Hybrid adsorber heat exchanging device and method of manufacture

Abstract

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 therebetween for providing one or more adsorbent materials; a coating of adsorbent material being provided on at least a part of said extensions.

Claims

1. A hybrid adsorption heat exchanging device comprising: at least one tubular or micro channel structure carrying a heat transfer fluid; the external surface of said structure being provided with extensions in at least two locations; said extensions forming an adsorbent bed there-between filled with one or more adsorbent materials; a coating of adsorbent material adhered onto at least a part of said extensions, said coating having been adhered in a separate process before filling of the adsorbent bed, wherein the adsorbent material filling the adsorbent bed comprises adsorbent granules or a sheet with the adsorbent being coated, deposited, impregnated, or generated in situ.

2. A device as claimed in claim 1 wherein the extensions run longitudinally along a length of the tubular or micro channel structure.

3. A device as claimed in claim 1 wherein the extensions run circumferentially around the tubular or micro channel structure.

4. A device as claimed in claim 1 wherein the height of each extension remains uniform along its entire length.

5. A device as claimed in claim 1 wherein the tubular or micro channel structure and the extensions are integral.

6. A device as claimed in claim 1 wherein the tubular or micro channel structure and the extensions are made of the same material.

7. A device as claimed in claim 1 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.

8. A device as claimed in claim 1 wherein the coating of adsorbent material on each extension is the same or different from the adsorbent filling in the adsorbent bed.

9. A device as claimed in claim 8 wherein the adsorbent material filling in said adsorbent 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, Zr.sub.6O.sub.4(OH).sub.4 bonded with linkers, MIL-101Cr, metal-organic frameworks, covalent organic frameworks, and functional adsorbent materials, singularly or in any combination thereof.

10. A device as claimed in claim 9 wherein the adsorbent material filling in the adsorbent bed comprises adsorbent granules having a pore diameter in the range of 3 to 100 Angstrom.

11. A device as claimed in claim 1 wherein the extensions are corrugated on an external surface thereof prior to coating the extension with adhered adsorbent material.

12. A device as claimed in claim 1 wherein the coating of adsorbent material on the extensions is 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, Zr.sub.6O.sub.4(OH).sub.4 bonded with linkers, MIL-101Cr, metal-organic frameworks, covalent organic frameworks, and functional adsorbent materials, singularly or in any combination thereof.

13. A device as claimed in claim 1 wherein the heat transfer fluid is selected from the group consisting of water, lower alcohols, and oils.

14. A device as claimed in claim 1 wherein the adsorbent material in the adsorbent bed 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, silica gel type S2, activated carbon fiber, granular activated carbon, activated alumina, highly porous activated carbon, Zr.sub.6O.sub.4(OH).sub.4 bonded with linkers, MIL-101Cr, metal-organic frameworks, covalent organic frameworks, and functional adsorbent materials, singularly or in any combination thereof.

15. A device as claimed in claim 14 wherein said filler in the adsorbent bed is a doped filler, wherein the doping agent is selected from the group consisting of inorganic metals salts calcium chloride, lithium bromide, magnesium chloride, magnesium sulphate, calcium nitrate, and manganese chloride.

16. A device as claimed in claim 1 wherein in addition to the adsorbent material in the adsorbent bed, one or more additives selected from the group consisting of copper, aluminum, and graphite/expanded graphite are added.

17. A device as claimed in claim 1 wherein a polymeric mesh is provided over the adsorbent materials filling said adsorbent bed.

18. A device as claimed in claim 17 wherein the polymeric mesh is a polyaniline mesh.

19. A device as claimed in claim 1 disposed in an environment requiring storage and subsequent release of adsorbate.

20. A device as claimed in claim 19 disposed within at least one of: an adsorption refrigeration machine, chilled beams, an automobile air conditioning unit, an integral air conditioning unit, and a split level air conditioning unit.

