US2666298A - Method and means of defrosting a cold diffuser - Google Patents

Description

Jan. 19, 1954" v I F. M. JONES 2,666,298

METHOD AND MEANS OF DEFROSTING A COLD DIFFUSER Filed Nov. 1, 950 r I 5 Sheets-Sheet 1 INVENTOR. I 2. FREDERICK M. JONES M ATTORNEYS Jan. 1 9, 1954 F. M. JONES METHOD AND MEANS OF DEFROSTING A COLD DIFFUSER Filed Nov. 1, 1950 3 Sheets-Sheet 2 INVENTOR. FREDERICK M. JONES ATTORNEYS F. M. JONES METHOD AND MEANS OF DEFROSTING A com DIFFUSER Filed Nov. 1, 1950 3 Sheets-Sheet 5 S E w R wm m m T 08 mK C m I I I I 1| I T M E m m wqwmw/ w 9% 0R 1 I wow wnm 0mm 3m 8w 6 3m- 9m N5 mom f mom 2w 8N. oom wvm ATTORNEYS Patented Jan. 19, 1954 OFFICE METHOD MEANS OF DEFROSTIN G A COLD DIFFUSER Frederick M. Jones, Minneapolis, Minn., assignor to U. S. Thermo Control 00., Minneapolis, Minn., a corporation of Minnesota Application November 1, 1950, Serial No. 193,340

12 Claims.

My invention relates to a methodand means of defrosting a cold diffuser. In general the invention is concerned with a means of defrosting a refrigerant heat exchanger or other cold diffuser by a heating medium, when the surface of the diffuser has accumulated a layer of frost or ice which effectively reduces its heat transfer capacity.

In particular my invention is concerned with the combination of a refrigerant system and a control device which is responsive to a condition of the cold diffusing heat exchanger that is indicative of excessive frosting, which condition may for example be a differential between the surface temperature of the diffuser and the space temperature ambient to the diffuser, and which because of excessive frostingof the diffuser is not properly cooled.

This application is a continuation in part of my previous applications Ser. No. 470,306 filed December 26, 1942, and its successor Ser. No. 695,657 filed September 9, 1946, both of which became abandoned.

In the operation of refrigerating systems in volving a cold diffuser that is in heat exchange relationship with the atmosphere of an enclosed space, the diffuser through contact with moisture carried by the air gradually accumulates a deposit of frost or ice on its outer surface, which acts as an insulating layer and must be periodically removed in order to efficiently transfer heat between the air and the cold diffuser. The frosting of cold diffusers has long been recognized as a deterrent to proper heat exchange and numerous means havebeen used heretofore to pcriodically defrost the outer. surface of the diffuser. It is well known to use such heating mediums as hot water or electrical heaters and other forms of transferring heat from a source of heat to the cold diffuser. In the instance of refrigerating systems of the closed circuit type incorporating the combination of a compressor,

condenser and evaporator, the compressed, re-

to enter the evaporator to heat the same.

In the present invention the refrigeration. system is'shown as incorporating the combination of a compressor, condenser and evaporator which areinterconnected in such a manner that the compressed refrigerant which is ,suppliedby a compressor that is in continuous operation during the defrosting cycle, may be used to accomplish the defrosting of the evaporator. However, my invention is not restricted to any particular type of refrigerating system nor to any particular medium for defrosting the same, since it is applicable to any form of cold diffuser in which defrosting is accomplished through the use of a medium capable of transferring heat from a source of heat to the cold diffuser, and wherein the only problem resides in the control of a second control device that is capable of controlling the flow of the heat transferring medium.

In particular, in the present invention a primary control device is used to control the operation of a secondary control device which regulates the flow of the heating medium to the diffuser, which medium in the present invention consists of the heated compressed refrigerant fluid that has been heated by the action of the compressor or by heat emanating from the prime mover that drives the compressor. The hot gas is introduced into the refrigerant heat exchanger either by reversing the normal path of the refrigerant fluid, or by modifying the path of the fluid so that the same enters the. heat exchanger at a suitable point between the inlet and outlet where the fluid therein is most likely to be in a saturated gaseous condition, and will not result in the forcing of liquid refrigerant into the compressor to cause injury thereto.

