US2895306A

US2895306A - Hot gas defrost system including bypass-suction line heat exchange

Info

Publication number: US2895306A
Application number: US642823A
Authority: US
Inventors: Bruce B Latter
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1957-02-27
Filing date: 1957-02-27
Publication date: 1959-07-21
Anticipated expiration: 1976-07-21

Description

July 21, 1959 B. B. LATTER 2 895,3

HOT GAS DEFROST SYSTEM INCLUDING BYPASS-SUCTION LINE HEAT EXCHANGE Filed Feb. 27, 1957 INVENTOR. BRucE s. LATTEP- His A'i'ToRuW-Y United States Patent Ofiice 2,895,306 Patented July 21, 1959 HOT GAS 'DEFROST SYSTEM INCLUDING BYPASS- SUCTION LINE HEAT EXCHANGE Bruce B. Latter, Louisville, Ky., assignor to General Electric Company, a corporation of New York Application February 27, 1957, Serial No. 642,823

2 Claims. (Cl. 62-152) The present invention relates to a refrigerating system including means for the hot gas defrosting of a low temperature compartment evaporator component of the system. It is more particularly concerned with a twotemperature refrigerating system including a low temperature compartment evaporator and a high temperature compartment evaporator in series connection in the system and improved means for the hot gas defrosting of the low temperature compartment evaporator.

Household refrigerators of the two-temperature type normally include a first evaporator which operates continuously at below-freezing temperatures for the storage of frozen foods and a second evaporator for maintaining the fresh food compartment of the refrigerator at above freezing temperatures. Because the accumulation of frost on evaporator surfaces lowers the etficiency of the refrigerating system, it is necessary periodically to remove the frost accumulation. Since the temperature of the fresh food compartment is above freezing, the removal of frost from the evaporator serving the compartment presents no particular problem. For example, the evaporator used to cool that compartment can be operated above freezing during part of the refrigerating cycle, thus permitting the accumulated frost to melt. However, since the freezer compartment must be held continuously at temperatures well below freezing for the proper storage of frozen food and since that evaporator is normally in contact with or closely adjacent to at least part of the contents of the freezer compartment, any acceptable automat-i defrosting arrangement for the freezer evaporator must not only effect rapid melting of the accumulated frost but must also accomplish this melting at the lowest possible temperature.

It is an object of the present invention to provide an automatic hot gas defrosting system for defrosting a freezer evaporator both rapidly and at temperatures close to freezing temperatures.

A more specific object of the invention is to provide a hot gas defrost system by means of which the compressed refrigerant gas is introduced into the evaporator at a temperature such that only the latent heat of the refrigerant is employed for defrosting purposes.

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 a part of this specification.

In carrying out the objects of the invention, there is provided a refrigerating system comprising a compressor, a condenser, a capillary tube flow restricting element, evaporator means including a low temperature or freezer evaporator, and a suction line connected in series refrigerating circuit. During normal operation of this system compressed refrigerant from the compressor is condensed in the condenser and passes through a capillary tube to the evaporator means Where it is evaporated for maintaining the proper refrigerating temperatures within a refrigerator. Vaporized refrigerant is returned through the suction line to the compressor. In accordance with the usual practice, the suction line and capillary tube are arranged in heat exchange relationship for reasons which are well known in the art. The system also includes a defrosting comprising conduit connecting the compressor directly to the inlet end of the freezer evaporator for in troducing hot compressed refrigerant directly from the compressor into the evaporator. In accordance with the present invention this conduit is arranged in heat exchange relationship with the suction line so that the cool gas in the suction line will remove from the hot compressed refrigerant substantially all of the superheat with the result that the defrosting gas as introduced into the freezer evaporator will be only slightly above its condensing temperature. Melting of the accumulated frost on the freezer evaporator is then accomplished by the latent heat given up by the defrosting gas. As a result the accumulated frost is removed from the freezer evaporator at the lowest possible temperatures. In addition the heat interchange between the bypass conduit and the suction line warms the suction line to prevent undesirable sweating thereof under humid ambient conditions. This warming of the suction line and hence the suction gas also serves to increase the load on the compressor. Also by operating the bypass conduit at temperatures somewhat lower than those which would exist without the heat exchange arrangement, heat losses to ambient between the compressor and the freezer evaporator are minimized or decreased.

For a better understanding of the invention reference may be had to the accompanying drawing in which:

Fig. 1 is a view of a'portion of a refrigerator incorporating an embodiment of the present invention; and

Fig. 2 is a schematic illustration of a refrigerating sys tem employed in the refrigerator of Fig. 1.

