US2745256A - Evaporator of high thermal mass - Google Patents

Description

May 15, 1956 F. A. SCHUMACHER EVPORATOR OF HIGH THERMAL MASS Filed May 9, 1955 INVENTOR.

FRANK A. SCHU MACH ER FIG. 2 n Q l DA@ United States Patent i EvAPoRAToR oF HIGH THERMAL MASS Frank A. Schumacher, Louisville, Ky., assignor to General Electric Company, a corporation of New York Application May 9, 1955, Serial No. 596,745

6 Claims. (Cl. 62-4) The present invention relates to refrigerator evaporators and more particularly to a high thermal mass evaporator for the freezer compartment of a two-temperature refrigerator.

Many of the present household refrigerators comprise both a freezer compartment and a food storage compartment, separate evaporators for each of the compartments and a single refrigerant condensing means for supplying refrigerant to both of the evaporators. The refrigerating system for such refrigerators is designed to maintain the fresh food storage compartment somewhat above freezing temperatures and the freezer compartment at temperatures well below freezing, ordinarily in the neighborhood of about to 5 F. In many two-temperature household refrigerators the operation of the refrigerant condensing unit is controlled by temperature responsive means positioned within the food storage compartment. Such an arrangement ris quite satisfactory for maintaining the desired storage temperatures within the storage compartment. In addition, it lends itself to a method of operation which permits automatic defrosting of the storage compartment evaporator by providing control means `which will energize the refrigerant condensing unit only after the storage compartment evaporator has reached a temperature somewhat above freezing at which all of the frost collected thereon during a prior operating cycle at sub-freezing temperatures has melted. However a comparable rise in the temperature of the freezer compartment evaporator during a condensing unit idle period cannot be tolerated since it is necessary to main` tain the temperature of this compartment and hence the freezer evaporator continuously at temperatures preferably not exceeding a few degrees above 0 F. for the proper preservation of the frozen foodstuffs contained in the freezer compartment. Since the rate of temperature increaseof either evaporator during the idle periods depends upon the thermal mass thereof and the cabinet thermal leakage it has been customary to provide a food storage evaporator of low thermal mass and a freezer compartment evaporator of relatively high thermal mass so that during an idle period when the temperature of the fresh food evaporator increases as much as 30 F., the temperature of freezer compartment evaporator will increase only a few degrees. To obtain the desired high thermal mass for the freezer compartment evaporator this evaporator isA constructed of, or placed in contact with, suicient material of high thermal mass to prevent any substantial rise in the temperature of this evaporator during the condensing unit idle periods. This added material has increased the cost of such evaporators when the material is of the high specific heat type such as metal, or has materially increased the bulk of the evaporator as well as the manufacturing costs when materials, such as silica-filled asphalt, having similar specific heats but much lower conductivity than metal are employed to provide the desired thermal mass.

Accordingly, it is an object of the present invention 2,745,256 Patented May 15, 1956 to provide an improved low-cost freezer evaporator for a two-temperature refrigerator.

A further object of the invention is to provide an improved freezer evaporator including means adapted to increase its thermal mass to the desired point during operation of the refrigerator.

Another object of the invention is to provide a freezer evaporator composed of relatively thin or light weight metal, which itself has insucient thermal mass but which includes means for increasing the total thermal mass of the evaporator structure during the initial periods of operation of the evaporator.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of this invention, there is provided a freezer evaporator to be disposed in the freezer compartment of a refrigerator including, in addition to the freezer compartment, a fresh food compartment and a separate evaporator for that compartment. The freezer evaporator is of the plate-type and includes a plurality of spaced horizontal refrigerant passageways or tubing and a plurality of substantially horizontally disposed containers between and spaced from the refrigerant passageways adapted to collect and retain defrost water formed during the defrosting of this evaporator in sucient quantities to increase the total thermal mass of the evaporator structure. The evaporator is primarily adapted to form part of a two-temperature refrigerating system comprising a single refrigerant condensing unit for supplying liquid refrigerant both to the freezer evaporator and the separate evaporator positioned within the food storage compartment of the refrigerator with the operation of the condensing unit being controlled by control means responsive to temperatures other than those existing within the freezer compartment, as for example the temperatures of the fresh food storage compartment evaporator. Means are also provided for periodically defrosting the freezer evaporator independent of any means for defrosting the food storage compartment evaporator.