Description

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

(1) The invention will be described in greater detail below inter alia, with reference to the accompanying drawings wherein:

(2) FIG. 1 is a representation of a typical finned type block adsorber that is used in the adsorber and desorber heat exchangers.

(3) FIG. 1(a) is an exploded view of the section marked A in FIG. 1, and FIG. 1(b) is an isometric view of the same.

(4) FIG. 2 is a representation of a typical spiral-finned type tube adsorber that is used in heat exchangers.

(5) FIG. 2(a) is an exploded view of the section marked A in FIG. 2, and FIG. 2(b) is an isometric view of the same.

(6) FIG. 3(a) is a representation of prior art finned block adsorbers wherein the adsorber bed is filled/packed with granular adsorbents.

(7) FIG. 3(b) is a representation of prior art coated finned block adsorbers.

(8) FIG. 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 interstitial spaces between the fins are filled with a second adsorbent material comprising granules, and covered with a suitable mesh.

(9) FIG. 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.

(10) FIG. 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.

(11) FIG. 4(d) and FIG. 4(e) are representations 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 either a corrugated or a plain desiccant coated substrate block and adsorbent granules interspersed in between the desiccant coated substrate block.

(12) FIG. 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.

(13) FIG. 4(g) depicts the hybrid adsorption heat exchanger of FIGS. 4(a) 4(f) being used in an environment requiring periodic or temporary storage and subsequent release of an adsorbate such as water.

(14) FIG. 4(h) depicts the hybrid adsorption heat exchanger of FIGS. 4(a) 4(f) being used as an adsorption refrigeration machine.

(15) FIG. 4(i) depicts the hybrid adsorption heat exchanger of FIGS. 4(a) 4(f) being used as chilled beams.

(16) FIG. 4(j) depicts the hybrid adsorption heat exchanger of FIGS. 4(a) 4(f) being used as an automobile air conditioning unit.

(17) FIG. 4(k) depicts the hybrid adsorption heat exchanger of FIGS. 4(a) 4(f) being used as a domestic integral air conditioning unit.

(18) FIG. 4(1) depicts the hybrid adsorption heat exchanger of FIGS. 4(a) 4(f) being used as a domestic split level air conditioning unit.

(19) FIG. 5 is a representation of the four heat transfer resistances developing the temperature gradient, during the heat transfer from/to the secondary fluid.

(20) FIG. 6 is a representation of a substrate material that is coated with adsorbent, and perforations are provided thereon in predetermined or desired patterns.

(21) FIG. 7 shows the adsorption isotherm of silica gel S2 proprietary to applicants herein on water and a coated silica gel S2/water adsorbent/refrigerant pairs.

(22) FIG. 8 shows the adsorption uptake data for silica gel S2/water pair at temperatures in the range of 30-70 C.

(23) FIG. 9 shows the adsorption uptake data for silica gel S2/water pair at pressures in the range of 5 kPa and 15 kPa.

(24) FIG. 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.

(25) FIGS. 11(a), (b) and (c) are temporal profiles of adsorption uptake and pressure of silica gel S2/water pair at adsorption temperatures of 30, 50 and 70 C. respectively.

(26) FIG. 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 the present invention.

(27) FIG. 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.

(28) FIG. 14 shows the temperature profiles of the major components of the adsorption chiller for the overall heat transfer coefficient of 350 W/m.sup.2K.

(29) FIG. 15 shows the performance comparisons of adsorption chiller for pellet, adsorbent-coated and hybrid heat exchangers.

DETAILED DESCRIPTION OF THE INVENTION

(30) A recognised need in the art has been the requirement to enhance the 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 desorption and adsorption heat, respectively. Other parameters that also affect adsorbent bed performance include adsorbent porosity and pore size, granular size and adsorbent to metal mass ratio.

(31) Heat transfer is subject to multiple levels of resistance within the adsorbent bed. These include the resistance induced by metal to secondary fluid convective heat transfer, conductive heat transfer resistance through the wall of the exchanger, metal to adsorbent contact heat transfer, and conductive heat transfer resistance through adsorbent material. Of these, the heat transfer resistance engendered by 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 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.

