US2907184A

US2907184A - Refrigerating system including hot gas defrosting circuit

Info

Publication number: US2907184A
Application number: US704184A
Authority: US
Inventors: Frank A Schumacher
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1957-12-20
Filing date: 1957-12-20
Publication date: 1959-10-06
Anticipated expiration: 1976-10-06

Description

REFRIGERATING SYSTEM INCLUDING HOT GAS DEFROSTING CIRCUIT Filed Dec. 20, 1957 INVENTOR. FRANK A. SCHUMACHER HIS ATTORNEY United States Patent ice REFRIGERATING SYSTEM INCLUDING HOT GAS DEFROSTING CIRCUIT Frank A. Schumacher, Louisville, Ky., assign'or to General Electric Company, a corporation of New York Application December 20, 1957, Serial No. 704,184 5 Claims. (Cl. 62-278) The present invention relates to refrigerating apparatus and is more particularly concerned with a refrigerating system including an improved circuit arrangement for employing compressed refrigerant gas-to warm the evaporator component of the system to defrosting temperatures.

In the copending application of Clyde J. Nonomaque, Serial No. 698,462, filed November 25, 1957, and assigned to the same assignee as the present invention, there is described and claimed a refrigerating system including an auxiliary hot gas defrosting circuit for quickly and effectively employing hot compressed refrigerant to defrosting the evaporator component of the refrigerating system. It is to be understood that the present invention is an improvement over the invention of the Nonomaque application and I therefore do not herein claim as my invention anything shown or described in said Nonomaque application, which is to be regarded as prior art with'respect to the present application. 1

The refrigerating system described and claimed in the Nonomaque application comprises a compressor, a condenser, a fixed flow restrictor and an evaporator connected to form a normal refrigerating circuit. For the purpose of periodically raising the evaporator to defrosting temperatures by means of hot compressed refrigerant from the compressor, there is provided an auxiliary circuit connected between the high and low pressure sides of the normal refrigerating circuit and in parallel with at least that part of the normal circuit including the fixed flow restrictor and the evaporator. The auxiliary circuit includes a defrost portion in heat exchange with the evaporator and a flow restricting means between the defrost portionand the compressor so that upon opening of a normally closed valve in the auxiliary circuit, hot compressed refrigerant will flow through the defrost portion ofthe auxiliary circuit in heating relation with the evaporator where condensation of refrigerant in the defrosting portion quickly and effectively warms the evaporator to defrosting temperatures.

In the refrigerating system described and claimed in the aforementioned Nonomaque application, the lesser flow resistance of the flow restricting means in the auxiliar'y circuit as compared with the flow resistance of the fixed flow restrictor in the refrigerator circuit under existing conditions is relied upon to cause substantially all of thecompressed refrigerant to flow through the defrost circuit during the defrosting operation even though both circuits are in communication with the compressor. While these desired flow conditions are obtained under most operating conditions, it has been found that under low ambient conditions the condenser temperature may be'so low as to cause some condensation of refrigerant in the'. condenser even during the early stages of defrost operation of the system with the result that condensed refrigerant from the condenser willfiow through the fixed flow restrictor and into the evaporator. The resultant cooling'efiect on the evaporator partially olfsets' 2,907,184 Patented Oct. 6, 1959 the heating effect of the defrost circuit and thereby slows down the rate of temperature rise of the evaporator and hence increases the time necessary to remove the accumulated frost from evaporator. It is therefore a primary object of the present invention to provide means for substantially reducing this low ambient fiow of. refrigerant through the refrigerating circuit during defrost operation of the above-described system.

In accordance with the present invention, condensed refrigerant is reduced in flow from the condenser to the evaporator by placing a portion of the auxiliary circuit between the control valve and the defrost portion of the Nonomaque system in heat exchange relationship with the refrigerating circuit ahead of or in contact with the capillary flow restrictor.

