US2635437A - Absorption refrigeration system having plural evaporators operable at different temperatures - Google Patents

Description

APrl] 21, 1953 H. M. ULLSTRAND 2,635,437

ABSORPTION REFRIGERATION SYSTEM HAVING PLURAL EVAPORATORS OPERABLE AT DIFFERENT TEMPERATURES Filed Dec. 5, 1947 3 Sheets-Sheet l INV EN TOR.

Mar/745429 Aprll 21, 1953 ULLSTRAND 2,635,437

ABSORPTION REFRIGERATION SYSTEM HAVING PLURAL EVAPORATORS OPERABLE AT DIFFERENT TEMPERATURES Filed Dec. 5, 1947 3 Sheets-Sheet 2 IN V EN TOR.

HM WM Z%WM- arm/W5) pr 1953 H M. ULLSTRANO 2,635,437

ABSORPTION REFRIGERATION SYSTEM HAVING PLURAL EVAPORATORS OPERABLE AT DIFFERENT TEMPERATURES Filed Dec. 5, 1947 5 Sheets-Sheet 5 l A i I I iII/IIIIIIIII/IIIIIIIIIIIIIIIIIIIIII/11/11/16,

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Patented Apr. 21, 1953 ABSORPTION REFRIGERATION SYSTEM HAVING PLURAL EVAPORATORS OPER- ABLE AT DIFFERENT TEMPERATURES Hugo Malcolm Ullstrand, Stockholm, Sweden, as-

signor to Aktiebolaget Elektrolux, Stockholm, Sweden, a corporation of Sweden Application December 5, 1947, Serial $10,789,893 In Sweden December 6, 1946 6 Claims. (01'. 62-99) My invention relates to refrigeration, and more particularly concerns cooling of subdivided compartments of a refrigerator with the aid of a refrigeration system employing evaporation of refrigerant fluid in the presence of an inert gas or auxiliary agent.

It is an object of my invention to provide improvements for cooling such subdivided compartments by a plurality of evaporators operable at different temperatures, particularly to cool compartments subdivided by a horizontal partition whereby powerful low temperature cooling is effected by one of the evaporators for freezing water and other matter 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 with the accompanying drawings forming a part of this specification, and of which:

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

Fig. 2 is a front elevation of a plurality of evaporators or cooling elements and connections thereto diagrammatically illustrating one practical form of the evaporator structure shown diagrammatically in Fig. 1;

Fig. 3 is a top plan view of the evaporators or cooling elements and the connections thereto as shown in Fig. 2; and

Figs. 4 to 6 inclusive are fragmentary sectional views, looking toward the rear of a storage space of a refrigerator, more or less diagrammatically illustrating different ways of embodying or associating at least one of the evaporators in Figs. 2 and 3 in or with a horizontal partition which serves to subdivide the storage space into a plurality of compartments one above the other.

In recent years there has been a definite trend toward a household refrigerator of the kind in which the storage space is subdivided into a plurality of compartments one above the other which are arranged to be cooled by a plurality of evaporators operable at different temperatures. The several subdivided compartments usually extend between the lateral side walls of the storage space, and one such subdivided compartment is adapted to be maintained at a low temperature for freezing water and other matter as well as for storing frozen food packages. In order to provide a maximum amount of usable storage space in the subdivided compartments the evaporators are more or less of horizontal shape and of minimum height and at least one of the evaporators may be associated with the being referred'to as a window opening.

partition dividing the storage space into several compartments. 1 n, In'absorption refrigeration systems of the inert gas type having evaporators adapted to operate at different temperatures, such evaporators are generally formed by piping which are shaped as coils and connected by conduits to other parts of the system for circulation of inert gas as well as to supply liquid refrigerant to the evaporators. When such an absorption refrigeration system of the inert gas type is employed in the cabinet of a household refrigerator, the evaporators and connections thereto are usually inserted into the storage space through an opening in a wall of the cabinet adapted to be closed by a closure member, such wall opening often It is desirable to keep the window opening as small as possible for practical reasons as well as to keep at a minimum the likelihood of heat leakage into the thermally insulated interior of the cabinet.

