US2702990A - Absorption refrigeration - Google Patents

Description

March 1, 1955 w. G. KOGEL ET A l 2,702,990

ABSORPTION REFRIGERATION Original Filed Feb. 26, 1949 4 Sheets-Sheet l 4 Sheets-Sheet 2 W. G. KOGEL ET AL ABSORPTION REFRIGERATION n u m I I a a n I March 1, 1955 Original Filed Feb. 26, 1949 March 1, 1955 w. G. KOGEL ET AL 2,702,990

I ABSORPTION REFRIGERATION Original Filed Feb. 26, 1949 4 Sheets-Sheet 4 United States Pate AnsoRPTIoN REFRIGERATION Wilhelm Georg Kogel, Stockholm, and -Gunnar Axel Grubh, Brornma, Sweden, assignors to Akfiebolaget Eleirtrolux, Stockholm, Sweden, a corporation of Sweden Continuation of application Serial No. 78,502, February 26, 1949. This application December 6, 1952, Serial No. 324,530

Claims priority, application SwedenMarch 2, 1948 7 Claims. (Cl. 6295) for cooling adjacent spaces or sections of a refrigerator.

by a substantially horizontally disposed evaporator or Cooling element of a refrigeration system of the above type, particularly to limit or restrict an increase in temperature in one of the sections upon increasein .load on the other section.

Another object of the invention is' to provide an improved evaporator structure of this type'for producing refrigeration at different temperatures at opposite sides of a substantially horizontally disposed evaporator.

A further object of the invention is to provide such an evaporator which makes use of a cold accumulator to maintain a safe refrigerating temperature at one side of the horizontally disposed evaporator when the opposite side thereof is subjected to an increase in load.

A still further object of the invention is to provide an improvement for cooling adjacent ice freezingand frozen food sections'of a freezing unit with the aid of absorption refrigeration apparatus of the inert gas type having a substantially horizontally disposed evaporator-in the form of a looped coil, particularly to insure an adequately low refrigerating temperature for the frozen food section .When the load on the ice freezing section is increased, as by placing several ice trays therein containing water to be frozen.

The above and other objects and advantages of the invention will be more fully understood .from the .following description taken in conjunction withthe accompanying drawings forming a part of this specification, and

of which:

Fig. 1 illustrates more or less diagrammaticallyan'absorption refrigeration system of the inert gas type to which the invention is applied;

Fig. 2 is a fragmentary front elevation looking'toward the rear of a storage space of a refrigerator embodying the invention, partly broken away and in section, the cooling unit being adapted to be connected in anabsorption refrigeration system like that diagrammatically shown ,in Fi 1;

l ig. 3 is a horizontal section taken at line3-3'of Fig. 2 to illustrate the construction more clearly;

Fig. 4 is a fragmentary side sectional view of a'refrigerator illustrating another embodiment of .theinvention;

Fig. 5 is a sectional view, taken at line 5"'5 of Figa4, to illustrate the cooling unit and connections thereto more clearly;

Fig. 6 is a fragmentary sectional view taken atfline 6-6 of Fig. 5; p

Fig. 7 is a front elevation, partly broken "away an'din section, of the refrigerator shown in Figs.'4 and '5; and

Figs. 8 and 9 are fragmentary front elevations of 'rehaving evaporators adapted to operate at different. term- 2,702,990 Patented Mar. 1, 1955 peratures, such evaporators or cooling elements are usually formed of piping which are shaped as coils and connected by conduits to other parts of the system. In a household refrigerator of the kind in which the interior is subdivided into aplurality of compartments one above another, the individual compartments are arranged to be cooled to different temperatures by the evaporators. In such case the evaporator coils are horizontally disposed I and constructed to providea maximum amount of usable storagespace in theinterior of the refrigerator.