More specifically, the refrigerating system of the present invention comprises an evaporator, a compressor, a condenser and a capillary flow restrictor, and conduit means connecting the compressor, condenser, capillary flow restrictor and evaporator in closed series-flow refrigerating circuit whereby the compressor normally withdraws low pressure refrigerant from the evaporator and discharges high pressure refrigerant to the condenser. For periodically raising the evaporator to defrosting temperatures by means of hot compressed refrigerant from the compressor, there is provided an auxiliary circuit having its inlet connected to the refrigerating circuit between the compressor and the capillary flow restrictor and its outlet end connected to the low pressure portion of the refrigerating circuit between the evaporator and the compressor. This auxiliary circuit includes in series connection, a normally-closed fiow control valve adjacent theinlet to the auxiliary circuit, a defrost portion 1 in heat exchange relationship with the evaporator and a normal refrigerating circuit during defrost operation of the system, a portion of the auxiliary circuit carrying hot compressed refrigerant is disposed in heat exchange relation with a portion of the normal circuit between the condenser and the outlet end of capillary flow restrictor. This heat interchange causes revaporization of the condensed liquid so that the flow of refrigerant through the capillary flow restrictor is reduced causing any refrigerating effect in the normal circuit to be negligible during defrost operation. 1

For a better understanding of the present invention reference may be had to the accompanying drawing in which the single figure is a diagrammatic illustration of a refrigerating system embodying the hot gas defrost arrangement of the present invention. 4

With reference to Fig. 1 of the drawing, the system comprises the usual components including a compressor unit 1, a condenser 2, a capillary flow restrictor 3, a cooling or evaporator unit comprising a serpentine evaporator circuit 5 and an accumulator 6, and a suction line 7 connected in closed series-flow relationship. f i

The motor compressor unit 1 comprises a motor 13 for driving a compressor 14, the two being sealed in a hernormal refrigerating system and is therefore filled with .low pressure refrigerant in cooling contact with the motor 13, while the compressor 14 having its inlet 14a communicating withthe .case 15 withdraws gaseous refrigerant from the case and discharges high pressure refrigerant directly to the discharge line 17 connected to the condenser 2. In this system, the evaporator unit and the case 15 form the low pressure side of the normal refrigerating-circuit while the compressor and condenser comprise the high pressure side. The evaporator circuitS andin the illustrated modification, also the accumulator 6, form part of .a roll-bond evaporator'structure 8 which includes the plate or body 9; the accumulator 8 in'such case conveniently being composed of a plurality of intersecting vertical and horizontal tubular portions in accordance with the known practices.

Also in accordance with the usual practice, the suction line 7 is in-heat exchange relationship with -a portion of the capillary tube restrictor 3 as indicated at 1-1 whereby condensed refrigerant passing to the evaporator is further cooled by the refrigerant vgas flowing through'the suction line to the compressor.

To accomplish the defrosting of the evaporator structure'8, there is provided an auxiliary circuit 18 which is in parallel flow relationship with the evaporator and the restrictor portions of the normal refrigerating circuit and which is designed to form with certain elements of the normal refrigerating circuit a defrost circuit .to conduct compressed refrigerant gas from the high pressure side of the system into heat exchange relationship with the evaporator structure 8 for the purpose of warming this structure :to defrosting temperatures. auxiliary circuit is connected to the discharge line 17 leading from the compressor to the condenser 2 and a normally closed valve 20 operated by a solenoid 28 is provided for controlling the flow of refrigerant through the auxiliary circuit 18. The auxiliary circuit also includes an-evaporator defrosting portion composed of a first section 21 in heat exchange relationship with the serpentine evaporator and a second section 22 in heat exchangerelationship with the accumulator 6.

The outlet end of the auxiliary circuit is connected to the suction line 7 as indicated by the numeral '24 by means of a restrictor tube 25 having a lower restriction than capillary tube 3 but which provides suflicient restriction to flow refrigerant through the auxiliary circuit to maintain the refrigerant gas in the defrosting sections 21.and 22 at condensing pressures.