For a better understanding of this invention, reference may be had to the accompanying drawing in which Fig. 1 is a side elevation view, partially in section, of a portion of a refrigerator incorporating an embodiment of this invention;

Fig. 2 is a view along line 2 2 of Fig. l; and

Fig. 3 is a sectional view along the line 3 3 of Fig. 2.

Referring to the drawing, there is shown a refrigerator cabinet 1 including an outer wall 2 and inner walls or liners 3 and 4 which respectively deiine a frozen food storage compartment 5 and a fresh or unfrozen foodV storage compartment 6. Suitable heat insulation 7 is provided in the spaces between the outer wall 2 and the inner walls or liners- 3 and 4.

In order to cool the storage compartment 6 there is1 provided an evaporator 8 positioned in the upper portion of the compartment 6 in an inclined position such that during defrosting of this evaporator the defrost water will flow down the surfaces of the inclined evaporator and drain into a trough 9 mounted on the wall 10 of the storage compartment 6. From the trough 9 the defrost water may be disposed of by any suitable means.

A second evaporator 12 is positioned within the freezer compartment 5 for maintaining the contents of this compartment at temperatures in the neighborhood of 0 F. This evaporator is preferably mounted adjacent but spaced partment.

The evaporators 8 and 12 are adapted to be supplied with liquid refrigerant from a suitable single refrigerant condensing means (not shown). In the illustrated moditication of the invention, liquid refrigerant is supplied from the condensing means through a capillary tube to the food storage compartment evaporator 8. From this evaporator refrigerant flows through the conduit 16 and an injector 17 into the lowermost pass 13 of the serpentine tubing 19 forming part of the evaporator 12.

The liquid refrigerant ows upwardly through the various horizontal passes of the serpentine tubing 19 into a header 20 through an upper connection 21. Vaporized refrigerant is withdrawn from the header 20 through the suction conduit 22 by the condensing unit while the liquid refrigerant stored in the header 2t) recirculates through the serpentine tubing 19r which is connected to a lower portion of the header 20 by a conduit 23 extending from the header to the lowermost pass 18 of the serpentine tubing. To obtain the desired heat transfer or exchange between the evaporator 12 and the contents of the freezer compartment 5, evaporator 12 in the illustrated embodiment is in the form of a flat plate evaporator including a thin plate or sheet of aluminum or the like 25 to which the various passes of the serpentine tubing 19 are secured in heat exchange relationship. The entire evaporator stnlcture is suitably secured to the rear wall 14 of the freezer compartment by means of studs 26.

As is the case with most household refrigerators of the two-temperature type, the operation of the condensing unit is under the control of a temperature responsive control switch 2S which includes a feeler bulb 29 responsive to temperatures within the food storage compartment 6. In the modilication illustrated the feeler bulb 29 is mounted in heat exchange relationship with the evaporator 8 and is adapted to energize the refrigerant condensing unit only when the temperature of this evaporator reaches a predetermined maximum somewhat above the freezing point of water and to de-energize the condensing unit when the temperature of the evaporator 8 reaches a predetermined minimum substantially below the freezing point of water. By this arrangement, suitable abovefreezing storage temperatures are maintained within the storage compartment 6 and as the evaporator S attains a temperature above freezing during each idle period of the condensing unit any frost formed on this evaporator during operation of the condensing unit melts and drains into the trough 9 during the idle period.

