US2720086A - Automatic defrosting systems for twotemperature refrigerators - Google Patents

Description

0 1955 F. L. TARLETON AUTOMATIC DEFROSTING SYSTEMS FOR TWO-TEMPERATURE REFRIGERATORS Filed Aug. 15, 1953 115V AC. POWER SOURCE -INVENTOR Frederic L. Iar/efon United States Patent AUTOMATIC DEFROSTIN G SYSTEMS FOR TWO- TEMPERATURE REFRIGERATORS Frederic L. Tarleton, Oak Park, Ill., assignor to Gencrai Electric Company, a corporation of New York Application August 13, 1953, Serial No. 374,047 Claims. (Cl. 62-4) The present invention relates to two-temperature refrigerators and more particularly to automatic defrosting systems therefor.

A conventional refrigerator of the two-temperature type comprises an upstanding heat insulated cabinet defining separate upper and lower food storage compart' ments, and a refrigeration system of the compressorcondenser-evaporator type including a low-temperature evaporator operatively associated with the upper compartment to cool it to a temperature below the freezing point (usually about 0 F.) and a high-temperature evaporator arranged in the upper portion of the lower compartment to cool it to a temperature above the freezing point (usually about 35 F.). Since the high-temperature evaporator is in contact with the convection currents of moist air circulated in the lower compartment frost accumulates thereon, whereby the high-temperature evaporator must be periodically defrosted to maintain a satisfactory operating condition. In order to achieve this objective, various defrosting schemes have been proposed that normally proceed on the basis of supplying heat to the high-temperature evaporator under the control of timing mechanism, counting mechanism, etc.

While these defrosting arrangements are reasonably satisfactory in operation, they are considerably more expensive to manufacture than is desirable.

Accordingly, it is a general object of the present. invention to provide a two-temperature refrigerator of the character noted, that incorporates an improved refrigeration system, whereby the high-temperature evaporator arranged in the lower or high-temperature food storage compartment is automatically defrosted at the conclusion of each on cycle of the compressor as a result of the inherent operating characteristic of the refrigeration apparatus, and without the provision of auxiliary control mechanism.

Another object of the invention is to provide a two temperature refrigerator of the character described, in which a continuous and unvalved conduit is arranged from the condenser back to the compressor and including in series relation the high-temperature evaporator in the form of a restricted evaporator tube and the low-temperature evaporator in the form of an unrestricted evaporator tube, whereby the gaseous refrigerant accumulating in the high-temperature evaporator during each off cycle-of the compressor eifects flushing ofthe liquid refrigerant therefrom into the low-temperature evaporator so that the temperature of the high-temperature evaporator rises above the freezing point before the next on cycle of the compressor in order to defrost the hightemperature evaporator following each on cycle of the compressor.

A further object of the invention is to provide a twotemperature refrigerator ofthe character described, and further including open heat-transfer structure arranged in the upper portion of the lower or high-temperature compartment in good heat exchangerelation with both the hi git-temperature evaporator and the convection currents of air circulated in the lower or high-temperature compartment, whereby the heat-transfer structure brings about cooling in the lower or high-temperature compartment during each on cycle of the compressor and brings about defrosting of the high-temperature evaporator during each ofi cycle of the compressor.

Further features of the invention pertain to the particular arrangement of the elements of the two-temperature refrigerator and the refrigeration apparatus, whereby the above-outline and additional operating features thcreof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing, in which:

Figure 1 is a vertical sectional view of a two-temperature refrigerator provided with refrigeration apparatus incorporating an automatic defrosting arrangement and embodying the present invention; and

Fig. 2 is a fragmentary perspective view of the hightemperature evaporator that is arranged in the upper portion of the lower or high-temperature food storage compartment of the refrigerator shown in Fig. 1.