Referring to the drawing there is shown in Fig. 1 a portion of a two-temperature refrigerator which includes a frozen food compartment 1 and a fresh food compartment 2. The refrigerating system employed to maintain these two compartments at their proper operating temperatures is shown schematically in Fig. 2. This system includes a hermetically sealed motor-compressor unit 3 and a condenser 4. The system further includes a low temperature or freezer evaporator 5 which is disposed in heat exchange relationship with the walls of the freezer compartment 1 and a fresh food evaporator 6 which is disposed in the fresh food storage compartment 2 and is designed to maintain this compartment at above freezing temperatures. During the normal refrigerating cycle, compressed refrigerant is supplied from the compressor 3 to the condenser 4. In the condenser 4 the hot com- -pressed refrigerant is cooled and liquified and passes through a capillary tube 8 into the freezer evaporator S which is arranged in the form of a serpentine coil along the top, back and side walls of the freezer compartment 1. From the freezer evaporator 5, the refrigerant passes through a loop 9 extending upwardly along the back wall of the freezer compartment 1 and then downwardly into the serpentine fresh food evaporator 6 arranged in the storage compartment 2. In these two evaporators liquid refrigerant is vaporized and the refrigerant vapor collecting in header 10 connected to the outlet end of the serpentine evaporator 6 is returned through the suction line 11 to the compressor 3. Preferably, the suction line 11 is in heat exchange relationship with the capillary 8 so that the cool refrigerant vapor in the suction line will further cool the refrigerant liquid passing to the evaporator system through the capillary 8. In addition the heat exchange between the capillary 8 and the suction line'11 tends to raise the temperature of the gas in the suction line 11 to maintain the portions of the line such as the portion 12 exposed to ambient conditions above the dew point and thus prevent sweating of the suction line.

The normal operation of the system 1s controlled by the switch 15 which is adapted to engage the contacts 16.

in a line 17 through which power is supplied to the motor compressorunit 3. The switch 15 is actuated by a bellows 18 in response to the temperature of the fresh food evaporator 6 by means of the thermostatic bulb 19 positioned in contact with the evaporator 6. Accordingly, the normal or refrigerating operation of the system is controlled by the temperature of the fresh food evaporator 6. To preventthe accumulation of frost on the evaporator, the switch 15 is arranged to energize the compressor unit 3 only after the fresh food evaporator 6 has attained a temperature above freezing .to assure the melting of accumulated frost collecting on this evaporator during the previous cycle of operation of the compressor and to de-energize the compressor unit 3 when the fresh food evaporator 6 has reached a sub-freezing temperature in the neighborhood of or close to that sought to be maintained in the freezer compartment 1.

Due to the fact that the freezer compartment 1 is separate from and insulated from the fresh food compartment 2, the temperature of the freezer compartment will fluctuate only a few degrees during the on and off cycles of the compressor unit 3 even though the evaporator 6 subjected to the higher temperatures of the fresh food compartment 2 will exhibit a temperature change over a range from approximately F. to 35-37 F.

Because the freezer evaporator operates continuously at well below freezing temperatures, there is a gradual accumulation of frost within the freezer compartment 1 and more specifically on the walls froming this compartment. reducing the etficiency of the freezer evaporator, it is necessary to remove the accumulated frost from time to time. Furthermore, since this frost must be removed in a manner which will not cause a substantial rise in the temperature of the frozen foods stored in that compartment, the means for hot gas defrosting of the freezer evaporator 5 provided in accordance with the present invention isdesigned .to eifect the periodic removal of frost from his evaporator both rapidly and at relatively low temperatures. To accomplish these purposes there is provided a conduit 21 bypassing the condenser 6 and the capillary 8 and connecting the outlet of the compressor 3 to the inlet portion 22 of the freezer evaporator 5. A solenoid valve 23 provided at the junction of the bypass line 21 with the line 24 connecting the compressor 3 with the condenser 4 is provided to control ofthe flow of refrigerant through the bypass line 21.

When the solenoid valve 23 is de-energized the refrigerant follows the normal path from the compressor 3-to the condenser 4. Energization of the valve 23 causes the refrigerantto flow through the bypass line 21 directly to the frozen food evaporator 5.

The operation of the valve 23 is controlled by a switch 26 which also controls the operation of the compressor 3 independent of the switch 15. The switch 26 may be of any suitable type. For example, it may be a manually controlled switch whereby the user of the refrigerator.

against which the compressor unit 5 must pump and there by increase the watt input to the compressor inptor sub- As this layer of frost has an insulating effect stantially abovethe input in the case where a nonrestricted hot gas flow line is employed.

During operation of the system of this type on the defrost cycle, compressed gaseous refrigerant flows from the bypass line 21 through the freezer evaporator 5 and raises the temperature of this evaporator to that which will effect melting of accumulated frost. In order to limit the temperature rise of any portion of the freezer refrigerant entering the freezer evaporator 5 is at a temperature such that substantially only the latent heat of the compressed refrigerant is employed for defrosting purposes. By thus removing the superheat from the compressed defrosting refrigerant gas and using only the latent heat, defrosting of the freezer evaporator is accomplished at the lowest possible temperature, and with the least possible temperature gradient from evaporator inlet to outlet. In other words by removing the superheat through heat exchange of the suction line 12 and the bypass line 21 local hot spots and hence local thawing of the contents of the freezer compartment 1 which may result when superheated refrigerant gas is passed directly to the freezer evaporator 5 are avoided.

