement contributes or provides any
5 improvement in performance kinetics.
JP Patent Publication No. 2005-291528 discloses a heat exchanger with
enhanced adsorber capacity. The heat exchanger comprises a plate fin tube type
heat exchanger with a specific fin pitch, fin length and fin height. Activated charcoal
is used as a filler adsorbent wherein the charcoal has specific steam adsorbing
10 capacity. the bed so formed is covered by a net like material to prevent leakage of
the adsorbent material. However, there is no disclosure or guidance therein on
whether this arrangement contributes or provides any improvement in performance
kinetics. Again, the focus in this disclosure is on modifying the fin dimensions and
adjusting the adsorbent material characteristics to ehhance adsorbent power.
15 SUMMARY OF THE INVENTION
The present invention provides a hybrid adsorption heat exchanging device
comprising at least one tubular or micro-channel structure for carrying a heat
transfer fluid, the external surface of said structure being provided with extensions
in at least two locations, said extensions forming a bed there between for providing
20 one or more adsorbent materials, a coating of adsorbent material being provided on
at least a part of said extensions.
In one embodiment, the extensions run longitudinally along the full length of
the tubular structure or can run circumferentially around the tubular structure, with
the height of each extension remaining substantially uniform along the entire length
25 , thereof.
If another embodiment, the tubular structure and the extensions are integral,
or can be connected to each other through separate connecting means.
If desired, the tubular structure and the extensions are made of the same
material and can be made from a heat conductive material which is metallic, ceramic
30 based, polymeric or carbon based materials.
In another embodiment of the invention, each extension is coated with an
. .- L.~.-- 3- I-'*B -- B-P-~ R ~w + tMh'o rk8t=b&'~=tfi&.-m =or-di#e"JpeLn-t -%&=the=ad~orbent~filli~~in=the=be-d - - -
In yet another embodiment, the adsorbent material provided in said bed is
selected from the group consisting of zeolites, mesoporous silicates, insoluble metal
silicates, silica gel type A, silica gel type RD, silica gel type S2, activated carbon fiber,
granular activated carbon, activated alumina, highly porous activated carbon,
5 Zr604(0H)4 bonded with linkers, MIL-lOlCr, MOFs (metal-organic frameworks), COFs
(covalent organic frameworks), FAMs (functional adsorbent materials), and the like,
singularly or in any combination thereof.
In yet another embodiment of the invention, the adsorbent material
comprises adsorbent granules having a pore diameter in the range of 3 to 100
10 angstromto or plain or corrugated sheets with adsorbent coated or deposited
thereon or a combination thereof disposed in any predetermined pattern.
In yet another embodiment of the invention, the plain or corrugated sheets
are made of a thermally conductive material selected from the group consisting of
aluminium, copper, graphite/expanded graphite, inorganic or organic fiber
15 substrates or combinations thereof, and can optionally be perforated sheets.
In another embodiment of the invention extensions are corrugated on the
external surface thereof prior to coating with adsorbent material, and wherein the
coating is selected from the group consisting of zeolites, mesoporous silicates,
insoluble metal silicates, silica gel type A, silica gel type RD, silica gel type 52,
20 activated carbon fiber, granular activated carbon, activated alumina, highly porous
activated carbon, Zr604(0H)4 bonded with linkers, MIL-IOlCr, MOFs (metal-organic
frameworks), COFs (covalent organic frameworks), FAMs (functional adsorbent
materials), and the like, singularly or in any combination thereof.
In yet another embodiment of the invention, the heat transfer fluid is
25 selected from the group consisting of water, lower alcohols, oils, and the like.
In another embodiment of the invention, the adsorbent material is provided
with one or more dopants selected from the group consisting of inorganic metals
salts such as calcium chloride, lithium bromide, magnesium chloride, magnesium
sulphate, calcium nitrate, manganese chloride, and the like
30 In another embodiment of the invention, one or more additives selected
from the group consisting of carbon fibers, graphite fibers, and the like are also
,. ---A & _ ~~~g~>e&t~em&&ct$Q,. . &.,- I$on&&i"it~ -.-
If desired, a polymeric mesh is provided over the adsorbent bed, wherein the
polymer is aniline.
The invention also provides a method for the manufacture of a hybrid
adsorption heat exchanging device, said method comprising:
5 - coating at least a part of a thermally conductive material with an adsorbent
material;
- converting the at least partially coated thermally conductive material into a
tubular structure for carrying a heat transfer fluid, and providing two or
more extensions thereon, said extensions being either integral with said
coated tubular structure, or comprising at least partly adsorbent coated
thermally conductive material, said extensions forming an adsorbent bed
therebetween;
- providing one or more adsorbent material in said adsorbent bed.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
15 The invention will be described in greater detail below inter alia, with
reference to the accompanying drawings wherein:
Figure 1 is a representation of a typical finned type block adsorber that is
used in the adsorber and desorber heat exchangers.
Figure l(a) is an exploded view of the section marked 'A' in Figure 1, and
20 figure l(b) is an isometric view of the same.
Figure 2 is a representation of a typical spiral-finned type tube adsorber that
is used in heat exchangers.
Figure 2(a) is an exploded view of the section marked 'A' in Figure 2, and
figure 2(b) is an isometric view of the same.
2 5 Figure 3(a) is a representation of prior art finned block adsorbers wherein the
4 adsorber bed is filled/packed with granular adsorbents.
Figure 3(b) is a representation of prior art coated finned block adsorbers.
Figure 4(a) is a representation of an adsorbent bed wherein the fins of the
adsorber heat exchange tube are coated with a first adsorbent material and the
30 interstitial spaces between the fins are filled with a second adsorbent material
comprising granules, and covered with a suitable mesh.
- - @.-EL @ L=k --g . k~! ~ - -3L.t- i. ~4 ':kS-k ;_k&L! _--dcn.5b~~~ --- r----------
Figure 4(b) is a representation of an adsorbent bed wherein the fins of the
adsorber heat exchange tube are coated with a first adsorbent material and the
interstitial spaces between the fins are filled with a second adsorbent material
comprising desiccant coated substrate.
