US2631441A - Refrigerator defrosting apparatus - Google Patents

Description

March 17, 1953 M. G. sHoEMAKER REFRIGERATOR DEFRosTING APPARATUS Filed 001:. 9, 1950 Patented Mar. 17, 1953 REFRIGERATOR DEFROSTING APPARATUS Malcolm G. Shoemaker, Doylestown, Pa., assgnor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application October 9, 1950, Serial No. 189,183

Claims.

The invention hereinafter disclosed and claimed has to do with refrigeration apparatus and, more particularly, is concerned with apparatus. of the type having provision for heating the evaporator, such heating being particularly useful in eecting automatic removal of frost deposited upon the surfaces of the evaporator or other element utilized to produce refrigeration.

Periodic removal of accumulated frost is necessary in order to maintain the operating efficiency of a refrigerating machine the evaporator of which is operating at temperatures below the freezing point of water, and such defrosting has frequently been accomplished by shutting down the refrigerating system. Since extended discontinuities of operation of the system result in thawing of frozen foods, with attendant deterioration, and since the defrosting operation has frequently been troublesome and time-consuming, it has been recognized that automatic and relatively frequent defrosting of the evaporator is desirable. Such defrosting can conveniently be accomplished by subjecting the evaporator 'to a considerable quantity of heat over a relatively short period of time and the most desirable and efficient modes of effecting defrosting have incorporated heat pump principles. It is with improvements in this class of apparatus that the present invention is concerned.

Prior to a detailed consideration of the improvements presented by my invention it is useful tov consider, briefly, approaches which have hitherto been made to the so-called heat pump defrosting problem. Perhaps the most widely known type of prior apparatus, used for heating purposes, in general, as Well as for defrosting, specifically, involves reversal of the normal refrigeration cycle, such reversal being effected by adding to the refrigeration system a valve which reverses the connections in such a way that what is. normally the evaporator becomes the condenser, whereas the condenser functions as the evaporator` While such apparatus has been useful for heating purposes, and it would at first appear that it would be satisfactory for defrosting the evaporator of a household refrigerator, such has not proven to be the case. The evaporator of a refrigerator, when covered with frost, constitu-tes a relatively large thermal mass which can absorb a considerable quantity of heat and only at temperatures at or below 32 F., until all of the frost has been removed. The temperature at which the heat is being absorbed during the condensation occurring in the evaporator, determines the discharge pressure at the compressor and there results a loW discharge pressure,

that is, a low pressure difference across the capillary tube which is customarily used as the restrictor in refrigeration system. This low pressure difference, in turn, results in reducing the ow through the capillary tube through which all of the refrigerant condensed in the evaporator must be returned to the condenser for reevaporation, and there is therefore an attendant reduction in the suction pressure with the result that the compressor capacity is reduced below the point at which sufficient refrigerant is circulated to do a quick and adequate job of defrosting. Additionally, the valves customarily used in such systems have been unduly complicated and expensive, and the over-al1 result has been that reverse cycle defrosting has proven unsatisfactory in refrigerators in which rapidity is required in the defrosting operation.

Another known system involves heating liquid refrigerant prior to its entry into the evaporator. This, as a broad principle, is well known and attempts have recently been made to modify it by adding a sump or receptacle within which is accumulated excess refrigerant not required and not utilized during normal refrigeration. When defrosting is required and the heater is energized, hot gas is forced into the sump and the liquid therein is forced through the evaporator and returns to the compressor, such extra liquid then being available during the defrosting operation. The refrigerant is returned to the gaseous state just prior to entrance into the compressor where it is, of course, compressed, being thereafter condensed and then fed through the capillary tube in accordance with the usual refrigeration cycle, after which it is re-evaporated by an electric heater just prior to entry into the evaporator and is available for condensation in the evaporator. The condensation of course effects the defrosting.