One manner of employing a plurality of such horizontally disposed evaporator coils 10 and 11 in accord with the invention is shown in Figs. 2 and 3. The evaporator coils '10 and llaredisposed in an insulated interior 12 of a refrigerator cabinet 14 adapted to be closed by a door or closure member (not shown) which is hinged to the front o'f the cabinet. The evaporator sections 10 and 11 form part of :an absorption refrigeration system of the inert gas type which is more or less diagrammatically illustrated in Fig. 1. In order to-simplify the drawings, the horizontally disposed evaporator coils 10 and 11 of Figs. 2 and 3 have simply been shown as straight conduit sections in Fig. l which-are connected by a vertical bend 15. I

Ina system of the type illustrated in Fig. 1 a refrigerant fluid, such asliquid ammonia, for example, is introduced through a conduit'16 into the evaporator sections 10 and 1-1. ln the evaporator sections 10 and 11 refrigerant fluid evaporates and diffuses into an inert gas, such as hydrogen, for example, to produce refrigeration and abstract heat from thesurroundings. The resulting gas mixture of refrigerant and. inert gas flows from the evaporator sections Illandll through an outer passage 17 of a gas heat exchanger '18 and vertical conduit 19 into an absorber comprising a vessel 20and a looped coil 21. In the absorber vessel 20-and coil .21 refrigerant vapor is absorbed by a suitable absorbent, such as water, for example, which is introduced into coil 21 through a conduit 22. The :hydrogen or'inert gas, which is practically insoluble and weak in refrigerant, returns to the evaporatorsections 10.and 11 throughan inner passage 23 of absorber coil 21is' heavier than the gas weak in refrigerant and flowingfrom the absorber coil 21 to the evaporator sections, aforce is-jpro'duced or developed within the system for causing circulation'of inert gas in the manner described.

From the'vessel 20 enriched absorption liquid flows through a conduit 25 and an innner passage 26 of a liquid heat exchanger27 into the lower end of a vapor lift tube i28-of a generator or vapor expulsionunit 29. The generatorunit 29 comprises a heating flue 30 having the vapor lift tube 28 and a boiler pipe 31 in thermal exchange relation therewith, as by welding, for example.

By heating generator unit 29, as by a gas burner 32, for

,28, and also vapor expelled from solution in the boiler tpipe,iflows upwardlyintoanair cooled condenser 33 provided with. a plurality of heat dissipating members or fins 34., Refrigerant vapor is liquefied in the condenser 33 and returnsito the evaporator sections 10 and 11 through the 'conduit116 tocornplete the refrigerating cycle.

The weakened absorption liquid, from which refrigerant vapor. has been expelled, .is conducted from boiler f 'as to the upper part of the absorber coil 21, for example,

so that anynon-condensable'gas which may pass into the condenser can fiow. to the gas circuit and notv be trapped in -e dea 1;? v

In adapting the refrigeration system of Fig. 1 for use in the refrigerator cabinet 14 of Fig. 2, the evaporator sections and 11 are disposed in the thermally insulated interior 12 thereof, and the gas heat exchanger 18, which is indicated in dotted lines in Fig. 2, and other parts may be disposed at the rear of the cabinet. .The horizontally dlsposed evaporator sections 10 and 11 are connected in series relation with inert gas from conduit 24 flowing through the upper evaporator section 10 in the presence of and in parallel flow with liquid refrigerant which is introduced through conduit 16. From evaporator section 10 inert gas then passes through the vertical connection for flow through the lower evaporator section 11. Unevaporated refrigerant is also conducted from evaporator section 10 through the connection 15 into the lower evaporator section 11 and flows therein in the presence of and in parallel flow with the inert gas. It is to be understood, however, that inert gas and liquid refrigerant may pass each other in counterflow relation in the lower evaporator section 11, and liquid refrigerant may be conducted thereto directly from a separate condenser section, if desired.

Since the inert gas flows successively through the evaporator sections 10 and 11, the gas in the upper evaporator section contains a lesser amount of refrigerant vapor than the gas in the lower evaporator section 11. The partial vapor pressure of the refrigerant is a gradient, so that the temperature of liquid refrigerant in the evaporator sections 10 and 11 also is a gradient, the evaporating temperature of liquid being lower in the upper evaporator section 10 which constitutes the freezing portion of the cooling unit.