Figure 4(c) is a representation of an adsorbent bed wherein the fins of the
adsorber heat exchange tube are coated with a first adsorbent material and the
interstitial spaces between the fins are filled with a second adsorbent material
comprising corrugated desiccant coated substrate block.
Figure 4(d) and Figure 4(e) are representations of an adsorbent bed wherein
10 the fins of the adsorber heat exchange tube are coated with a first adsorbent
material and the interstitial spaces between the fins are filled with a second
adsorbent material comprising either a corrugated or a plain desiccant coated
substrate block and adsorbent granules interspersed in between the desiccant
coated substrate block.
15 . Figure 4(f) is a representation of an adsorbent bed wherein the fins of the
adsorber heat exchange tube are shaped to enhance their surface area and are
coated with a first adsorbent material and the interstitial spaces between the fins
are filled with a second adsorbent material comprising adsorbent granules, and
covered with a suitable mesh.
20 Figure 5 is a representation of the four heat transfer resistances developing
the temperature gradient, during the heat transfer from/to the secondary fluid.
Figure 6 is a representation of a substrate material that is coated with
adsorbent, and perforations are provided thereon in predetermined or desired
patterns.
2 5 Figure 7 shows the adsorption isotherm of silica gel 52 proprietary to
applicants herein on water and a coated silica gel S2/water adsorbentlrefrigerant
pairs.
Figure 8 shows the adsorption uptake data for silica gel S21water pair at
temperatures in the range of 30-70°C.
30 Figure 9 shows the adsorption uptake data for siica gel S2/water pair at
pressures in the range of 5kPa and --__ -._ 15kPa. I L- -_ -_-- -- I I - ---- --
-- 1 L I F E :,:&g S.41c-h.l. I$ y h - R - D t E , -, B E l l ; b 1%. PBIP c.-T-
___*.E.- - - - ~ . - - ~ - - ~ d c r - - ~ r P g . - ~ - * 2 L I - - ~ c * 1 C 1 ~ 1 C ~ - - - -
Figure 10 is a comparative representation of adsorption isotherms of water
on silica gel S2 type proprietary to applicants and commercially available Fuji RD type
silica gel.
Figure ll(a), (b) and (c) are temporal profiles of adsorption uptake and
5 pressure of silica gel S2/water pair at adsorption temperatures of 30°, 50" and 70°C
respectively.
Figure 12 is a comparative representation of the specific capacity, in terms of
cooling Watts per liter of adsorbent heat exchanger, both for prior art adsorbers and
the potential specific capacity with different hybrid adsorption heat exchangers of
10 the present invention.
Figure 13 shows the cooling capacity and the COP of the adsorption chiller
using conventional packing method, the advanced adsorbent-coated method and
the adsorbent-coated hybrid heat exchangers.
Figure 14 shows the temperature profiles of the major components of the
15 adsorption chiller for the overall heat transfer coefficient of 350 w/~*K.
Figure 15 shows the performance comparisons of adsorption chiller for pellet,
adsorbent-coated and hybrid heat exchangers.
DETAILED DESCRIPTION OF THE INVENTION
A recognised need in the art has been the requirement to enhance the
20 performance of the adsorbent bed that is used in heat exchangers in order to
improve the cycle overall performance. Amongst other factors the key parameters
that determine the efficiency of the performance of an adsorbent bed are heat and
mass transfer aspects. Mass transfer influences both adsorption capacity and
adsorption uptake rate. Heat transfer is critical for delivery and extraction of both
25 desorption and adsorption heat, respectively. Other parameters that also affect
adsorbent bed performance include adsorbent porosity and pore size, granular size
and adsorbentto metal mass ratio.
Heat transfer is subject to multiple levels of resistance within the adsorbent
bed. These include the resistance induced by metal to secondary fluid convective
30 heat transfer, conductive heat transfer resistance through the wall of the exchanger,
metal to adsorbent contact heat transfer, and conductive heat transfer resistance
... " ..% . - . , . , , .. . , , ; . " ,'< .<: ' "' 3'. & = & ~ ' . i r j - C % ~ ~ ~ ~ ~ P ~ O U ~ ~ ~ s ~ ~ F ~ e n t t ~ ~ t ~ ~ ~ ~ p ; ~ ~ $ ~ k e s & ~ e e ~ e a t t ~ F a
metal to adsorbent contact interface plays a predominant role in affecting the
efficiency of a heat exchanger, and is dependent on the nature and level of physical
contact between the adsorbent and the heat exchanger metal. For example, in
simple granular packed adsorbent bed systems, even though the mass transfer
5 performance is very high, the level of heat transfer performance is generally low due
to high contact thermal resistance between the adsorbent granules and the heat
exchanger metal surface.
It is possible to enhance heat transfer performance of adsorbent material
that is used in an adsorbent bed, by mixing adsorbent granules with metal additives
10 to increase thermal conductivity, coating of bed heat exchanger metal with the
adsorbent and avoiding the use of granules totally in order to eliminate all contact
thermal resistance, covering the adsorbent granules with a polyaniline net,
adsorbent deposition over metallic foam, and use of consolidated bed methods.
One of the techniques to enhance heat transfer performance by increasing
15 overall thermal conductivity is by adding metal such as aluminium, copper,
or graphite/expanded graphite to adsorbent granules of zeolitic materials. While it is
reported that the thermal conductivity increases significantly, and the method is also
easy to follow, the limitations appear to be a reduction in mass transfer performance
and also material limitations. The latter is a serious limitation since it limits the scope
20 of applications where such adsorbent beds are used;
Another technique that is discussed in the art as a replacement to the
granular bed approach is to avoid their use altogether and instead coat the metal of
the heat exchanger with the adsorbent. This generally involves use of an organic
agent to clean the metal surface, formation of a slurry of the adsorbent with an
25 organic binder, and then application on the cleaned metal surface, followed by
heating to remove the residual binder. Several different coating techniques are
discussed and disclosed in the art. One advantage of this method is that it avoids the
heat contact resistance of adsorbent and metal significantly. This method has been
considered an alternative to the granular bed approach. .