While the control arrangement such as that just described provides a simple means for obtaining automatic defrost of the storage compartment evaporator S, it provides a definite problem with regards to the maintenance of the desired freezing temperatures within the freezer compartment 5. During the idle periods of the refrigerant condensing system, no refrigerant is being supplied to the evaporator 12 and unless some means are provided for preventing this evaporator from warming up to too great an extent during the defrosting cycle of the evaporator S, spoilage of the contents of the freezer compartment 5 may result. Y

y One means for minimizing the swing in the temperature of the freezer evaporator 12 during cycling of the refrigerant condensing unit comprises making this evaporator sufficiently larger than the storage compartment evaporator 8 so that its relatively higher thermal mass will prevent it from warming more than a few degrees above zero during the condensing unit idle period. For example, in order to maintain a storage temperature in the neighborhood of 40 F. in the compartment 6, the control 2S .may be arranged toy energize the compressor whenever the evaporator 8 attains a temperature of about 38 F. following an idle and defrosting cycle and to deenergize the compressor when the temperature of the evaporator 8 reaches a minimum of about 18 F. Thus it is seen that during the idle period the temperature of the evaporator 8 rises a total of 20 F. While the restrictive effect of the injector 17 and any other restrictive means provided in the line 16 leading from the storage compartment evaporator 8 to the freezer evaporator 12v causes the freezer evaporator to operate normally at a much lower temperature range, this evaporator also exhibits a swing in temperatures between the on and ofi cycles. in the absence of some precautions to prevent such action, the freezer evaporator 12 will will also tend to undergo a substantial temperature swing in the neighborhood of 20. Since in most household refrigerators, the freezer evaporator is cooled to a temperature only a few degrees below 0 F. during the on cycle, it is obvious that a 20 rise of 15 F. or more cannot be tolerated.'

The presently known arrangements for increasing the thermal mass of the freezer evaporator in order to cut down the temperature swing thereof have as a major disadvantage the increased cost or increased bulkiness, or both of a high thermal mass evaporator. For example, an evaporator made of the same material as the storage evaporator 8 e. g. aluminum, must contain at least two or three times as much material as the storage evaporator S in order to limit the temperature swing of the freezer evaporator to a safe range of not more than 8 to 10 F. This results in a freezer compartment evaporator having at least twice the material cost of the storage compartment evaporator. While cheaper materials such as silicatilled asphalt or the like can be used in conjunction with the freezer evaporator to increase its over-all thermal mass, the resultant increased volume of the evaporator materially cuts down on the available storage volume ofv the freezer compartment 5.

In accordance with the present invention there is provided an evaporator structure for the freezer compartment 5 having the advantages of relatively low initial cost and relatively low bulk or volume. In addition to the flat plate 25 and the serpentine tubing 19, this evaporator comprises a plurality of receptacles or containers 31 which are mounted on the plate 2S between adjacent passes of the serpentine tubing in heat exchange relationship with the plate 2S. These receptacles 31 which are preferably positioned about midway between adjacent horizontal passes of the serpentine tubing 19 are adapted to collect and retain defrost water formed during the defrosting of the freezer evaporator. This water freezes in the containers 31 and the resultant mass of ice increases the total thermal mass of the freezer evaporator. Since the thermal mass of ice is more than twice that of aluminum, it will be seen that on a weight basis the ice contained in the containers 31 provides over twice the thermal mass of this same weight of aluminum. Furthermore, since this ice, or more specifically the water fromwhich it is formed, costs nothing but rather results from the inherent operationof the refrigerating system, there is provided an extremely low cost means for obtaining a high thermal mass evaporator structure.

If desired, the containers 31 may be lled with tap water when the refrigerator is initially put into use. However, since considerable condensation takes place during the initial operating periods, the condensate formed on the evaporator 12 which collects in the containers 31 until the time that the evaporator 12 reaches and continuously operates at sub-freezing temperatures may be sufiicient to lill the containers 31 to overowing.