In the refrigerator cabinet 14 of Fig. 2, the interior 12 thereof is subdivided into a plurality of compartments one above the other by a horizontal partition 40 which is constructed to thermally insulate the compartments from one another. The heat insulating partition 40 desirably extends over the entire width of the interior of the cabinet, and from the rear wall toward the open front of the cabinet so that circulation of air between the spaces above and below the partition is substantially prevented when the door or closure member of the cabinet is in its closed position. The lower evaporator section 11 may be positioned immediately beneath the insulating partition 40, and, since this evaporator section is the higher temperature section or portion of the cooling unit, it may be effectively utilized to cool air in the lowercompartment 41. To provide adequate heat transfer surface, the coils of the lower evaporator section 11 may have. a plurality of fins 42 secured thereto. The compartment above the insulating partition 40 is adapted to serve as a freezing section of the refrigerator cabinet 14 in which the lower temperature evaporator section 10 is positioned.

In accordance with the invention the freezing unit of the refrigerator is subdivided into an upper section 43 and a lower section 44 by a horizontally disposed heat conductive member 45 with which the upper evaporator coil 10 is thermally associated. As shown, this is accomplished by arranging the looped coil forming the evaporator section 10 in thermal exchange relation wit the upper side of the member 45. In addition, a horizontal plate 46 having downwardly depending flanges 47 is positioned over the evaporator section 10 in good thermal contact therewith. This may be accomplished by providing clamping members 48 along the straight portions of the evaporator coil or section 10 that envelop the piping and have flanges 49 which are secured, as by brazing, for example, to the underside of the plate 46.

The upper section 43 of the freezing unit may be referred to as an ice freezing section adapted to receive ice trays for freezing water and the like, the plate 46 being substantially fiat and serving as a supporting shelf for such ice trays. The lower section 44 of the freezing unit desirably is of greater depth than the upper portion 43 and may be referred to as a frozen food section adapted to receive frozen food packages and other matter to be frozen. Since the low temperature evaporator coil 10in the direction of its length is in good heat conductive relation with the heat conducting member 45 and also the.

plate 46, heat is effectively abstracted from ice trays positioned on the plate 46 and also from matter stored in the frozen food section 44. Although not shown, a suitable closure member or members desirably may be provided at the front opening of the freezing unit to close both the upper and lower portions 43 and 44, respectively.

In order to insure a low refrigerating temperature in the frozen food section 44 under all operating conditions, the heat conducting member 45 desirably is constructed as a cold accumulator having a hollow interior which is filled with a congealable liquid body, that is, a solution that freezes at a low temperature. Such a cold accumulator may comprise a pair of spaced apart plates which are relatively close to one another and sealed at the peripheral edges thereof to provide a hollow interior for holding a substance, such as a eutectic solution, for examp5le,(\:vhich freezes at a temperature of about l0 to -1 During the periods when the ice freezing section 43 is under a small load, the low temperature evaporator sec tion 10 is effectively employed to abstract heat from the body of eutectic solution in the member 45, thereby lowering the eutectic solution to a very low temperature adequate to maintain frozen food in the frozen food section 44 well below the freezing temperature. When ice trays containing water to be frozen are placed on the supporting shelf or plate 46, the load on the ice freezing section 43 is increased. With a substantial increase in ice freezing load, the temperature of the low temperature evaporator section 10 may increase to a value which is not far below the freezing temperature of water.

If the cold accumulator 45 were not provided the evaporator coil 10 alone would have to be relied upon to keep frozen food in the frozen food section at a safe refrigerating temperature. However, a substantial increase in ice freezing load may cause the evaporator coil 10 to rise to a temperature which is not far below the freezing temperature and which will remain substantially constant for a considerable length of time during the entire ice freezing period. Under such conditions the ability of the evaporator coil 10 alone to maintain frozen food at a safe refrigerating temperature is decreased, and under severe operating conditions the evaporator section 10 may be ineffective to keep frozen food at a sufficiently low temperature.

