US3041851A - Refrigeration - Google Patents

Description

July 3, 1962 R. N. STENERSON REFRIGERATION Filed April 25, 1960 VIIIIIIIIIIIIIIIIIIIIIIIIIAVI INVENTOR. RANDOLPH N. STENERSON BY ATTORNEY ing.

long flexible conduits would have 3,041,851 REFRIGERATHQN Randolph N. Stenerson, East Syracuse,'N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Apr. 25, 1%0, Ser. No. 24,313 3 Claims. (Cl. 62-304) This invention relates to a refrigerated article and a method of refrigeration. More particularly, this invention relates to the refrigeration of metal bodies without the use of conventional compressors and heat exchange devices by the improved utilization of evaporative cool- The refrigeration of a small article is conventionally accomplished by constructing a mechanical refrigeration system, a heat absorbing element of which is placed in heat exchange relation With the article to be refrigerated. Such systems are generally satisfactory and economically feasible only where Weight and space considerations permit their use. Frequently, however, these considerations militate against the use of a conventional mechanical refrigeration system especially where the body to be cooled United States Patent is small in size or the additional space avail-able for the refrigeration apparatus is limited.

In addition, a conventional mechanical refrigeration system is required to have a mechanical or electrical power input. However, situations are encountered where a convenient power source is either lacking or the use of a cooling system requiring substantial apparatus in connection with it or a substantial power input to operate it also militates against the feasibility of utilizing conventional refrigeration. The use of a mechanical refrigeration system may also be impractical because the smallest system which it is feasible to make frequently has a minimum capacity far in excess of the cooling requirement of the body to be cooled. This is particularly true in the case of cooling small metal objects, such as the substage of a biological microscope or the jumper of a thermoelectric element, where the cooling required may be small or the requirement for cooling intermittent rendering the use of conventional refrigeration uneconomical and impractical.

Furthermore, practical utilization of typical external mechanical refrigeration systems to cool such bodies frequently requires substantial and expensive design changes in the construction of the body itself for the purpose of accommodating heat exchange tubes. Alternatively, a cooled heat exchange medium may be flowed over the surface'of the body but under some circumstances this is undesirable and frequently the heat transfer whichis obtainable by this method is poor. Also,- it may be very difficult to obtain satisfactory refrigeration by conventional means of an irregularly shaped or inaccessibly placed body because of the necessity of uniformly supplying heat exchange medium to an irregular surface of the body. Furthermore, if the body need be portable, either the entire refrigeration system must be can-led with it or to be attached to it. It is well known that-a substantial amount of heat is required to vaporize a liquid.- This principle, which is referred to as evaporative coolin is often used to remove In addition, if' the ambient COIldlllOIlS are such that the liquid on the surface of a body boils, then the rateof heat transfer can be very great. Furthermore,'a fairly connice stant temperature may be maintained by means-of evaporative cooling because the rate liquid from the surface of a body is evaporated will depend on the heat added to the body. However, this principle has serious drawbacks in practical application because of the necessity of continuously replenishing the liquid supply. In addition, if any substantial quantityof liquid exists on the surface of the body, the thickness of the iiquid itself tends to insulate the body and retain the heat therein. On the other hand, if the film of liquid on the body surface is thin so portable metal bodies, spray system to provide evaporative would be prohibitive. In addition, a

V evaporation can surface of the body and it will be ima uniform distribution of liquid on the surface which is to be cooled. Since any liquid has a certain tension, the liquid even when body in the form of a finely divided spray tends to coalesce consequently, no evaporative cooling will take place in these regions. It is, conseq'uently, diificult but highly desirable to maintain a uniformly thin film of liquid over the entire surface of the body to be ev-aporatively cooled for eificient heat transfer.

Accordingly, it is an object of this inventionto provide an improved metal body which-is especially adapted to being evaporatively cooled.