Referring now to Fig. 1 of the drawing, the twotemperature refrigerator 10 there illustrated and embodying the features of the present invention comprises an upstanding heat insulated cabinet 11 defining separate upper and lower food storage compartments 12 and 13, as well as a machinery compartment 14disposed below the lower food storage compartment 13. The upper compartment 12 constitutes a low-temperature compartment and is defined by a sheet metal liner 15 having a front ccess opening, and the lower compartment 13 constitutes a high-temperature compartment and is defined by a sheet metal liner 16 having a front access opening; and the cabinet 11 carries a heat insulated main front door 17 for closing the front openings mentioned in order to prevent the admission of heat and air thereinto, the front door 17 being pivoted to the cabinet 11 along one upstanding marginal edge thereof in a conventional manner, not shown. Also the front access opening into the upper compartment 12 is provided with an auxiliary front door 18, hinged adjacent to the lower edge thereof, and serving the general purpose of closing the upper compartment 12 against the admission of air thereinto when the main front door 17 is open to render accessible the lower compartment 13. Of course, the auxiliary front door 18 may be opened, when the main front door 17 occupies its open position, so as to render accessible the upper compartment 12. Finally, the front of the machinery compartment 14 is closed by a removable front panel 19 that is normally disposed substantially flush with the main front door 17 so as to lend a smooth and unbroken appearance to the front of the refrigerator 10.

The refrigerator 10 incorporates refrigeration apparatus of the compressor-condenser-evaporator type and. including a composite electric motor-compressor unit 20 and a condenser 21 of the fan-cooled type (provided with an electric operating motor), all disposed in the machineiy compartment 14, as well as a high-temperature evaporator 22 disposed in the upper portion of the lower compartment 13, and a low-temperature evaporator 23 arranged in heat exchange relation with the upper compartment 12. Alternatively the condenser 21 may be of the natural draft stack type and disposed at the rear of the cabinet 11. The compressor, not shown, of the motorcompressor unit 263 is provided with suction and discharge ports and is operative to compress. expanded gaseous refrigerant, the compressed gaseous refrigerant being conducted from the discharge port of the compressor, not shown, via a connection 24 into the upper inlet of the condenser 21 that may comprise a series of serpentine condenser tubing provided with suitable heat-transfer structure. The motor-compressor unit 20 and the condenser 21 together constitute a refrigerant liquifying unit; and a continuous and unvalved conduit is arranged from the lower outlet of the condenser 21 to the suction port of the compressor, not shown, of the motor-compressor unit 20. This continuous and unvalved conduit includes in series relation a capillary tube 25, the high-temperature evaporator 22, the low-temperature evaporator 23 and a suction tube 26. The high-temperature evaporator 22 essentially comprises a section of evaporator tube 27 of relatively small inside diameter; and the low-temperature evaporator 23 essentially comprises a section of evaporator tube 28 having a larger inside diameter as compared with the tube 27. For the purpose of differentiation, the evaporator tube 27 will be referred to as the restricted tube and the evaporator tube 28 will be referred to as the unrestricted tube, in view of the dimensional differences thereof. The inner end of the capillary tube 25 is connected to the outlet of the condenser 21; the outer end of the capillary tube 25 is connected to the inner end of the evaporator tube 27; the outer end of the evaporator tube 27 is connected to the inner end of the evaporator tube 28; the outer end of the evaporator tube 28 is connected to an accumulator 29; the inner end of the suction tube 26 is connected to the accumulator 29; and the outer end of the suction tube 26 is connected to the suction port of the compressor, not shown, of the motor-compressor unit 20.

The high-temperature evaporator 22 may comprise a relatively conventional fin and tube construction, or a composite sinuous structure; as illustrated in Fig. 2, the latter construction includes, in addition to the evaporator tube 27, open heat-transfer structure 30 formed of metal, to which tube 27 is suitably secured in good heat-transfer relation. In any event, the evaporator 22 Will advantageously have one or more brackets or legs 31 facilitating the support of the high-temperature evaporator 22 upon a wall of the lower compartment 13 in spaced relation therewith.

