US2664716A - Refrigeration apparatus and method employing - Google Patents

Description

Jan. 5, 1954 N. M. WARMON 2,664,715

REFRIGERATION APPARATUS AND METHOD EMPLOYING COLD ACCUMULATOR Filed Feb. 26, 1949 /I x/ xx INVENTOR.

ka WT F/VEY Patented Jan. 5, 1954 ath ne UNITED STA'EES PATENT OEFEE REFRIGERATION APPARATUS AND METHOD EMPLOYING COLD ACCUMULATOR Nils Magnus Warmon, Stockholm, Sweden, as-

signor to Aktiebolaget Elektrolux, Stockholm, Sweden, a corporation of Sweden 10 Claims.

My invention relates to refrigeration, and more particularly to preservation of frozen food packages and the like and freezing of foods preparatory to storage and preservation thereof.

It is an object of my invention to provide an improvement in 'efrigerators for storing frozen food packages and the like and freezing foocls to prepare them for such storage and preservation, which is particularly suited for refrigerators of this type operated by continuous absorption refrgeration systems employing an inert gas or pressure equalizing agent, whereby a maximum amount of useful storage space is made available for a refrigerator of a given size. I accomplish this by providing cold accumulators containing a suitable eutectic solution which may be placed in the storage space of a refrigerator of this type during periods of light or normal load, the eutectc solution in such cold accumulators freezing during such Operating periods and serving as a source of refrgeration which supplements the refrigerating effect produced by the refrigeration system of the refrigerator during periods of increased load, as when pachages containing food to be frozen are placed in the storage space, for example.

The above and other objects and advantages of this invention will be better understood from the following description and accompanying drawing forming a part of this specification, and of which:

Fig. 1 is a front vertical section more or less diagrammatically illustrating a refrigerator einbodying the invention;

Fig. 2 is a side vertical section of the refrigerator shown in Fig. l to illustrate details more clearly;

Fig. 3 is a front vertical section of a refrigerater diagrammatically illustrating another embodinent of the invention; and

Figs. 4 and 5 are front and side elevations of a part employed in the refrigerators of Figs. 1 to 3 inclusive.

Referring to Figs. 1 and 2, the invention is shown in connection with a refrigerator comprising a cabinet I@ having an inner metal shell ii arranged to be supported within an outer metal shell 2 and insulated therefrom with any suitable insulating material i i. The inner metal shell !i defines a thermally insulated storage space 95 for storing frozen food packages iii and also holding packages il containing food to be .frozern as will be described presently. Access to the storage space [5 is had through the open top thereof which is adapted to be closed by a removable closure member or lid !8 containing a suitable insulating material.

The storage space !5 is arranged to be cooled by an evaporator !9 in the form of a coil which is disposed about the inner metal shell and in good thermal contact therewith, as by welding. The evaporator is is connected to a condenser ZE! which is in heat exchange relation with a cooling element Zi, the evaporator li) and condenser 28 forming a secondary heat transfer system in which the evaporator is of the fiooded type and at a lower level than the condenser.

The evaporator 59 and condenser 26) form a closed fluid circuit which is partly filled with a suitable volatile fluid that evaporates in the evaporator [9 and takes up heat thereby producing cold. The vapor fiows from evaporator iii into condenser 2!) in which the vapor is cooled and condensed by cooling element 2 i. The liquid condensate formed in condenser 29 returns by gravity through Conduit 22 to the evaporator !8.

The cooling element 2! forms part of a refrigeration system of the absorption type containing an inert gas or pressure equalizing agent. In such a system refrigerant vapor is expelled from absorption liquid in a boiler 23 by heating and flows through a conduit 24 to an air cooled condenser 25. The refrigerant vapor, such as arnmonia, is liquefied in the condenser 25 and fiows through conduit 26 into cooling element Zi in which liquid refrigerant evaporates and diifuses into an inert gas, such as hydrogen, to produce a refrigerating effect for condensing vapor in the condenser 20.