In the normal operation of the refrigerating system, the motor compressor unit 1 withdraws vaporizedrefrigerant from the top of the accumulator 6 through the suction line 7 and discharges compressed refrigerant to the con denser 2. The refrigerant liquified in the condenser 2 passes through the capillary flow restrictor .3 into the evaporator circuit 5 where, at a lower pressure, it isvap'orized by the absorption of heat from a refrigerator cabinet (not shown) to cool the contents of the cabinet. .Any liquid refrigerant not evaporated in the evaporator circuit 5 collects in the accumulator 6; the connection of the evaporator 5 to the accumulator preferably being at the lower part of the accumulator while the suction line 7 is connected to the upper portion thereof so that, during normal refrigerating operation of this system,zonly gaseous refrigerant is withdrawn from the accumulator through the suction line 7 by the motor compressor unitl.

As a layer of frost collects on the evaporator structure 8 during normal operation of the refrigerating system, it becomes necessary periodically to remove this frost layer in order tomaintain the operating efiiciency of theevaporator unit. When defrosting of the evaporator structure is desired, the valve 20 is-opened with result that due to the lower flow restriction of the auxiliary circuit, substantiallyall of therefrigerant withdrawn from the accumulator '6'by the compressor then flows from the compressor into the auxiliary circuit 18 instead of the normal refrigerating circuit.- In other words When the valve 20 is opened substantially all of the refrigerant passes through what may be 'termeda 'defrost circuit comprising, in

The inlet .end 19 of the series=flow connection, the compressor 14,the defrost sections 21 and 22, the restrictor 25 and the case 15. In the defrost sections 21 and 22, which correspond to the condenser component of a inormal refrigerating circuit, the hot compressed refrigerant condenses liberating heat which melts the frost accumulated on the evaporator structure 8. The condensed refrigerant then flows through restrictor 25 andireturns to the compressor case 15 as a liquid or'as a-mixtureof;liquidlandigas.

By means of the auxiliary circuit 18 including the defrost sections in heat exchange relationship with the evaporator and accumulator, both the 'stored'dieat in the compressor case and the inputwatts to the compressor motor .are used .as heat ISOUECQS 'for defrosting zthe evaporator structure. Since the stored compressor heat is quickly dissip-ated,the principal source of heat energy is the input watts to the motor during the remaining portion of the defrost period, this energy being transferred by the refrigerant to the evaporator structure as heat energy. To increase the input watts to the "compressor "motor in order to providequick defrosting of the evaporator, the entire system is'preferably designed that the load on'the compressor motor'ishigh during the'defrostcycle. This result is attained by designing 'thesystem for higherpressure operation during the defrost cycle with themajor part ofthe increased load on the motor'being obtained by an increase in the low "side or suction pressure resulting from a concentration ofmost of the'refrigerant charge in 'the compressor case 15 or more broadly in the low side portion of the circuit'b'etweenthe restrictor 25 and the compressor 14 during'defrost operation ofthe system. As this refrigerant cools the compressor-motor 13, all of the heat liberated'by'the motor is transferred to the circulating refrigerant and therefore to the 'de' frostingiportions of the auxiliary circuit '18 in heat exchange relationship with'the evaporatorstructureS. To obtain an increased amount of heat fromthe compressor during defrost operation, the-main refrigeratingcircuit'is preferably designed so that as the accumulator *6 is warmed duringthe defrost'op'eration, the liquidrefrigerant stored therein is partially vaporized and rtransferred through the suction line 7 to the compressor case as a mixture of liquid and gas where it serves'to 'raisethe low side'pressure on the compressor 14.

