Method of bringing to temperature and holding at temperature the interior of a thermally insulated enclosure with no continuous supply of energy and the associated device

Abstract

A method for changing a temperature of the interior volume of a thermally insulated space to a preset temperature and maintaining it at the preset temperature using two thermochemical systems which can be connected to an external energy source. The reactor of one of the systems is heated until fully regenerated, while the other system keeps the temperature at the preset temperature; when the reactor is fully regenerated, the system comprising the regenerated reactor is used to maintain the preset temperature and the reactor of the other system is heated to regenerate it as long as it is connected to the external energy source.

Claims

1. A method of changing a temperature of an internal volume of a thermally insulated enclosure to a preset temperature and maintaining said temperature at said preset temperature, wherein: a device is provided comprising: at least a first and a second system chosen independently of each other from among absorption systems, adsorption systems and thermochemical systems, said first and second systems each comprising: at least one reservoir containing a fluid, connected to a reactor which contains a reagent capable of reacting exothermically and reversibly with said fluid, said reagent being consumed during said exothermic reaction and being able to be regenerated during the reverse reaction, which can be induced by heating said reactor, and a heater for heating said reactor and capable of regenerating said reagent by inducing said reverse reaction; said heater being capable of being connected to an energy source external to said device and able to be disconnected from said external energy source; wherein said device further comprises: at least one thermally insulated enclosure disposed in such a way that its internal volume can be heated and/or cooled by said first and second systems; wherein all of the fluid of each of said systems is contained in said reservoir of said system before the method is performed; the method comprising: using at least said first system of said systems to change said temperature of the internal volume of said enclosure to said preset temperature by said exothermic reaction; connecting said heater of said first system to said external energy source when said preset temperature is reached; a) heating the reactor of said first system of said systems until complete regeneration of said reagent, while said second system maintains said temperature of the internal volume of said enclosure at said preset temperature by said exothermic reaction; b) when the reagent is completely regenerated, said heater of said first system is disconnected from said external energy source, and said first system having the reactor whose reagent has just been regenerated is used to maintain said temperature of the internal volume of said enclosure at said preset temperature before all the reagent and/or all the fluid of said second system is consumed in said exothermic reaction, and the reactor of said second system, which still contains reagent and said fluid capable of reacting, is heated by connecting said heater of said second system to said external energy source until the complete regeneration of the reagent, at which time said heater of said second system is disconnected from said external energy source; c) connecting said heater of said first system to said external energy source; and d) returning to step a); while said heaters of said first system and said second system are connected to said external energy source, the aforementioned steps a), b), c), and d) are repeated; when each of said heaters of said first and second systems is disconnected from said external energy source, each of said first and second systems is used successively to maintain said temperature of the internal volume of said enclosure at said preset temperature.

2. The method according to claim 1, wherein when said first and second systems are used to change said temperature of the internal volume of said enclosure to said preset temperature, the quantity of unreacted fluid is determined in each of said first and second systems, and the reactor of the system that contains the smallest quantity of unreacted fluid is heated.

3. The method according to claim 1, wherein said reactors of each of said first and second systems are kept isolated from said reservoirs for a given period of time after a beginning of said exothermic reaction.

4. The method according to claim 1, wherein the reactor in which the reagent has just been regenerated is used in order to maintain said temperature of the internal volume of the enclosure at said preset temperature before a temperature of said reactor reaches a temperature of the environment external to said enclosure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents an embodiment of the device according to the invention, the thermally insulated enclosure being disposed in such a way that its internal volume is cooled to a setpoint temperature and then held at that temperature;

(2) FIG. 2a represents an operational diagram of the device represented in FIG. 1 according to a method called in phase opposition; the curves represent, for each of the systems, the change in pressure in the system concerned as a function of time, and the change of temperature in the enclosure as a function of time; and