As shown in Fig. l, the cabinet 11 has a forwardly tapered heat insulated dividing wall 32 disposed between the upper and lower compartments 12 and 13, whereby the upper liner 15 is provided with a substantially horizontal bottom wall 33 and the lower liner 16 is provided with a downwardly and rearwardly sloping top wall 34. Finally, the high-temperature evaporator 22 is secured to the top wall 34 by the legs 31, as previously noted. The high-temperature evaporator 22 is disposed substantially parallel to the top wall 34 and in spaced relation therebelow so that it is disposed in the moist convection currents of air circulated in the lower compartment 13, as indicated by the broken lines 35. Accordingly, the hightemperature evaporator 22 slopes downwardly and to the rear in the upper portion of the lower compartment 13 to facilitate the draining of condensate therefrom incident to defrosting thereof, as explained more fully hereinafter; and a laterally extending trough 36 is operatively associated with the lower rear end of the high-temperature evaporator 22, for the purpose of receiving the drippings, the trough 36 communicating with a drip pan 37 disposed therebelow in the rear upper portion of the lower compartment 13 and carried by the rear portion of an open wire-work shelf 38' supported therein.

Finally, the refrigerator is provided With a control system including a source of electric power supply of 115-volt single-phase A. C., as well as a thermal control switch 38. The thermal control switch 38 includes a resilient bellows 39 connected by a tube 40 to a temperature responsive bulb 41 arranged in good heat exchange relation with the side wall of the lower liner 16, whereby the thermal control switch 38 is governed in response to the temperature of the lower compartment 13. Also, the thermal control switch 38 may have a contact bridging member 42 in series circuit relation with the source of power supply and the electric motor, not shown, of the motor-compressor unit 20. Finally, the thermal control switch 38 has a manual adjustment indicated at 43, for adjustment of the control temperature.

In a typical two-temperature refrigerator, the capillary tube 25 may have an inside diameter in the range of 0.022" to 0.040"; the evaporator tube 27 may have an inside diameter of about 0.187"; and the evaporator tube 28 may have an inside diameter of about 0.375". The inside diameter of the suction tube 26 is not critical, it being well understood in the art that one of the factors of its selection is the passage of refrigerant vapor from the accumulator to the compressor with as low a pressure drop as is consistent with practical manufacturing and economic considerations. The inside diameter of the evaporator tube 27 is, of course, predicated upon the fundamental consideration that during the off period of the compressor, heat transfer from the air in the compartment 13 to the evaporator tube 27 will quickly vaporize some liquid refrigerant therein, and that the vaporized refrigerant will, in percolator fashion, quickly flush the liquid refrigerant out of the evaporator tube 27 and into the evaporator tube 28. This enables the heat of the contents of the compartment 13 during the off period of the compressor to melt any frost which may have accumulated on the evaporator 22 during the preceding on period. A tube diameter such as given above for the evaporator tube 27 insures that the surface tension of the liquid refrigerant is sufiicient to resist the penetration of the liquid refrigerant by the refrigerant vapor bubbles pressing thereagainst, and these refrigerant vapor bubbles therefore efiiciently drive the liquid refrigerant before them.

In the two-temperature refrigerator 10, there is a further expansion of the liquid refrigerant as it passes into the evaporator tube 28. The above noted size difference between the evaporator tubes 27 and 28 provides the required expansion of the liquid refrigerant within the evaporator tube 28 for the desired heat absorption from the compartment 12.

Alternatively, such expansion of the liquid refrigerant may be achieved, without the above-described differential between the cross-sectional areas of the evaporator tubes 27 and 28, by installing a plug, not shown, at the junction of the evaporator tubes 27 and 28, this plug having a restricted orifice communicating between the evaporator tubes 27 and 28, whereby effectively the above noted relationship between the evaporator 22 and the evaporator 23 may be achieved.

In the operation of the refrigerator 10, the upper low temperature compartment 12 is normally maintained at about 0 F., and the lower high-temperature compartment 13 is normally maintained at about 35 E; which temperature differential is maintained by the normal operation of the refrigeration apparatus since the evaporator tube 27 accommodates expansion of a portion of the liquid refrigerant therein, and further expansion of the liquid refrigerant is accommodated in the evaporator tube 28. More particularly, when the temperature of the lower compartment 13 rises slightly above the control temperature, of about 35 F., normally set to govern the thermal control switch 38, this control switch is operated into its closed position so that operation of the motor-compressor unit 20 is initiated. Expanded gaseous refrigerant is drawn from the suction tube 26 into the compressor, not shown, of the motor-compressor unit 20 and compressed and discharged therefrom 24 into the condenser 21. The compressed gaseous refrigerant is liquified in the condenser 21 and immediately passes therefrom via the capillary tube 25 into the restricted evaporator tube 27; the capillary tube 25, because of its extremely small inside diameter, accommodating substantially no expansion of the liquid refrigerant therein. The liquid refrigerant is not fully expanded in the restricted evaporator tube 27 whereby the discharge from the reimmense stricted evaporator tube 27 into the unrestricted evaporator tube28 contains quantities .of liquid refrigerant.