(32) 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 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.

(33) One of the techniques to enhance heat transfer performance by increasing overall thermal conductivity is by adding metal particles 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 of applications where such adsorbent beds are used.

(34) 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 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.

(35) Another method that is discussed in the art is the formation of a polymeric net such as a polyaniline net over the granular bed. This can be done in situ using oxidative in situ polymerisation of aniline on the surface of the adsorbent granules. The disadvantage noted with this method is that while heat transfer resistance is reduced, the mass transfer performance is affected adversely.

(36) Other attempts include deposition of adsorbent over a metallic foam. One example of this method includes deposition of zeolite and copper metal foam. The 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, but results in an increase in metallic mass.

(37) 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 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.

(38) 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, and the only solution is to seek a replacement for this method.

(39) 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 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.

(40) The object of this invention is to provide a hybrid adsorption heat exchanger that is compact, efficient in converting input cooling power and affordable.

(41) 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/ethanol/methanol/other assorted refrigerants are 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 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.

(42) FIGS. 1, 1(a) and 1(b) are a representation of a typical finned type block adsorber that is used in the adsorber and desorber heat exchangers.

(43) FIGS. 2, 2(a) and 2(b) are a representation of a typical finned type tube adsorber that is used in heat exchangers.

(44) FIG. 3(a) is a representation of prior art finned block adsorbers wherein the 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 covered with a metallic mesh. The fins are typically made of aluminium.

(45) FIG. 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 which promotes heat transfer.

(46) The granular packing in FIG. 4(a) is finally covered with a metallic mesh. The fins are typically made of aluminium and are coated with the adsorbent material using techniques disclosed in the art. The coating procedures are discussed in some detail in this document, and involve the use of resins and binders to ensure uniform deposition of adsorbent on the fins.

(47) FIG. 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 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.

(48) FIG. 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 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.

(49) FIG. 4(d) and FIG. 4(e) are representations 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 either a corrugated or a plain desiccant coated substrate block and adsorbent granules interspersed in between the desiccant coated substrate block. In FIGS. 4(b), 4(c) and 4(d) the substrate blocks are provided perpendicular to the axis of the tube, whereas in FIG. 4(e) the substrate blocks are provided parallel to the tube axis. The desiccant coated substrate may be one wherein the desiccant is pre-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 FIG. 4(b) to FIG. 4(e) may also be perforated to enhance both mass and heat transfer. FIG. 4(e) may also be perforated to enhance both mass and heat transfer.

(50) FIG. 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 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.

(51) FIG. 5 is a representation of heat transfer regions in a coated fin, and is described in detail below.

(52) FIG. 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), for the heat exchanger, and adsorbent material filled in the beds formed thereby.

(53) 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 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, activated alumina, or silica gel. Alternatively, the filler material can comprise fibers 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.

(54) The hybrid heat exchanger of the invention provides flexibility in combining different adsorbent forms. Tests establish that this hybrid heat exchanger provides significant enhancement both in terms of mass transfer and heat transfer performance.

(55) 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 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:

(56) a. increase the watts output per liter of adsorbent heat exchanger volume, thus decreasing the overall volume, footprint and cost.

(57) b. to improve the adsorption and desorption kinetics in order to additionally enhance the watts per absorber heat exchanger output thus further reducing the footprint, volume and cost of the adsorption chiller. The present invention achieves both simultaneously.

(58) In order to increase and optimize the performance of adsorbent heat exchanging devices, multiple variables were utilized. These comprise:

(59) 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 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 overall heat exchanger design, will typically range from 0.5 mm-2.0 mm, more typically from 0.1 mm to 1.0 mm.
3. Substrate shape: Depending on the choice of the substrate, the substrate may be flat, corrugated, square sign wave, or differently shaped e.g. triangular etc.
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 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 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 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.