The primary control device is composed of a pair of thermal motors, one of which responds to the surface temperature of the cold diffuser, and the other responds to the temperature of the space adjacent the diffuser. In refrigerating an enclosed space, by circulating the air therein into contact with the cold diffuser, either by a thermal cycle or by the forced movement of air, a substantial differential will exist between the air temperature and the surface temperature of the heat exchanger. The two thermal motors utilize this temperature differential as a means of control so that when the differential is substantially varied, as will occur when the diffuser becomes excessively frosted, the conjoint action of the two thermal motors is utilized to bring about a defrosting operation. A linkage is provided in the primary control device between the two thermal motors, and the movement of this linkage in either one of two directions is utilized to operate a switching mechanism that is electrically connected to the secondary conwhen an accumulation of frost on thesurface of the latter precludes proper cooling of the enclosed space.

In refrigerating a compartment, the desired temperature of the enclosed space is determined by pre-setting of a thermostat which controls the operation of the refrigeration system and is independent of the present invention. Assuming for example that the desired space temperature to be about 45 F., the heat exchanger when operative will have a surface temperature considerably below the space temperature and may for example be about 25 F. In this example, to maintain the space at a temperature of 45 F; with the surface temperature of the diffuser being 25 F. a differential of 20 will exist between the surface temperature of the diffuser and the temperature of the controlled space. In the present invention one of the thermal motors through a suitable temperature responsive means responds to the space temperature, whilethe other thermal motor through a suitable temperature responsive means responds to the surface temperature of the cold diffuser, and the two motors operate on a differential which in the foregoing example is 20. If for any reason the temperature of the heat exchanger is lowered, as for example by changing the setting of the space thermostat, and there is efficient heat exchange with the enclosed space, both of the thermal motors will respond to the temperature variation and the differential will remain substantially unchanged. When, however, the heat exchanger accumulates a layer of frost or ice, the latter forming an insulating layer which diminishes heat exchange, this frost layer will cause the surface temperature of the heat exchanger beneath the layer to be reduced through ineflici'ent' heat transfer, while the space temperature will gradually rise since the air is brought into contact with the frost layer having a temperature of about 32 F., which is generally incapable of sufficiently cooling the air within the enclosed space.

As this condition will be aggravated by the progressive thickening of the layer, the differential between the two thermal motors will gradually exceed the predetermined differential of 20, whereupon the conjoint action of the two thermal motors will rotate the linkage to the extent that the latter will move the switching mechanism to a position to effect defrosting.

In those refrigerating systems which utilize means for forcibly circulating air from the enclosed space into contact with the refrigerant heat exchanger, it may be desirable to terminate the flow of air during defrosting so as to prevent blowing the melted moisture into the enclosed space where it may cause damage to products stored therein. To this extent a double throw switch is provided which breaks a circuit to an air flow control means, such as a damper or a fan motor, before it makes another circuit to the control device that initiates the flow of the heating medium to defrost the cold diffuser. During initial stages of defrosting the surface temperature of the diffuser will remain at substantially 32 F. until all of the frost has been removed, whereafter as a result of continued heating, the surface temperature of the diffuser rises rapidly so as to substantially reduce the differential between the two thermal motors below the predetermined differential. When. this occurs the switch operating linkage is moved in an opposite direction to terminate defrosting and if necessary re-initiate the circulation of air.

The primary control device is not normally concerned with the temperature involved in a specific refrigeration plant but is pre-set to operate on a specific differential which may be desired in a specific application. Accordingly, therefore,

means are provided for adjusting the difierential between the two: motors, and normally this is a factory setting or by an experienced'service man. As it is recognized that under certain circumstances a considerable differential between the two thermal motors may exist for a short time after a refrigeration system, which has been in-' active and is initially started, safety latching means are provided to prevent a defrosting action from occurring until after the refrigeration plant hasbeen in operation for a sufficient length of time for the surface temperature of the evaporator to be. below. the freezing temperature of water.