30 Another method that is discussed in the art is the formation of a polymeric
net such as a polyaniline net over th.e granular bed. This can be done in situ using
..., . , , .. , .. . fir;. w , y . : . . : ; i ' 'r.:'C' " " ' --
.--2--F.&---. oxidaWe=~n=' wpo m n s a t i o ~ f a n i h ~ o n = t h - e = ~ ~ ~ r f a ~ e ~ f ~ f h ~ d ~ a r b ~
The disadvantage noted with this method is that while heat transfer resistance is
reduced, the mass transfer performance is affected adversely.
Other attempts include deposition of adsorbent over a metallic foam. One
example of this method includes deposition of zeo'lite and copper metal foam. The
5 method essentially comprises coating of the metallic part of the heat exchanger with
an epoxy resin, a foaming agent and a metal powder. The adsorbent material is
deposited using a colloidal seed solution. For example, in the case of zeolite, this
involves seeding, followed by hydrothermal synthesis, washing and drying. It is
reported that this method improves the heat transfer characteristics significantly,
10 but results in an increase in metallic mass.
The consolidated bed approach relies on several different steps. For example,
compressed adsorbent granules and clay, expandable graphite, moulding granules
and addition of binder and metallic foam impregnated with adsorbent granules. It is
reported that this method results in a significant increase in heat transfer
15 performance. However, the method may not be efficient in the case of all adsorbent
materials, and also has the limitation of bed permeability and cracking.
As can be seen, the approaches that have been proposed in the art look at
various solutions as alternatives to the granular bed approach. Conventional wisdom
in the art is that granular bed approach adversely affects heat transfer performance,
20 and the only solution is to seek a replacement for this method.
The applicants herein have determined that a hybrid approach provides not
only the mass transfer performance which is a significant advantage of the granular
bed approach, but also enhanced heat transfer performance. The method of the
invention involves an integrated approach to heat exchanger performance
25 enhancement which involves not only adopting a coating for the metal portions of a
heat exchanger (or parts thereof), but also ensuring the presence of additional
adsorbent material provided between such metallic parts. It has been observed in
test studies that such a hybrid adsorbent based heat exchanger provides significant
performance enhancement both in terms of heat and mass transfer characteristics.
30 The object of this invention is to provide a hybrid adsorption heat exchanger
that is compact, efficient in converting input cooling power and affordable.
., .U- @'' .k
, , , ' . - ; , , , [ . 8. '.' - K:;::.&- . . - . . - .
The essence of the invention involves heat transfer enhancement by a
hybridisation technique which includes both coating of the heat exchanger fins as
well as use of loose porous adsorbent materials between the fins. A refrigerant such
as water/ammonia/ethanoI/methanol/other assorted refrigerants are
5 exothermically adsorbed and endothermically desorbed, from the porous adsorbent,
which 'is usually packed in an adsorbent bed having good heat transfer
characteristics of a single adsorbent. In an adsorbent bed, the major thermal
resistances come from the fin of the adsorber and adsorbent material which can be
fully eliminated through coating of the adsorbent material. The specific power is
10 intensified through packing of loose adsorbent grains between the coated fins. The
invention combines the coated adsorbent as well as packing of the loose adsorbent
grains or alternate means such as glass fibres wherein desiccant is either generated
in situ or are pre-impregnated, or a combination of different means such as granules
and glass fibres.
15 Figure 1 is a representation of a typical finned type block adsorber that is
used in the adsorber and desorber heat exchangers.
Figure 2 is a representation of a typical finned type tube adsorberthat is used
in heat exchangers.
Figure 3(a) is a representation of prior art finned block adsorbers wherein the
20 adsorber bed is filled/packed with granular adsorbents. As is evident from Fig. 3(a),
the secondary fluid flows through the adsorber heat exchange tube, and the fins are
provided on the external surface of the heat exchange tube. The interstitial spaces
between the fins are packed with adsorber granules. The tube itself may be made of
a metal such as copper which promotes heat transfer. The granular packing is finally
25 covered with a metallic mesh. The fins are typically made of aluminium.
Figure 3(b) is a representation of prior art finned block adsorbers. The
secondary fluid flows through the adsorber heat exchange tube, and the fins are
provided on the external surface of the heat exchange tube. The interstitial spaces
between the fins are vacant. The tube itself may be made of a metal such as copper
30 which promotes heat transfer. The granular packing is finally covered with a metallic ~ mesh. The fins are typically made of aluminium and are coated with the adsorbent I
in some detail in this document, and involve the use of resins and binders to ensure
uniform deposition of adsorbent on the fins.
Figure 4(a) is a representation of an adsorbent bed wherein the fins of the
adsorber heat exchange tube are coated with a first adsorbent material and the
5 interstitial spaces between the fins filled with a second adsorbent material
comprising granules. The first and second adsorbents may be same or different. The
granular bed is then covered with a metallic mesh. The coating can be uniform
across the external surface of the heat exchange tube. In the alternative, only the
fins are coated, and the surface of the heat exchanger tube between two fins
10 remains uncoated.
Figure 4(b) is a representation of an adsorbent bed wherein the fins of the
adsorber heat exchange tube are coated with a first adsorbent material and the
interstitial spaces between the fins filled with a second adsorbent material
comprising desiccant coated paper. The desiccant coated substrate may be one
15 wherein the desiccant is coated or impregnated into the glass fiber or may be one
wherein the desiccant is generated in situ. The first and. second adsorbents may be
same or different. The coating can be uniform across the external surface of the heat
exchange tube. In'the alternative, only the fins are coated, and the surface of the
heat exchanger tube between two fins remains uncoated.
20 Figure 4(c) is a representation of an adsorbent bed wherein the fins of the
adsorber heat exchange tube are coated with a first adsorbent material and the
interstitial spaces between the fins filled with a second adsorbent material
comprising corrugated desiccant coated substrate block. The desiccant coated
substrate may be one wherein the desiccant is coated or impregnated into the glass
25 fiber or may be one wherein the desiccant is generated in situ. The first and second
adsorbents may be same or different. The coating can be uniform across the external
surface of the heat exchange tube. In the alternative, only the fins are coated, and
the surface of the heat exchanger tube between two fins remains uncoated. '
Figure 4(d) and Figure 4(e) are.representations of an adsorbent bed wherein
30 the fins of the adsorber heat exchange tube are coated with a first adsorbent
material and the interstitial spaces between the fins filled with a second adsorbent
-...,. w..> ... - k,:. -
,J c.'ilf ;$,, $& ""' '"' g - t"i;, K: "I. bz;'CG 'i;: .". '& - - -- --f - ~.-~~&ter~~O~~Rsifi~~A~r~a~~&p~~-ated-Or~a=P~ain=deSieC-ant=C-Oated=subS-trate=~~
and adsorbent granules interspersed in between the desiccant coated substrate
block. In Figure 4(d) the substrate blocks are provided perpendicular to the axis of
the tube, whereas in Figure 4(e) the substrate blocks are provided parallel to the
tube axis. The desiccant coated substrate may be one wherein the desiccant is pre- .