(60) 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, lithium bromide, magnesium chloride, magnesium sulphate, calcium nitrate, manganese chloride etc.,

(61) 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 etc. in small quantities.

(62) In some cases, there can be a combination of both doping and addition of thermally conductive materials.

(63) 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 but this invention is not limited to the existing art or methods:

(64) 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.

(65) b. Substrates, particularly porous substrates, the adsorbent can be 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.

(66) c. In yet another method, the substrate, particularly porous substrate, the adsorbent can be synthesized in situ without the use of binders of glues.

(67) 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.

(68) Heat transfer in the adsorbent bed is managed by regeneration and adsorption 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 FIG. 5. The resistances are:

(69) R.1 The convective heat transfer resistance between the secondary fluid and the metal wall.

(70) R.2 The heat transfer resistance through the wall of the heat exchanger.

(71) R.3 The contact heat transfer resistance between the metal and adsorbent.

(72) R.4 The conductive heat transfer resistance through the desiccant mass

(73) As can be seen the heat exchanging device design can affect the heat transfer resistances.

(74) 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 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 gets limited in the applied coating, thus reducing the adsorbent to metal mass ratio.

(75) The present invention aims to maintain a near optimal adsorbent to metal mass ratio by combining the desiccant coated extended surface of metal/fin 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.

(76) 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.

(77) The coating on the extensions can be achieved by any method that is already known, such as that disclosed in U.S. Pat. No. 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.

(78) 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 binder/glue.

(79) 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:

(80) 1. Plane naturally granular adsorbent, of suitable mesh size e.g. silica gel

(81) 2. Adsorbent in powder form but made into granules of suitable mesh.

(82) 3. Adsorbent adhere to a substrate, as a sheet, or as sheet glass or in any other shape e.g. corrugated, square/rectangular, triangular etc. with or without doping, with or without thermally conductive additives like expanded graphite, graphene etc.

(83) 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 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 m.sup.2/g and bulk density of 700-900 g/liter, depending upon the whether the material is beaded or granular, and if granular on the mesh side.

(84) 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 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.

(85) Adsorption capacity of adsorbent/refrigerant pair depends on the porous 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 standard nitrogen gas adsorption/desorption measurements on various adsorbents at liquid nitrogen of temperature 77.4 K are performed. Surface area of each adsorbent is determined by the Brunauer, Emmett and Teller (BET) plot of nitrogen adsorption data. Table 1 shows the surface area, pore volume and apparent density of silica gels (A and RD type), activated carbon fibers of type FX-400 and A 20, granular activated carbon, activated carbon powder of type Maxsorb III and two different MOFs. As can be seen from Table 1, the BET surface area of Maxsorb III and MIL-101Cr are as high as 3140 and 4100 m.sup.2/g, respectively. However, utilization of Maxsorb III and MIL-101Cr as adsorbents in commercial adsorption chillers has been hindered due mainly to its cost, which is above USD 300 per kg. On the other hand silica gels have been used in commercial adsorption chillers and the cost of silica gel samples is around 10-15 USD per kg.

(86) TABLE-US-00001 TABLE 1 Porous properties of various potential adsorbent materials. Pore Apparent Surface area volume density Adsorbent (m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (g .Math. cm.sup.3) Silica gel (type A) 650 0.28 0.73 Silica gel (type RD) 720 0.37 0.7 Silica gel (type S2) 700 0.34- 0.73 Activated carbon fiber (FX 400) 700-2500 0.5-1.4 0.3 Activated carbon Fiber (A-20) 1900 1.028 0.25 Granular activated carbon 700-1500 0.5-1.0 0.4 Highly porous activated 3140 1.7 0.31 carbon (Maxsorb III) Zr.sub.6O.sub.4(OH).sub.4(Linker).sub.6 2064 0.97 MIL-101Cr 4100 2.0

(87) Turning now to FIG. 7 onwards, the graphical representations display the enhanced adsorbent capacity of the invention.

