US3172269A

US3172269A - Thermoelectric refrigerator

Info

Publication number: US3172269A
Application number: US234313A
Authority: US
Inventors: Melrose R Cole
Original assignee: Technical Operations Inc
Current assignee: Technical Operations Inc
Priority date: 1962-10-31
Filing date: 1962-10-31
Publication date: 1965-03-09
Anticipated expiration: 1982-03-09

Description

March 9, 1965 M. R. COLE THERMOELECTRIC REFRIGERATOR 2 Sheets-Sheet 1 Filed Oct. 31. 1962 FIG.

FIG. 2

INVENTOR. M ELROSE R. COLE BY 'ROMQ Sm ATTORNEYS M. R. COLE THERMOELECTRIC REFRIGERATOR March 9, 1965 2 Sheets-Sheet 2 Filed Oct 31, 1962 MELROSE R. COLE BY M8} SM.

AT TO RN EYS United States Patent C) This invention relates to thermoelectric refrigerators, and more particularly to improvements which will reduce Icw the time required to freeze water to ice in such refrigerators.

The art of thermoelectric cooling has reached the state where refrigerators of small capacity, such as for making ice cubes, are commercially competitive, in that their simplicity of construction and low maintenance cost outweigh their comparatively high initial cost. It is understood that thermoelectric cooling elements are improving so rapidly that refrigerators of larger sizes will soon be similarly available. One characteristic of currently available low-volume refrigerators which can advantageously be improved is the long time required to freeze water from room temperature. In practice, it is desirable to provide at least two trays of ice cubes, holding together about one kilogram of water. It has been found that a practical refrigerator will freeze this quantity of water, from about C. starting temperature, in about six hours. If a'user then removes one tray of ice cubes and substitutes an equal quantity (about 500 grams) of water, it will take about three hours to freeze the water in the fresh tray.

It is the principal object of this invention to provide a thermoelectric refrigerator in which when one of two or more ice cube trays is removed and replaced with a tray full of water at room temperature, the water will be frozen in less time than heretofore, for example, onethird to one-half of the time heretofore required. According to the invention in its broader aspects, this object is achieved by providing in a thermoelectric refrigerator a thermal sink or cold source which is maintained at low temperature substantially at or below the freezing temperature of water and which exchanges substantially more calories in going from room temperature to the said low temperature than the contents of one ice-cube tray. Preferably, in a two-tray refrigerator, the thermal capacity of the thermal sink is approximately the same as that of the water contents of both trays between the same temperature limits. Such a thermal sink is cooled by the thermoelectric cooling means along with the original charge in the ice cube trays, until the entire system is brought to the temperature at which ice cubes are formed. Thereafter, the refrigerator may continue to operate. Removal of one tray of ice cubes depletes the cold contents by less than half, and atray of water which replaces the ice cubes is cooled by the combined efforts of the thermal sink, the remaining ice cubes, and the thermoelectric element. By choosing for the thermal sink a liquid, such as water, which has a high specific heat, the temperature of the new charge of water is quickly brought near to the freezing point of water, thereby drastically reducing the time required to freeze a new tray of ice cubes. It is accordingly another important object of the invention to provide a thermoelectric refrigerator having a heat sink of substantially the same thermal capacity as the material to be cooled, over the same temperature range, particularly for use with two or more ice-cube trays.

I have found that a small thermoelectric refrigerator, capable originally of freezing a given quantity of ice over a long period of time (e.g., six hours or more) can be efiiciently operated to freeze it fresh tray of ice cubes 3,172,269 Patented Mar. 9, 1965 in a short period of time when supplied with a thermal sink according to the invention. That is, by increasing the initial load on the cooling element, and thereafter using part of the initial load to help cool new components of the useful load, I have provided a small, or low power refrigerator which can be operated to provide quick freezing of ice cubes or the like with no increase in power consumed.