(3) FIG. 2b represents an operational diagram of the device represented in FIG. 1 according to the method of the invention, the curves represent, for each of the systems, the change in pressure in the system concerned as a function of time, and the change of temperature inside the enclosure as a function of time.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(4) With reference to FIG. 1, a particular embodiment of the present invention will now be described. According to the embodiment represented, the device of the invention comprises two thermochemical systems TCU1 and TCU2 and a thermally insulated enclosure 5 the internal volume of which is intended to be cooled to a setpoint temperature Tc, then held at said temperature. The first thermochemical system TCU1 comprises a reservoir 1 connected to an evaporator 13 disposed inside the thermally insulated enclosure 5. The reservoir 1 is also connected to the reactor 15, disposed opposite the evaporator 13. A condenser 17 is mounted between the reactor 15 and the reservoir 1. A solenoid valve EV1 is mounted between the condenser 17 and the reactor 15. Fans 12, 14 and 16 enable the heat transfer to be accelerated at the evaporator 13, the condenser 17 and the reactor 15. The second thermochemical system TCU2 has the same structure as the first and comprises a reservoir 2 connected to an evaporator 23. The reservoir 2 is also connected to the reactor 25, disposed opposite the evaporator 23. A condenser 27 is mounted between the reactor 25 and the reservoir 2. A solenoid valve EV2 is mounted between the condenser 27 and the reactor 25. Fans 22, 24 and 26 enable the heat transfer to be accelerated at the evaporator 23, the condenser 27 and the reactor 25. The reactor 15 comprises heating means 19 which are electric and capable of being connected to a source of electricity by means of the plug P1. The reactor 25 also comprises electrical heating means 29 which are capable of being connected to a source of electricity by means of a plug, not shown. According to one variant, a switch enables power to be supplied alternatively to the heating means 19 and 29.

(5) The systems TCU1 and TCU2 are thermally insulated from each other. However, the reactors 15 and 25 and/or the condensers 17 and 27 can be thermally connected with the interior of the enclosure 5. They can therefore potentially heat said enclosure when the setpoint temperature is higher than the ambient temperature.

(6) As represented in FIG. 1, the reactor 15 is in the process of regeneration while the second system TCU2 produces frigories at its reservoir 2 and its evaporator 23 in order to cool the enclosure 5. In the present case, the setpoint temperature is always lower than the ambient temperature and the enclosure 5 should be cooled.

(7) In the embodiment represented in FIG. 1, the evaporators 13 and 23 and the reservoirs 1 and 2 are situated in the thermally insulated enclosure 5, while the rest of the elements of the two thermochemical systems TCU1 and TCU2 are situated in a box outside the enclosure 5. For purposes of clarity, the control means as well as the means of determining the progress of the reaction are not represented in FIG. 1.

(8) One mode of operation of the device of the invention will now be explained with reference to FIG. 1.

(9) At t=0, the internal temperature of the enclosure 5 is substantially equal to 25 C., which is the ambient temperature. The ambient temperature does not vary throughout the implementation of the method. The two reservoirs 1 and 2 are filled with liquid ammonia in equilibrium with ammonia gas. To cool the enclosure 5, the solenoid valve EV1 of the first system TCU1 is opened, thus causing the gas to enter from the reservoir 1 to the reactor 15. The gas is consumed during its exothermic reaction with the solid reagent contained in the reactor 15. The evaporation of the liquid in the evaporator 13 generates an absorption of heat inside the enclosure 5, thus cooling it. A certain quantity of fluid is consumed to bring the temperature of the enclosure 5 to the setpoint temperature Tc.

(10) When the setpoint temperature Tc is reached, the plug P1 is connected to the mains to regenerate the reactor 15 of the system TCU1. This configuration is represented in FIG. 1.

(11) The second system TCU2, which still contains fluid and reagent capable of reacting, is then used to hold the temperature in the enclosure 5 at the setpoint value Tc. The solenoid valve EV2 is then opened. While the second system TCU2 cools the enclosure 5, the regeneration by heating the reactor 15 produces calories which should compensate for the cooling of the second system TCU2. The quantity of liquid ammonia present in the reservoir 1 is measured in the first system TCU1 as a function of time. When the level of liquid ammonia returns to the same value as at t=0, the heating of the reactor 15 is stopped, which is thus fully regenerated, and the reactor 25 is heated. The reactor 15 is therefore fully regenerated and is quickly used to maintain the enclosure 5 at the setpoint temperature.

(12) The aforementioned steps are repeated as long as it is possible to connect the heating means 19 and 29 to the mains.

(13) At t=t1, the heating means 19 and 29 are disconnected from the mains and the systems TCU1 and TCU2 are used to maintain the temperature of the enclosure 5 at the value Tc until all of the reagent of the reactor has reacted or all of the fluid has reacted, depending on how the quantity of fluid or reagent limits the exothermic reaction. A switchover is then made to the second system which is used to maintain temperature. As will be explained later, the aforementioned steps make it possible to optimize the quantity of fluid not having reacted in both of the systems TCU1 and TCU2.