While this system has, in many respects, proven desirable it is, inherently, subject to certain disadvantages. Perhaps most importantly it involves presence in the system of an excess quantity of refrigerant not required during normal refrigeration, this amount also being critical in order to insure that sufficient refrigerant will be available during defrosting. Also such apparatus necessitates the inclusion of an accumulator (sump) and additional piping, as Well as the cost and operating expense of a resistance heater. Such a system requires considerable power in operation, since all of the flow taking place in the system during a defrosting cycle must be driven through the capillary tube.

A .third approach to the problem has involved normal refrigeration system in that a by-pass is provided Vwhich delivers the compressed gas directly to the region of the inlet of the evaporator 4during defrosting, effectively by-passing the condenser and the capillary tube, due to the restriction presented by the latter. Such known systems include a valve in the by-pass line, this valve being opened only when defrosting is required.

This latter arrangement has also not proven satisfactory, from the standpoint of rapidity of defrosting. It is recognized that this diiiculty can be overcome, providedV that a substantial quantity of refrigerant is made available, at the compressor, during the defrosting operation.

This might be done by the addition of a complicated system of valving and connections used to modify the normal distribution of refrigerant within the system, in order to insure that liquid refrigerant is available at the compressor during defrosting. Such approaches to the problem are undesirable from the standpoint of high initial cost and unreliabliity'in service.

With the foregoing in mind, i-t is the primary object of the present invention to provide a heat pump defrosting system which is not only highly effective in producing adequate defrosting in unusually short periods of time, but which system is also extremely simple and inexpensive. The system presents no charging problems, and the quantity o-f refrigerant with which the system is charged is no greater than that customarily employed in a comparable refrigerating system of standard type.

1n the achievement of the foregoing general objectives, the apparatus of the invention utilizes a novel, continuo-usly open by-pass conduit or connection and an extremely simple valve, the latter being included in the suction line. The by-pass connection performs a useful function during normal refrigeration, as well as during defrosting, in that it serves under normal condi-V tions of operation to return directly to the compressor ash gas inevitably formed in the capillary tube.

In another aspect of the invention it is an important. object to provide a heat pump defrosting system in which the valve and the connections are of the simplest and most trouble-free type. No heaters or sumps are required, land the power utilized during the defrosting cycle is sharply reduced, as compared with that required by arrangements of the prior art.

It is a feature of my invention that the now of refrigerant through the evaporator, during defrosting, is in a direction reverse with respect to the -direction of flow through the evaporator during the normal cycle. As will later appear, this feature, Vin combination with use of a continuously open by-pass connection, insures that the system will have sufficient liquid refrigeran-t available at the beginning of a defrosting cycle to insure that the compressor pumping capacity will be such as to make suicient gaseous refrigerant available at the evaporator during defrosting.

vThe foregoing objects and features of my invention, together with certain significant details f construction thereof, will be understood from a vconsideration of the following description vtaken 4 in conjunction with the accompanying drawings, in which:

Figure l is a diagrammatic representation of a refrigerati-on system including Idefrosting apparatus embodying the present invention, the setting of the control valve being such that normal refrigeration results;

Figure 2 is a View similar to Figure 1, and illustrative of the defrosting cycle; and,

Figure 3 is a cross-sectional illustration, on an enlarged scale, showing a valve of the type prefi erably utilized in the practice of the invention.

,In the achievement of the objects of my invention, and first briefly described, the illustrated embodiment -comprises a refrigerati-on system of conventional type having a compressor It, a condenser II, a continuously open restricted connection or capillary tube I2 (other suitable flow control devices could be used), and an evaporator I3 which is disposed in high heat exchange rel-ation with a compartment or zone to be coo-led, said compartment being diagrammatically represented by the broken line I4. The aforesaid elements are connected in series flow circuit through the agency of suitable conduits and connections which need not be described in detail, and including the aforesaid capillary tube and a suction line illustrated at I5. The normal operation of such a .system is well known and requires no detailed description herein.