The resulting gas mixture of refrigerant and inert gas fiows from cooling element 2! through a Conduit 21 and one passage of a gas heat exchanger 28 to an absorber which may be of an air cooled type including a coil and an absorber vessel. In the absorber refrigerant is absorbed from the gas mixture into absorption liquid, such as water, which is delivered thereto. The inert gas is returned from the absorber to the lower end of cooling element Zi through another passage of gas heat exchanger 28, and absorption liq uid enriched in refrigerant fiows from the absorber to the boiler 23 in which refrigerant vapor is expelled from liquid. Absorption liquid deprved of refrigerant returns from the boiler 23 to the absorber to absorb refrigerant vapor, such circulation of liquid usually being effected by vapor-liquid lift action. In order to simplify the drawing, the boiler 23 is schematically illus trated while the absorber and connections thereof to other elements of the refrigeration system 3 have net been shown, such parts being well known and their iliustration not being necessary for an understandin of my invention.

In accordanoe with the invention I provide cold accunulators E@ containing a suitable eutectic solution which 'may be placed in the storage space !5 during periods of light or normal load on the absorption refrigeration system, thereby causing the eutectic solution to freeze and serve as a source of refrigeration which supplements the rerigerating efiect produced by the absorption refrigeration system during periods of increased load. In this way the cold accumulators become "charged during periods of light or normal load, that is, are conditioned to serve as a supplementary source of 'cold which is advantageously utilized to take care of socalled peai loads, as when a number of packages containing food to be frozen are placed in the storage space i at practically the same time.

As best shown in Figs. i and 5, the cold accumulators Sii comprise substantially flat sheets i and 32 which are relatively close to one another, the peripheral edge portions of the sheet 3! being fianged peripheral edge portions of the sheet 32, as indicated at 33. Fhe spaced apart sheets 32 and 32 may be iormed of galvanized iron sheeting or any other suitable material, and the joint therebetween may be brazed or soldered to provide a liquid tight seal. In order that the cold accumulators 39 will stand up under continued use, the outer 'surfaces thereof may be coated with a layer of corrosion resisting material, such as an asphalt lacquer, for example.

An end Wall of the cold accumulators 39 desirably is formed with two threaded openings adapted to receive threaded caps or closure members S i and respectively, one of which serves as a filling opening for a suitable eutectic solution and the other as a vent for Venting air from the interier of the cold accumulator When it is being filled withthe solution. The closure members sa and 35 should effectively seal the eutectic solution within the interior of the cold accumulators 3& and may be shaped so that the latter can be raised and readily moved With the aid of a suitable tool or clamp having parts adapted to take hold of the closure members and readily removable therefrom.

In the refrigerator ill illustrated in Figs. l and 2, frozen food packages !3 positioned in the storage space !5 are stacked upon one another in several rows adjacent opposing side walls and an end wall of the inner metal shell or liner i i. At the opposite end of the storage space !5 are positioned a number of cold accumulators 30 which serve as a supplementary source of cold and cooperate with the refrigerat'ng eect produced by the absorption refrigeration system to eect freezing of food within the packages H. In Figs. i and 2, a cold accumulator 30 is horizontally positioned directly on the bottom of the inner metal shell H. Each package !1 is positioned between adjacent horizontally disposed cold accumulators, so that heat will be rapidly taken up by the cold accumulators from opposite sides of each package at the same time, thereby promoting quick freezing of oods which is desirable in certain instances in order that the physical characteristics of the food will not be impaired.