The refrigerating system as thus far described with reference'to the drawing is more'specifically described in'the aforementioned fNonomaque'application. Byfollowing the teachingsof that application, restrictors'S and 25 are so proportioned as to cause substantially all of the refrigerant'to flow through the auxiliary circuit when the valve 20 is open even though both the auxiliary circuit "18 and the normal refrigerating circuit including the condenser 2, the restrictor 3 and the evaporator 5 are in .open connection with the compressor. The'lower resistance'to refrigerant flowprovided'by the auxiliary circuit 18 causes most .of the refrigerant 'to how through this circuit particularly under high ambient conditions where the condenser which is at ambient temperature will be filled only with gaseous rather 'than liquid refrigerant during'the defrost cycle. I

However, it has been found that while quick and efficient defrosting of the evaporator circuit is obtained in accordancewith the Nonomaque'invention under normal orhigh ambient temperature conditions, under relatively low ambient conditions of, for example, 'from 40 to '60" F., the time required for defrost maybe disproportionately long. It has been found that this prolonging .of the defrost period at low ambients was caused'by refrigerant condensing in the condenser atlow arcibients and flowing to the evaporator as a'liquid Where it produced refrigeration opposing the-defrosting action of the warm refrigerant in the auxiliary circuit. refrigerating effect was noted particularly during-the later stages of defrost operation during which the system pressures are highe and ther ss r'e in the condenser reaches refrigerant liquificationpoint'. "This liquifred condition permits approximately 6 times the mass flow rate of the gaseous state; I

In accordance with the present invention, the flow of refrigerant condensed in the condenser during the defrost period is reduced by heat interchanging a section of the auxiliary circuit 18 with a portion of the normal refrigerating circuit ahead of or in contact with the capillary tube 3. Preferably this heat exchanger is between the outlet from the condenser and the first part of the capillary tube 3 as indicated at 29 so that the heat of the hot compressed refrigerant from the compressor passing through the auxiliary circuit 18 will maintain this portion of the normal refrigerating circuit attemperatures which will vaporize any condensed refrigerant leaving the condenser 2 thereby substantially increasing the flow restriction of the capillary 3 which, as is well known, will conduct gaseous refrigerant at a much slower rate than liquid refrigerant. v

Tests have indicated that by providing the heat interchange 29 between the auxiliary circuit 18 and the normal refrigerating circuit, complete defrost of the evaporator structure 8 could be obtained as quickly at low ambient said condenser and the outlet end of said capillary flow restrictor to maintain said section at refrigerant vaporizing temperature and thereby limit flow of refrigerant to said evaporator during operation of said system with said valve in the open position. i

2. A defrostable refrigerating system comprising an evaporator unit, a compressor, a condenser, and a capillary flow restrictor, conduit means connecting thecompressor, condenser, capillary flow restrictor andevapora tor unit in closed series-flow refrigerating circuit whereby said compressor normally withdraws low pressure refrig erant from said evaporator and discharges high pressure refrigerant to said condenser, and means for periodically raising said evaporator to defrosting temperature by means of hot compressed refrigerant from said compressor comprising an auxiliary circuit including alnor mally closed valve for controlling flow of refrigerant to said auxiliary circuit, said circuit having its inlet co'n nected to said refrigerating circuit between said comtemperature conditions of for example 40 F. as under the high ambient temperature conditions of 80 to 100 F. In other words it has been found that at low ambients the time required for complete defrosting of the evaporator structure employing the heat interchange 29 is about half that'required if no heat interchange between the auxiliary circuit and the normal refrigerating circuit is provided ahead of the restrictor'3.

The refrigerating system of the present invention is adapted of course to be controlled either manually or automatically. A suitable electrical circuit for automatic control is described in the copending Nonomaque application. It will also be understood that the' present invention is not restricted to the particular system illustrated in the accompanying drawing but is equally applicable to various modifications or arrangements of the auxiliary circuits and normal refrigerating circuits such as are shown for example in the aforementioned Nonomaque application. Therefore, While there has been shown and described a specific embodiment of the invention, the invention is not limited to the particular construction shown and described and it is intended by the appended claims to cover all modifications within the true spirit and scope of the invention.