When an absorption refrigeration system of the inert gas type and having a plurality of evaporators is employed in a household refrigerator of the kind referred to above, it will now be understood that it is desirable to provide evaporator coils adapted to operate at different temperatures which are horizontally disposed and relatively close to one another to avoid an unduly large window opening. In such case it is desirable to provide an arrangement in which the fluid connections to the evaporators are as simple as possible. In accordance with my invention, this is accomplished by providing low and higher temperature evaporators through which inert gas or auxiliary agent circulates in the same direction or in parallel flow with liquid refrigerant. In addition, provision is made for precooling liquid refrigerant which flows from the condenser to the low temperature evaporator.

An absorption refrigeration system of the inert gas type to which the invention is applicable is more or less diagrammatically shown in Fig. 1. In order to simplify Fig. 1, the evaporator structure l2 has been illustrated in a more or less conventional manner apart from a household refrigerator having subdivided compartments one above the other. The manner in which evaporator structure l2 may be constructed in accordance with the invention is illustrated in other figures of the drawings and will be described hereinafter.

The absorption refrigeration system shown in Fig. 1 is of a uniform pressure type in which an inert gas or auxiliary pressure equalizing fluid is employed. In a system of this type a refrigerant fluid, such as liquid ammonia, for example, is introduced through a conduit 4-] into the evaporator structure I2. The refrigerant fluid evaporates and diffuses in the evaporator structure l2 into an inert gas, such as hydrogen, for example, to produce refrigeration and abstract heat from the surroundings.

The resulting gas mixture of refrigerant and inert gas flows from the cooling structure through an outer passage 14 of a gas ,heat .exchanger l5 and vertical conduit 116 into an absorber comprising a vessel l1 and a looped coil I 8. In the absorber vessel VI! and coil l8 refrigerant vapor is absorbed by a suitable absorbent, such as water, for example, which is introduced into coil [8 through a conduit .19. The hydrogen or inert .gas, which is practically insoluble and weak in refrigerant, returns to the cooling structure l2 through inner passage .20 of the gas heat exchanger 15 and a conduit 2|.

The circulation of gas in the :gas circuit ust described is due to the difference in specific weight of the columns of gas rich and weak, respectively, in refrigerant vapor. Since the column of gasrich in refrigerant vapor andflowing from evaporator structure l2 to the absorber coil 18 is heavier than the gas weak'in refrigerant and flowing from' the absorber coil 18 to the-evaporator structure 12, a force is produced or developed within the system for causing circulation of inert gas .in the manner described.

Form the vessel l1 enriched absorption liquid flows through a conduit -22 and an inner passage 23 of a liquid heat exchanger into the lower end of a vapor lift tube 24 of a generator or vapor expulsion unit 25. The generator unit 25 comprises a heating flue 26 having the vapor lift tube 24 and a boiler pipe 21 in thermal exchange relation therewith, as by welding, for example. By heating generator unit 25,'as by a gas burner 28, for example, liquid from the inner passage 23 of the liquid heat exchanger is raised by vapor lift action through tube 24 into the upper part of the boiler pipe 21. The liberated refrigerant vapor entering boiler pipe 21 from the tube 24, and also vapor expelled from solution .in the boiler pipe, flows upwardly into an air cooled condenser 29 provided with a pluralityof heat dissipating members or fins 30. Refrigerant vapor is liquefied in the condenser 29 and returns to the evaporator structure l2 through the conduit H to complete the refrigerating cycle.

The weakened absorption liquid, from which refrigerant vapor has been expelled, is conducted from boiler pipe 21 through a conduit 3!, outer passage 32 of the liquid heat exchanger and conduit 19 into the upper part of the absorber coil [8. The lower end of the condenser 29 is connected by conduit 33 to the gas circuit, as to the upper part of absorber coil l8, forexample, so that any non-condensable gas which may pass into the condenser can flow to the gas circuit and not be trapped in the condenser.