5 coated/ impregnated into the glass fiber or may be one wherein the desiccant is
generated in situ. The first and second adsorbents may be same or different. The
coating can be uniform across the external surface of the heat exchange tube. In the
alternative, only the fins are coated, and the surface of the heat exchanger tube
between two fins remains uncoated. The substrate blocks in cases of Figures 4(b) to
10 Figure 4(e) may also be perforated to enhance both mass and heat transfer.
Figure 4(f) is a representation of an adsorbent bed wherein the fins of the
adsorber heat exchange tube are coated with a first adsorbent material and the
interstitial spaces between the fins filled with a second adsorbent material
comprising adsorbent granules. The fins are corrugated in this embodiment and may
15 also if desired, be perforated in any desired pattern in order to enhance heat and
mass transfer. The first and second adsorbents may be same or different. The
coating can be uniform across the external surface of the heat exchange tube. In the
alternative, only the fins are coated, and the surface of the heat exchanger tube
between two fins remains uncoated.
20 Figure 5 is a representation of heat transfer regions in a coated fin, and is
described in detail below.
Figure 6 is a representation of a substrate material that is coated with
adsorbent, and perforations are provided thereon in predetermined or desired
patterns. This substrate material can be converted into the external extensions (fins),
25 for the heat exchanger, and adsorbent material filled in the beds formed thereby.
The invention essentially resides in hybridising the adsorbent bed such that
not only is the fin coated with an adsorbent material, the interstitial spaces between
the fins are provided with an additional adsorbent material. The second filler
adsorbent material may be the same as the adsorbent material provided in the
30 coating or may be different. For example, the filler adsorbent material may be in the
form of granules that are available such as zeolite material, activated carbon,
T-;E,-i-i - i;b g-g ib ,g. ;:; -. k:&. kL - &b,' g:. I<,' __--,.- 8:- '& --,-= -;"- .-- 1: -by-=---. . _--: dC -*-en- =- - act~vaTeTl alumina, or siKa gel. Alternatively, the f i l l F m ~ i Z l ~ i F f i
or sheets of glass, ceramic, activated carbon, graphite, organic or inorganic
substances having adsorbent material provided thereon either by coating, dipping,
impregnation or by formation in situ or any other method.
The hybrid heat exchanger of the invention provides flexibility in combining
5 different adsorbent forms. Tests establish that this hybrid heat exchanger provides
significant enhancement both in terms of mass transfer and heat transfer
performance.
The approach to the invention comprised assessing current state of the art in
respect of granular adsorbent provided within an uncoated finned space. It is known
10 in the art that the efficiency (specific capacity) of such systems is around 100 watts
per liter of adsorbent heat exchanger. In view of this, the approach was to:
a. increase the watts output per liter of adsorbent heat exchanger volume, thus
decreasing the overall volume, footprint and cost.
b. to improve the adsorption and desorption kinetics in order to additionally
15 enhance the 'watts per absorber heat exchanger output thus further reducing the
footprint, volume and cost of the adsorption chiller. The present invention achieves
I
both simultaneously.
In order to increase and optimize the performance of adsorbent heat
exchanging devices, multiple variables were utilized. These comprise:
20 1. Substrate: the hybrid absorber heat exchanger of the invention relies on one
part of the heat exchanger having an adsorbent adhered thereto. The invention
provides flexibility in terms of substrate choice depending on the method of
adhesion that is employed to ensure adhering of the adsorbent to the substrate. The
substrates can be. aluminum foil, copper foil, organic metal fiber sheet, inorganic
25 fiber sheet carbon reinforced plastic, etc. The fin types include flat/plain, corrugated,
louvered, sine wave, rippled, pyramid, or pin type.
2. Substrate thickness: The substrate thickness, depending on the type of support
the substrate provides to the adsorbent, and thermal conductivity as part of the
ov&all heat exchanger design, will typically range from 0.5 mm - 2.0 mm, more
30 typically from 0.1 mm to 1.0 mm.
3. 'Substrate shape: Depending on the choice of the substrate, the substrate may
-~ -~ ~ ~ ~ ~ ~ ~ ~ ~ ~ r ~ ~ ~ ~ ~ ~ & ~ & ~ ~ @ ~ e ~ i & ~ & & e ~ ~ g. & ~ ~ ~ . , ~ ~
4. Adsorbent: The adsorbent material to be adhered to the substrate will typically
be silica gel, molecular sieve, composites, or activated carbon, and can also comprise
under development adsorbents which have a high surface area and are heat transfer
fluid tolerant. For example, if water is used as the refrigerant, then the adsorbent
5 should be water tolerant. If other refrigerants are used in the adsorption chillers
such as ethanol, methanol and ammonia and HFC based refrigerants, the adsorbents
should be chemically inert to such refrigerants. Some of these adsorbents already
exist while others are under development. Typically these would be from the family
of MOFs, aluminum phosphate, COFs, FAMs and FMMs, composites, etc. As the
10 enhanced surface area and bulk density are complementary factors, the adsorbents
of choice can depend on both the useful capacity under operating capacity of
boundaries of the adsorbent but will be of higher bulk density so that the overall
adsorption, and hence the specific performance in kW per adsorbent heat
exchanger, is maximized. Further the kinetics of the adsorbent, in terms of
15 adsorption and desorption, and the means to -enhance the 'kinetics' of a given
adsorbent, will also play a significant role to maximize the overall capacity in terms
of Watt per liter of adsorbent heat exchanger.
These adsorbents, to enhance the useful capacity, can further be doped with
doping agents such as inorganic metal salts such as sodium chloride, calcium chloride,
20 lithium bromide, magnesium chloride, magnesium sulphate, calcium nitrate,
manganese chloride etc., .
