Solar device for autonomous refrigeration by solid-gas sorption

Abstract

A device is provided for the autonomous production of refrigeration approximately 40° C. lower than ambient temperature from a low-temperature solar thermal source, the device including: (i) a reactor arranged to cool and/or heat the solid reagent; (ii) a condenser; (iii) a first tank for storing the liquid refrigerant at ambient temperature; (iv) an enclosure arranged to store a phase-change material and also including an evaporator; (v) a second tank for storing the liquid refrigerant at a low temperature; (vi) apparatus for conveying the refrigerant and (vii) apparatus for controlling the flow of the refrigerant.

1 . An autonomous device for the production of refrigeration from a low-temperature solar thermal source between 50° C. and 130° C., said refrigeration being produced with a temperature difference 5° C. to 40° C. lower than ambient temperature and said device implementing a method for the thermochemical sorption of a refrigerant by a solid reagent, said device comprising:
 a reactor arranged to contain the solid reagent and comprising at least one heat exchanger to cool and/or heat said reactor; 
 a condenser capable of liquefying the gaseous refrigerant coming from the reactor; 
 a first tank for storing the liquid refrigerant produced by the condenser at ambient temperature; 
 an enclosure arranged to store a phase-change material and also comprising an evaporator in direct contact with said phase-change material and capable of evaporating the liquid refrigerant; 
 a second tank for storing the liquid refrigerant at a temperature lower than ambient temperature, connected to the first tank on the one hand and the evaporator and the reactor on the other hand; 
 at least one means of conveying the refrigerant arranged to circulate said refrigerant in liquid or gaseous form between the reactor, the first tank, the second tank and the evaporator; and 
 at least one means of controlling the flow of the refrigerant acting on the means of conveying the refrigerant, said at least one control means being arranged to regulate the flow of the refrigerant independently as a function of the pressures prevailing in the reactor, the first and second tanks, the condenser and the evaporator. 
 
     
     
         2 . The device according to  claim 1 , characterized in that the enclosure and/or the second tank are thermally insulated. 
     
     
         3 . The device according to  claim 1 , characterized in that the evaporator is supplied with liquid refrigerant from the second tank by the difference in the density of said refrigerant between the inlet and outlet of said evaporator. 
     
     
         4 . The device according to  claim 1 , characterized in that the reactor also comprises an isothermal housing arranged to contain the heat exchanger and/or the reactor and capable of reducing the heat losses of said reactor. 
     
     
         5 . The device according to  claim 1 , characterized in that the reactor is made up of a plurality of tubular elements comprising the solid reagent and connected to each other by said means of conveying the refrigerant. 
     
     
         6 . The device according to  claim 5 , characterized in that the plurality of tubular elements is coated with a solar-absorbing coating to improve the thermal efficiency of the plurality of tubular elements, said coating being in close contact with the wall of the plurality of tubular elements. 
     
     
         7 . The device according to  claim 6 , characterized in that the solar-absorbing coating has low infrared emissivity. 
     
     
         8 . The device according to  claim 5 , characterized in that the reactor also comprises at least one covering element transparent to solar radiation, arranged to reduce the heat losses and enhance the solar collection efficiency, said at least one covering element extending beyond the surface of the reactor exposed to the sun. 
     
     
         9 . The device according to  claim 5 , characterized in that at least one of the surfaces of the reactor not exposed to the sun is thermally insulated in order to reduce the heat losses. 
     
     
         10 . The device according to  claim 5 , characterized in that the reactor also comprises actuation means in order to orient the plurality of tubular elements of the reactor in a plane substantially perpendicular to the direction of the sun and thus present the maximum possible solar-absorbing area. 
     
     
         11 . The device according to  claim 8 , characterized in that the night-time cooling of the reactor is provided by natural circulation of the air in the reactor. 
     
     
         12 . The device according to  claim 11 , characterized in that the reactor also comprises at least one flap for the ventilation of the plurality of tubular elements, said at least one flap being located at the top and/or bottom of said reactor. 
     
     
         13 . The device according to  claim 12 , characterized in that the at least one ventilation flap is arranged to seal the reactor when it is in the closed position. 
     
     
         14 . The device according to  claim 12 , characterized in that the at least one ventilation flap also comprises drive means to open and/or close it. 
     
     
         15 . The device according to  claim 14 , characterized in that the drive means consists of a low-power electric motor. 
     
     
         16 . The device according to  claim 15 , characterized in that the electric motor is powered by an electricity production and/or storage device. 
     
     
         17 . The device according to  claim 14 , characterized in that the drive means consists of a rack and pinion device actuated by a compressed air rotary jack connected to a compressed air reserve. 
     
     
         18 . The device according to  claim 17 , characterized in that the compressed air reserve is refilled by an air compressor powered by photovoltaic panels. 
     
     
         19 . The device according to  claim 14 , characterized in that the drive means consists of a rack and pinion device actuated by a single-acting hydraulic linear jack controlled by a thermostat bulb in thermal contact with an absorbing plate exposed to the sun. 
     
     
         20 . The device according to  claim 11 , characterized in that the plurality of tubular elements also comprises a plurality of circular fins the base of which is in close thermal contact with the wall of the tubular elements in order to enhance the heat exchanges. 
     
     
         21 . The device according to  claim 20 , characterized in that the plurality of fins is covered with a solar-absorbing coating to enhance the heat exchanges. 
     