It will be understood that the cooling stucture l2 in Fig. 1 is diagrammatically shown in the form of a coi1 and comprises a low temperature evaporator l2a and a higher temperature evaporator [2b having heat transfer members or fins 34 to provide a relatively extensive .heat transfer surface. In Figs. 2 and v3 I have shown a practical form of the evaporator structure 12 in Fig. 1

which is suitable for abstracting heat from a plurality of subdivided compartments disposed one above another in a storage space of a household refrigerator. In order to simplify Figs. 2 and 3 and bring .out .more clearly the connections of the evaporatorstructure to other parts of the refrigeration system, the manner in which the storage space is horizontally partitioned has not been shown, such partitioning being illustrated in Figs. 4 to 6 which will be described presently.

In Figs. 2 and 3, in which parts corresponding to those shown in Fig. 1 are designated by the same reference numerals, the evaporator structure I2 is horizontally disposed and includes two looped coils [2a and Nb at different levels, the former serving as the low temperature evaporator and the'latter as the higher temperature evaporator. The evaporator structure i2 is adapted to be positioned in a storage space 35 of a refrigerator cabinet which is indicated in dotted lines in Figs. 2 and 3, the cabinet having thermally insulla'ted lateral :side walls '36, top wall 37 and rear wall 38. Each of the evaporator coils 12a and I2!) is positioned in a single substantially horizontal plane and adapted to extend from one lateral side wall '36 to the opposite lateral side wall of the storage space. As best shown in Fig. 3, the gas heat exchanger I5 is arranged exteriorly of the thermally insulated storage space 35, as in a vertical space usually provided at the rear of the cabinet, for example, and desirably is embedded in insulation.

In the horizontal evaporator structure l2 of Figs. 2 and 3, inert gas weak in refrigerant flows from one passage of the gas heat exchanger l5 through the conduit 2| which is connected at 39 to one end of the upper looped coil 12a. Liquid refrigerant flows from the condenser through the conduit II which is also connected at 39 to the upper looped coil [2a. Inert gas and liquid refrigerant pass from the opposite end 40 of the upper looped coil 12a through a vertical conduit connection 4| to one end of the lower looped coll l2b, the opposite end 42 of which is connected by a conduit 43 to the outer passage of the gas heat exchanger in the manner diagrammatically shown in Fig. l.

The straight sections of the upper looped coil l2a are shown as being parallel to the lateral side walls 36 and adapted to be at such elevations that liquid refrigerant will flow by gravity from the point 39 at one end to the point 40 at the opposite end of the coil. The straight sections of the lower looped coil I 2b are transverse to the straight sections of the upper looped coil 12a and provided with heat transfer members or fins 34, the straight sections of the lower coil being at such elevations that liquid refrigerant will flow by gravity from the end section connected to the vertical conduit connection 4| to the opposite end 42 through which inert gas rich in refrigerant passes from the evaporator structure I2.

In adapting the horizontal evaporator structure l2 of Figs. 2 and 3 in a household refrigerator of the kind which is horizontally partitioned to subdivide the storage space into a plurality of compartments one above the other, the low temperature evaporator l2a may be embodied in a partition which extends from one lateral side wall to the opposite side wall of the storage space. Such an arrangement is shown in Fig. 4 in which the partition 44 comprises a casing 45 which subdivides the storage space 35 into upper and lower compartments 46 and 41, respectively.