To improve the thermal conductivity of the heat flow from within the
adsorbent to the substrate, as well as overall kinetics, use can be made of
adding highly conductive materials like graphite, expanded graphite, copper powder
25 etc. in small quantities.
In some cases, there can be a combination of both doping and addition of
a thermally conductive materials.
5. General methods of adhering the adsorbent to the substrate: There are several
known methods, as enumerated below, of adhering the adsorbent to the substrate
30 but this invention is not limited to the existing art or methods:
a. One method of adhering the desiccant to the substrate, particularly
impervious substrates, is to use non-masking binders or glues. The binder of glues
can be inorganic, organic and also the combination of both.
b. Substrates, particularly porous substrates, the adsorbent can be
5 impregnated again with the help of suitable non masking binders/loops. The binder
of glues can be inorganic, organic and also the combination of both. The
impregnation may also include a dip coating method.
c. In yet another method, the substrate, particularly porous substrate, the
adsorbent can be synthesized in situ without the use of binders of glues.
10 d. In yet another method, starting with the substrate, typically an
aluminum foil, the adsorbent can be synthesized in situ on the surface of the
substrate, utilizing the substrate material as one of the elements to grow the
adsorbent crystals.
Heat transfer in the adsorbent bed is managed by regeneration and
15 adsbrption using a secondary fluid such as water. For the heat transfer to and from
the secondary fluid there are'four heat transfer resistances as is shown in Figure 5.
The resistances are:
R . l The convective heat transfer resistance between the secondary fluid and the
metal wall.
20 R.2 The heat transfer resistance through the wall of the heat exchanger.
R.3 The contact heat transfer resistance between the metal and adsorbent.
R.4 The conductive heat transfer resistance through the desiccant mass
As can be seen the heat exchanging device design can affect the heat transfer
resistances.
2 5 In the above, R3 is predominant and most significant. Thus far, the effort and
attempt has been to coat adsorbents on the heat exchanger metal surface, typically
the extended fin, typically aluminium. In doing so the conductive heat transfer
resistance through the desiccant mass (R4) has been ignored and eliminated as no
further adsorbent is placed between the extended heat exchanger surfaces. While
30 the benefit is gained through reduction of R3, there is a significant trade off and loss
of adsorption capacity and therefore mass transfer as the amount/mass of desiccant
The present invention aims to maintain a near optimal adsorbent to metal
mass ratio by combining the desiccant coated extended surface of metallfin by not
only reducing R3 but also considerably improve the kinetics, along with the use of
granular material within the coated fins spaces even though limited R4 will be
encountered, thus providing an overall performance enhancement of >35/40% in
terms of Watts per liter of adsorbent heat exchanger using the traditional adsorbent
heat exchanger with adsorbent granular material packed within the heat exchanger
fin surface. There are also other methods of filling the voids as described hereinafter.
The adsorbent is adhered to the substrate by applying silica gel
granular/powder to aluminum foil using a non-masking binder from a class
of organic and as well as separately inorganic binders, and also using pore cleaning
agent[s] for the adsorbent. Zeolites can also be used instead of silica gel.
The coating on the extensions can be achieved by any method that is already
known, such as that disclosed in US Patent 8,053,032 (direct crystallization of a
zeolite layer on a substrate), US Patent Publication 2010/0136326 (coating the
substrate surface with a silicate layer obtained through solvothermal synthesis),
US Patent Publication 2011/0183836 (coating an aluminium containing substrate
with a microporous layer of aluminium phosphate zeolite), or any other method
known in the art for coating the substrate and fins.
Irrespective of the method of adhering the adsorbent to the substrate or the
substrate type, the amount of adsorbent has to be optimal so that too much
adsorbent does not inhibit heat transfer from the outside layer to the heat
exchanger. Typically the adsorbent quantity can vary from 10 GSM to 500 GSM but
will more specifically lie within 150 to 300 GSM depending upon the adsorbent, the
method of adhering the absorbent to the substrate, the bulk density of adsorbent
and the use, if any, of the binderlglue.
In the hybrid adsorbent heat exchanger, while the heat exchanger surface
has adsorbent adhered to by means and methods explained above but not limited
thereto, in the present invention, the adsorbent is filled within the voids of the
extended fin heat exchanger surface. The choice of the type and methods of
placement of such adsorbents can be as follows:
2. Adsorbent in powder form but made into granules of suitable mesh.
3. Adsorbent adhere to a substrate, as a sheet, or as sheet glass or in any other
shape e.g. corrugated, squarelrectangular, triangular etc. with or without doping,
with or without thermally conductive additives like expanded graphite, graphene
5 etc.
In the present invention of the hybrid heat exchanger, extensive testing has
been done using granular silica gel. In the application of adsorption chillers, while
there is a choice of many working pairs of adsorbent and refrigerants, the most
typically and commonly used or employed is the silica gel-water pair. In most
10 adsorption chillers under manufacturer and also the research being done in this field
around the world, the outstanding silica gel of choice is and has been the high
density granular or beaded silica gel as available from Fuji Sylsia Co. Ltd., Japan. This
material typically has a surface area in the range of 600-800 m21g and bulk density of
700-900 g/liter, depending upon the whether the material is beaded or granular, and
15 if granular on the mesh side.
The present invention also benchmarks a new hybrid adsorbent heat
exchanger with the traditional adsorbent heat exchanger using Fuji RD type silica gel.
Fuji RD type silica gel, because of its characteristics and kinetics, has become the
adsorbent of choice for silica gel-water pair based adsorption chillers, globally, both
20 in commercial production and research. Applicants herein have also developed a
proprietary silica gel labeled S2, which through extensive testing, has shown
outstanding performance potential as an adsorbent for silica gel-water based
adsorption chillers. Examples of its performance and kinetics are shown in Figs. 7-11.
