WO2001016535A1

WO2001016535A1 - Self-contained cooling device with enhanced characteristics

Info

Publication number: WO2001016535A1
Application number: PCT/US2000/023415
Authority: WO
Inventors: Matthew A. Keyser; Steven Burch; Ahmad Pesaran
Original assignee: International Thermal Packaging, Inc.
Priority date: 1999-08-27
Filing date: 2000-08-25
Publication date: 2001-03-08
Also published as: AU6938800A

Abstract

Disclosed is a self-contained multi-chamber cooling device (10) capable of storing evolved waste heat and a method for activating a desiccant (18) for use in a self-contained multi-chamber cooling device (10) having a desiccant chamber (16). The present invention includes an evaporation chamber (12), a desiccant chamber (16), and a valve (20). The evaporation chamber (12) contains a refrigerant liquid (14). The desiccant chamber (16) contains a desiccant (18) subjected to microwave irradiation such that the desiccant (18) is activated and capable of adsorbing the refrigerant liquid (14). The valve (20) prevents the flow of vaporized refrigerant liquid (14) between the evaporation chamber (12) and the desiccant chamber (16) until the valve (20) is opened.

Description

SELF-CONTAINED COOLING DEVICE WITH ENHANCED CHARACTERISTICS

1. Field of the Invention

The present invention relates to the chemical arts. The present invention relates to a method of pre-treating desiccant for use in multi-chamber cooling devices. In addition, the present invention relates to an improved method for assembling a self contained multi -chamber cooling device with a getter and a system which incorporates said getter.

2. Discussion of the Related Art

Multi-chamber cooling devices such as those disclosed in U.S. Pat. Nos. 5,197,302, 5,018,368, 4,911,740, 4,759,191 effectively transfer heat from a first evaporative chamber to a second desiccant chamber so as to thereby cool the evaporative chamber. In these types of cooling devices, the evaporative chamber contains a refrigerant liquid such as water and is separated by a valve from the desiccant chamber which contains a desiccant and is evacuated. When the valve is initially opened, the sudden drop in pressure in the evaporative chamber causes the refrigerant liquid inside to evaporate while removing heat from the surroundings. Simultaneously, refrigerant vapor is adsorbed and/ or absorbed by the desiccant causing further refrigerant liquid to vaporize until the desiccant material becomes saturated or substantially all of the refrigerant liquid has been collected by the desiccant. This endothermic reaction removes heat from the evaporative chamber resulting in the removal of heat from the surroundings of the evaporative chamber so as to cool any gas, liquid, and / or solid in contact. Multi-chamber cooling devices are being employed in beverage containers (e.g., beer cans and soda cans) to automatically cool beverages when opened and for medical applications to maintain medical supplies and / or human tissue at a desired temperature level in remote areas where refrigeration is not possible, and in everyday use when refrigeration is inconvenient. The use of such devices when fully mature will become widespread, requiring large amounts of activated desiccant for the desiccant chambers. Conventional methods of activating desiccants which require an unnecessarily long period of time and resources significantly add to the costs of each cooling device and conventional alternatives previously did not exist.

In multi -chamber cooling devices, it is essential that the desiccant chamber be properly evacuated to ensure that the liquid within the evaporative chamber vaporizes whereby the resulting endothermic reaction removes heat from the surroundings. Conventional methods of obtaining and maintaining a sufficient evacuation level required a hard vacuum with special handling to prevent loss of vacuum due to leaks within the desiccant chamber. Evacuating and sealing the desiccant chamber can be quite costly and is a major hurdle in the mass production of inexpensive miniaturized self-contained cooling devices.

It should therefore be appreciated that due to the critical nature of desiccant in the multi- chamber cooling device industry, that there remains a need for an effective, less time consuming system and method for activating desiccant prior to or simultaneous to its introduction to a desiccant chamber. It should also be appreciated that there remains a need for an effective method for evacuating the desiccant with reduced costs.