The cooling of the high-temperature evaporator '22which takes place by reason of the refrigerantexpansion therein suitably cools the convection currents of air circulated in the lower or high-temperature compartment 13-. The liquid refrigerant entering "the unrestricted evaporator tube 28 isfurther expanded, the pressure intheunrestricted evaporatortubel 28 beingdetermined entirely*by the pressure in the suction tube 26, that, in" tu'rn,is established directly by 'the suction of the compressor, not

shown, of the motor-compressor unit whereby the cooling of thelow-temperatu-re evaporator 23 resulting from such expansionprovides thedesired cooling of the upper or low-temperature compartment 12. By virtue of the arrangement of the differential pressures automatically established in the restricted evaporator tube'27 and in theunrestricted evaporatortubels, the lower compartment 13 is cooledto a temperature of about F.

when the upper compartmentIZ is cooled to about a temperature of 0 F; whereby at this time the bulb 41 is governedto effect operation of the thermal control switch 38 into its open circuit positionin order to arrest operation of the electric 'motor of themotor-compressor unit 2t). In the oncycle ofthe motor-compressor unit 20, the convection currents 'ofair circulated in the lower compartment 13 effectthe transfer of "heat to "the hightemperature evaporator 22, -while heat from the upper liner 15 is directlytransferred to the low temperature evaporator 23.

During the off cycle of the motor-compressor unit 20, the convection currents of air circulated'in the lower compartment 13 continue to transfer heat'to thehightemperature evaporator 22; whereby some of the liquid refrigerant in the restricted evaporator tube 27 isgasified so that the expanded gaseous refrigerant therein flushes the liquid refrigerant therein forwardlytherefrom into the unrestricted evaporator tube 28; this action in the restricted evaporator tube 27 being analogous to that involved in the operation of a normal percolator; whereby a small amount of gaseous refrigerant sweeps forwardly a large amount of Iiquidrefrigerant. This arrangementreduces the latent heat in the high-temperature evaporator 22 so that shortly thereafter the continued transfer of heat thereto causes the temperature thereof to rise above the freezingpoint; whereby the high-temperature evaporator 22 is defrosted, thecondensate draining downwardly thereonand falling into thetrough 36 and-then running into the drip pan 37. After this complete defrosting of the high-temperature evaporator 22 in the off cycle of the motor-compressor unit 20, the thermal control switch 38 is subsequently governed in order again to initiate 7 operation of the motor-compressor unit 20. On the other hand, there is very little heating-of the upper compartment 12 during the off cycle of the motor-compressor unit 2d; whereby the temperature thereinis maintained substantially constant, at about 0 F.

In view of the above, it will beunderstood that following each on cycle of the motor-compressoriunit 20, the high-temperature evaporator 22 is automatically defrosted by virtue of the inherent operating characteristic of the refrigeration apparatus; whereby it is unnecessary to incorporate in the refrigerator 10 any auxiliary control or heating apparatus to bring about the necessary defrosting. of the high-temperature evaporator 22. The defrosting operation of the high-temperature evaporator 22 takes place automatically, as described above, by virtue of the fact that the restricted evaporator tube 27 is connected at the inlet end thereof to the exceedingly restricted capillary tube 25 and is connected at the outlet end thereof to the unrestricted evaporator tube 28; whereby the small heating of the high-temperature evaporator 22 in the off cycle ofthe motor-compressor unit 2 0eifects the limited gasification of the liquid refrigerant inthe restricted evaporatortube'27 so thatthe mass of liquid 6 refrigerant therein is swept forwardly therefrom due to the percolator-like action, previously described.

