COOLING METHOD

Abstract: A method for cooling a material in contact with a cooling medium comprises evaporating water contained in the cooling medium and adsorbing the evaporated water to soft burnt lime and causing the evaporation and the adsorption to be carried out under a reduced pressure to cool the material. An apparatus for carrying out the method is provided.

Description: BACKGROUND OF THE INVENTION (1) FIELD OF THE INVENTION The present invention relates to a cooling method and in particular to a simple cooling method in which soft burnt lime is used as an adsorbent. (2) DESCRIPTION OF THE PRIOR ART Hitherto, there has been known a cooling method by means of a heat pump in which an adsorbent is used. For example, a cooling method in which zeolite is used as such an adsorbent is known in the field of air conditioning and refrigeration. However, the adsorptivity of zeolite is not so high in the low vapour pressure region (eg., 5% by weight at 133.3 N/m² (1 mmHg) and 100 o C) and, therefore there is a problem that a relatively large amount of zeolite is required for cooling a unit weight of a specific material to be cooled. In addition, there is another problem that the adsorptivity of zeolite is remarkably reduced due to the generation of heat accompanied by the adsorption of water. In US-A-3 642 059 an apparatus is disclosed having an evaporation chamber and an absorption chamber in separable interconnection. Cooling of a material can be effected by the latent heat produced when a vaporizable liquid is vaporized in the evaporation chamber and heating of a material can be effected by the heat of absorption produced when this liquid is absorbed by a vapor-absorptive chemical in the absorption chamber. In DE-A-29 39 423 a heating plant having an absorber heat pump and a method for running the heating plant are disclosed. The heating plant comprises a working medium circuit including a heat reservoir with an absorbent. The absorbent serves for storing the working energy of the heat pump. SUMMARY OF THE INVENTION An object of the present invention is to provide a cooling method using an improved adsorbent adsorbing a large amount of water per unit weight thereof. Another object of the present invention is to provide a cooling method using an improved adsorbent which keeps a desired adsorptivity irrespective to the generation of heat accompanied by the adsorption of water. A further object of the present invention is to provide a cooling apparatus applying the cooling method using the improved adsorbent. The inventors of the present invention found an adsorbent which makes it possible to eliminate the aforementioned problems associated with zeolite used as the adsorbent for a chemical heat pump, adsorb a large amount of water per unit weight thereof, and maintain a desired adsorptivity irrespective of the generation of heat accompanied by the adsorption of water, and thus completed the present invention. Accordingly, the present invention relates to a method for cooling a material which contacts with a cooling medium which comprises evaporating water contained in the cooling medium and adsorbing the evaporated water to soft burnt lime and causing the evaporation and the adsorption to be carried out under a reduced pressure to cool the material. Further, the present invention relates to an apparatus for cooling a material which comprises an adsorption chamber and an evaporation chamber, the adsorption chamber and the evaporation chamber being separated by a partition having at least one valve, the evaporation chamber containing a container accommodating a material to be cooled, the container being surrounded with a cooling medium containing substance, the adsorption chamber containing soft burnt lime as an adsorbent and the pressure of the adsorption chamber and the evaporation chamber being reduced. Figures 1 and 2 are schematic diagrams for illustrating the apparatus employed to carry out the method of this invention. Figure 3 is a sectional view of an embodiment of the apparatus for carrying out the method of the present invention. Figures 4 and 5 are sectional views of the apparatus shown in Figure 3 taken along the line A - A. DETAILED DESCRIPTION OF THE INVENTION The present invention will hereunder be explained in more detail. In the present invention, soft burnt lime is used as the adsorbent. The soft burnt lime is also referred to as lightburnt lime and is generally prepared by calcining limestone at a temperature of about 800 to 1100 o C, preferably about 850 to 1050 o C under atmospheric pressure. The soft burnt lime is porous since it has a volume approximately equal to that of the smarting limestone and CO₂ is released from the starting limestone during calcination. In other words, the resultant CaO is in fine crystalline state, has a large void volume and a low bulk density and is highly reactive. In this connection, the method of preparing a soft burnt lime is not restricted to any specific one in the present invention. Therefore, the soft burnt lime as used herein also includes CaO obtained by decomposition of CaCO₃ or Ca(OH)₂ at a temperature of about 300 to 800 o C, preferably about 300 to 500 o C under a reduced pressure, in vacuo or in the presence of a carrier gas such as N₂ gas. For example, CaO with a large specific surface area, which is called reactive powder, disclosed in the paper of ARAI et al., Gypsum & Lime, 1982, No. 178, pp. 31-40 may also be used in the present invention. Such CaO is preferred since it has a large specific surface area, is highly reactive and has a highly improved cooling capacity per unit weight thereof. In the present invention, the soft burnt lime is distinguished from hard burnt lime which is produced by calcining at a high temperature of not less than about 1200°C and has a low specific surface area and a