The foregoing and other objects and features of the invention will become more readily apparent from the following description of certain exemplary embodiments. This description refers to the accompanying drawings, wherein:

FIG. 1 is a front-sectional view of an embodiment of the invention;

FIG. 2 is a section along line 22 of FIG. 1;

FIG. 3 is an exploded view, partially schematic, of the embodiment of FIG. 1; and

FIG. 4 is an isometric view of another embodiment of the invention.

Referring to FIGS. 1, 2 and 3, a thermoelectric cooling device 10, having a heat-absorbing surface 11 and a heat radiating surface 12, is the cooling means for a thermoelectric refrigerator generally designated by the reference character 20. A generally U-shaped body 15, which may be made of aluminum, for example, having first and second

horizontal arms

16 and 17 and a vertical bight portion 18, is thermally coupled at the bight portion to the heat-absorbing surface 11 of the cooling device 10. As is shown in FIG. 3, the thermoelectric cooling device, which as illustrated is of a known commercial form, is abutted to the bight portion 18 of the body 15 with a thin film of electrical insulating material 19 between them. For simplicity of illustration, this film is omitted in FIG. 1. The film 19 may be a plastic, such as the plastic available under the commercial or trade designation Mylar, approximately 0.001 inch thick, coated on both sides with silicon grease. When sandwiched between the heat-absorbing surface 11 and the bight portion 18 of the body 15, this film affords electrical insulation and minimizes junction thermal drop in the thermoelectric elements. At the same time, this film, being quite thin, has negligible influence upon the heat transfer across it, from the body 15 to the heat absorbing surface 11. The thermoelectric cooling device 10 is attached to the body 15 by means of bolts (represented by dashed lines'21, 21) through

holes

22, 22 in the bight portion 18 (FIG. 3). These bolts may preferably be made of stainless steel.

A tank 25, which may be made of aluminum, copper or brass, for example, is thermally bonded at one side to the free end of one arm 16 of the body 15, and at the bottom to an extension of the other arm 17. This arrangement provides good thermal-conductivity between the tank 25 and the body 15. The two may conveniently be welded together. The top '26 of the tank has an opening with an extension 27 through which it may 'be'filled with a liquid 28, and a cap 29 to close the opening. The properties of the liquid 29 will be described in some detail .below.

Ice cube trays

31, 32 may rest on the

arms

16, 17, respectively, of the body 15, which function as shelves for this purpose.

While it is not material to an understanding of the invention, it will be understood that a cabinet will in'pract ice surround the tank 25 and body 15, providing a thermally-insulated compartment (not shown) for the

trays

31, 32. Walls for such a cabinet are indicated at 33. Insulation 34 may be contained within such walls, outside of them or between pairs of such walls (no-t shown) as is well-known in the art. The walls 33 and insulation 34 are indicated only in FIG. 1. In any event, it

will be convenient to fit radiator fins 35 to the heat emitting side 12 of the thermoelectric cooling device 10, and these fins will be outside the cabinet. A fan (not shown) may be employed to aid in removing heat from the fins 35. In addition, it will be understood that a suitable electric circuit, known in the art, will in practice be provided for the thermoelectric cooling device 10.

The liquid 29 in the tank 25 should be capable of releasing a substantial quantity of heat energy to the heat absorbing sun-face 11 through the thermally

conductive shelves

16, 17 of the body 15. Conveniently, the shelves may be about A inch thick, to give them flatness and to implement heat flow. Conversely, a corresponding quantity of heat can be absorbed by the liquid 29 (when .cold) from water (not shown) in the

trays

31, 32 through the

shelves

16, 17, respectively, when water at room temperature is present in the trays.