The casing 45 may be formed of suitable sheet metal and of such size that it extends substantially over the entire width of the space 35, and from the rear wall thereof toward the open front of the cabinet to a region at which it is relatively close to the rear face of the cabinet door when the latter is in its closed position, so that circulation of air between the upper and lower compartments 46 and 47 is substantially prevented. In addition, the upper compartment 46 may be provided with a hinged door (not shown) at the forward edge of the casing 45 arranged to be resiliently biased to its closed position and readily opened by grasping a part thereof. Suitable members 48 may be positioned at the inner sides of the lateral side walls36 to provide support for the casing 45, if this should be desired. However, since refrigeration systems of the type under consideration are formed of piping and conduits of ferrous metal which are connected together, as

by welding, for example, the upper coil or evaporator I211 will be self-supporting or self-sustaining in the storage space 35 and hence the casing 45 does not actually require cabinet support, as by the members 48, for example.

The upper coil or evaporator l2a is embodied in the casing 45 in such manner that it will primarily be effective to abstract heat from the upper compartment 46 which is defined by the partition M and thermally insulated walls of the storage space 35. In Fig. 4 this is accomplished by'arranging the looped coil 12a in thermal exchange relation with the underside of the upper or top horizontal wall of the casing 45. Such thermal conductive connection of the casing 35 to the looped coil I266 preferably extends continuously along the straight sections and connecting bends of the coil. The casing 45 may be of such depth that a gap is provided between the upper looped coil I211 and the bottom horizontal wall of the casing, and the latter may be filled with suitable insulating material 49 for thermally shielding the looped coil iZa from the lower compartment ll and looped coil |2b horizontally disposed in the upper part thereof. In this way the lower looped coil or evaporator [2b will be primarily efiective to abstract heat from the lower compartment 41.

The partitioning of the storage space 35 may be effected in a variety of ways. Another manner of partitioning the storage space is illustrated in Fig. 5 which differs from Fig. 4 in that no insulating material is provided in the interior of the casing 45'. In Fig. 5 the straight sections and connecting bends of the upper looped coil in are in good thermal contact along the entire length of the coil to the underside of the top horizontal wall of the casing d5, as by brazing, for example. A gap may or may-not be provided between the upper looped coil lza and the bottom horizontal wall 56 of the casing 55' which is formed of material having poor thermal conducting properties, such as a synthetic resinous substance, for example. By providing such a bottom 50 for the casing 45', the upper and lower compartments i8 and 4'! are thermally shielded and segregated from one another whereby each of the evaporators !2a and lZb will be primarily effective to abstract heat from one of the subdivided compartments.

Another manner of thermally segregating the upper and'lower compartments 46 and Al is shown in Fig. 6 which differs from the arrangements previously described in that the upper looped coil I'Za is disposed in the metal casing 45' to the bottom horizontal wall of which is fixed a layer of thermal insulation 5! in anysuitable manner. As shown, such thermal insulation layer 5! may be arranged to rest on the side members 48 for laterally supporting the upper evaporator IZa although this is not necessary, as previously explained.

In accord with my invention liquid refrigerant flows downwardly in the upperloop coil or evaporator 52a. and also in the lower looped coil or evaporator l2b in the presence of and in parallel flow with inert gas. This will be evident when reference is made to Figs. 2 and 3 in which liquid refrigerant conducted through conduit II and inert gas flowing through conduit 2! enter the upper looped coil I 2a at the point 39 and flow in the same direction through such coil to the point as at the opposite end thereof.

Unevaporated refrigerant is conducted from the upper looped coil l2a through the vertical conduit connection 4| into one end of the lower looped coil 2b, and such refrigerant and inert gas continues to flow in the same direction and in parallel fiow through the lower looped coil l2b to the point 42 from which the mixture of inert gas and refrigerant vapor passes from the evaporator structure. Since the inert gas flows successively through the evaporators In and l2b, the gas in the upper evaporaor I'Za contains a lesser amount of refrigerant vapor than the gas in the lower cooling element I222. The partial vapor pressure of the refrigerant is a gradient, whereby the temperature of liquid refrigerant is also a gradient, the evaporating temperature of liquid being lower in the upper cooling element 12a which constitutes the freezing section of the evaporator structure.