Adsorption capacity of adsorbent~refri~eranpta ir depends on the porous
25 properties (pore size, pore volume and pore diameter) of adsorbent and isothermal
characteristics of the pair. The porous properties of various zeolites, silica gels,
activated carbons, activated alumina, MOFs (metal-organic frameworks), COFs
(covalent organic frameworks), and FAMs (functional adsorbent materials) are
presented which are determined from the nitrogen adsorption isotherms. The
30 standard nitrogen gas adsorption/desorption measurements on various adsorbents
at liquid nitrogen of temperature 77.4 K are performed. Surface area of each
T-z....r:.c ,,& .cf ,;. ,@ ...i y, S{ 5 ky: 16 .- ;t,;, 'a ~n,9b.e=7se: ser _i-f Ga mb ,~~iog.~=~ehta ~ t ,-~ . -
=- --sac---$me
Adsorbent
Silica gel (type A)
Silica gel (type RD)
Silica gel (type,S2)
Activated carbon fiber (FX 400)
Activated carbon Fiber (A-20)
Granular activated carbon
Highly porous activated
carbon (Maxsorb Ill)
Zr604(OH)4(Likne r)6
MIL-101Cr
Surface area
(m2ag-l)
650
720
700
700-2500
1900 ,
700-1500
3 140
2064
4100
Pore
volume
3 -1 (cm .g )
0.28
0.37
0.34-
0.5-1.4
1.028
0.5-1.0
1.7
0.97
2.0
Apparent density
(g.cm-3)
0.73
0.7
0.73
0.3
0.25
0.4
0.31
-
the adsorption capacity of silica gel S2lwater pair is as high as 0.34 kg kg-'at
adsorption temperature of 30°C and pressure at around 3.6 kPa. The adsorption
capacity of coated silica gel SZ/water pair is similar to that of the parent SZIwater
pair. It can be observed that, for both parent S2lwater pair and coated SZ/water pairs,
5 the adsorption capacity increases linearly with the increase of pressure in the whole
studied range.
Figures 8 and 9 show the adsorption uptake data of silica gel S2/water pair for
temperatures 30 - 70°C and pressure up to 5 kPa and 15 kPa, respectively. The
former pressure rage is suitable for adsorption cooling applications and the relatively
10 higher pressures are required for adsorption desalination applications. As can be
observed from Figs. 8 and 9, the adsorption uptake values increase linearly with the
increase in pressure for all measured adsorption temperatures, which implies that
the parent silica gel S21water paper is suitable for both adsorption cooling and
desalination applications.
15 Figure 10 shows the adsorption isotherms of silica gel SZ/water pair and silica
gel RDIwater pair for temperatures between 30 and 70°C and pressure up to 5 kPa,
which is the operation range of silica gellwater based adsorption chillers. It is evident
from Fig. 10 that the adsorption isotherms data of .silica gel SZ/water and silica gel
RDIwater pairs are comparable and one can choose either adsorbent depending on
20 the cost and availability of the adsorbent.
Figures ll(a), l l ( b ) and l l ( c ) show the temporal profiles of adsorption
uptake and pressure of the silica gel ~21waterp air at adsorption temperatures of 30,
50 and 70°C, respectively. It is visible from Figs. l l ( a ) - l l ( c ) that the adsorption
kinetics of the studied pair is relatively faster at the early stages of adsorption
25 processes. Moreover, more than 80% of total uptake occurs within the first 5 minutes
and thus the silica gel SZ/water pair seems to suitable for adsorption cooling
applications.
The starting point for the production of an adsorption heat exchanger in accordance
with the invention is at first a heat exchanger structure which is produced separately.
30 It is produced according to the known method from materials of high thermal
conductivity. Suitable for this purpose have proven to be metallic systems such as
-? -. -- -g.,. %:,&-, . -r:. s;1- 'E. $; ; ~ 3 ,. - :>. ~3,g; .ic; '& ,%GF: .'
E.
~ - .
------ - D = =* ,* -+;.a;.mr- - ~ . ~ l ; b - - - - s - r d r d ~ ' . 2 . - - = = - - - ~ -
ones made of copper, aluminum, carbon, reinforced plastic or special steel. Ceramic
materials or combined material systems are also possible.
Suitable heat exchanger structures realize a circulation system for a heat
carrier medium which is in connection with the outside area of the adsorption heat
5 exchanger. In addition, heating wires or other heat sources can be embedded for
heating the heat exchanger structures. In order to produce the largest possible
surface towards the sorbent material system, a lamella-like or honeycomb-like
structure is preferred. It can also be in the form of a sponge or foam. Based on this
heat exchanger structure which is produced separately at first, an inside coating with
10 sorbent material is now carried out as follows.
In a first method step, an adhesive layer is applied to the wall of the heat
exchanger facing towards the sorbent material, which hereinafter shall be referred
to as inside wall. An adhesive is used for this purpose which forms a solid layer at
first. For realizing said adhesive layers it is possible to use different methods such as
15 i.mmersion, flooding or spraying. The method steps of adhesive coating can further
be repeated for setting an optimal layer thickness. It is especially advantageous in
this respect to set the viscosity of the applied adhesive by tempering or by enriching
or evaporation with solvents for example. It is alternatively also possible to apply the
adhesive in a solid powdery state to the walls of the heat exchanger. Such powder
20 coating is Pspecially useful in planar heat exchanger structures.
The heat exchanger can further be filled at first with powdery adhesive which
is then activated by heating of the heat exchanger structure in regions of the heat
exchanger close to the wall, so that there is bonding in the area close to the walls
and the subsequent removal of the non-adhering powdery adhesive material from
25 the areas remote of the walls is possible by shaking, blowing or rinsing. Irrespective
of the choice of adhesive or the chosen application method, the adhesive layer in the
region close to the wall must adhere at least in such a stable manner that during the
subsequent method step in which the sorbent m'aterial is introduced into the heat
exchanger there is no functionally impairing mixture of the adhesive of the sorbent
30 material.
After the coating steps are completed and the coating on the metallic
adsorbent material, or with glass fiber sheets that are impregnated with adsorbent
material (or where the adsorbent is formed in situ using technology proprietary to
applicants). Contrary to disclosures in the art, the heat transfer performance of this
hybrid heat exchanger is significantly high over what has hitherto been known in the
5 art.
Studies show that the heat transfer performance of the hybrid heat
exchanger device of the invention are significantly higher than those of either of the
two currently available prior art systems - which use either a granular bed or a
coated fin system in isolation.