By providing the cold accumulator 45, undesirable increase in temperature of the frozen food section 44 is avoided, particularly frozen food stored in the uppermost part of such freezing section. In accord with the invention the total melting heat of the cold accumulator 45 desirably is balanced so that the eutectic solution will remain frozen during the interval of time that water stays in a liquid state in the ice trays. The cold accumulator desirably may be oversize and larger than actually necessary to insure that it will take care of the most severe load on the ice freezing section 43. However, the cold accumulator should not needlessly be made unduly large because this reduces the maximum amount of storage space made available for ice trays, frozen food and other matter adapted to be placed in the freezing sections 43 and 44. When the eutectic solution in the cold accumulator is frozen or charged at the time ice trays containing water are positioned in the ice freezing section 43, the decrease in temperature of the supporting shelf or plate 46 that would otherwise occur is substantially reduced, thereby accelerating the rate at which ice is formed to a relatively high extent.

Figs. 4 to 7 inclusive illustrate another embodiment of the invention in which there is provision for maintaining a frozen food section 44a at a safe refrigerating temperature even when the load on the ice freezing section 43a is increased at times. The embodiment of Figs. 4 to 7 differs from the embodiment of Figs. 2 and 3 and just described in that no cold accumulator is employed.

As best shown in Figs. 4 and 7, the cooling unit comprises a shell or casing 50 having a top wall 51, bottom wall 40a and side walls 52. The shell extends across the entire width of the interior 12a of the cabinet 14a, and from the rear wall 53 toward the open front of the cabinet so that circulation of air between the space 41a and freezer sections 43a and 44a is substantially prevented when the door of the cabinet, not shown, is in its closed position. As in the embodiment first described, one or more closure members desirably may be provided at the front openings of the freezer portions 43a and 44a.

The low temperature evaporator 10a is disposed in the upper part of the shell 50, as will be described more fully hereinafter, while the higher temperature evaporator 11a is positioned in the upper part of the lower compartment or space 410. The evaporator sections 10a and 11a are adapted to be connected to other parts of an absorption refrigeration system of the inert gas type and like that diagrammatically shown in Fig. 1. However, the parts of the refrigeration system which are shown in Figs. 4, 5 and 7 diifer from those illustrated in Fig. 1 in that a horizontal gas heat exchanger 18a is provided to which the evaporator sections ltla and 11a are connected.

In Figs. 4 and 5 inert gas weak in refrigerant fiows from the upper end of the absorber coil through a conduit 21a, an inner passage of the horizontal gas heat exchanger 18a and conduit 24:; to which is connected one end of the evaporator section a, as indicated at 54 in Fig. 5. Liquid refrigerant from the condenser is also conducted to the same end of the evaporator section 10a through a conduit 16a, so that liquid refrigerant passes through the upper evaporator section 10a in parallel flow with inert gas. Both liquid refrigerant and inert gas pass from the upper evaporator section 10a at 55 through the vertical connection a for parallel flow in the lower evaporator section 11a which is provided with heat transfer members or fins 42a.

inert gas rich in refrigerant fiows from the higher temperature evaporator section 11a at 56 into an outer passage of the gas heat exchanger 18a and thence through a conduit 19a which is connected at its lower end to the absorber vessel in a manner similar to the conduit 19 in Fig. 1. As best shown in Fig. 4, the conduit 21a for inert gas weak in refrigerant envelops and surrounds the conduit 1% through which inert gas rich in refrigerant returns to the absorber. In order to'precool liquid refrigerant conducted to the upper evaporator section 10a through the conduit 16a, the latter is connected at spaced apart regions to the outer passage of the gas heat exchanger 18a by conduits 57, as shown in Fig. 5. In this way natural circulation of inert gas from the outer passage of the gas heat exchanger 18 takes place through a part of conduit 16a and evaporation and diffusion of refrigerant into inert gas takes place, thereby taking up heat from liquid refrigerant before being introduced into the evaporator section 10a.