SUMMARY OF THE INVENTION

The present invention is embodied in a self contained multi-chamber cooling device capable of storing evolved waste heat, comprising an evaporation chamber containing a refrigerant liquid, a desiccant chamber containing a desiccant subjected to microwave irradiation such that the desiccant is activated and capable of adsorbing the refrigerant liquid, and a valve for preventing flow of vaporized refrigerant liquid between the evaporation chamber and the desiccant chamber until it is opened. The microwave irradiation of the desiccant acts to substantially evaporate moisture from the pores of the desiccant and further acts to remove non-condensable gases from the pores. Desiccant is subject to microwave frequencies in the range of 850 - 2500 MHz, with particular emphasis on 915 MHz and 2450 MHz for several minutes for sufficient activation to occur.

In an exemplary method for preparing a desiccant for use in a multi-chamber cooling device with a desiccant chamber, the desiccant is subjected to microwave irradiation and then placed in the desiccant chamber. The desiccant chamber is then sealed and evacuated. In an exemplary manufacturing process for activating desiccant for use in a multi- chamber cooling device having an evaporative chamber and a desiccant chamber, desiccant is placed on a moving conveyor belt capable of agitating the desiccant while thereupon to ensure uniform exposure to microwave irradiation before it is placed within the desiccant chamber. The desiccant chamber is then sealed and evacuated. In a second exemplary embodiment, a getter is added to the desiccant chamber of the multi-chamber cooling device. After the desiccant chamber is sealed, heat is applied to the getter to sublimate to cause a vacuum while removing non-condensable gases from the desiccant chamber. This increased vacuum greatly facilitates the two-chamber endothermic reaction described above by ensuring a proper vacuum level and by removing non-condensable gases which would otherwise be absorbed or adsorbed by the desiccant.

Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawing, which illustrates, by way of example, the principles of the invention.

DESCRIPTION OF THE DRAWING FIG. 1 illustrates a two-chamber cooling device within a beverage can with desiccant activated by microwave irradiation and a getter both within the desiccant chamber further including a valve between the two chambers wherein the valve automatically opens upon the release of pressure within the beverage can.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

To illustrate the system and method in accordance with the invention, the first exemplary embodiment primarily concentrates on the preparation of desiccant for use in a self- contained multi -chamber cooling device. It should be readily apparent to the skilled artisan that this description, with little modification might also be applied to other systems or processes wherein activated desiccant is employed.

Referring to FIG. 1, the invention is directed to a two chamber cooling device 10 with an evaporative chamber 12 containing a refrigerant liquid 14 (e.g. , water) and an inner desiccant chamber 16 containing a desiccant 18. The inner desiccant chamber is evacuated to at least 10^"3 torr to ensure that a sufficient amount of refrigerant liquid is vaporized. A valve 20 separates the two chambers and operates to permit and prevent communication between the two chambers depending on its polarity (open/closed). When the valve is first opened, and communication between the chambers is initially established, a sudden drop in pressure in the evaporative chamber (which is evacuated to the vapor pressure of the refrigerant liquid) causes the refrigerant liquid inside to evaporate. Refrigerant vapor is adsorbed by the desiccant causing further refrigerant liquid to vaporize. The liquid-to-gas phase change of the refrigerant liquid vaporization can only occur if the liquid loses heat equal to the latent heat of evaporation of the liquid. Such a removal of heat acts to cool the evaporative chamber and depending on the heat transfer qualities of the evaporative chamber, the heat removal also cools the nearby environment. It is often desirable for the refrigerant liquid 14 in the evaporative chamber 12 to be mixed with a miscible nucleating agent having a greater vapor pressure than the liquid to promote ebullition so that the liquid evaporates rapidly and uniformly and so that supercooling of the refrigerant liquid does not occur. Suitable nucleating agents include isobutyl alcohol, ethyl alcohol, acetone, propyl alcohol and methyl alcohol, all of which are miscible with water. The assembly of the desiccant chamber 16 for use in the above described two chamber cooling device 10 requires that the desiccant 18 is sufficiently activated prior to the sealing of the desiccant chamber. A large quantity of desiccant may be subjected to microwave radiation in the frequency range of 850 - 2500 MHz, with particular emphasis on 915 MHz and 2450 MHz which correspond to industry standard microwave tube frequencies. A skilled artisan may adjust the microwave frequency accordingly to maximize the molecular resonance, and thus the rate of evaporation for the specific refrigerant liquid 14 utilized.

