Patent Application: US-92271201-A

Abstract:
a novel modular and miniature chiller is proposed that symbiotically combines absorption and thermoelectric cooling devices . the seemingly low efficiency of each cycle individually is overcome by an amalgamation with the other . this electro - adsorption chiller incorporates solely existing technologies . it can attain large cooling densities at high efficiency , yet is free of moving parts and comprises harmless materials . the governing physical processes are primarily surface rather than bulk effects , or involve electron rather than fluid flow . this insensitivity to scale creates promising applications in areas ranging from cooling personal computers and other micro - electronic appliances , to automotive and room air - conditioning .

Description:
referring to the drawings , fig1 illustrates a schematic view of one embodiment of an electro - adsorption chiller equipped with a flooded - pressure expansion valve that constitutes one aspect of the present invention . from the evaporator 1 , heat is transferred from the heat spreader or substrate 1 a where the latter is in direct contact with a surface to be cooled . after adequate heat transfer is effected , boiling of refrigerant ( e . g ., water vapour ) takes place within the evaporator 1 and the generated vapour flows into the reactor 5 via the pipe 2 and an on - off valve 3 ( which is activated during the adsorption mode ). the presence of a positive pressure gradient across the evaporator 1 and the reactor 5 affects the flow of refrigerant . accordingly , the other end of reactor 5 is shut to the condenser 9 by valve 7 . reactor 5 contains a pre - determined amount of absorbent 5 a , sealed within the finned surfaces 4 on one end and a perforated stainless steel mesh 5 b on the other . the absorbent adsorbs refrigerant , and heat generated by the exothermic process is rejected via the finned surfaces 4 . the temperature of the finned surfaces 4 is maintained at a temperature below that of the ambient environment by the cold junctions of the thermoelectric device 6 , which is powered by an electric current ( dc ) from a power source or battery 20 . electricity flows through the electrical leads 19 and 21 to the thermoelectric device 6 . depending on the operation mode of the reactor 5 in a batch - operated cycle , the direction of the dc current can be reversed should reactor 5 be operated as a desorber . accordingly , in another mode of operation ( referring to fig1 ), the condenser 9 is opened to the reactor 12 via the pipe 10 and an on - off valve 11 ( which is activated during the desorption mode ). vapour flows from the reactor 12 into the condenser 9 under the effect of a positive pressure gradient . in this mode , the other end of the reactor 12 is shut to the evaporator 1 via valve 14 . the reactor 12 contains a pre - determined amount of absorbent 12 a , sealed within the finned surfaces 13 on one end and a perforated stainless steel mesh 12 b on the other . refrigerant is desorbed from the absorbent and heat is received via the finned surfaces 13 . the high temperature of the finned surfaces 13 is maintained by the hot junctions of the thermoelectric device 6 , where the latter is powered by an electric current ( dc ) from a power source or battery 20 . electricity flows through the electrical leads 19 and 21 . depending on the operation mode of the reactor 12 , the direction of current can be reversed should the reactor 12 be operated as an adsorber . in order to ensure that the thermoelectric device 6 operates properly , each of the two junctions are separately connected in a thermally conductive but electrically non - conducting manner . this can be achieved by providing ceramic plates between the two reactors 5 and 12 . the thermoelectric device is connected to the battery 20 in such a manner that this dc power source is capable of performing a voltage polarity switch so that each of the two junctions can operate as a heating end and a cooling end at any given time . the entire system is operated under the control of a control device , which is connected to each of the various elements . the control device controls the process time interval of the system , the on - off control valves 3 , 7 , 11 and 14 , the voltage polarity of the dc power source , and the power supply by the dc power source to the thermoelectric device 6 . accordingly , each of the two junctions of the thermoelectric device 6 is capable of being operated as a cooling end or a heating end . when operating as a cooling end , the reactor 5 or 12 attached to the cooling end is cooled down while it is isolated from both the condenser 9 and the evaporator 1 and subsequently connected serially to the evaporator 1 to operate as an adsorber , adsorbing