EXAMPLE

(14) Cooling of a Thermally Insulated Enclosure to a Setpoint Temperature

(15) A device according to FIG. 1 is prepared to cool a thermally insulated enclosure having an internal volume of 75 L. The overall heat transfer coefficient of the enclosure is evaluated at 0.362 W/m.sup.2/ C. The setpoint temperature in the enclosure is 2 C. Two identical thermochemical systems are used, each comprising a reservoir 88.9 mm in diameter and 504 mm long and comprising a wall 3 mm thick. Each system comprises an evaporator of the same dimensions as the reservoir. Each system contains 1.3 kg ammonia (or 75 moles) capable of reversibly reacting with a block formed by compaction of a mixture of expanded natural graphite and manganese chloride in powder form. Each system comprises a reactor 114.3 mm in diameter, 680 mm long and having a wall 3 mm thick. Each reactor is surrounded by two heating elements each providing power of 266 W. Fans are used to cool the reactors of the systems. The device also comprises an electric battery to supply the fans when the device functions in autonomous mode, as well as to supply the solenoid valves.

(16) At the end of regeneration, the reactors are cooled to return them to a lower temperature, which is either the ambient temperature or a temperature above ambient temperature but which allows the use of the system for producing heat and/or cold. The reactors are also cooled during their use for producing heat and/or cold, whether the device is functioning in autonomous mode or is connected to an external source of energy (the mains). The cooling of the reactors makes it possible to have a lower temperature on the evaporators. The fans can therefore be supplied with 12 V by the battery mounted in the device and capable of being supplied through a transformer connected to the mains.

(17) The reversible exothermic chemical reaction taking place in the reactors is as follows:
(MnCl.sub.22.NH.sub.3)+4NH.sub.3.fwdarw.MnCl.sub.2,6.NH.sub.3 (47 kJ/moleNH.sub.3)

(18) The temperatures and pressures in the various elements of the system are measured while it is in operation to verify that they correspond properly to the values calculated with the Clapeyron diagram.

(19) In the step during which the exothermic reaction takes place in the reactor, for a setpoint temperature equal to 2 C., an ambient temperature substantially constant and equal to 25 C., the maximum temperature in the reactor is 80 C., which is reached at the beginning of reaction and the minimum temperature is 60 C. at the end of reaction. During the exothermic reaction, the temperature in the reactor is substantially stable and equal to 70 C. When the reaction is ended, the temperature in the reactor decreases. The pressure in the system drops then remains constant when the setpoint temperature is reached, due to the adjustment of the flow of ammonia entering the reactor. All ammonia entering is consumed in the exothermic reaction. When the setpoint temperature is reached, the pressure P1 is 2.2 bar. An increase in pressure in the system indicates that the ammonia is no longer being consumed in the reactor and that the exothermic reaction is ended. The temperature in the evaporator is substantially equal to minus 20 C. when the valve means are opened. The temperature increases slightly to stabilize at minus 15 C. during the exothermic reaction, once the setpoint temperature is reached. The increase in temperature in the evaporator indicates the end of the exothermic reaction. The temperature and pressure values are given by the Clapeyron equation diagrams.

(20) Operation with a Single System

(21) If a single thermochemical system is used, a temperature of 2 C. in the enclosure can be reached in 30 minutes (the initial temperature in the enclosure being 25 C.). Said drop in temperature consumes 68.8% of the ammonia of the reservoir. The temperature can then be maintained at 2 C. for 23 hours, which corresponds to an autonomous operation of 23.5 hours.

(22) Operation with Two Systems in Phase Opposition

(23) FIG. 2a represents an operational diagram of the aforementioned device, the two systems being in phase opposition, that is, one reactor is fully regenerated (i.e., until the maximum pressure of ammonia in the system is obtained), then it is cooled to ambient temperature before using it completely to maintain the enclosure 5 at temperature; the reactor of the other system is completely regenerated during the period of use of the first system. The duration of nonuse of the system in process of regeneration corresponds to the duration of regeneration plus the duration of cooling to ambient temperature.

(24) The curve A represents the variations in pressure P in the first thermochemical system as a function of time. The curve B represents the variations in pressure in the second thermochemical system. The curve C represents the variations of the temperature in the thermally insulated enclosure 5, the setpoint temperature being equal to 2 C. The two reservoirs 1 and 2 are filled before beginning to cool the enclosure 5. Each of the regeneration phases lasts six hours, including the increase in temperature of the reactor concerned and the decrease of its temperature down to ambient temperature after regeneration and prior to its use for cooling the enclosure. At t=18.6 hrs, the heating means of the reactors are disconnected from the mains.