In particular accordance with the present invention, however, the apparatus includes novel means for causing condensation within the evaporator and consequent heating of the latter, comprising: ,a valve I6 disposed in `the suction line and having connection, through a conduit Il, `with the discharge pipe leading from the compressor I0, this valve being operable substantially to by-pass the restrictor I2 and concurrently to establish flow of refrigerant from the discharge side of the compressor, through the suction line I5 and thence through the evaporator in a direction reverse with respect to the normal direction of ow through said evaporator. A continuously open yby-pass conduit or connection I8 is so disposed in the system as to conduct refrigerant which flows out of the inlet side of the evaporator, under defrosting conditions, directly back to the compressor. This refrigerant is in the liquid state, due to the condensation occurring within the evaporator during defrosting, and is returned to the gaseous state by heat exchange taking place within the low pressure shell or domeof the compresso-r.

Now making more particular reference to the drawings, and especially to Figure 1 thereof, it will be seen that the Vsystem is conventional, as respects the normal refrigeration cycle. As will be understood the capillary tube I2 and the suction line I5 may, if desired, be disposed in heat exchange relation, but such association of these elements has been omitted from the disclosure in the interest of simplicity and clarity in illustration. During the normal refrigerating cycle, in

. the capillary tube i2 and `into the evaporator I3,

the by-pass connection i8, which is open under all conditions of operation, performs a useful function in that the hash gas formed in the capillary tube is returned directly to the compressor throughl said by-pass I8, 'rather than reducing the effectiveness of the evaporator by passing therethrough. The flash 'gas may be separated in any one of a variety of ways and, in the illustrated embodiment, such separation is effected by gravity within a small chamber shown at 20. As is clear from Figure 1, gaseous refrigerant owing from the evaporator I3 through the suction line I5 passes through the lower p0rton of valve I6 beneath the lower surface of a vertically shiftable plunger 2| included in said valve, and thence outwardly of the valve body and to the suction port 22 of the compressor, by means of that portion of the suction line represented at I5a.

The valve is of extremely simple type which, as will later appear, includes only one seated part and, as clearly appears in Figure 2, the valve plunger 2I is movable to a lower position when it is desired to modify the connections in such manner as to produce defrosting of the evaporator I3.

Actuation of the valve is preferably accomplished through the agency of a solenoid winding 23, and in accordance with the determinations of any suitable apparatus effective to initiate and control the defrosting operation. Since the present invention is not concerned with the circuitry or apparatus used to control the Valve I6, illustration and description of these elements of the system is not required herein. However, the valve may, for example, be controlled by the use of a switching device of the type described and claimed in the co-pending disclosure of Elmer W. Zearfoss, Jr., bearing Serial No. 183,757, led September 8, 1950.

y When defrosting is required, and now making reference to Figures 2 and 3, the solenoid winding 23 is energized by the control switch (not shown) with the result that the solenoid plunger or armature 24 is moved to its upper position in which a valve member 25 is disassociated from a seat shown at 26. As will be recognized, raising of the valve member 25 permits the high pressure gas discharged by the compressor to pass through the conduit I1 into the valve body whence said high pressure gas passes downwardly through the opening provided by valve seat 26 and reacts against the inner surface of cup shaped plunger ZI thereby moving said plunger, against the pressure of a spring 21, t the lower position shown in Figure 2. The downward travel of the plunger is determined by a stop member 28 (Figure 3) and, when the plunger is in said lower position, the high pressure gaseous refrigerant flowing to the valve through conduit I1 is delivered to the suction line I (see Figure 2) through suitable ports provided in the plunger 2 I, and designated in Figure 3 by the reference numeral 29.