10 The primary difficulty of adsorption heat pumps is the poor heat transfer
between the adsorbent materials and the heat transferring media namely cooling
medium for adsorption process and heating medium for desorption process.
Conventional adsorber heat exchangers or the conventional manner of packing the
adsorber materials is packing the adsorbent around the finned-tube of the ,heat
15 exchanger. This method is widely used due to the simplicity in the manufacturing
and the limitation in the attachment or coating technology of the adsorbent to the
fins of the heat exchanger.
The effective coating of the adsorbent materials on the extended surfaces of
the heat exchanger can greatly improve in the heat and mass transfer mechanism of
20 the adsorber of adsorption cycles. Two significantly outstanding features or
advantages of the coated adsorber heat exchangers are (1) the improvement in
adsorption kinetics via effective heat transfer and (2) the reduction in thermal mass.
The major contribution of the former feature is the reduction in cycle tirrle whilst the
less thermal mass directly translates to better performance or coefficient of
25 performance (COP). These two features synergistically improve the adsorption cycle
both energetically, footprint-wise and more importantly the lowering in capital cost.
Figure 13 shows the cooling capacity and the COP of the adsorption chiller
using conventional packing method, the advanced adsorbent-coated method and
the adsorbent-coated hybrid heat exchangers. It should be noted that the
30 evaporator and the condenser remain the same for both cases. It is observed that
the adsorbent-coated and adsorbent-coated hybrid types provide significant
. .. .. < . .. , , , . ! fi;, ,&c ; - , . '& 8's ?' K. >&,
u p 2-- -- "lrWr6rmrflmt?e-.i mvpQ mem5d---d=->
The overall heat transfer coefficient of the advanced adsorbent-coated and
adsorbent-coated hybrid heat exchanger is around 350 to 350 w / ~ *dKep ending on
the adsorber/desorber configuration. Figure 14 shows the temperature profiles of
the major components of the adsorption chiller for the overall heat transfer
5 coefficient of 350 w / m 2 ~A.s can be seen from Figure 14, all four heat exchangers
work efficiently and the chiller prod.uces effective cooling due to faster adsorption
kinetics resulted from improved heat transfer and smaller thermal mass.
Figure 15 shows the performance comparisons of adsorption chiller for pellet,
adsorbent-coated and hybrid heat exchangers. The performance comparisons have
10 been made in terms of specific cooling power (SCP), coefficient of performance
(COP) and volumetric efficiency. As can be seen from Figure 15, the SCP and COP
values for coated and hybrid type heat exchangers are comparable. However, SCP
increases about 8% and COP increases more than 100% in case of coated and hybrid
type heat exchangers due to faster kinetics and less thermal mass. On the other
15 hand, the volumetric efficiency of hybrid heat exchanger is about 35% higher than
the pellet type heat exchanger and about 18% higher than that of the adsorbentcoated
heat exchanger due to higher mass of adsorbent in the same volume which
results in more cooling power and thus significantly contribute in the reduction of
adsorption system footprint and capital cost.
20 Another advantage of the invention that has beemobserved from studies
conducted is that the specific capacity of the hybrid heat exchanger device of the
invention is significantly better than those of prior art adsorbers. Figure 12 is a
comparative representation of the specific capacity, in terms of cooling Watts per
liter of adsorbent heat exchanger, both for prior art adsorbers and the potential
25 specific capacity with different hybrid heat exchangers of the present invention.

We claim:
1. A hybrid adsorption heat exchanging device comprising:
at least one tubular or micro channel structure for carrying a heat
transfer fluid;
the external surface of said structure being provided with extensions in
at least two locations;
said extensions forming a bed therebetween for providing one or more
adsorbent materials;
a coating of adsorbent material being provided on at least a part of said
extensions.
2. A device as claimed in claim 1 wherein the extensions run longitudinally along
the full length of the tubular or micro channel structure.
3. A device as claimed in claim 1 wherein the extensions run circuhnferentially
around the tubular or micro channel structure.
4. A device as claimed in claim 1 to 3 wherein the height of each extension
remains uniform along its entire length.
5. A device as claimed in claim 1 to 4 wherein the tubular or micro channel
structure and the extensions are integral.
6. A device as claimed in claim 1 to 4 wherein the extensions are connected to
the tubular or micro channel structure by external connectors.
7. A device as claimed in claim 6 wherein the tubular or micro channel structure
and the extensions are made of the same material.
8. A device as claimed in claim 1 to 7 wherein the tubular or micro channel
structure and/or the extensions comprise a heat conductive material selected
from metallic, ceramic based, polymeric or carbon based materials.
9. A device as claimed' in claim 1 wherein each extension is coated with an
adsorbent being the same or different from the adsorbent filling in the bed.
10. A device as claimed in claim 9 wherein the adsorbent material provided in said
bed is selected from the group consisting of zeolites, mesoporous silicates,
insoluble metal silicates, silica gel type A, silica gel type RD, silica gel type S2,
activated carbon fiber, granular activated carbon, activated alumina, highly
fiOTOus-activatea^rarlaonp^^
organic frameworks, covalent organic frameworks, functional adsorbent
materials, and the like, singularly or in any combination thereof
11. A device as claimed in claim 10 wherein the adsorbent material comprises
adsorbent granules having a pore diameter in the range of 3 to 100 Angstrom.
12. A device as claimed in claim 10 wherein the adsorbent material comprises
corrugated sheets with adsorbent coated or deposited thereon.
13. A device as claimed in claim 12 wherein the corrugated sheets are made of a
thermally conductive material selected from the group consisting of aluminium,
copper, graphite/expanded graphite, inorganic or organic fiber substrates or
any combinations thereof
14. A device as claimed in claim 12 and 13 wherein said corrugated sheets
comprise perforated sheets.
15. A device as claimed in claim 10 to 14 wherein the adsorbent material
comprises of a combination of adsorbent granules and adsorbent coated or
deposited sheets.
16. A device as claimed in any preceding claim wherein the extensions are
corrugated on the external surface thereof prior to coating with adsorbent
material.