In an exemplary mass production embodiment (not shown in FIG. 1), an agitating conveyor belt tilted downwards moves desiccant 18 placed thereupon through a microwave while being shaken. The shaking of the desiccant provides more uniform desiccant exposure to the microwave radiation as compared to the prior art baking process. The exposure time to the microwave is several minutes. The conveyor belt ends above a sifter that sifts and divides the desiccant into predetermined amounts into a plurality of unassembled desiccant chambers 16 placed underneath. Once the desired amount of desiccant is placed within the unassembled desiccant chamber, the chamber is thereby evacuated to 10^"3 torr and sealed. Optionally, the desiccant chamber may have a plug allowing it to be evacuated subsequent to its sealing. Alternatively if the desiccant chamber is glass or the desiccant chamber is made from a metal and has a inert gas, such as argon, surrounding it, the desiccant chamber may be sealed, evacuated and then subjected to the microwave irradiation. Once the desiccant 18 is activated, it is important that it not be exposed to air which acts to undo most if not all of the activation. During the microwave process, the desiccant is heated as are the non-condensable gases within air such as N, CO₂, SO₂, S0₃, and ozone on the surface of the desiccant. Once the desiccant is placed under vacuum, the excess moisture and the non- condensable gases are removed from the desiccant permitting enhanced adsorption characteristics. Re-exposure to air, even very dry air, acts to re-deposit the non-condensable gases in and on the desiccant. Non-condensable gas deposited on the desiccant acts to prevent refrigerant vapor from entering moisture adsorption pores, thereby reducing the effectiveness of the moisture adsorption ability when the evaporative and desiccant chambers 12 and 16 are in communication. Subsequent evacuation of the desiccant chamber further removes the non- condensable gases and moisture from the desiccant.

Any suitable molecular sieve zeolite may be used in this invention. Molecular sieve materials are crystalline, hydrated metal aluminosilicates which are either made man-made or made from naturally occurring minerals. Molecular sieve zeolites contain in each crystal, interconnecting cavities of uniform size, separated by narrower openings, or pores, of equal uniformity. When initially formed, this crystalline network is full of water. Moderate heating acts to drive the moisture from the cavities without changing the crystalline structure. This phenomenon permits the cavities with their combined surface area and available pore volume to adsorb water or other materials. The process of evacuation and refilling the cavities may be repeated indefinitely under favorable conditions if desired with the particular multi-chamber cooling device employed.

Molecular sieves are preferred because they typically provide uniform sized pores of the crystalline network rather than of varied dimensions, as is the case with other adsorbents. With the large surface area and pore volume, molecular sieves can make separations of molecules, utilizing pore uniformity, to differentiate on the basis of molecular size and configuration. For this reason, the preferred molecular sieve zeolite has a pore size of approximately 10 A. A larger pore size is preferred because it permits greater numbers of refrigerant liquid molecules to be adsorbed by an individual pore before it is clogged and can no longer accept further molecules. The larger pore sizes also allow for the adsorption of any nucleating agent such as alcohol added for quicker liquid evaporation.

Desiccants 18 other than zeolites are suitable for the above identified applications so long as they are able to absorb or adsorb all the vapor produced by the refrigerant liquid 14, while complying with all applicable government safety standards for use in an environment. Suitable alternative desiccants include but are not limited to: barium oxide, magnesium perchlorate, calcium sulfate, calcium oxide, activated carbon, calcium chloride, glycerine silica gel, alumina gel, calcium hydride, phosphoric anhydride, phosphoric acid, potassium hydroxide, and sodium sulfate.

Referring again to FIG. 1, in a second exemplary embodiment utilizing a two chamber cooling device 10 similar to those described above, where the cooling device is made up of an evaporative chamber 12 with a refrigerant liquid 14 and an inner desiccant chamber 16 which needs to be evacuated to a vacuum of 10^"3 torr for the cooling device to properly operate. The addition of a getter 22 (as used in the vacuuming of vacuum tubes) can readily create a hard vacuum in the desired range within the desiccant chamber without the use of expensive packaging and manufacturing techniques.

There are two types of getters 22, evaporative and non-evaporative. For use in the second exemplary embodiment, the ideal evaporative getter is titanium which is typically available in cylindrical form. Non-evaporative getters may also be employed. Preferred non- evaporative getters include gadalinium, zirconia aluminum, zirconia vercadium iron, gadalinium-magnesium or more specifically, SD707 offered by the SAES company which comes in a powdered formation.