As will be understood from a consideration of the arrows which indicate the direction of ow in Figure 2, the warm gaseous refrigerant is delivered to the exhaust header of the evaporator I3, passing downwardly through the parallel passages shown at 30 and forcing the liquid refrigerant standing in said parallel passages out of the evaporator through the series convolutions 3 I. Under such conditions, that is, Vwhen defrosting has been initiated, the liquid refrigerant present in the evaporator I3 is forced back to the compressor through the by-pass connection I8 and is evaporated in the shell of the compressor as above described. In this way, as soon as defrosting is initiated, a substantial supply of liquid refrigerant is almost immediately available at the compressor, and the suction pressureV is maintained at a value suflciently high to insure sup- 6 ply of an adequate quantity of refrigerant to be condensed in the evaporator.

It is signicant to note that, in the preferred embodiment, the novel valve and continuously open by-pass connection of the present invention are utilized in conjunction with a series-parallel evaporator of the kind illustrated and described. In such an evaporator, in which flow normally occurs in the direction shown by the arrows applied to Figure 1, a considerable quantity of liquid refrigerant customarily accumulates in the parallel portion of the evaporator. y

Since the direction of flow in the system, during defrosting, is rst through the parallel passages, and thereafter through the series convolutions, the aforesaid liquid refrigerant is forced or blown out of the evaporator and delivered to the compressor. When an evaporator of this type is used. if the flow through the evaporator during defrosting were in the normal direction, that is, rst through the series convolutions, the hot gas delivered to the evaporator would tend to bubble or pass upwardly through the parallel passages 3Q and the liquid refrigerant would tend to remain in the evaporator, rather than returning to the compressor.

It is to be noted that the by-pass conduit I8 is preferably a restricted connection, the restriction being just sufficient to prevent ow of liquid refrigerant (passing through the capillary tube) backwardly through the by-p-ass during normal operation of the system, rather than flowing through the evaporator as is required. In a representative system which has yielded good results, the by-pass conduit I8 has comprised six feet of tubing having an inside diameter of 0.060 a very much lesser restriction than is presented by the capillary tube, and slightly more than is presented by the evaporator circuit.

That condensation occurs in the evaporator, with resultant utilization of latent heat to melt the frost thereon, will perhaps be better understood in the light of the following explanation. When defrosting is first initiated, the compressor, which is at a relatively elevated temperature, acts in a manner similar to a boiler, heat available in the compressor immediately evaporating the liquid refrigerant returned thereto and, as a result of such evaporation, gaseous refrigerant is available to be delivered by the compressor to the evaporator through suction line I5, the valve plunger 2l occupying the position shown in Figure 2. The available heat present in this gaseous refrigerant is given up to the cold evaporator by condensation, and at a temperature near 32 F.

rIhis temperature is, of course, maintained until all of the frost has been melted. Thesource of heat required to vaporize the returned liquid is supplied by the thermal mass of the compressor system and by the electrical losses which occur in the compressor.

Although it would be possible, if desired, to control the refrigerating system in such a way as to insure that defrosting is always initiated during a period when the compressor is idle, this need not necessarily be done since it is possible to utilize a valve which will operate under any normal pressure conditions existing within the system. Such valves are well known, being commonly referred to as impact type solenoid valves. In the representative embodiment illustrated and described herein, the solenoid valve I6, which is shown somewhat diagrammatically, is to be understood as being of this type.

From the foregoing description it is clear that the present invention provides a heat pump defrosting system which is characterized by unusual constructional simplicity and by a 'high degree of rapidity and reliability in operation. No heaters, sumps or extra quantities of refrigerant are utilized, and the power requirements of my novel system are considerably reduced as compared with arrangements known heretofore.