vapour refrigerant from the evaporator 1 for a substantial period of time . when operating as a heating end , the reactor 5 or 12 attached to the heating end is cooled down while it is isolated from both the condenser 9 and the evaporator 1 and subsequently connected serially to the evaporator 1 to operate as an desorber , desorbing vapour refrigerant from the evaporator for a substantial period of time the roles of the condenser 9 and evaporator 1 are functionally similar to those found in a conventional chiller , that is , the condenser 9 rejects heat to the ambient environment via air - cooled finned surfaces 9 a or coiled - tubes , while the evaporator 1 draws heat from the heat source surface . the link between the condenser 9 and evaporator 1 is via small tubes 16 and 18 as well as the expansion valve 17 . the configuration shown here is that of a conventional flooded - u - tube arrangement , and thus no control strategy is offered for the operation of valve 17 . another drawing , fig2 illustrates a schematic view of another embodiment of the chiller , equipped with an electromechanical spray nozzle 23 and housed within the evaporator 1 . together , they constitute another aspect of the claimed invention . an electrically operated pump or injector 22 is used to inject the liquid refrigerant at a suitable pressure into the spray nozzles 23 . within the evaporator 1 , heat is transferred from the heat spreader substrate la where the latter is in direct contact with a surface to be cooled . boiling of refrigerant ( e . g ., water vapour ) takes place within the evaporator 1 and the generated vapour flows into the reactor 5 via the pipe 2 and an on - off valve 3 ( which is activated to be opened during the adsorption mode ) caused by the presence of a positive pressure gradient . at this time , the other end of reactor 5 is shut to the condenser 9 by valve 7 . reactor 5 contains a pre - determined amount of absorbent 5 a , sealed within the finned surfaces 4 on one end and a perforated stainless steel mesh 5 b on the other . refrigerant ( water vapour ) is adsorbed by the absorbent , and the heat generated by the exothermic process is rejected by the finned surfaces 4 . the temperature of the finned surfaces 4 is maintained low by the cold junctions of thermoelectric device 6 , where the latter is powered by an electric current ( dc ) from a power source or battery 20 . the electricity flows through the electrical leads 19 and 21 . depending on the operation mode of the reactor 5 , the direction of current can be reversed should the reactor 5 be operated as a desorber . accordingly , in another mode of operation ( referring to fig2 ), the condenser 9 is opened to the reactor 12 via the pipe 10 and an on - off valve 11 ( which is activated to be opened during the desorption mode ). vapour flows from the reactor 12 into the condenser 9 under the effect of a positive pressure gradient . in this mode , the other end of chamber 12 is shut to the evaporator 1 . reactor 12 contains a predetermined amount of absorbent 12 a , sealed within the finned surfaces 13 on one end and a perforated stainless steel mesh 12 b on the other . refrigerant ( water vapour ) is desorbed from the absorbent and heat is received via the finned surfaces 13 . the temperature of finned surfaces 13 is maintained high by the hot junctions of thermoelectric device 6 , where the latter is powered by an electric current ( dc ) from a power source or battery 20 . the electricity flows through the electrical leads 19 and 21 . depending on the operation mode of the reactor 12 , the direction of current can be reversed should the reactor 12 be operated as an adsorber . the roles of the condenser 9 and evaporator 1 are functionally similar to those found in any conventional chiller ; that is the condenser 9 rejects heat to the ambient environment via air - cooled finned surfaces or coiled - tubes whilst the evaporator 1 draws heat from the heat source surface . spray nozzles 23 can be incorporated that deliver streams of micro droplets ( liquid droplets up to tens or hundreds of microns acting like projectiles ) landing on the heated surfaces of the heat spreader before vaporizing into vapour . the rate of droplet delivery can be varied digitally by a computerized system through a feedback signal according to the cooling demand of the evaporator 1 . the link between the condenser 9 and evaporator 1 ( other than the reactors ) is via small tubes 16 and 18 as well as the expansion valve 17 . a piezoelectric - activated spool valve can be used in all of the above - mentioned embodiments and constitutes another aspect of the present invention . fig3 shows a schematic view of an electro - adsorption chiller with a piezoelectric - activated spool - valve 24 , sealed