The upper compartment 46 may, therefore, be referred to as a freezing space adapted to receive ice trays, frozen food packages and other matter to be frozen, the top horizontal wall of each of the casings in Figs. 1, 5, and 6 being substantially flat and serving as a supporting shelf for the upper freezing compartment. The lower evaporator !2b, which is the higher temperature section of the evaporator structure, is effectively utilized to cool air in the lower compartment 41.

One of the major requirements in horizontally disposed evaporators of the type just described is to provide a low temperature evaporator which will be highly effective to produce low temperature cooling for the freezing space. In horizontally disposed evaporator structure it hasgenerally been the practice heretofore toconnect the low temperature evaporator coil or section to other parts of the system in such manner that inert gas flows therethrough in counterflow to liquid refrigerant. When the low temperature evaporator is connected in the system in such manner that inert gas and liquid refrigerant pass therethrough in parallel flow, it would be expected that the mean or average temperature of the low temperature evaporator would be sufficiently disturbed by reason of the fact that inert gas weak in refrigerant and flowing from the gas heat exchanger to the low temperature evaporator passes into the presence of liquid refrigerant without previous cooling. Even though inert gas weak in refrigerant flows from the gas heat exchanger into the low temperature evaporator and no provision is made for abstracting heat therefrom prior to coming into the presence of liquid refrigerant, it has been found that low temperature evaporators connected for parallel flow of liquid refrigerant and inert gas and embodied in or associated with a horizontal partition, as disclosed herein, are highly satisfactory and capable of producing powerful low temperature cooling 'for freezing purposes.

When liquid refrigerant entering the upper looped coil or low temperature evaporator l2a is precooled, evaporation of liquid refrigerant will take place at a lower temperature at the gas and liquid inlet end of the upper looped coil. Such provision for abstracting heat from liquid refrigerant in its path of fiow from condenser 30 may be accomplished by arranging the conduit II in thermal exchange relation with the coil of the low temperature evaporator i2a, or in thermal exchange relation with the fins 34 of the higher temperature evaporator l2b. For maximum precooling of liquid refrigerant, the conduit II may be arranged in thermal contact with both the fins 34 and the coil of the low temperature evaporator I2a.

In Fig. 1 this is diagrammatically shown by the thermal contact of the conduit H with a fin 34, as indicated at 52, and the thermal contact of the conduit II with the coil of the low temperature evaporator structure 1 2a, as indicated at 53. In the horizontally disposed evaporator structure in Figs. 2 and 3, one part of the conduit ll may be arranged parallel to the straight coil section of the higher temperature evaporator [2b which is adjacent to the rear wall of the cabinet and pass through openings in fins 34. A good thermal connection 52' may be provided in any suitable manner between the conduit i l and each fin 34 through which it extends. Also, another part of conduit I! may be arranged in thermal contact with the upper looped coil I'Za, as indicated at 53'. By first passing in thermal transfer relation with the fins 34 of the higher temperature evaporator I21) and then passing in thermal transfer relation'with the coil of the low temperature evaporator lZa, liquid refrigerant is effectively precooled before passing into the presence of inert gas at the point 39 of the low temperature evaporator [211.

Even when no precooling liquid refrigerant is effected in the manner just described, it should be understood that horizontally disposed evaporator structure like that described above and embodied in or associated with a horizontal partition has been found to be highly satisfactory for low temperature cooling purposes. When the low temperature evaporator is connected for parallel fiow of inert gas and liquid refrigerant therethrough, an important advantage is gained in that the connections for circulating :fiuids through the low and higher temperature evaporators are simplified to a great extent.

Modifications of the embodiments of my invention which I have describedwill occur to those skilled in the art, so that I desire my invention not to be limited to the particular arrangements set forth. Therefore, I intend in the claims to cover all those modifications which do not depart from the spirit and scope of my invention.