It will be obvious of course that the heat exchange arrangement of the bypass line 21 and the suction line 12 is preferably designed so that all of the superheat is removed from the bypass refrigerant gas and the gas enters the freezer evaporator 5 at approximately its condensing temperature. The heat liberated by condensation of the compressed refrigerant in the freezer evaporator 5 quickly effects melting of the frost accumulated on this evaporator and on the walls of the compartment only while the freezer evaporator is at a temperature colder than the fresh food compartment air. The liquid refrigerant which may flowfrom the fresh food evaporator 6 through the header 10 and into the suction line 12 connecting the header 10 to the compressor 3 during the defrost cycle will be evaporated by the heat exchange of the suction line 12 which the bypass line 21 thereby avoiding the introduction of liquid refrigerant into the compressor 3.

Since the portions 32 of the suction line 12 adjacent the compressor unit 3 are normally subjected to ambient conditions, heat interchange between the suction line 12 and the bypass line 21 is preferably arranged to maintain these portions of the suction line. at temperatures above the dew point thereby preventing any undesired sweating of the suction line during the defrosting operation.

From the above description it will be seen that the present invention provides means for effecting defrosting of the freezer evaporator at low and safe temperatures. Also by the arrangement for heat exchanging the suction line and the bypass line those portions of the suction line exposed to ambient conditions are maintained well above the dew point thereby eliminating any sweating problem of the suction line. Furthermore, since all of the heat given up by the bypass line to the suction line is carried by the suction gas through the compressor and back to the bypass line and hence to the freezer evaporator 5, this heat is not lost and is therefore available for defrosting purposes. In addition since the heat exchange between the bypass line 21 and the suction line 12 at a point close to'the compressor unit 3 lowers the temperature of the hot compressed refrigerant passing through the bypass line 21 heat losses of the system during the defrost cycle in the form of radiation and convection losses from the bypass line are correspondingly reduced.

While there has been shown and described a specific embodiment of the present invention, it is not desired that the invention be limited to the particular construction shown and described. For example, the invention is: not limited to the application to the defrosting of the freezer evaporator of the two-temperature refrigerator but can be applied equally Well to the defrosting of the evaporator means for a food freezer.

What I claim as new and desire tosecure by Letters Patent of the United States is:

1. A refrigerating system comprising a compressor, a condenser, a capillary tube flow restricting element, a freezer evaporator for cooling a frozen food compartment, a fresh food evaporator for maintaining a fresh food compartment at above-freezing temperatures and a suction line, said compressor, condenser, capillary tube element, freezer evaporator, fresh food evaporator and suction line being connected in series in a closed refrigcrating circuit, a portion of said suction line being in heat exchange relationship with said capillary tube flow restricting element, control means responsive tothe temperature of said fresh food evaporator for starting said compressor only when said fresh food evaporator has attained a temperature above freezing to assure defrosting of said fresh food evaporator prior to energization of said compressor and means for periodically defrosting said freezer evaporator including a conduit bypassing said condenser and flow restricting element and connecting said compressor directly to the inlet to said freezer evaporator for the introduction of hot gas into said freezer evaporator, a valve in said conduit controlling the flow of refrigerant therethrough, control means for controlling the operation of said valve and energizing said compressor when said valve is open, said bypass conduit being in heat exchange contact with a part of said suction line adjacent said compressor and between said portion of said suction line in heat exchange relationship with said capillary tube flow restricting element and said compressor thereby to remove from the hot compressed gas entering said freezer evaporator during defrosting operation of the system substantially all of the superheat whereby defrosting of the freezer evaporator is effected substari tially by the latent heat of the compressed gas.

2. A refrigerating system comprisinga compressor, a condenser, a capillary tube flow restricting element, a freezer evaporator for cooling a frozen food compartment, a fresh food evaporator for maintaining a fresh food compartment at above-freezing temperatures and a suction line, said compressor, condenser, capillary tube element, freezer evaporator, fresh food evaporator and suction line being connected in series in a closed refrigerating circuit, control means responsive to the temperature of said fresh food evaporator for starting said compressor only when said fresh food evaporator has. attained a temperature above freezing to assure defrosting of said fresh food evaporator prior to energization of said compressor and means for periodically defrosting said freezer evaporator including a conduit bypassing said condenser and flow restricting element and connecting said compressor directly to the inlet to said freezer evaporator for the introduction of hot gas into said freezer evaporator, a valve in said conduit controlling the flow of refrigerant therethrough, control means for controlling the operation of said valve and energizing said compressor when said valve is open, said bypass conduit being in heat exchange contact with said suction line adjacent said compressor thereby to cool the hot compressed gas entering said freezer evaporator during defrosting operation of the system to a temperature such that defrosting of the freezer evaporator is effected substantially only by the latent heat of the compressed gas.

References Cited in the file of this patent UNITED STATES PATENTS 2,526,379 Maseritz Oct. 17, 1950 2,694,904 Lange Nov. 23, 1954 2,694,906 Didion Nov. 23, 1954 2,698,521 Mann Jan. 4, 1955 2,783,621 Staebler Mar. 5, 1957 2,801,523 Hansen Aug. 6, 1957 2,807,149 Williams Sept. 24, 1957