I claim:

1. Defrostable refrigeration apparatus comprising, 'in combination: a compressor; a condenser; a restrictor; an evaporator; conduitY means including suction and feed lines interconnecting-said condenser, compressor, restrictor and evaporator in series flow circuit in such manner that refrigerant normally flows from the discharge side of said compressor through said condenser and restrictor to said evaporator, the refrigerant thereafter returning to the suction side of said compressor through said suction line; valve means including a valve element disposed in the suction line between said evaporator and said compressor, said valve means being operable to modify the aforesaid normal flow and to cause at least the major portion of the refrigerant delivered from the discharge side of lsaid compressor to flow through said suction line toward and into the evaporator without passing through said restrictor, whereby to provide for condensing of refrigerant in the evaporator; and a continuously open restricted conduit having one end thereof connected in the circuit between said restrictor and said evaporator, and the other end thereof connected in the suction line between said valve element and said compressor, said restricted conduit having lesser restriction than that presented by said restrictor and having greater restriction than that presented by said evaporator.

2. In a refrigeration system of the type having compressor, condenser, restrictor and evaporator elements normally so connected through suction and feed lines that refrigerant flows through said elements in the order named whereby to vaporize refrigerant within said evaporator, means for modifying the ow of refrigerant through said system to cause condensation of refrigerant Vwithin the evaporator and consequent heating of the latter, comprising: means operable substantially to by-pass said restrictor and to establish modified flow of refrigerant from said compressor through said suction line to the evaporator; a separator device connected to said evaporator and to which is delivered refrigerant fiowing through said restrictor during normal operation of the system, said device having a liquid-collecting portion and a gas-collecting portion; and a continuously open conduit communieating with said compressor and said gas-collecting portion, said conduit serving, during normal operation of the system, to bleed off flash gas from said gas-collecting portion and to return suchy gas directly to the compressor, said conduit further being operable, under the modified condition of operation, to receive from said device condensed refrigerant flowing out of said revaporator and to return said cendensed refrigerant to said-compressor.

3. A system in accordance with claim 2, and further characterized in that said conduitxcomprises a restricted connection having lesser restriction than that presented by said restrictor and having greater restriction than that Apre-- sented by said evaporator.

4. Apparatus in accordancev with claim 1 and in which the said valve means includes .a single seated member and a ported valve plunger, unseating of said `member being effective to cause high pressure refrigerant Iiowing from the discharge side of said compresso-r to react Vagainst said plunger and to shift said plunger to align its port with the said suction line, whereby to provide for ow of ygaseous refrigerant from Athe discharge side of said compressor, through said valve means and thence into thesaid-suction line for delivery to the evaporator.

5. Defrostable refrigeration apparatus comprising, in combination: a compressor; a condenser; a restrictor; an evaporator; conduit means including suction and feed lines interconnecting said compressor, condenser, restrictor and evaporatorlin series now circuit in such manner that refrigerant normally ows from the discharge side-of said compressor, through-said condenser and restrictor, to said evaporator, the refrigerant thereafter returning to the suction side of said compressor'through said suction line; valve Vmeans including a valve element disposed in thesuction line between said evaporator and said compressor, said valve meansbeing operable to modify the aforesaid normal flow and to cause at least theV major portion of the refrigerant delivered from the discharge side of said compressor to flow through -said suction line toward and into the evaporator without passing through said restrictor, whereby `to provide for condensing of refrigerant in the evaporator; and means for returning the condensed refrigerant to said compresser .comprising a conduit having one end thereof in communication with said evaporator and the other end thereof in communication with the suctionside of said compressor, said apparatus beingfurtherfcharacterized in that said evaporator is of the series-parallel type, the said normal iovv of refrigerant through the evaporator taking place first kthrough the series portion of theevaporator and'thereafter through theparallel portionv thereof, said modified ow through said evaporator being first through the parallel portion thereof and thereafter through the series portion thereof.

VIVIALCOLM G. SHOEMAKER.

REFERENCES CITED The following references are of recordin the le of this patent:

UNI-TED STATES PATENTS Number Name Date 2,694,565 Wolfert Sept. 28, 1937 2,423,386 .Hubacker July 1, 1947 2,433,574 Newton Dec. 30, 1947 v2,446,910 Dickens Aug. 10, 1948 V2,451,385 Great Oct.'12, 1948

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