In order to position the evaporator sections Illa and 11a and shell in the thermally insulated interior 12a of the cabinet 14a, the rear wall 53 is formed with an opening 58 defined by a rectangular frame 59 which may be formed of wood, for example. A cover or closure member 60 for the opening, which contains insulating material 61 and in which the gas heat exchanger 18a is embedded, is arranged to bear against a gasket 62 of suitable insulating material and is removably secured at d3 to the rear wall 53.

In accordance with the invention the top wall 51 of the shell 50 comprises spaced apart plates 46a and 45a, and the low temperature evaporator section 10a is formed to provide two looped coils 10a and 10a", each ofwhich in the direction of its length is in thermal exchange relation with one of the plates 45a and 46a. As best shown in Fig. 5, each looped coil 10a and 10a" includes spaced apart straight portions which are more or less parallel to one another and connecting bends, thereby forming a number of U-shaped pipe portions which are serially connected to one another. Further, the legs of certain U- shaped elements or pipe portions are disposed between the legs of other U-shaped elements to provide a compact arrangement of the looped coils 10a and 10a.

As best shown in Fig. 6, the looped coil 10a is arranged in thermal relation with the upper side of the plate 45a, and the looped coil 10a" is arranged in thermal relation with the underside of the plate 46a. It will be seen that the diameter of the piping forming the looped coil ltla is smaller than that of the piping forming the looped coil 10a", and that the horizontal planes tangential to the top and bottom portions of the looped coil 10a are at levels between the horizontal planes tangential to the top and bottom portions of the looped coil 10a. The looped coils Mia and file" may be arranged in good heat conducting relation with the plates 45a and 46a in any suitable manner, as by clamping members 48a which envelop the straight portions of the coils and are secured to the spaced apart plates forming the top wall 51 of the shell 50.

Essentially, the spaced apart plates 45a and 46a form a container or vessel which desirably is filled with a suitable insulating material 64 for thermally shielding the two portions Mia and 10a" of the evaporator section 10a from one another. In order to obtain the compact arrangement of the looped coils 10a and 10a" in the manner just described, it will be seen that the bottom plate 45a is formed with a depressed region 65 immediately beneath looped coil 10a along the length thereof, as seen in Fig. 6, so that each looped coil is out of physical contact and removed from the plate to which it is not thermally connected.

In the operation of the embodiment being described, liquid refrigerant and inert gas weak in refrigerant first flow through the looped coil 1011' which is in thermal contact with the bottom plate 45a of the top wall 51 of the cooling unit. With such arrangement strong cooling of the plate 45a is effected which serves as the ceiling or roof of the frozen food section 44a, the bottom wall 40a of which is constructed to insulate such frozen food section from the lower food compartment 41a.

From the looped coil 10a liquid refrigerant and inert gas then flow in the presence of each other into the looped coil 10a which is in thermal contact with the upper plate 46a of the top wall of the freezing unit. In this manner strong cooling of the plate 46a is also effected which serves as a supporting shelf of. the ice freezing section 43a of the freezing unit. When the load on the ice freezing section 43a is increased by placing ice trays containing water to be frozen on the plate 46a, the temperature of the looped coil or evaporator portion 10a increases. However, such rise in temperature of the evaporator portion 10a does not adversely affect or cause any rise in temperature of the looped coil or evaporator portion 10a, because liquid refrigerant and inert gas weak in refrigerant are continuously introduced into the latter. Hence, the plate 45a will always be strongly cooled by the looped coil 10a to keep frozen food in the frozen food section 44a at a safe refrigerating temperature of about -15 to l8 C., irrespective of sudden increase in load on the ice freezing section 43a.

