Production of Very Low-Temperature Refrigeration in a Thermochemical Device

Abstract

The invention relates to a thermochemical device and to a method for producing refrigeration at very low temperature. The device produces refrigeration at a temperature T f <−20° C., from an available heat source at a temperature T h of 60-80° C. and a heat sink at the ambient temperature T o of 10° C.-25° C. It comprises two coupled dipoles, operating in phase. One of the dipoles may be regenerated from a heat source at the temperature T h and a heat sink at T o , and produce refrigeration at the temperature T f with a heat sink at a temperature below the ambient temperature T o . The other dipole may be regenerated from a heat source at the temperature T h and a heat sink at the temperature T o .

1 . A device for producing refrigeration at a temperature T f  below −20° C., from an available heat source at a temperature T h  of around 60-80° C. and a heat sink at the ambient temperature T o  of around 10° C. to 25° C., which comprises a refrigeration producing dipole Db and an auxiliary dipole Da, characterized in that:
 Da comprises an evaporator/condenser ECa and a reactor Ra connected by a line enabling the flow of gas, and Db comprises an evaporator/condenser ECb and a reactor Rb connected by a line enabling the flow of gas;   ECa contains a gas Ga and Ra contains a sorbent Sa able to form a reversible phenomenon with Ga, and ECb contains a gas Gb and Rb contains a sorbent Sb able to form a reversible phenomenon with Gb; the gases and the solids being chosen so that, at a given pressure, the equilibrium temperatures of the thermochemical phenomena in the reactors and the evaporators/condensers are such that T(ECb)≦T(ECa)<T(Rb)<T(Ra) during the refrigeration production step;   the thermochemical processes implemented in the dipole Db are such that this dipole may be regenerated from a heat source at the temperature T h  and a heat sink at T o , and produce refrigeration at the temperature T f  with a heat sink at a temperature below the ambient temperature T o ;   the thermochemical phenomena in the dipole Da are such that this dipole may be regenerated from a heat source at the temperature T h  and a heat sink at the temperature T o ; and   the dipoles are equipped with means that enable ECa and Rb to be thermally coupled during the refrigeration production step.   
   
   
       2 . The device as claimed in  claim 1 , characterized in that the thermochemical phenomena in the reactors/condensers are chosen from the L/G phase change of ammonia (NH 3 ), the L/G phase change of methylamine (NH 2 CH 3 ) and the L/G phase change of H 2 O. 
   
   
       3 . The device as claimed in  claim 1 , characterized in that the thermochemical phenomena in the reactors are chosen from the reversible chemical sorptions of NH 3  by CaCl 2 , by BaCl 2 , by PbBr 2  or by NH 4 Br; the chemical sorption of NH 2 CH 3  by CaCl 2 ; the adsorption of water by a zeolite or a silica gel; the adsorption of methanol (MeOH) or of ammonia in active carbon; and the absorption of NH 3  in a liquid solution of ammonia (NH 3 .H 2 O). 
   
   
       4 . The device as claimed in  claim 1 , characterized in that each of the elements EC is composed of an assembly comprising an evaporator E and a condenser C connected together and with the reactor of the same dipole by lines equipped with valves enabling the flow of gas or of liquid. 
   
   
       5 . A method for producing refrigeration at the temperature T f  from a heat source at the temperature T h  and a heat sink at the ambient temperature T o  consisting in operating the device as claimed in  claim 1  from an initial state in which the dipoles Da and Db are to be regenerated (that is to say, that the sorbents are in the reactors Ra and Rb respectively in the form “Sa+Ga” and “Sb+Gb”), the two elements of a given dipole being isolated from one another, said method being characterized in that it comprises a series of successive cycles made up of a regeneration step and a refrigeration production step:
 at the beginning of the first step, which is the step of regenerating the device, the two elements of each of the dipoles are connected and heat at the temperature T h  is supplied to each of the reactors Ra and Rb for the decomposition reactions in Ra and Rb, the gas Ga and the gas Gb released being transferred respectively toward the evaporators/condensers ECa and the ECb in which they condense, the heat of condensation being extracted in the heat sink at T o ; and   during the second step, which is the refrigeration production step, Rb and ECb are connected, which causes the spontaneous endothermic evaporation phase in ECb (refrigeration producer) which releases Gb in gas form, said gas flowing into the reactor Rb in which the exothermic absorption of Gb by the sorbent Sb takes place; the heat released in Rb is transferred toward ECa to cause the release of the gas Ga that flows into Ra to be absorbed by the sorbent Sa exothermically, the heat released in Ra being extracted toward the environment at T o .   
   
   
       6 . The method as claimed in  claim 5 , characterized in that the thermochemical phenomena are chosen such that Ga and Gb are different. 
   
   
       7 . The method as claimed in  claim 5 , characterized in that the dipoles Da and Db of the device involve the same working gas G. 
   
   
       8 . The method as claimed in  claim 7 , characterized in that the second step comprises two phases: during the first phase, the elements of the dipole Da are isolated from one another, and ECb and Rb are connected, which causes the release of Gb in ECb and the exothermic synthesis in Rb, the heat released in Rb being transferred toward the reactor ECa; when the pressure in ECa is such that it enables operation of the dipole Da with the heat sink at the ambient temperature T o , the second phase begins by connecting the elements of the dipole Da, which causes an endothermic evaporation in ECa and a concomitant exothermic sorption of Ga in Ra. 
   
   
       9 . The method as claimed in  claim 7 , characterized in that the reactors Ra and Rb contain sorbents whose thermodynamic equilibrium curves are close to one another, that is to say that the deviation observed between the equilibrium temperatures for a same pressure does not exceed 10° C. 
   
   
       10 . The method as claimed in  claim 7 , characterized in that the reactors Ra and Rb contain the same sorbent S.