It is a further object of this invention to provide an improved method for heat is conducted liquid through capillary action. The body is then located in a suitable ambient atmosphere which is unsaturate with respect to the vapor of the liquid. Under these conditions, a thin film of the liquid is continuously supplied to the surface of the body from its pores through the surface interstices by capillary action. The thin film of liquid continuously evaporates by absorbing heat from the body and since the body is metallic in composition, from the interior ofthe body to its surface and the body itself may beefiectively cooled by this method for a substantial period of time.

The method and construction of a preferred embodiment of this invention will be apparent from the following specification having reference to the attached drawing wherein:

FIGURE 1 is an elevational view, partly cut away, of a body made in accordance with this invention;

FIGURE 2 is a cross-sectional view illustrating the compacting step of the described method; and FIGURE 3 is a cross-sectional view illustrating the impregnating step.

Referring to the drawing, there is shown a metal article or body which is adapted to be refrigerated. Body 10 is characterized by having a large number of internal communicating pores or voids throughout at least a portion of its interior. At at least one surface 16 of the body, these pores form interstices. The pores and interstices are preferably of minute or capillary size so that a liquid in contact with the surface is drawn into the interior of the body by capillary action. If the use to which the body is to be put permits it, it is desirable that all of its surfaces have interstices therein, but it will be appreciated that if only one surface need be cooled or if only one surface will be exposed to ambient atmosphere, that this surface alone may contain interstices. The voids should preferably occupy a substantial portion of the volume of the body for a reason which will become apparent.

Body 10 is conveniently made by compacting powdered metal into a relatively homogeneous mass having a large number of minute internal pores. For effective cooling of the body, it is desirable that the metal powder be copper, aluminum or some other metal having relatively high thermal conductivity. It will be appreciated that various electrical and chemical processes are feasible for manufacture of metal powders; for example, powder 14 may be made by electrolytic decomposi fon of a metal salt. Such processes are well known in the metallurgical arts and need not further be described. The process which is used to form the metal powder will to some extent determine the nature of the powder. For example, ball milling may produce chunky particles which may be in the form of generally spherical balls. On the other hand, electrolytic deposition may form dendritic crystals of the metal which are especially desirable for the purposes of this invention. Dendritic crystals characteristically are long needle or pine tree shaped particles which compact into a relatively solid mass upon the application of reasonably low pressures. A body formed by compacting dendritic metal crystals is highly desirable for the purposes of this invention because of the very large number of minute internal voids or pores which are characteristic of such compacts. Such compacts readily absorb liquids due to capillary action and at the same time hold substantial quantities of the liquid within the compacted metal body. However, other forms of crystalline metal powders may be used to make a body in accordance with this invention.

Mold 11 is formed with an open cavity having the desired shape of the finished article and may be inserted in the base of a hydraulic press 13. It will be understood that the shape of article 10 may be irregular if desired. A ram 12 having an appropriately shaped face is depressed by the action of a hydraulic piston into the cavity of mold 11 for the purpose of apply pressure to the powder 14 therein. It is desirable to use no more pressure in compacting powder 14 than is necessary to provide a body of the desired rigidity so as not to seal off or eliminate the pores within the body by overcompacting the metal powder. It will be understood that the precise pressure to be applied will depend upon the crystalline nature of the powder being compacted and upon the material of which the powder is made. By way of example, dendritic crystals of electrolytically deposited copper may be compacted into a suitable rigid body by a pressure of approximately 800 p.s.i.

It will also be understood that other processes than the one described may be used for compacting powder 14. For example, powder 14 may be sintered to form a relatively rigid body 10. However, care must be exercised to insure that the process used is controlled so that compacting or fusing of the particles of metal powder is stopped before the internal voids in the material are eliminated or sealed, the crystals fusing or coalescing so that they no longer communicate with a surface of the body. Unless the voids communicate with the surface of body 10, the body will be unable to hold sufficient liquid to be useful for the purposes of this invention.