In view of the foregoing, it is apparent that there has been provided a two-temperature refrigerator incorporating refrigeration apparatus that is so constructed and arranged that automatic defrosting of the high-temperature evaporator arranged in the upper portion of the lower or high-temperature food storage compartmentthereof takes place in each off cycle of the motor-compressor unit and before the next on cycle thereof; which defrosting arrangement is entirely automatic and dependent altogether upon the inherent operating characteristic of the refrigerator apparatus, and requires no supervision, adjustment or attention on the part of the user of the refrigerator.

While the preferred embodiment of the invention has been disclosed as being incorporated in the two-temperature refrigerator 10, having the upper compartment 12 provided with the unrestricted evaporator 23 and the lower compartment 13 provided with the restricted evaporator 1 :cabinet 11.

While there has been described what is atpresent considered to be the preferred embodiment of the invention, it will be understood that various modificationsmay be made therein, and it is intended tocover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a refrigerator including an upstanding heatinsulated cabinet defining separate first and .secondfood storage compartments, a compressor operative to compress expanded gaseous refrigerant, a condensenand a connection for conducting compressed gaseous refrigerant from said compressor to said condenser; the combination comprising a continuous conduit from said condenser back to said compressor and including in series relation in the order named a capillary tube and a first restricted evaporator tube and a second unrestricted evaporator tube and an unrestricted suction tube, whereby said first restricted evaporator tube is located between said capillary tube and said second unrestricted evaporator tube in said conduit, said first evaporator tube being arranged in the upper portion of said first compartment and said second evaporator tube being arranged in heat-exchange relation with said second compartment, said capillary tube accommodating substantially no expansion of the liquid refrigerant therein, said first evaporator tube accommodating predetermined expansion of the liquid refrigerant therein so as to cool said first compartment to a temperature above the freezing point, said second evaporator tube accommodating further expansion of the liquid refrigerant therein so as to cool said second compartment to a temperature below the freezing point, thermal responsive means controlled by the temperature of said first compartment for operating said compressor between off and on cycles, and open heat-transfer structure arranged in the upper portion of said first compartment in good heat exchange relation. with both said first evaporator tube and the convection currents of air circulated in said first compartment, the gaseous refrigerant accumulating in said first evaporator tube during each off cycle of said compressor as a consequence of the heat transferred thereto from said structure and as a result of said location of said first evaporator tube in said conduit effecting flushing of the liquid refrigerant therefrom into said second evaporator tube so that the temperature of said first evaporator tube rises above the freezing point before the next on cycle of said compressor, whereby said first evaporator tube and said structure are defrosted following each on cycle of said compressor.

2. Therefrigerator combination set forth in claim 1, wherein the cross-sectional area of said-first evaporator tube is about 20 to 70 times greater than that of said capillary tube, and the cross-sectional area of said second evaporator tube at its junction with said first evaporator tube is substantially greater than that of said first evaporator tube.

3. The refrigerator combination set forth in claim 1, wherein said cabinet also defines a separate machinery compartment disposed below said food storage compartments, and said compressor and said condenser are disposed in said machinery compartment.

4. The refrigerator combination set forth in claim 1, wherein said first and second food storage compartments are provided with respective first and second sheet metal liners, said first evaporator tube and said structure are arranged interiorly of said first liner and substantially out of contact therewith, and said second evaporator tube is arranged exteriorly of said second liner and in contact and good heat exchange relation therewith.

5. The refrigerator combination set forth in claim 1, wherein said thermal responsive means operates said compressor between off and 011 cycles about two to three times per hour.