The liquid 29 is preferably a mixture of water and a suitable chemical which will reduce the freezing point of the mixture to approximately -5 C., at which point the mixture preferably becomes a heavy crystal-like slush. This temperature is selected to be below zero (centigrade) so that heat will readily transfer to the tank 25 from trays of Water on one or both of the shelves 16, '17, thereby constituting the liquid 29, at such a temperature, a cold reservoir or heat sink adequate for the purposes of the invention, while at the same time it is suthciently warm to assure an optimum temperature differential between the heat absorbing and heat emitting sides 11 and 12, respectively, of the thermoelectric cooling device 10 to maximize its heat pump efficiency. Ethylene glycol (C H O and alcohol are additives which are suitable to provide a mixture having an icecrystal, slush, temperature which is about 6 C. A

vmixtureof 22% by volume of ethylene glycol in water is a preferred blend for optimized performance characteristics in accordance with the foregoing criteria, while assuring minimum expansion associated with the freezing of water. Where the

trays

31, 32 have a capacity of 500 cc. each, the tank 25 may be made of aluminum /8 inch thick, and may have a volume of 1300 milliliters, and the liquid 29 may be 1000 cc. of such a liquid mixture. The

shelves

16, 17 may be aluminum A inch or inch thick; The thermoelectric cooling device may have a capacity of 15,000 calories per hour, as aheat pump. Operation of a refrigerator with these characteristics will be approximately'as follows:

(a) At initial turn-on, the entire system, including .all parts and water (not shown) in the

trays

31, 32, will be at room temperature, assumed to be 20 C.;

(b) Initial heat pumping action will establish a thermal gradient along the shelves, from the thermoelectric device 10 to the tank 25;

(c) During initial cooling, because of the thermal gradient along the

shelves

16, 17, heat is removed faster fromthe water in the

trays

31, 32 than from the liquid 29in the tank 25;

(d) Upon reaching C. at the trays (in about 2 to 2 /2 hours), freezing of the water in the trays begins, and

this temperature is maintained at the trays until all of the latent heat of fusion of the water (80 calories per gram, or 80,000 calories) is given up to the heat absorbing surface .11; this will take about five and one-half hours additional;

; (a).:Dur-ing the freezing of water in the trays, the liquid mixture 29 remains at 0 C., which is above its freezing point; thereafter theentire load (ice in the trays and liquid 29) is further cooled to the freezing point (about C. or 6 C.) of the liquid 29, which then gives up its latent heat of fusion, namely, an additional 80,000 calories, approximately;

(1) With both the liquid 29, and the Water in the trays frozen, the refrigerator will continue to pump the temperature of the load down to a minimum temperature within the capacity of the system.

Thus it is seen that, during initial cooling, the system of this invention provides that the ice cubes are frozen before the heat sink is frozen, which is an advantage that assures that the presence of the heat sink will not significantly delay the production of ice cubes, as compared with prior thermoelectric refrigerators which do not have a heat sink as herein described. When one or both of the ice cube trays are removed, emptied, and refilled with room temperature water, and replaced in the refrigerator, during the period when the liquid mixture 29 is in the ice crystal state, the liquid mixture 29 and the thermoelectric cooling device 10 will both function as heat pumps relative to this freshly introduced water load. If the ice cube trays are filled to the top to contain 1000 grams of water, requiring 100 calories per gram to convert it from room temperature water to ice, this can be accomplished in less than three hours. The liquid mixture 29, having the aforesaid composition, is 1000 cc. of a 60 calorie per gram mixture at a temperature of 6 C., or lower, and therefore represents 60,000 calories available to absorb heat from a load warmer than 6 C. Assuming no thermal gradient within the system, and 15,000 calories per hour pumping capacity for the thermoelectric cooling device 10, more than 100,000 calories can be removed from the Water in three hours. If the

trays

31, 32 are filled full, to hold 750 grams of water, then only 75,000 calcries are required to be removed to freeze the water, and this can be done in 1 hour. One tray, so used, can produce new ice cubes in approximately one-half hour, even if the contents of a frozen tray are ignored. Thus, in the present invention, it is clear that increased heat pumping capacity is afforded for a short time, which is sufficient to freeze ice cubes for practical purposes, and

this is achieved with a system containing a heat pump reservoir and a medium-to-low' capacity thermoelectric heat pump.