Since the frozen food section 44a will be primarily employed for storing frozen food packages, the load on the looped coil or evaporator portion 10a will be relatively small. Consequently, liquid refrigerant will practically always be supplied to the looped coil or evaporator portion 10a, and the inert gas which is introduced therein will not be too rich ,in refrigerant vapor, so that the evaporator portion 10a will be quite effective to effect cooling of the ice freezing section 43a for the purpose of producing ice.

Another embodiment of the invention is shown in Fig. 8 which is generally like the embodiment of Figs. 4 to 7 and differs therefrom in that a cold accumulator is provided for the frozen food section 44b. It will be understood that the provision of the cold accumulator 45b in Fig. 8 will act to restrict changes or variations in temperature of the frozen food section 44b, and this is particularly true when the operation of the refrigeration system is thermostatically controlled responsive to a temperature condition of the air being cooled or temperature of an evaporator section. In such case the supply of heat to the generator unit is reduced from time to time to regulate the refrigerating effect produced by the evaporator sections. During the periods when the heat input to the generator unit is reduced, the cold accumulator 45b exerts a stabilizing influence and acts to maintain the frozen food section 44b at a safe refrigerating temperature at all times.

Since'the plate 46b and evaporator portion 10b" of the ice freezing section 43b are thermally shielded from the evaporator portion 10b of frozen food section 44b, the cold accumulator 45b does not influence ice freezing in the ice freezing section 43b to any significant extent.

If it is desired to utilize the cold accumulator 45b to accelerate freezing of ice in the ice freezing section 43b, heat conductive members may be provided which provide a thermal connection between the top plate of the cold accumulator and plate 46b. Such an arrangement is preferable to that of providing direct thermal contact between the plate 46b and top wall of the cold accumulator, or between the looped coils 10b and 10b". In certain instances it may be advantageous to provide the cold accumulator on the plate 46b, so that ice trays containing water to be frozen can be placed thereon, or a second cold accumulator may be provided on top of the plate 46b in addition to that shown in Fig. 8 which is in thermal relation with the looped coil 10b.

In certain instances advantages are realized by providing a construction in which the ice freezing section is located below the frozen food section of the freezing unit. Such an arrangement is shown in Fig. 9 in which the looped coil 100 is positioned at the roof or ceiling of the frozen food section 44a. The looped coil 10c is fixed to a plate 66 which is insulated from the inner lining 67 of the cabinet interior 120 in any suitable manner. The bottom of the frozen food section 440 is formed by a partition 40c constructed to be heat insulating, such partition also serving as the roof or ceiling of the ice freezing section 430. The looped evaporator coil 10c is in thermal relation with the underside of plate 46c which serves as the supporting shelf of the ice freezing section 43c. The plate 46c and plate 68 closely adjacent thereto form a container or vessel in which the looped coil 10c and another looped coil 110 are disposed, the latter being in thermal contact with the upper side of the plate 68. The looped coils 10c and 110 are thermally shielded from one another by suitable insulation 64c, and a plurality of members 69 are fixed to the underside of plate 68 to provide a relatively extensive heat transfer surface to promote efficient cooling of air in the space 410 by the looped evaporator coil 110.

In the embodiment of Fig. 9, the looped evaporator coils are connected in series whereby inert gas first flows through the uppermost looped coil 10c, then through the looped coil 10c and finally through the looped coil 11c which constitutes the higher temperature evaporator section corresponding to evaporator section 11 in Fig. l and evaporator section 11a in Figs. 4 and 7. Hence, inert gas weak in refrigerant initially flows through looped coil 10c which corresponds to looped coil 10a in Fig. 6, and the cooling effect produced by this looped coil is utilized to maintain the frozen food section 44c at a safe refrigerating temperature irrespective of changes in load on looped coil 10c" which is utilized to produce ice in the ice freezing section 430. The operating temperature of the higher temperature looped coil 110 may be about C. or slightly below this value. A cold accumulator may be provided for one or both of the looped coils c and 100", if desired.