For a getter 22 to be activated, it is necessary to heat it. For an evaporative getter, a NiChrome wire 24 is grounded to the outside of the desiccant chamber 16 with a titanium getter mounted on the resistive element of the wire. An insulated plug in the desiccant chamber allows for a positive voltage source to be applied to the wire resulting in the heating of the resistive element and thus the titanium to an upwards of 500-600°C. When heated, the outer layers of the titanium sublimate allowing for increased absorption of non-condensable gasses by the getter until the pressure within the desiccant chamber is reduced below the desired level. Optionally, a plurality of filters may be placed in the lower half of the desiccant chamber above the NiChrome wire / getter combination such that when the titanium sublimates, it does not deposit particles on the desiccant. Radiation shields may also be employed to minimize the heat transfer caused by the activation of the NiChrome wire to prevent the evaporation of the refrigerant liquid 14 (which is likely going to be water).

For a non-evaporative getter 22 to be activated, the entire desiccant chamber 16 may be heated until the getter is activated. The heating of the entire chamber also acts to heat the desiccant 18 so as to further remove the non-condensable gasses from the desiccant. This arrangement is preferred because of the dual improvements of increased desiccant absorption ability once the two chambers 12 and 16 are in communication, and the less complicated packaging and manufacturing required for the production of the desiccant chamber. In the alternative, a perforated chamber containing the non-evaporative getter may be placed on a NiChrome wire 24 such that when a current is run across the wire, it heats up the resistive element of the wire resulting in the contents of the coupled chamber being heated thereby activating the getter. Although some of the above-described getters can create a vacuum level sufficiently low for the cooling reaction to take place without the need for additional vacuuming, it is preferred to include an additional vacuum source when sealing the desiccant chamber. While a particular form of the invention has been illustrated and described, it will be apparent that various modifications can be made without departing from the scope and spirit of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.

Claims

1. A self contained multi-chamber cooling device capable of storing evolved waste heat, comprising: an evaporation chamber containing a refrigerant liquid; a desiccant chamber containing a desiccant subjected to microwave irradiation such that the desiccant is activated and capable of adsorbing said liquid; and a valve for preventing flow of vaporized refrigerant liquid between said evaporation chamber and said desiccant chamber until said valve is opened.

2. The self contained multi-chamber cooling device of claim 1 wherein said desiccant is subjected to microwave irradiation in the frequency range of 850 - 2500 MHz.

3. The self contained multi -chamber cooling device of claim 1 wherein said desiccant is subjected to microwave irradiation at the frequency of approximately 915 MHz.

4. The self contained multi-chamber cooling device of claim 1 wherein said desiccant is subjected to microwave irradiation at the frequency of approximately 2500 MHz.

5. A method for activating a desiccant for use in a self contained multi-chamber cooling device having a desiccant chamber comprising the steps of: subjecting the desiccant to microwave irradiation; and placing the desiccant in the desiccant chamber.

6. The method for activating a desiccant for use in a self contained multi -chamber cooling device of claim 5 wherein said desiccant is subjected to microwave irradiation in the frequency range of 850 - 2500 MHz.

7. The method for activating a desiccant for use in a self contained multi-chamber cooling device of claim 5 wherein said desiccant is subjected to microwave irradiation at the frequency of approximately 915 MHz.

8. The method for activating a desiccant for use in a self contained multi-chamber cooling device of claim 5 wherein said desiccant is subjected to microwave irradiation at the frequency of approximately 2500 MHz.

9. A method for activating a desiccant for use in a self contained multi-chamber cooling device having a desiccant chamber comprising the steps of: placing the desiccant on a moving conveyor belt; agitating the desiccant while on the moving conveyor belt; subjecting the desiccant to microwave irradiation; and placing the desiccant in the desiccant chamber.

10. The method for activating a desiccant for use in a self contained multi -chamber cooling device of claim 9 wherein said desiccant is subjected to microwave irradiation in the frequency range of 850 - 2500 MHz.

11. The method for activating a desiccant for use in a self contained multi-chamber cooling device of claim 9 wherein said desiccant is subjected to microwave irradiation at the frequency of approximately 915 MHz.

12. The method for activating a desiccant for use in a self contained multi-chamber cooling device of claim 9 wherein said desiccant is subjected to microwave irradiation at the frequency of approximately 2500 MHz.