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

l. A defrostable refrigerating system comprising an evaporator unit, a compressor, a condenser, and a capillary flow restrictor, conduit means connecting the compressor, condenser, capillary flow restrictor and evaporator unit in closed series-flow refrigerating circuit whereby said compressor normally withdraws low pressure refrigerant from said evaporator and discharges high pressure refrigerant to said condenser, and means for periodically raising said evaporator to defrosting temperature by means of hot compressed refrigerant from said compressor comprising an auxiliary circuit including a normally closed valve for controlling flow of refrigerant to said auxiliary circuit, said circuit having its inlet connected to said refrigerating circuit between said compressor and said capillary flow restrictor and its outlet connected to the low pressure portion of said refrigerating circuit between the outlet end of said evaporator and said compressor, said auxiliary circuit including, in series connection, a defrost portion in heat exchange relation with said evaporator and a flow restricting means for restricting the flow of refrigerant from said defrost portion to said compressor thereby to maintain refrigerant in said defrost portion at condensing pressure conditions when said valve is open, a portion of said auxiliary circuit between said inlet and said defrost portion being in heat exchange relation with a section of said refrigerating circuit between pressor and said capillary flow restrictor and its outlet connected to the low pressure portion of said refrigerating circuit between the outlet end of said evaporator and said compressor, said auxiliary circuit including,,in series con nection, a defrost portion in heat exchange relation with said evaporator and a flow'restricting means for restricting the flow of refrigerant from said defrost portion to said compressor thereby to maintain refrigerant in said defrost portion at condensing pressure conditions when said valve is open, a portion of said auxiliary circuit between said inlet and said defrost portion being in heat exchangerelation with a section of said refrigerating circuit between said condenser and said capillary flow restrictor to main-' tain said section at refrigerant vaporizing temperatures and thereby limit flow' of refrigerant to said evaporator during operation of said system with said valve in the open, position. I a

3. A refrigerating system comprising a hermetic cornpressor unit including a casing and a compressor and a motor for driving said compressor Within said casing, a condenser, a fixed'fiow restrictor and an evaporator, conduit means connecting said compressor, condenser, fixed flow restrictor, evaporator and casing to form aclosed series-flow normal refrigerating circuit in which'said compressor withdraws low pressurev refrigerant frornf said evaporator and through said casing and discharges high pressure refrigerant to said condenser, said motor'being cooled by the low pressure refrigerant-in said casing, means for periodically warming said evaporator todefrosting temperatures comprising an auxiliary circuit having an inlet end connected to said normal refrigerating circuit between said compressor and said fixed flow restrictor and its outlet end connected to said normal refrigerating circuit between the outlet end of said evaporator and said compressor, said auxiliary circuit including a defrost portion in heat exchange relation with said evaporator and a flow restricting means, conduit means connecting said compressor, said defrost portion, said flow restricting means and said casing to form a seriesfiow defrosting circuit, a normally closed valve in said auxiliary circuit for preventing flow of refrigerant through said circuit, opening of said valve permitting flow through either said refrigerating circuit or said auxiliary circuit, said flow restricting means in said auxiliary circuit having a flow restriction sufiicient to maintain condensing pressures in said defrost section when refrigerant is flowing through said defrost section but being substantially less than the flow restriction provided by said fixed flow restrictor when said valve is opened whereby opening of said valve causes substantially all of the circulating refrigerant to flow through said defrost circuit, a section of said auxiliary circuit between said valve and said defrost portion being in heat exchange relation with said refrigerating circuit between said condenser and said capillary flow restrictor to vaporize any refrigerant flowing from said condenser to said capillary flow restrictor in said normal refrigerating circuit and thereby limit flow to reh'igerant to s'ai'd evaporator during operation of said system when said valve is in the open position.