hermetically . the function of the spool valve 24 is to provide ( i ) ease of control for the switching of the reactors 5 and 12 , alternating as adsorber and desorber beds over a prescribed cycle time , and ( ii ) compactness for the reactors to be linked to the condenser 9 and evaporator 1 . depending on the number of pairs of reactors ( 5 and 12 ) of thermoelectric device 6 , the spool - valve can be arranged in a compact manner to provide the passage links to the condenser 9 and the evaporator 1 , as shown in fig4 ( a ). also in fig4 ( a ), the reactor 5 ( when operated as an adsorber ) and the reactor 12 ( when operated as a desorber ) are linked to the evaporator 1 and condenser 9 , respectively . in another mode of operation of the spool - valve ( shown here in fig4 ( b )), the roles of the reactors 5 and 12 in each pair of electro - adsorption chillers can be switched to adsorber and desorber modes , respectively . this is achieved by the change in the direction of current flow of the power source to the piezoelectric actuator . accordingly , the spool piston of the compact spool - valve can be positioned such that the reactors ( functioning as a desorber ) are switched to the condenser 9 and the evaporator 1 . in fig4 ( c ), the position of the piston of the spool valve 24 can be manoeuvred to a null position where the reactors ( 5 and 12 ) of each pair of electro - adsorption chillers are isolated from the condenser 9 and evaporator 1 . this switching mode is a requirement of the batch operation of the electro - adsorption cycle . internally , the spool valve 24 is sealed hermetically with grooves 24 a on the piston 24 b . sealing of refrigerant ( under partial vacuum ) flowing between chambers is affected by “ o ”- rings 24 c . specially designed compartments connect the reactors with fine flow passages within the valve body , linking them to the condenser 9 and evaporator 1 at suitable parts of the batch cycle . movement of the piston 24 b during the above - mentioned modes of operation is kept minimal to avoid excessive induced wear on the “ o ”- rings 24 c . fig5 shows a compact design of the device with multiple pairs of reactors and the spool - valve 24 . the reactors and spool valve 24 represent part of the present invention . the proposed parallel layout of electro - adsorption chillers provides a boost to the total cooling capacity seen by the evaporator 1 , and yet the claimed invention remains compactly designed . another object of incorporating a spool - valve 24 in the claimed invention is that it permits the remote installation of the “ outdoor ” unit comprising the reactors ( 5 and 12 ), thermoelectric device 6 , condenser 9 and the spool valve 24 from the “ indoor ” unit which consists of the expansion valve 17 and the evaporator 1 . the “ outdoor ” and the “ indoor ” units are connected by suitable tubes or pipes 2 and 10 that transport the refrigerant , as shown in fig5 . this design feature has many advantages in the cooling of compact microchips and printed circuit boards ( pcbs ), in terms of simplicity , compactness and zero vibration on the cpu or pcbs . in the electro - adsorption chiller just described , the bed switching is performed simply by reversing the polarity of battery 20 to the thermoelectric device 6 . what was formerly the cold junction becomes the hot junction , and vice versa , as shown in fig6 ( a ). the ideal adsorption cycle abcd is depicted on a plot of the amount of absorbate adsorbed ( q ) versus the vapour pressure ( p ), as shown in fig6 ( b ). the desorption process commences from b to d with bc as a switching interval and cd is the cycle interval . similarly , adsorption starts from d to b with da and ab as the switching and adsorption intervals . the isotherms associated with the ideal cycle are t 1 and t 5 , which correspond to the adsorber and desorber bed temperatures , respectively . the cycle is now completed . the heating and cooling of the two beds 5 and 12 repeat , along with the flow of refrigerant to and from the condenser 9 , evaporator 1 , adsorber and desorber . the evaporator 1 design is distinctly important for the envisioned applications for the following reasons . first , high cooling densities are demanded . second , the device must be orientation independent and the incorporation of the pump 22 and spray nozzles 23 would enable the evaporator 1 to function in a variety of orientations . the nozzles 23 would inject micro liquid droplets onto a heated substrate 1 a . the cop of the electro - adsorption chiller can be expressed in terms of the cops of the individual adsorption ( subscript “ ads ”) and thermoelectric ( subscript “ te ”) chiller by considering the overall energy flows ( with all energy flows defined as positive ). referring to fig1 or 2 