(88) FIG. 7 shows the adsorption isotherms of parent silica gel S2/water and coated S2/water adsorbent/refrigerant pairs for adsorption temperature of 30 C. and pressure ranges from 0.7 to 3.8 kPa. For the said adsorption isotherm, the adsorbent sample temperature is kept constant whilst the evaporator temperature increases stepwise until the relative pressure reaches above 0.9. It can be seen from FIG. 7 that, the adsorption capacity of silica gel S2/water pair is as high as 0.34 kg kg.sup.1 at adsorption temperature of 30 C. and pressure at around 3.6 kPa. The adsorption capacity of coated silica gel S2/water pair is similar to that of the parent S2/water pair. It can be observed that, for both parent S2/water pair and coated S2/water pairs, the adsorption capacity increases linearly with the increase of pressure in the whole studied range.

(89) FIGS. 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 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 S2/water paper is suitable for both adsorption cooling and desalination applications.

(90) FIG. 10 shows the adsorption isotherms of silica gel S2/water pair and silica gel RD/water pair for temperatures between 30 and 70 C. and pressure up to 5 kPa, which is the operation range of silica gel/water based adsorption chillers. It is evident from FIG. 10 that the adsorption isotherms data of silica gel S2/water and silica gel RD/water pairs are comparable and one can choose either adsorbent depending on the cost and availability of the adsorbent.

(91) FIGS. 11(a), 11(b) and 11(c) show the temporal profiles of adsorption uptake and pressure of the silica gel S2/water pair at adsorption temperatures of 30, 50 and 70 C., respectively. It is visible from FIGS. 11(a)-11(c) that the adsorption kinetics of the studied pair is relatively faster at the early stages of adsorption processes. Moreover, more than 80% of total uptake occurs within the first 5 minutes and thus the silica gel S2/water pair seems to suitable for adsorption cooling applications.

(92) 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. 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 ones made of copper, aluminum, carbon, reinforced plastic or special steel. Ceramic materials or combined material systems are also possible.

(93) 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 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 sorbent material is now carried out as follows.

(94) 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 immersion, 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 coating is especially useful in planar heat exchanger structures.

(95) 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 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 material is introduced into the heat exchanger there is no functionally impairing mixture of the adhesive of the sorbent material.

(96) After the coating steps are completed and the coating on the metallic portions are dry, the interstitial spaces can be filled in with conventional granular 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 art.

(97) 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 systemswhich use either a granular bed or a coated fin system in isolation.

(98) 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 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.

(99) 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 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 time whilst the less thermal mass directly translates to better performance or coefficient of performance (COP). These two features synergistically improve the adsorption cycle both energetically, footprint-wise and more importantly the lowering in capital cost.

(100) FIG. 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 evaporator and the condenser remain the same for both cases. It is observed that the adsorbent-coated and adsorbent-coated hybrid types provide significant performance improvement.

(101) The overall heat transfer coefficient of the advanced adsorbent-coated and adsorbent-coated hybrid heat exchanger is around 350 to 350 W/m.sup.2K depending on the adsorber/desorber configuration. FIG. 14 shows the temperature profiles of the major components of the adsorption chiller for the overall heat transfer coefficient of 350 W/m.sup.2K. As can be seen from FIG. 14, all four heat exchangers work efficiently and the chiller produces effective cooling due to faster adsorption kinetics resulted from improved heat transfer and smaller thermal mass.

(102) FIG. 15 shows the performance comparisons of adsorption chiller for pellet, adsorbent-coated and hybrid heat exchangers. The performance comparisons have been made in terms of specific cooling power (SCP), coefficient of performance (COP) and volumetric efficiency. As can be seen from FIG. 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 pellet and hybrid type heat exchangers due to faster kinetics and less thermal mass. On the other 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 adsorbent-coated 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.

(103) Another advantage of the invention that has been observed 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. FIG. 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 heat exchangers of the present invention.