FIG. 4 illustrates an alternative embodiment of the invention in which a metal reservoir tank is thermally coupled at one side to the heat absorbing surface 62 of a thermoelectric heat pump 60, and at the other side to the edges of two

shelves

66 and 67, madeof thermally conductive material. All other details are similar to corresponding details'in FIG. 1. While this embodiment does not appear, as does FIG. 1, to provide that cooling will be effective at the shelves before being effective at the reservoir, the fact that water on the

shelves

66, 67 will freeze before theliquid 2 (not shown) in the reservoir is inherentin the liquids themselves, so that here, too, ice cubes will be made before the heat sink liquid 29 freezes. As in FIG. 1, the reservoir 55, when charged with an appropriate heat-sink liquid at a temperature below 0 C., will cause quick freezing of water which .is subsequently placed in trays on the

shelves

66, 67.

The embodiments of the invention which have been illustrated and described herein are but a few illustrations of the invention. Other embodiments and modifications will occur to those skilled in the art. No attempt has been made to illustrate all possible. embodiments of the invention, .but rather only to illustrate its principles and the best manner presently known to practice it. Therefore, while certain specific embodiments have been described as illustrative of the invention, such other forms as would occur to one skilled in this art on a reading of the foregoing specification arealso Within .the spirit and scope of the invention, and it is intended .meanshaving twohorizontal arms spaced apart to pro- 5 vide shelves and a vertical bight portion, said hight portion being thermally coupled to said heat-absorbing surface and said arms being thermally-coupled to said thermally-conductive part of said Wall means.

2. In a thermoelectric cooling refrigerator, in combination, thermoelectric means having a heat-absorbing surface and a heat-emitting surface, a liquid reservoir having Wall means at least a part of which is thermallyconductive, and U-shaped thermally-conductive shelf means having two horizontal arms spaced apart to provide shelves and a vertical bight portion, said hight portion and said heat-absorbing surface being each thermally coupled to a thermally-conductive part of said wall means.

3. In a thermoelectric cooling refrigerator, in combina- .tion, thermoelectric means having a heat-absorbing surface and a heat-emitting surface, a liquid tank having metal Walls, and a U-shaped 'body of aluminum having its two arms horizontally-disposed and fastened at their free ends to a Wall of said tank in thermally-conductive relation therewith, the bight portion of said body being thermally-coupled to said heat-absorbing surface.

4. In a thermoelectric cooling refrigerator, in comb-ination, thermoelectric means having a heat-absorbing surface and a heat-emitting surface, a metal tank of rectangular configuration, and a U-shaped metal body having its arms horizontally disposed one above the other and its lbight portion vertically disposed, the lower arm 'being longer than the upper arm, said tank having its bottom thermally coupled to a side surface of the lower arm and one side Wall of the tank thermally bonded to the free end of the upper arm, said b ight portion b ing thermally coupled to said heat-absorbing surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,255,459 Vretman Sept. 9, 1941 2,664,716 Warmon Jan. 5, 1954 2,978,875 Lackey Apr. 11, 1961 3,040,539 Gaugler June 26, 1962 3,064,440 Waller Nov. 20, 1962

Claims

1. IN A THERMOELECTRIC COOLING REFRIGERATOR, IN COMBINATION, THERMOELECTRIC MEANS HAVING A HEAT-ABSORBING SURFACE AND A HEAT-EMITTING SURFACE, A LIQUID RESERVOIR HAVING WALL MEANS AT LEAST A PART OF WHICH IS THERMALLYCONDUCTIVE, AND U-SHAPED THERMALLY-CONDUCTIVE SHELF MEANS HAVING TWO HORIZONTAL ARMS SPACED APART TO PROVIDE SHELVES AND A VERTICAL BIGHT PORTION, SAID BIGHT PORTION BEING THERMALLY COUPLED TO SAID HEAT-ABSORBING SURFACE AND SAID ARMS BEING THERMALLY-COUPLED TO SAID THERMALLY-CONDUCTIVE PART OF SAID WALL MEANS.