and 6 , the cops of the individual components are defined as the nominal cooling rate produced relative to the particular ( electric or thermal ) power input : equation 5 demonstrates the amplification of the net cop when both systems are symbiotically combined to operate in tandem . the above equations 1 to 5 relate to a single cooling module . far larger cooling loads can be accommodated with an assembly of many individual modules , as shown in fig5 . a single condenser 9 and evaporator 1 would then be interfaced to the modules , locally or remotely , via a customary spool valve 24 . detailed operating schedules for the 2 - bed , 4 - bed and multi - bed electro - adsorption chillers are presented in tables 1 to 3 . the plurality of the absorbent beds operating with either one or more pairs of condenser - evaporator forms a part of the present invention . the horizontal width of each box shown in the schedules represents the time interval required with respect to the total cycle time . as an example , the performance of a two - bed electro - adsorption chiller has been simulated using the specifications listed in table 4 . for these mentioned parameters , fig7 shows a sample of the numerical solutions to these coupled differential equations . it depicts the predictions of the dynamic temperatures of adsorber 5 , desorber 12 , condenser 9 and evaporator 1 for 4 full cycles of the electro - adsorption chiller operation . as can be seen from these results , cyclic steady state conditions in the chiller can be achieved in three full cycles . at the specified cooling rate , the net cop of the single electro - adsorption chiller in this particular situation is about 1 . 2 , which is higher than the individual cops of the thermoelectric or adsorption chiller . sw : switching from adsorber to desorber , i . e . adsorber reactor receives heat from the hot junction of the thermoelectric module or switching from desorber to adsorber , i . e . desorber reactor becomes cool by the cold junction of the thermoelectric module . the reactor operating under this mode is isolated from both the condenser and evaporator . jun - 1 : hot or cold junction of the first junction of a thermoelectric module . jun - 2 : hot or cold junction of the second junction of a thermoelectric module . the width of each box is an indication of the relative time duration over one cycle . sw : switching from adsorber to desorber , i . e . adsorber reactor receives heat from the hot junction of the thermoelectric module or switching from desorber to adsorber , i . e . desorber reactor becomes cool by the cold junction of the thermoelectric module . the reactor operating under this mode is isolated from both the condenser and evaporator . jun - 1 : hot or cold junction of the first junction of a thermoelectric module . jun - 2 : hot or cold junction of the second junction of a thermoelectric module . te - i : i - th thermoelectric module , where i ranges from 1 to 2 . vps - j : voltage polarity switch for the j - th thermoelectric module , where j ranges from 1 to 2 . the width of each box is an indication of the relative time duration over one cycle . sw : switching from adsorber to desorber , i . e . adsorber reactor receives heat from the hot junction of the thermoelectric module or switching from desorber to adsorber , i . e . desorber reactor becomes cool by the cold junction of the thermoelectric module . the reactor operating under this mode is isolated from both the condenser and evaporator . jun - 1 : hot or cold junction of the first junction of a thermoelectric module . jun - 2 : hot or cold junction of the second junction of a thermoelectric module . te - i : i - th thermoelectric module , where i ranges from 1 to n where 2n is the total even number of reactors . vps - j : voltage polarity switch for the j - th thermoelectric module , where j ranges from 1 to n . the width of each box is an indication of the relative time duration over one cycle . the invention being thus described , it will be obvious that the same may be varied in many ways . such variations are not to be regarded as a departure from the spirit and scope of the invention , and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims . the following references have been referred to by footnote numbers throughout the specification and are hereby incorporated by reference thereto : drost m . kevin ., michele friedrich , miniature heat pumps for portable and distributed space conditioning applications , aiche spring national meeting , new orleans , march 1998 . lee , d . y . and k . vafai . comparative analysis of jet impingement and micro channel cooling for high heat flux application , int . j . heat mass transfer , vol . 42 , pp . 1555 - 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