Since the freezer evaporator 12 is positioned Within the freezer compartment 5 and hence is exposed to the air within this compartment, frost also tends to collect on all of the surfaces of theA freezer evaporator. In order to eliminate the insulating characteristics of the resultantV frost layer it is desirable periodically to defrost this evaporator. However, it is not necessary to defrost it as often as the storage compartment evaporator 3. Therefore separate defrosting means are advantageously provided for the purpose of periodically defrosting the freezer evaporator. In the modification shown thisdefrosting means comprises an electrical heating element 33 arranged in heat exchange relationship with the lower lpass' 18 of the .serpentine tubing 19. Energizationof the heater 33 is under the control ofa switch 34 which may be either manually operated or controlled by aA timer adapted for example to energize the heater 33 after a predetermined operating period of the refrigerator. When the heater 33 is energized the refrigerant within the lower pass 18 becomes warmed and this warming and partial evaporation of vaporization ,of the refrigerant effects a natural circula-Y tion of the warmed refrigerant upwardly through the various passes of the serpentine tubing 19,to the header 20. At the same time, fresh refrigerant is owing from the header down the' connection 23 to the lower pass 18.

The heater 33is de-energized by any conventional control device which is operated for example by means of a temperature Yresponsive bulb 35 connected by a tube 36 tolthe control device. When the circulation of warmed refrigerant-through the serpentine 19 nally raises the temperature ofthe upper part of the plate 25 above the melting'point of'the frost, the warming of the control bulb 35 terminates the defrosting cycle;A

The broad idea of a defrosting larrangement in which heat is supplied to a continuous evaporator tubing is not part of the present invention. Various arrangements for accomplishing such defrosting are described and claimed in Patents 2,665,567-King et al. and 2,665,566-Grimshaw assigned to the same assignee as the present invention, and reference is made to these patents for detailed description of the manner in which the defrosting is accomplished.

During defrosting of evaporator 12 by the circulating warmed refrigerant with the serpentine tubing 19, the plate 25, and the walls 38 of the containers 31 become warmed to defrosting temperatures, i. e. temperatures above freezing, due to the high heat conductivity of the aluminum or other metal of which the evaporator 12 is formed. In general, the ice within the containers 31 will not be melted except for a relatively thin layer thereof adjacent the container walls. However, this slight melting of the ice plus the ow of defrost water down over the frozen contents of the containers effects a gradual leaching or washing action during each defrost period with the result that the ice contained in the containers 31 is kept substantially odor-free.

Excess defrost Water 'om the evaporator 12 collects on the bottom Wall 39 of the freezer compartment from which it is conducted by means of a drain tube 40 into the storage compartment 6 above the trough 9 provided in that compartment for collecting defrost water from the lower evaporator water 8.

From the above description it will be seen that .there has been provided by the present invention a relatively low-cost freezer evaporator having su'icient thermal mass to limit the temperature swing of the freezer evaporator during the condensing unit idle periods. The invention is adapted to any freezer evaporator where it is necessary that the control point be located remotely from the evaporator or compartment served by that evaporator. The increased thermal mass of the evaporator obtained by the provision of the trough 31 will depend, of course, upon the number of troughs and their total volume. Preferably a separate trough is provided between each pair of adjacent horizontal passes of the serpentine tubing 19 and each trough is preferably positioned midway between the adjacent passes for most eicient defrosting of all the surface area of the evaporator. It will be obvious,.of course, that the trough cannot enclose or overlap the various passes as this would materially interfere with the cooling capacity of the passes and the ease of defrosting thereof. As the evaporator is positioned or disposed within the freezer compartment of a household refrigerator, a more pleasing appearance is obtained by positioning the troughs 31 and the serpentine tubing 19 on the back of the plate 25 or in other words out of view or hidden by the plate 25. While the invention has been shown in the form' of a' vertically disposed ooded evaporator it will be obvious that the evaporator may be of the series type'and may also be disposed in a sloping position, the only limitation being that the arrangement must be one in which the defrost water can be collected'andr retained by the troughs.

`What I claim as new and desire'to secure by Letters Patent of the United States is:

. l. A refrigerator including a storage compartment andy only after said storage compartment evaporator hasy warmed to defrosting temperature, said freezer compartment evaporator comprising a at plate and including a plurality of substantially horizontal passes of refrigerant passageways and receptacles mounted on said plate betweenV adjacentfpassageways inna position to receive and retain defrost water formed during defrosting said evaporator whereby the ice formed during operation of said evaporator effectively increases the thermal mass of said evaporator.