In accord with the the invention the cold accumulators 353 are placed in the storage space !5 when space is available and the load in the refrigerator is normal. By a normal load is meant bent back and overlying the outwardly a load which is made up primarily of frozen food packages which are already at a low temperature. Under such conditions the load on the refri erator is relatively light because the refrigeration then required must only be sufficient to balance the heat leakage of the refrigerator cabinet. When the cold accumulators 30 are placed in the storage space 15 to be conditioned for use, they may be placed horizontally on top of one'another without any inserts therebetween, or in upright positions adjacent to one another so that air can circulate therebetween. The greater the surface contact is between the inner metal shell ii and the cold accumulators, the less time Will then be required to condition the cold accumuiators ready for use in the manner previously described and shown in Figo. l and 2.

Another manner of employing the cold accumulators E@ to effect quick freezing of packaged food is shown in Fig. 3 which illustrates a rerigerator like that shown in Figs. 1 and 2, like parts 'being designated by the same reference numerals. In Fig. 3 the packagcs ll containing food to be frozen are positioned vertically between vertically disposed cold accumulators 3%, one of which bears directly against a side Wall of the inner metal shell i i. While in Figs. 1 and 2 the weight of the aceumulators themselves insures a good thermal contact between the latter and the packages il, this is not so in the arrangement of Fig. 3. Accordingly, provision must be made to cause the cold accumulators to bear against the opposing sides of the vertically disposed packages. This may be accornplished by providing a suitably shaped clamp 35 which acts to hold a group of assembled cold accumulators and packages resiliently together, thereby snugly holding the accumulators against the sides of the packages.

It is especially desirable to employ in the cold accumulators 3& an eutectic solution possessing corrosion resisting properties, and I have found that sodium nitrite and potassium chromate, and in certain instances sodium chromate, have such desirable properties. In employing sodium nitrite to provide an eutectic solution, I have found that an aqueous solution of sodium nitrite with a dehydrated salt content of about 397% by weight has a freezing temperature or eutectic point of about -15.5 C. In employing potassium chromate to provide an eutectic solution, I have found that an aqueous solution of potassium chromate with a dehydrated salt content of about 355% by weight has a freezing temperature or eutectic point of about -l1.4 C., and a melting heat of about 49 to 50 kcaL/kg. In employing sodium chromate to provide an eutectic solution, I have found that an aqueous solution oi` such a salt has a reezing temperature or eutectic point of about -5 C.

It is desirable to employ an eutectic solution whose freezing and melting temperature is more or less constant and is not subject to excessive undercooling or supercooling. stated another way, the freezing temperature of eutectic solutions often varies and such solutions often actually freeze at a temperature which is below the temperature at which reezing actually should take place. When this occurs, it may be said that the eutectic solution is "undercooled or "supercooledi' While the aqueous solution of sodium nitrite referred to above possesses corrosion resisting properties, it frequently freezes at a temperature of -23 C. although its eutectic point is in the neighborhood of -15 C. The

is admirably suited for use as an eutectic solution.

When the temperature of the refrigerator storage space is 'maintained at a temperature in the neighborhood of -16 C., the undercooling of 'an eutectic solution of potassium -chromate has been found to be about 4 C. Hence, the maxiimum variation in freezing temperature of the aqueous solution of potassium chromate which can be expected is relatively small and in a range of only 4 C., while such variation in freezing temperature of the aqueous solution of sodium nitrite is greater 'and in a range of about 8 C Since the freezing temperature or eutectic point of the -aqueous solution of sodium chromate is in the neighborhood of -5 C., such an eutectic solution is not satisfactory to effect rapid freezing of food since the freezing temperature of most foods is about -2 C., and this difference in temperature is not sufiicient.

The length of time required to freeze food is more or less in inverse ratio to the difference in temperature of the freezing point of foods and the temperature of the surfaces of the cold accumulators when the eutectic solution therein is frozen and conditioned for use. In order to insure freezing of the eutectic solution employed in the cold accumulators 3!) at all times, and disregarding undercooling or variations in freezing temperature of the eutectic solution which possibly may occur, the freezing temperature of the eutectic solution desirably should be at least 3 to 4 C. above the temperature at which the freezing space of the refrigerator is normally maintained, and less than C., preferably in a temperature range of about -10 to -17 C.