After body 10 has been properly compacted so that the minute voids are homogeneously distributed throughout at least a portion of its interior and in communication with interstices in at least one of its surfaces, the body is impregnated with a volatile refrigerant liquid. The particular liquid which is selected by impregnation into body 10' will be determined by the ambient atmosphere which will surround the body during its use. The liquid should have sufficient vapor pressure so that it evaporates or boils rapidly enough to remove the desired amount of heat from the body. On the other hand, the refrigerant vapor pressure should not be so high as to entirely boil or evaporate from the body too quickly to maintain the desired temperature for the desired period of time. Also the refrigerant should be one which is not present to such an extent in the ambient atmosphere in which the body is to be placed to inhibit a satisfactory rate of vaporization from the surface of the body. For example, if the body is impregnated with Freon ll (trichloromonofiuoromethane), the body would not be suitable for use in a saturated ambient atmosphere of Freon 11, but would be generally satisfactory for use in normal room air containing little, if any, Freon 11.

Any suitable refrigerant liquid including water having the desired evaporation or boiling characteristics may, of course, be used to impregnate the body and the liquids suitable for this use are not limited to those which are customarily referred to as refrigerants in a mechanical system. Precautions must be taken, however, to insure that the particular refrigerant liquid employed does not carry in it sufficient impurities to clog the pores or interstices of the body and the liquid must be noncorrosive when used with the particular metal of which the body is formed.

Impregnation of the body is conveniently performed by taking advantage of the minute size of the pores therein and utilizing them to attract the refrigerant by capillary action. FIGURE 3 shows a vessel 15 partially filled with liquid 17 into which body 10 has been placed. By this means, surface 16 of body 10 have interstices therein in communication with the internal pores of the body, is placed in contact with liquid 17 and, as shown, may be spaced from the bottom of vessel 15 during this step. Consequently, liquid 17 is drawn into the pores of body 10 where it is held for a period of time after the body is removed from vessel 15.

Body 10 is then placed in ambient atmosphere which is nonsatuarted with respect to the vapor of liquid 17 with which it has been impregnated. As the thin film of liquid which will adhere to surface 16 is vaporized therefrom, additional liquid will be fed to the surface of the body by capillary action from the internal pores of the body through the surface interstices to replenish thesurface film. Consequently, the vaporization process may continue for several hours depending on the capacity of the internal pores or voids and the ambient conditions before the supply of liquid in the pores of body isexhausted. When the supply of liquid Within the pores is exhausted It will be noted that at no time during the vaporization process is there an excess of accumulated liquid on the surface of the body and consequently, the heat transfer external apparatus.

Numerous applications of this invention will occur to those skilled in the art. For example, by this means it surface without the inclusion of external fins or other heat Consequently, 'body 10 may comprise the jumper of a thermoelectric device or other heat a porous refrigerantimpregnated heat conducting section between the handle and end of the tool. As the refrigerant vaporizes from the porous section, it Will carry away I claim:

1. A metal structure adapted to be refrigerated comprising a relatively rigid body of compacted dendritic metal powder 0 a relatively good heat conducting material, said body having a large number of specially constructed, minute, internal voids of capillary size occupysaid internal voids being in communication with an exterior surface of said body through a large number of surface interstices therein, and a volatile liquid contained within said voids so that exposure of said surface of said body to an ambient atmosphere which is nonsaturated with respect to vapor of said liquid produces evaporative cooling of saidsurface and heat may be conducted to said surface is replenished by capillary movement of liquid from said pores to said surface through said interstices, the heat conducting characteristics of said metal body serving to facilitate removal of heat from said body by vaporization at its surface.

References Cited in the file of this patent UNITED STATES PATENTS 1,980,533 Kile Nov. 13, 1934 1,959,934 Smith May 22, 1934 2,350,348 Gaugler June 6, 1944 2,721,378 Oliver et al. Oct. 25, 1955 2,892,251 Felt June 30, 1959 2,941,759 Rice June 21, 1960 UNITED sTATEs PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,041,851 July 3. 1962 Randolph N. Stenerson It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Co1umn 3, line 75, for "apply" read applying column .1., llne 29. for "by" read for same column 4, 11ne 63, for "have" read having Signed and sealed this 23rd day of October 1962.

(SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER Commissioner of Patents Attesting Officer

Images