low reactivity. In the present invention, any cooling mediums may be used so far as it contains water. Examples thereof include water per se and brines such as aqueous solutions of sodium chloride and calcium chloride. The method according to the present invention can be carried out as follows: For instance, the method of the present invention can be carried out utilizing the apparatus illustrated schematically in Fig. 1. The apparatus shown in Fig. 1 comprises: an adsorption chamber 1 containing soft burnt lime as the adsorbent; an evaporation chamber 2 which contains a cooling medium and a material to be cooled; a vacuum pump 3 for reducing the pressure of the adsorption chamber 1 and the evaporation chamber 2; a path 4 for communicating the vacuum pump 3 with the adsorption chamber 1 and the evaporation chamber 2; and valves 5, 6 and 7 mounted on the path 4. First of all, the pump is started and the valves 5 and 7 are opened while the valve 6 is closed to reduce the pressure in the adsorption chamber 1. After the pressure in the adsorption chamber 1 is reduced to a desired value, the valve 5 is closed and the valve 6 is opened to reduce the pressure in the evaporation chamber 2. Thus, the pressure in the evaporation chamber 2 is reduced to a desired value. Then, the valve 7 is closed and the valve 5 is opened to communicate the adsorption chamber 1 with the evaporation chamber 2 through the path 4. In the evaporation chamber 2, water included in the cooling medium evaporates while absorbing sensible heat from the material to be cooled, the evaporated water arrives at the adsorption chamber 1 through the path 4 and is adsorbed to the soft burnt lime. The material is cooled by maintaining the system under such condition for a desired period of time. In the method of the present invention, it is preferred to reduce the pressure in the adsorption chamber 1 and the evaporation chamber 2 down to 13.3 to 3999 N/m² (0.1 to 30 torr), preferably 66.7 to 1333 N/m² (0.5 to 10 torr). The method of the present invention may be carried out according to various other manner than that using the apparatus shown in Fig. 1. For example, as shown in Fig. 2, an integral container is divided into two compartments by a partition 9, one of which serves as an adsorption chamber 1 and the other of which serves as an evaporation chamber 2. Furthermore, the partitioning 9 is provided with a valve 8. Within such a container, each of the soft burnt lime as the adsorbent, and a cooling medium and a material to be cooled are previously charged in the adsorption chamber 1 and the evaporation chamber 2, respectively. The container is sealed while reducing the pressure therein, and the valve 8 is then opened to cool the material as in the case explained above. In the present invention, the soft burnt lime contained in the adsorption chamber may be agglomerated (or granulated) or may be formed into a desired shape. Powdered form thereof may also be used without causing any troubles. Moreover, if the soft burnt lime is wrapped up in cloth or wire gauze to form a sheet having a thickness of 2 to 20 mm, preferably 5 to 10 mm, the soft burnt lime becomes very easy to handle and a proper diffusion of water vapour therein can be established. In addition, the cooling medium may be in the form of liquid per se or may be absorbed on a substance having appropriate water absorption properties. Examples of such substance having water retention characteristics include polymers (polyelectrolyte hydrogel) having water absorption properties. When the cooling medium is used in the form of liquid per se, the contact between the cooling medium and the material to be cooled is assured by charging the cooling medium around the material to be cooled. On the other hand, when the cooling medium is used in the state absorbed on a polymer having water absorption properties, the contact between the cooling medium and the material to be cooled is assured by winding the polymer round the material to be cooled or round a container containing the material. According to the method of this invention, a large amount of material can be cooled with a relatively small amount of the adsorbent. Therefore, it is useful as a cooling system to be attached to containers for beer, wine, juice, cooling beverages and the like. Moreover, portable refrigerators may be realized by making use of the method according to the present invention. Example The present invention will hereunder be explained in more detail with respect to the following examples. This example was carried out by employing the apparatus shown in Fig. 3. Fig. 3 shows a sectional view of an apparatus of a cylindrical shape. A material 12 to be cooled is charged in a container 11 (a single-walled can) for receiving the material, the outside of which is wound with cloth or sheet impregnated with a cooling medium such as water or brine and the space 14 (within a double-walled can) is in the condition of saturated vapour pressure. An adsorption chamber 17 (a triple-walled can) contains soft burnt lime. The soft burnt lime is wrapped up in cloth or wire gauze of fine mesh in order to be formed into a thin layer having a thickness of 5 to 20 mm and the thin layer has a plate-like or spiral shape (see Figs. 4 and 5). The cloth or the wire gauze plays an important role in preventing consolidation of the soft burnt lime as well as in promoting the diffusion of vapour therein. The single-walled can 11, the double-walled can 14 and the triple-walled can 17 are independent systems. The single-walled can 11 is under ordinary temperature and pressure conditions, the double-walled can 14 is in the state of ordinary temperature and vapour pressure of the cooling medium, and the triple-walled can 17 is in the state of ordinary temperature and a reduced pressure condition. The double-walled