When the storage spaces of the refrigerators shown in the drawing are maintained at a normal Operating temperature of about -16 C. by the absorption refrigeration system employing an inert gas, it will be seen that cold accumulators se containing an eutectic solution of potassium chromate like that referred to above Satisfactorily meet these requirements. The eutectic point of the aqueous solution of potassium chromate being about -11.4 C., such eutectic point is about 4.6` C. above the temperature at which the storage space is normally maintained and also falls below -10 C. and in the temperature range of .-10 to -17 C.

When the cold `accumulators 30 are charged with a suitable eutectic solution, the accumulators should not be completely filled with liquid because the eutectic solution expands to a considerable extent upon freezing. When the cold accumulators 30 are vertically disposed in the manner shown in Fig. 3, the air pockets therein are at the extreme upper regions and will not impair the effectiveness of the cold accumulators because the frozen mass is in good contact with both of the opposing surfaces 31 and 32.

However, when the cold accumulators 30 are horizontally disposed in the manner shown in Figs. 1 'and 2, air pockets in 'parts thereof which bear against packages containing food tobe frozen is not desirable. In such case, provision should be made in any suitable manner to provide an air pocket which will not impair the usefulness of the cold :accumulators to eifect rapid freezing of foods. However, even when the cold accumulators 3!! are to be used in the manner shown in Figs. 1 and 2, such accumulators may be conditioned for use by placing them vertically in the storage space l5.

In view of the foregoing, it will now 'be evident that by employing cold accumulators 3@ like those illustrated and just described, -a refrigerator adapted to -operate at a sufciently low temperature for storing frozen food packages and freezing foods prior to storage may be of minimum size to take care of a definite maximum load. This is especially true when a refrigerator employed as a freezer is maintained at a low temperature with an absorption refrigeration system of the inert gas type which operates continuously and hence differs from compression refrigeration systems which only operate a part of the time, such intermittent Operating interval of time depending upon the character of the load, that is, whether only frozen food `packages 'are being kept at a safe refrigerating temperature to prevent thawing thereof, or such a load is supplemented by a load required to freeze food contained in Dackages or wrapped in 'any other manner.

since the very character of absorption refrigeration systems of the inert gas type lena themselves to continuous operation, the provision of cold accumulators 30 is admirably suited for refrigerators particularly constructed for freezing purposes which are operated by inert gas absorption refrigeration systems. By way of example and without limitation, it is only necessary to provide a refrigerating or cooling eifect of about 50 kcaL/hr. in a freezer space of about 3 cubic feet for a normal or light load primarily consisting of frozen food packages which are already at a low temperature, and in such case the refrigerating effect necessary must only be suicient to balance the heat leakage of the refrigerator cabinet, as previously explaned. Accordingly, a freezing unit of minimum size` may be employed in accord with the invention when a continuously Operating absorption refrigera tion system of the inert gas type is employed which meets the minimum requirements for such a normal or light load and maintains the thermally insulated storage space at a temperature in a range of -l2 to -20 C. When the load on the refrigerator increases above the normal or light load the cold accumulators, previously conditioned for use, can be efifectively employed to provide an additional or supplementary source ;f refrigeration to take care of such additional oad.

Modifications of the embodiment of my invention which I have described will occur to those skilled in the art, so that I desire my invention not to be limited to the particular arrangements set forth. For example, a corrosion resisting agent may be added to an eutectic solution as well as employ an eutectic solution formed of salts which in themselves possess corrosion resisting properties, as described above. 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:

In a method of refrigeraticn, the steps which comprise artificially producing a refrigerating efiect by a refrigeration system at a place of cooling which is disposed exteriorly of a thermally insulated space and in thermal relation therewith to maintain such space at a desired low temperature to preserve matter therein below the freezing temperature of water when the load in said space is in a first range, positioning one or more readily movable bodies of eutectic