(25) It can be seen in FIG. 2a that the setpoint temperature can be preserved even when a reactor is being regenerated. It will also be noted that the device can function autonomously, i.e. without regeneration of the reactors.

(26) The following Tables I and II show the results concerning the consumption and regeneration of gaseous ammonia in the systems of the device as a whole at the different times indicated in FIG. 2a. The number shown in each case indicates, at the instant t concerned, the percentage of ammonia gas contained in the system and therefore available for generating the heat and/or cold. At t=0 the cooling of the enclosure 5 is begun by opening the valve EV1. A switchover is then made from one totally used system to the other in order to maintain the setpoint temperature at 2 C. The reactors are heated to regenerate them only when the quantity of reagent they contain has been totally consumed in the exothermic reaction.

(27) TABLE-US-00001 TABLE I Time (h) 0 0.5 0.6 1.6 4.6 6.6 7.6 System 1 100 68.8 68.5 68.5 100 100 100 System 2 100 100 100 100 75.9 56.7 56.7 Total 200 168.8 168.5 168.5 175.9 156.7 156.7

(28) TABLE-US-00002 TABLE II Time (h) 10.6 12.6 13.6 16.6 18.6 35.6 Reservoir 1 75.9 56.7 56.7 100 100 100 Reservoir 2 100 100 100 75.9 56.7 0 Total 175.9 156.7 156.7 175.9 156.7 100

(29) It will be noted from the above results that with two systems in opposition cold can be produced continuously for as long as the heating means of the reactors are supplied with electricity. If the device is disconnected from said external source of energy, after the enclosure has been brought to temperature and after at least one regeneration of the first system used to bring it to temperature, the device contains at least 156.7% of gaseous ammonia still usable in autonomous mode, which corresponds to 50 hours of autonomous refrigeration.

(30) Operation according to the Method of the Invention

(31) FIG. 2b represents an operational diagram according to the method of the invention. The curves A to C represent the same elements as those explained with reference to FIG. 2a. As was previously explained, the regenerated reactor is used for cooling the enclosure before its temperature reaches ambient temperature. In the present case, the regenerated reactor is cooled to a temperature substantially equal to 70 C. before being used to cool the enclosure 5 via its evaporator and reservoir. The regeneration of the reactor of the system being used to maintain the temperature of the enclosure at the setpoint value is initiated as soon as the reactor of the other system is totally regenerated, and advantageously before its temperature reaches ambient temperature.

(32) In the following example, a quantity of ammonia is determined that is available for reacting in the reactor by measuring the pressure in the system concerned. It is known that when the pressure is maximal, the reactor is totally regenerated. The stopping of the regeneration phase of the reactor is triggered when the pressure in the system that includes the reactor concerned is substantially equal to Pmax. The regeneration phases last from 2.4 to 2.8 hours each depending on the quantity of reagent to be regenerated. The regeneration phases become shorter and shorter when the steps a and b are repeated.

(33) Tables III and IV below assemble the results obtained from a model of operation of the aforementioned device with the mode of operation according to the invention. The numbers also indicate the percentage of gaseous ammonia, as explained with reference to Tables I and II.

(34) TABLE-US-00003 TABLE III Time (h) 0 0.5 0.6 1.7 3.4 4.7 5.8 System 1 100 68.8 68.5 68.8 100 100 87.7 System 2 100 100 100 100 87.7 87.7 100 Total 200 168.8 168.5 164.3 187.7 187.7 187.7

(35) TABLE-US-00004 TABLE IV Time (h) 6.9 8.3 10.5 29.3 59.3 Reservoir 1 87.7 100 100 100 0 Reservoir 2 100 87.7 43.9 0 0 Total 187.7 187.7 143.9 100 06

(36) At t=8.3 hrs, the heating means are disconnected from the mains and the autonomous operation begins. In view of the aforementioned results, shown in Tables III and IV above, it will be seen that after having achieved a regeneration of the reactor of the first system that was used to bring the interior of the enclosure to the setpoint temperature, the device contains a minimum of 187.7% ammonia in the form of gas at any time. Thus, if the device is disconnected from the mains after said regeneration phase, an autonomy of 59.3 hours is achieved. The autonomy is therefore increased compared to the in opposition operation explained previously.