The cold accumulators may employ any well known eutectic solution having a sufiiciently low freezing temperature, so that heat can be abstracted at a low temperature which is below 0 C., for example. Various substances can be employed to provide the eutectic solution desired depending upon the operating temperatures of the different sections of the cooling unit. It will be understood that homogeneous substances having a melting point below the freezing temperature of water can be employed as well as eutectic solutions.

Modifications of the embodiments of our invention which we have described will occur to those skilled in the art, so that we desire our invention not to be limited to the particular arrangements set forth and intend in the claims to cover all modifications which do not depart from the spirit and scope of the invention. However, the provision of a cold accumulator for a low temperature evaporator section, in a manner generally like that shown, for example, in the embodiment of Fig. 1, which also embodies a higher temperature evaporator section, is being claimed in copending application Serial No. 305,966, filed August 23, 1952.

What is claimed is:

1. In a refrigerator comprising a cabinet having a thermally insulated interior, an absorption refrigeration system of the inert gas type including an evaporator in which refrigerant evaporates in the presence of an inert gas, said evaporator comprising a looped coil providing an elongated path of flow for fluids therethrough and in which practically all effective parts along the length thereof have a region in substantially the same single horizontal plane, said coil including a first portion in such horizontal plane in which refrigerant evaporates at a first average or mean temperature in the presence of the inert gas and a second portion in such horizontal plane in which refrigerant evaporates at a second higher average or mean temperature in the presence of the inert gas, a horizontal partition in the interior of said cabinet, means including one of said coil portions for effecting cooling primarily of matter above said partition, and means including the other of said coil portions for effecting cooling primarily of matter below said partition.

2. Apparatus as set forth in claim 1 in which said partition includes spaced apart upper and lower horizontally extending walls, the first coil portion in said single horizontal plane being in heat conductive connection with the under side of said upper wall and the top surface of which provides a supporting surface for matter to be refrigerated, and the second coil portion in said single horizontal plane being in heat conductive connection with the top side of said lower wall arranged to effect cooling primarily of matter below said partition.

3. In a refrigerator comprising a cabinet having a thermally insulated interior, an absorption refrigeration system of the inert gas type including an evaporator in which refrigerant evaporates in the presence of an inert gas, said evaporator being formed of piping which provides an elongated path of flow for fluids therethrough and includes a first horizontally extending portion in which refrigerant evaporates at a first average or mean temperature in the presence of the inert gas and a second horizontally extending portion in which refrigerant evaporates at a second higher average or mean temperature in the presence of the inert gas, said evaporator portions being disposed with respect to one another so that a horizontally extending plane tangential to one side of the piping forming one of said portions is located between the horizontally extending planes tangential to the opposite sides of the piping forming said other portion, and a horizontal partition in the interior of said cabinet, one of said evaporator portions being arranged to effect cooling primarily of matter above said partition and the other of said evaporator portions being arranged to effect cooling primarily of matter below said partition.

4. Apparatus as set forth in claim 3 in which the diameter of the piping forming one evaporator portion is different from that of the piping forming said other evaporator portion.

5. Apparatus as set forth in claim 3 in which the piping forming each evaporator portion includes U- shaped sections, the sides of a U-shaped section of one evaporator portion being disposed between the sides of a U-shaped section of the other evaporator portion.

6. Apparatus as set forth in claim 3 in which said partition includes a horizontally disposed plate forming the top surface thereof and upon which matter to be refrigerated may be placed, the piping forming said first evaporator portion being heat conductively connected to the under side of said plate.

7. Apparatus as set forth in claim 3 in which said evaporator portions are thermally shielded from one another.

References Cited in the file of this patent UNITED STATES PATENTS 2,257,924 Vretman Oct. 7, 1941 2,257,925 Vretman Oct. 7, 1941 2,345,453 Brace Mar. 28, 1944 2,350,347 Gaugler June 6, 1944 2,504,784 Ashby Apr. 18, 1950 2,598,240 Edel May 27, 1952

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