What is claimed is:

1. In the art of refrigeration with the aid of an absorption refrigeration system having first and second evaporators. in which liquid refrigerant evaporates in the presence of an inert gas, the improvement which comprises flowing liquid refrigerant solely by force of gravity through said first and second evaporators, fiowing inert gas in parallel with liquid refrigerant in said first evaporator in a circuitous path of fiow extending substantially horizontally over a major portion of a first definite cross-sectional area at one'level, introducing inert gas and liquid refrigerant to said second evaporator only from said first evaporator, flowing inert gas and liquid refrigerant in said second evaporator in a circuitous path of fiow extending substantially horizontally over a major portion of practically the same definite cross-sectional area at a different level in vertical alignment with said first area, effecting said flow of inert gas through said first and second evaporators by force resulting solely from the difference in specific weight of columns of gas rich and weak, respectively, in refrigerant vapor, and utilizing said evaporators to cool different places segregated from one another.

.2. In the art of refrigeration with the aid of an absorption refrigeration system having first and second evaporators in which liquid refrigerant evaporates in the presence of an inert gas, the improvement which comprises flowing liquid refrigerant solely by force of gravity through said first and second evaporators, fiowing inert gas in parallel fiow with liquid refrigerant in said first evaporator in a circuitous path of flow extending substantially horizontally over a major portion of a first definite cross-sectional area at one level, introducing inert gas and liquid refrigerant to said second evaporator only from said first evaporator, fiowing inert gas in parallel fiow with liquid refrigerant in said second evaporator in a circuitous path of fiow extending substantially horizontally over a major portion of practically the same definite cross-sectional area at another lower level in vertical alignment with said first area, effecting said flow of inert gas through said first and second evaporators by force resulting solely from the difference in specific weight of columns of gas rich and weak, respectively, in refrigerant vapor, utilizing said first evaporator primarily to cool a first place, and utilizing said second evaporator primarily to cool a second place which extends beneath said first place and is segregated therefrom.

3. An absorption refrigeration system of the inert gas type including a low temperature evaporator connected for fiow of inert gas in parallel with liquid refrigerant, ahigher temperature evaporator provided with a relatively extensive heat transfer surface, and a conduit for supplying liquid refrigerant to said low temperature evaporator having one part thereof in heat transfer relation with said heat transfer surface and another part in heat transfer relation with said low temperature evaporator for precooling liquid refrigerant supplied to said low temperature evaporator.

4. An absorption refrigeration system as set forth in claim 3 in which said liquid refrigerant conduit is in heat transfer relation with spaced apart regions of said low temperature evaporator.

5. A refrigerator comprising a cabinet having an inner liner defining a storage space and thermally insulated walls disposed about such liner, an absorption refrigeration system containing inert gas in the presence of which refrigerant fluid evaporates, said system including a condenser outside the storage space at a level below the top of the cabinet and low and higher temperature evaporators comprising substantially horizontally disposed looped coils positioned relatively near to one another at different levels in said space in the upper part thereof, means for conducting refrigerant fiuid from said condenser to said low temperature evaporator and said higher temperature evaporator for gravity 'fiow therethrough, a partition including a horizontally disposed member having the looped coil forming said low temperature evaporator as a unitary part thereof to subdivide said space into an upper freezing compartment extending upwardly from the top surface of said member and a larger lower food storage compartment extending downwardly from the bottom surface of said member to abstract heat from said freezing compartment primarily by said low temperature evaporator and abstract heat from said food storage compartment primarily by said higher temperature evaporator, said higher temperature evaporator receiving inert gas from said low temperature evaporator and the latter being connected in the system for parallel flow of inert gas with liquid refrigerant, said horizontally disposed member serving as the bottom or floor of said freezing compartment for supporting ice trays and frozen food packages and the like, said higher temperature evaporator being provided with a relatively extensive heat transfer surface, and said means for conducting liquid refrigerant from said condenser to said low temperature evaporator including a conduit having one part thereof in heat transfer relation with said heat transfer surface and another part in heat transfer relation with said low temperature evaporator for precooling refrigerant fluid supplied to said

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