2. A refrigerator including a storage compartment and a freezer compartment, refrigerant evaporator means in each of said compartments for maintaining the desired temperatures therein, electrically operated refrigerant condensing means for periodically supplying liquid refrigerant to both of said evaporator means, means responsive to the temperature of the evaporator in said storage compartment controlling the operation of said condensing means and adapted to energize said condensing means only after said storage compartment evaporator has warmed to defrosting temperature, said freezer compartment evaporator comprising a at plate, a plurality of substantially horizontal passes of refrigerant tubing mounted on said plate and defrost water collecting means mounted on said plate between adjacent tubing passes for collecting and retaining defrost Water formed during defrosting said evaporator thereby increasing the thermal mass of said evaporator.

3. A refrigerator including a storage compartment and a freezer compartment, refrigerant evaporator means in each of said compartments for maintaining the desired temperatures therein, electrically operated refrigerant condensing means for periodically supplying liquid refrigerant to both of said evaporator means, means responsive to the temperature of the evaporator in said storage compartment controlling the operation of said condensing means and adapted to energize said condensing means only after said storage compartment evaporator has warmed to defrosting temperature, said freezer compartment evaporator comprising a at plate including a plurality of substantially horizontal passes -of refrigerant tubing and water containing receptacles mounted on said plate between adjacent tubing passes for increasing the thermal mass of said evaporator.

4. A plate-type evaporator adapted to be disposed in the freezer compartment of a refrigerator including in addition to said freezer compartment, a fresh food storage compartment, a second evaporator for said storage compartment and refrigerant condensing means for periodically supplying liquid refrigerant to both of said evaporators in response to cooling requirements of said second evaporator, said plate-type evaporator including a plate and a plurality of substantially horizontal spaced refrigerant passes and defrost water collecting means mounted on said plate between adjacent passes of said tubing for collecting and retaining a substantial portion of the defrost Water formed during defrosting of said plate-type evaporator thereby increasing the zthermal mass of said plate-type evaporator.

5.f A platetype evaporator. adapted to be disposedin the frezeer compartment of a refrigerator including iny addition to said freezer compartment, a fresh food storage compartment, a second evaporator for said storage compartment .and refrigerant condensing means for periodically supplying liquid refrigerant to both of said evaporators in response to cooling requirements of said second evaporator, said plate-type evaporator including` a.plate, a pluralityof substantially horizontal spaced passes of refrigerant tubing secured in heat exchange relationship with said plate, and defrost water collecting means mounted on said plate between adjacent passes of said tubing for collecting and retaining a substantial portion of the Ydefrost water formed during defrosting. of said plate-type evaporator thereby increasing the thermal mass of saidplate-type evaporator.

y6. A plate-type evaporator adapted to be disposed in the freezer compartment of a refrigerator including in addition to said frezer compartment, a fresh food stor-f age compartment, a second revaporator for saidstorage rodicallysupplying liquid" refrigerant A`to both offsaid cvaporatorsY in kresponse'to cooling requirements of said second evaporatonisaid plate-type: evaporator including a plate, a plurality of substantially horizontal spaced passes of refrigeranttubing secured in heat exchange relationship withrsaid plate, and horizontally disposed recepfu tacles mounted on said plate between adjacent pa'ssesfof said tubing'or collecting and retaining a substantial portion ofthe defrost water formed during defrosting of said plate-type'evaporator thereby increasing the Ythermal mass ofV 'said plate-type evaporator.

References'Cited inthe 1`e. of this patent Y STATES A'lllrll`sl 2,145,776 p Mlrly Ian. 31.1939 Y2,250,612 vTanner July 29, 1941 2,319,522 Schwell'erar. .YMay 18,1943` 2,585,736 Burr t. ...`.,-Feb. 12, 1952 2,665,566v Grtmsigaw Jan. 12,1954 2,665,567 King ,etaL- z Jan. 12, 1954 2.672.020

. Wurtz etA al,j Mar. 16. 1954

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