can 14 and the triple-walled can 17 are separated by a partition 19 with a valve 8, however, these cans can be communicated with one another by pulling a wire 20 through a rubber plug 21 to open a valve 8 at the time of application. A packing 15 is disposed to make more difficult the transfer of heat generated by the soft burnt lime from the triple-walled can to the single-walled and double-walled cans. The double-walled can (the space 14) is in the condition of a reduced pressure during use and there is almost no air in the space. Therefore, heat transfer from the space to the single-walled can 11 due to the convection is prevented. When the wire 20 is externally pulled upon cooling, the valve 8 on the partition 19 is opened, the water vapour in the double-walled can flows into the triple-walled can and the vapour reacts with the adsorbent contained therein. CaO + H₂O = Ca(OH)₂ + 63 639 J (15200 cal) At the same time, the double-walled can 14 is in the state of a reduced pressure, the evaporation of the cooling medium commences at the surface of the cloth or the sheet 13 and the cloth or the sheet per se is cooled. When the cloth or the sheet 13 is cooled, the single-walled can and then the material 12 to be cooled are in turn cooled. Thus, the cooling of the material to be cooled 12 is commenced by pulling the wire 20 externally and is continued till adsorption equilibrium is established between the soft burnt lime and the cooling medium and thus there is no longer observed any transfer of the vapour therebetween. The temperature of the soft burnt lime is raised up to 200 to 300 o C due to the heat of reaction during use. However, the capacity of adsorption thereof remains unchanged up to the decomposition temperature of the products (decomposition temperature of Ca(OH)₂ is 450 o C), which is different from the case of physical adsorption. In addition, in order to protect the user from burns, a heat reflection plate 22 may be placed on the internal wall of the triple-walled can. The method of the present invention was carried out utilizing a can commercially available (diameter = 53 mm; height = 88 mm) containing 165 g of juice as the single-walled can, cans for fruit (diameter = 84 mm; height = 115 mm) as the double-walled and the triple-walled cans respectively. The can 11 has a frusto-conical shape. The can defining the space 14 has a cylindrical shape, surrounding the can 11, whereby the space 14 partly surrounding the can 11 and partly on top of the can 11 is formed. The can defining the chamber 17 has a cylindrical shape and is arranged on top of the can defining the space 14. (Advantages of the Invention) According to the method of the present invention, a large amount of material can be cooled by using a relatively small amount of adsorbent since soft burnt lime is used as the adsorbent.

Claims: A method for cooling a material which contacts with a cooling medium which comprises evaporating water contained in the cooling medium and adsorbing the evaporated water to soft burnt lime and causing the evaporation and the adsorption to be carried out under a reduced pressure to cool the material. A method according to claim 1 wherein the evaporation and the adsorption is carried out under a reduced pressure of from 13.3 to 3999 N/m² (0.1 to 30 torr). A method according to claim 1 wherein the evaporation and the adsorption are carried out under a reduced pressure of from 66.7 to 2666 N/m² (0.5 to 20 torr). A method according to any one of claims 1 to 3 wherein the cooling medium is water or brine. A method according to any one of claims 1 to 4 wherein the cooling medium is absorbed on a substance having appropriate water absorption properties. A method according to claim 5 wherein the substance is a water absorbable polymer. A method according to any one of claims 1 to 6 wherein the soft burnt lime is obtained by calcining limestone at from 800 to 1100 o C. A method according to claim 7 wherein the soft burnt lime is obtained by calcining limestone at from 850 to 1050 o C. A method according to any one of claims 1 to 6 wherein the soft burnt lime is obtained by calcining slaked lime at from 500 to 800 o C. An apparatus for cooling a material which comprises an adsorption chamber and an evaporation chamber, the adsorption chamber and the evaporation chamber being separated by a partition having at least one valve, the evaporation chamber containing a container accommodating a material to be cooled, the container being surrounded with a cooling medium containing substance, the adsorption chamber containing soft burnt lime as an adsorbent and the pressure of the adsorption chamber and the evaporation chamber being reduced. An apparatus according to claim 10 wherein the pressure of the adsorption chamber and the evaporation chamber is 13.3 to 3999 N/m² (0.1 to 30 torr). An apparatus according to claim 10 wherein the pressure of the adsorption chamber and the evaporation chamber is 66.7 to 2666 N/m² (0.5 to 20 torr). An apparatus according to claim 10 wherein the cooling medium is water or brine. An apparatus according to any one of claims 10 to 13 wherein the cooling medium containing substance is in the form of cloth or sheet. An apparatus according to any one of claims 10 to 14 wherein the substance has appropriate water absorption properties. An apparatus according to claim 14 wherein the substance is a water adsorbable polymer impregnated with the cooling medium. An apparatus according to any one of claims 10 to 16 wherein the soft burnt lime is obtained by calcining limestone at from 800 to 1100 o C. An apparatus according to claim 17 wherein the soft burnt lime is obtained by calcining limestone at from 850 to 1050°.

Inventors: HEIMA, HARUO
Applicants: SHINAGAWA FUEL CO., LTD.
Application year: 1987
Main classification: C09K5
IPC codes: C09K5, F25D7, F25B17