     
         22 . The device according to  claim 11 , characterized in that the plurality of tubular elements is arranged horizontally in order to improve the flow of air around said tubular elements. 
     
     
         23 . The device according to  claim 11 , characterized in that the condenser is of the finned tube exchanger type and cools, during the day, by natural air convection around said finned tubes. 
     
     
         24 . The device according to  claim 5 , characterized in that the night-time cooling of the reactor is provided by a heat pipe loop operating as a thermosyphon and comprising:
 a working fluid capable of performing thermodynamic work, said working fluid propagating in the heat pipe loop by means of at least one means of conveying;   a so-called heat pipe evaporator, working in conjunction with the plurality of tubular elements of the reactor and arranged to evaporate the working fluid and absorb the heat released by the reactor;   a so-called heat pipe condenser, working in conjunction with the evaporator and the reactor, said condenser being arranged to liquefy the working fluid and perform a heat transfer with the outside air;   a working fluid tank arranged to store said liquid working fluid and enable the optimum filling of the at least one tubular element of the reactor with working fluid;   a passive, autonomous device for controlling the flow of the working fluid in the heat pipe loop comprising:
 a first working fluid flow control means, located between the working fluid tank and the bottom of the at least one means of conveying the working fluid, said first control means being arranged to control the liquid working fluid supply to the at least one means of conveying the working fluid; and 
 a second working fluid flow control means, located between the outlet of the heat pipe evaporator and the heat pipe condenser, arranged to control the movement of the gaseous working fluid in the at least one means of conveying the working fluid. 
   
     
     
         25 . The device according to  claim 24 , characterized in that it also comprises a valve for starting the heat pipe loop, arranged to fill said heat pipe loop with working fluid and/or drain it. 
     
     
         26 . The device according to  claim 24 , characterized in that the heat pipe evaporator comprises at least one means of conveying the working fluid arranged inside the plurality of tubular elements of the reactor and in close thermal contact with the solid reagent, said at least one means of conveying the working fluid associated with each tubular element being connected to each other by manifolds at the top and bottom. 
     
     
         27 . The device according to  claim 24 , characterized in that the heat pipe condenser is made up of at least one finned tube connected to each other by means of conveying the working fluid. 
     
     
         28 . The device according to  claim 27 , characterized in that the at least one finned tube of the heat pipe condenser are arranged substantially horizontally at the rear of the reactor, with a slight tilt to enable the gravity flow of the liquefied working fluid to the working fluid tank. 
     
     
         29 . The device according to  claim 24 , characterized in that the working fluid tank is arranged to maintain a minimum working fluid level in the means of conveying said working fluid of between one third and three quarters of the height of a tubular element of the reactor. 
     
     
         30 . The device according to  claim 24 , characterized in that the working fluid tank is arranged to evaporate the working fluid and also comprises the refrigerant condenser arranged to liquefy said refrigerant. 
     
     
         31 . The device according to  claim 24 , characterized in that the device for controlling the flow of working fluid in the heat pipe loop also comprises at least one autonomous control means, arranged to respectively open and close the first and second working fluid flow control means. 
     
     
         32 . The device according to  claim 31 , characterized in that the at least one autonomous control means of the first and second working fluid flow control means comprises:
 an absorbing plate capable of absorbing solar radiation and emitting in the infrared, said absorbing plate being arranged to heat by means of day-time solar radiation and cool during the night;   a thermostat bulb in thermal contact with the absorbing plate, comprising a fluid capable of expanding under the effect of a temperature variation; and   a connecting element working in conjunction firstly with the thermostat bulb and secondly with the first and/or second working fluid flow control means, said connecting element being arranged to open or close said working fluid flow control means.   
     
     
         33 . The device according to  claim 5 , characterized in that it consists of a modular architecture made up of:
 a plurality of first assemblies each comprising:
 the reactor made up of a plurality of tubular elements and comprising the heat exchanger; 
 the condenser capable of liquefying the refrigerant; 
 the tank for storing the refrigerant at ambient temperature, the volume of which corresponds to the volume of the plurality of tubular elements of said first assembly; 
 refrigerant flow control means; 
   a second assembly comprising:
 the enclosure arranged to store a phase-change material and comprising thermal insulation; 
 the second tank for storing the liquid refrigerant at a temperature lower than ambient temperature and comprising thermal insulation; 
 the evaporator for evaporating the refrigerant, located in the enclosure and working in conjunction with the second tank; 
 first means of controlling the flow of refrigerant between the evaporator and the second tank; and 
 second means of controlling the flow of refrigerant to ensure the connection between the second assembly and the plurality of first assemblies. 
   
     
     
         34 . The device according to  claim 33 , characterized in that the evaporator is of the flooded type and comprises at least one tubular element arranged to circulate the refrigerant by thermosyphon with the second tank. 
     
     
         35 . The device according to  claim 33 , characterized in that the second assembly comprises a tight isolation valve, arranged to fill the device with refrigerant and/or drain it. 
     
     
         36 . The device according to  claim 1 , characterized in that the refrigerant is ammonia. 
     
     
         37 . Use of the device according to  claim 1  to produce refrigeration. 
     
     
         38 . Use of the device according to  claim 1  to produce water. 
     
     
         39 . The use of the device according to  claim 38 , characterized in that water is produced by condensing water vapour contained in the air on a wall kept cold by the device according to  claim 1 .