17. A device as claimed in claim 1 wherein the extensions are coated with an
adsorbent material selected from the group consisting of zeolites, mesoporous
silicates, insoluble metal silicates, silica gel type A, silica gel type RD, silica gel
type S2, activated carbon fiber, granular activated carbon, activated alumina,
highly porous activated carbon, Zr604(OH)4 bonded with linkers, MIL-lOlCr,
metal-organic frameworks, covalent organic frameworks, functional adsorbent
materials, and the like, singularly or in any combination thereof.
18. A device as claimed in any preceding claim wherein the heat transfer fluid is
selected from the group consisting of water, lower alcohols, and oils, and the
like.
19. A device as claimed in any preceding claim wherein the adsorbent material is
provided with one or more fillers selected from the group consisting of zeolites,
mesoporous silicates, insoluble metal silicates, silica gel type A, silica gel type
=RD^sill§a%1^t^e^s2^
activated alumina, highly porous activated carbon, Zr604(OH}4 bonded with
linkers, MIL-lOlCr, metal-organic frameworks, covalent organic frameworks,
functional adsorbent materials, and the like, singularly or in any combination
thereof.
20. A device as claimed in claim 19 wherein said filler is a doped filler, wherein the
doping agent is selected from the group consisting of inorganic metals salts
such as calcium chloride, lithium bromide, magnesium chloride, magnesium
sulphate, calcium nitrate, manganese chloride, and the like
21. A device as claimed in any preceding claim wherein in addition to the
adsorbent material in the bed, one or more additives selected from the group
consisting of copper aluminium, graphite/expanded graphite, and the like are
added to enhance thermal conductivity.
22. A device as claimed in any preceding claim wherein a polymeric mesh is
provided over the adsorbent bed.
23. A device as claimed in claim 22 wherein the polymeric mesh is a polyaniline
mesh.
24. A method for the manufacture of a hybrid adsorption heat exchanging device,
said method comprising:
coating at least part of a thermally conductive material with an adsorbent;
converting the at least partially coated thermally conductive material into a
tubular structure for carrying a heat transfer fluid, and providing two or
more extensions thereon, said extensions being either integral with said
coated tubular structure, or comprising at least partly adsorbent coated
thermally conductive material, said extensions forming an adsorbent bed
therebetween;
providing one or more adsorbent material in said adsorbent bed.
25. A method as claimed in claim 24 wherein each extension is coated with an
adsorbent being the same or different from the adsorbent filling in the bed.
26. A method as claimed in claim 25 wherein the adsorbent material provided in
said bed is selected from the group consisting of zeolites, mesoporous silicates,
insoluble metal silicates, silica gel type A, silica gel type RD, silica gel type S2,
=a%#vatli^arbiP$b!^^
porous activated carbon, Zr604(OH)4 bonded with linkers, MIL-lOlCr, metalorganic
frameworks, covalent organic frameworks, functional adsorbent
materials, and the like, singularly or in any combination thereof.
27. A method as claimed in claim 26 wherein the adsorbent material comprises
adsorbent granules having a pore diameter in the range of 3 to 100 Angstrom.
28. A method as claimed in claim 26 wherein the adsorbent material comprises
corrugated sheets with adsorbent coated or deposited thereon.
29. A method as claimed in claim 28 wherein the corrugated sheets are made of a
thermally conductive material selected from the group consisting of aluminium,
copper, graphite/expanded graphite, inorganic or organic fiber substrates or
any combinations thereof.
30. A method as claimed in claim 28 and 29 wherein said corrugated sheets
comprise perforated sheets.
31. A method as claimed in claim 26 to 29 wherein the adsorbent material
comprises of a combination of adsorbent granules and adsorbent coated or
deposited sheets.
32. A method as claimed in any preceding claim 24 to 31 wherein the extensions
are corrugated on the external surface thereof prior to coating with adsorbent.
33. A method as claimed in claim 24 wherein the extensions are coated with an
adsorbent material selected from the group consisting of zeolites, mesoporous
silicates, insoluble metal silicates, silica gel type A, silica gel type RD, silica gel
type S2, activated carbon fiber, granular activated carbon, activated alumina,
highly porous activated carbon, Zr604(OH)4 bonded with linkers, MIL-lOlCr,
metal-organic frameworks, covalent organic frameworks, functional adsorbent
materials, and the like, singularly or in any combination thereof.
34. A method device as claimed in any preceding claim 24 to 33 wherein the heat
transfer fluid is selected from the group consisting of water, lower alcohols,
and oils, and the like.
35. A method as claimed in any preceding claim 24 to 34 wherein the adsorbent
material is provided with one or more fillers selected from the group consisting
of zeolites, mesoporous silicates, insoluble metal silicates, silica gel type A,
- Ji I iea-gl&ly pe 4 l ^
carbon, activated alumina, highly porous activated carbon, Zr604(OH)4 bonded
with linkers, MIL-lOlCr, metal-organic frameworks, covalent organic
frameworks, functional adsorbent materials, and the like, singularly or in any
combination thereof.
36. A method as claimed in claim 35 wherein said filler is a doped filler, wherein
the doping agent is selected from the group consisting of inorganic metals salts
such as calcium chloride, lithium bromide, magnesium chloride, magnesium
sulphate, calcium nitrate, manganese chloride, and the like.
37. A method as claimed in any preceding claim 24 to 36 wherein in addition to the
adsorbent material in the bed, one or more additives selected from the group
consisting of copper aluminium, graphite/expanded graphite are also added to
enhance thermal conductivity.
38. A method as claimed in any preceding claim 24 to 37 wherein a polymeric
mesh is provided over the adsorbent bed.
39. A method as claimed in claim 38 wherein the polymeric mesh is a polyaniline
mesh.
40. A method as claimed in claim 24 wherein the adsorbent bed is provided with a
desiccant coated substrate wherein the desiccant is coated or impregnated or
generated in situ onto said substrate.
41. A method as claimed in claim 24 wherein the desiccant is attached to the
substrate through non-masking binder or glue or a combination thereof.
42. A device as claimed in any of preceeding claims 1 to 24 for use in an
environment requiring periodic or temporary storage and subsequent release
of adsorbate such as water.
43. A device as claimed in claim 42 an adsorption refrigeration machine, chilled
beams, an automobile air conditioning unit, a domestic integral air
conditioning unit, a domestic split level air conditioning unit, and the like.