6. In a refrigerator including an upstanding heatinsulated cabinet defining separate upper and lower food storage compartments having corresponding front openings, a heat-insulated door for closing said front openings, a compressor operative to compress expanded gaseous refrigerant, a condenser, and a connection for conducting compressed gaseous refrigerant from said compressor to said condenser; the combination comprising a continuous and unvalved conduit from said condenser back to said compressor and including in series relation in the order named a capillary tube and a first restricted evaporator tube and a second unrestricted evaporator tube and an unrestricted suction tube, whereby said first restricted evaporator tube is located between said capillary tube and said second unrestricted evaporator tube in said conduit, said first evaporator tube being arranged in the upper portion of said lower compartment and said second evaporator tube being arranged in heat-exchange relation with said upper compartment, said capillary tube accommodating substantially no expansion of the liquid refrigerant therein, said first evaporator tube accommodating sufficient expansion of the liquid refrigerant therein to cool said lower compartment to a temperature above the freezing point, said second evaporator tube accomodating further expansion of the liquid refrigerant therein so as to cool said upper compartment to a temperature below the freezing point, thermal responsive means controlled by the temperature of said lower compartment for operating said compressor between off and on cycles, and open heat-transfer structure arranged in the upper portion of said lower compartment in good heatexchange relation with both said first evaporator tube and the convection currents of air circulated in said lower compartment, the gaseous refrigerant accumulating in said first evaporator tube during each cycle of said compressor as a consequence of the heat transferred thereto from said structure and as a result of said location of said first evaporator tube in said conduit effecting flushing of the liquid refrigerant therefrom into said second evaporator tube so that the temperature of said first evaporator tube rises above the freezing point before the next on cycle of said compressor, whereby said first evaporator tube and said structure are defrosted following each on cycle of said compressor, said structure sloping downwardly toward the rear of said lower compartment to facilitate the collection of drippings therefrom incident to defrosting thereof.

' 7 The refrigerator combination set forth in claim 6, wherein said cabinet includes a forwardly tapered dividing wall disposed between said upper and lower compartments and providing said upper compartment with a substantially horizontal bottom wall and providing said lower compartment with a downwardly and rearwardly sloping top wall.

8. In a refrigerator including a heat-insulated cabinet defining a storage compartment, a compressor operative to compress expanded gaseous refrigerant, a condenser, and a connection for conducting compressed gaseous refrigerant from said compressor to said condenser; the combination comprising an evaporator arranged in the upper portion of said compartment and provided with a refrigerant passage for circulation of refrigerant therethrough, an accumulator, first means defining a highly restricted communication between said condenser and the inlet of said refrigerant passage to conduct liquid refrigerant thereto, whereby during periods of operation of said compressor said evaporator provides substantially continuous expansion and evaporation of liquid refrigerant therein to lower the temperature thereof sufficiently below the freezing point of water to maintain said compartment at a temperature in a desired range above said freezing point, second means defining a moderately restricted communication between the outlet of said refrigerant passage and said accumulator, third means defining an unrestricted passage from said accumulator to said compressor for the return of expanded gaseous refrigerant to said compressor, and thermal responsive means controlled by a predetermined variation in the temperature of said cabinet for operating said compressor between 01f and on cycles; said evaporator including an open heat-transfer structure in good heat exchange relation with said refrigerant passage and the convection currents of air in said compartment, and the cross sectional area of said refrigerant passage being such that upon heat transfer from the air in said compartment to said refrigerant passage during an off period of said compressor vaporization of liquid refrigerant in said refrigerant passage will be effective as a result of the location of said refrigerant passage between said first means and said second means quickly to flush remaining liquid refrigerant from said refrigerant passage into said accumulator to reduce the latent heat in said evaporator and thereby permit the temperature of said evaporator to rise above the freezing point of water before the next 'on period of said compressor.

9. The refrigerator combination set forth in claim 8, wherein said first means defining said highly restricted communication between said condenser and said evaporator consists essentially of a capillary tube, and said second means defining said moderately restricted communication between said evaporator and said accumulator consists essentially of a restricted evaporator tube forming at least a part of said refrigerant passage and being many times larger in inside diameter than said capillary tube, and said third means defining said unrestricted communication between said accumulator and said compressor consists essentially of a relatively large inside diameter suction tube.

10. The refrigerator combination set forth in claim 9, wherein said capillary tube and said suction tube are arranged in heat exchange relation with each other.

References Cited in the file of this patent UNITED STATES PATENTS 1,622,376 Davenport Mar. 29, 1927 2,306,480 Ketcham Dec. 29, 1942 2,319,522 Schweller May 18, 1943 2,333,899 Stickel Nov. 9, 1943 2,423,386 Hubacker July 1, 1947 2,446,946 Morton Aug. 10, 1948 2,487,182 Richard Nov. 8, 1949 2,622,405 Grimshaw Dec. 23, 1952 2,641,109 Mufiily June 9, 1953 2,647,375 Zearfoss Aug. 4, 1953

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