t. Arf-rig'eratingsystem comprising a "hermetic cornpressorunitincluding'acasingand a compressor and a motor for driving said compressor within 'said casing, acondensena capillary fi'ow'restrictor'and an evaporator, conduit means "connecting said compressor, condenser, capillaryftow restrictor, evaporator, and'casing to form a closed series-flow norma'l refrigerating circuit in which said eompressorwithdraws low pressure refrigerant from said evaporator and through said casing and discharges high .pressure refrigerant to said condenser, said motor being cooled by the low pressure refrigerant flowing through saide'asing, means for periodically warming said evaporator to defro'sti'ngtemperatures comprising an auxiliarycircuit having an inlet end connected to said normal refrigerating circuit'hetweenthe outlet end of said evaporator and 'said'compre'ssor, said auxiliary circuit includinga defrost'portionin heatexchange relation with said evaporator and a flow restricting means, conduit means connecting said compressor, said defrost portion, said flow restricting means and said casing to form a seriesflow defrosting 'circuit, a normally closed valve in said auxiliary circuit for preventing flow of refrigerant through said circuit, the "flow restriction provided by saidfiow restricting means in said auxiliary circuit being sufficie'ntto maintain condensing pressures in said defrost section when refrigerant is flowing through said defrost section, opening of said valve permitting new of refrig'e'rant 't'h-roughbo'th said refrigerating circuit and said defrost circuit, a portion of said auxiliary circuit between saidinlet and said defrost portion being in heating relationshi with a portion of said refrigerating circuit adjacent the inlet end of said capillary flow restrictor to vaporize any refrigerant flowing from said condenser to said capillary flow restrictor and thereby limit the flow of -refrigerant through said refrigerating circuit when saidvalve is open.

5. A refrigerating system comprising a hermetic compressor unit including a casing and a compressor and a motor for driving said compressor within said casing, a condenser, a capillary iiow restrictor, an evaporator and an accumulator, conduit means connecting said compressor, condenser capillary flow restrictor, evaporator, accumulator and casing to form a closed series-flow nor- 'n'i'al refrigerating circuit in which said compressor withdraws low pressure refrigerant from saidnaccumulator and through said casing and discharges high pressure refri'ger'ant to said condenser, said motor being cooled by the low pressure refrigerant in said casing, means for periodically warming said evaporator to defrosting temper'atures by means of hot compressed refrigerant comprising an auxiliary circuit having aninle't end connected to said normal refrigerating circuit between said compressor and said condenser and it's outlet end connected to said normal refrigerating circuit "between the outlet end of said evaporator and said compressor, said auxiliary circuit including a defrost portion in heat exchange relation with said evaporator and a flow restricting means, conduit means connecting said compressor, said defrost portion, said flow restricting means and said casing to form a series-flow defrosting circuit, a normally closed valvein said auxiliary circuit for controlling flow of refrigerant through said circuit, said flow restricting means in said auxiliary circuit having a flow restriction suflicient to maintain condensing pressures in said .defrost section when refrigerant is flowing through said defrost section but substantially less than the flow restriction providedby said fixed flow restrictor when said valve is opened whereby opening of said valve causes substantially all of the circulating refrigerant to flow through said defrost circuit, said defrost bircuit'having a lower effective volume than said normal refrigerant circuit'whereby the amount of refrigerant in said casing and therefor the load on said motor 'are higher during defrosting operation of said system than during .normal refrigerating operation thereof, aportion of .said auxiliary circuit between said valve and-said defrost portion being in heat vexchange relation with said refrigerating circuit between said \condenser and said capillary flow restrictor to vaporize any refrigerant flowing to said capillary flow restrictor and thereby limit flow of refrigerant to said evaporator during operation of said system when said valve is in the open position.

References Cited in the file of this patent UNITED STATES PATENTS 1,863,427 Warren June 14, 1932 2,080,358 Kucher May 11, 1937 2,693,683 Toothman :Nov. 9, 1954 2,720,759 Philipp Oct. 18, 1955 2,759,339 Kundert Aug. 21, 1956