Two different refrigerating systems are shown which incorporate-the control" device. In one instance a mechanical" refrigerating system is shown. in which acomplete reversal: of flow ofthe refrigerant is effected by the control device. In the other instance hot gas is introduced into an evaporator at an area between the inlet and the outlet andzin sucha manner asto divide the contents of the evaporator-intoa liquid portion and a gaseous portion, the former being returned to a liquid receiver, and the latter being withdrawn by a compressor.

The principal object of the invention is to provide in combination. with a refrigeration system of the compressor, condenser, evaporator type means which are independent of the system for automatically introducing: hot gas from the high pressure side of the. compressor into the evaporator, when the latter is in need of defrosting. Another objectv is to providev in combination with a refrigerating system of; the, compressor, condenser,- evaporator type that is provided with flow control means for modifying the path of refrigerant flowto effect defrosting of the evaporator, a control device which is independent of the operation of the compressor and responsive to a condition of. excessive frosting; of the evapo rator, to effect thefiow of hot gas into the evaporator to defrost the same and thereafter termihate the flow of thehot gas. as soonasdefrosting is completed.

Another object is. to provide a. method of defrosting the evaporator of a mechanical refri crating sy tem in which a. liquid refrigera t s v porated at. reduced pressure. by introducing heated refrigcrantvapors into the evaporator above the liquid level therein so. as: to divid the contents ofthe evaporator into two portions, one of which returns to a liquid receiver and the other of which is withdrawn by a compressor whereby both portions are replaced by the heated vapors.

Another object is to provide a method of defrosting a cold diffuser by measuring the difference between the surface temperature thereof and the space ambient thereto, and utilizing a variation in this differential to effect defrosting and thereafter a return to normal refrigeration.

Another object is to provide a refrigerant control device, utilizing a pair of thermal motors, one of which responds to the surface temperature of the cold diffuser and the other of which responds to the temperature of the space ambient to the diffuser, and wherein the joint efforts of the two thermal motors are utilized to effect defrosting of the cold diffuser when the latter has accumulated an excessive layer of frost.

Another object is to provide in combination with a refrigerant plant including two heat exchangers and having a control valve which when opened is capable of modifying or reversing the path of the fluid refrigerant so as to defrost one of the heat exchangers, together with means for controlling the circulation of air from an enclosed space over the said heat exchanger, a control device which is responsive 'to a condition of excessive frosting of the heat exchanger and is capable of simultaneously opening the control valve and terminating the flow of the circulated air over the one heat exchanger during defrosting and thereafter reversing the operation as soon as defrosting is completed.

Another object is to provid in combination with a refrigerant heat exchanger having air passages and a control devic having a firstther mal responsive element mounted on the surface of the heat exchanger, and a second thermal responsive element which responds to the temperature of air drawn through the passages, means for drawing air through the passages to contact the second thermal responsive device when the heat exchanger becomes frosted to the extent that the passage of air therethrough is precluded.

A further object is to provide in a refrigerant control device composed of a pair of thermal motors which operate on a differential principle, and a switching device, a linkage interconnecting the two motors and which is capable of operating the switching device, together with a safety latching mechanism which is cooperable with one of the motors for restraining the action of the same under unusual conditions.v

, erating system incorporating the structure shown in Fig. 1; and, r

Fig. 5. is a schematic showing of another type of commercial refrigerating system incorporating the control device shown in Fig. 1.

Referring first to Fig. 1, general reference numeral It indicates a schematic showing of a refrigeration system of which a practical commercial aspect is shown in Fig. 4.. Reference character I2 indicates a prime mover that is suitably connected to a compressor I4. Th operation of 6 the prime mover; which'may'be either-an internal combustion engin or an electric motor, is controlled in response to the temperature within an enclosed space, not shown. Extending from the high pressure side of compressor I4 is a conduit I6 which joins the inlet of a condenser I8. Condenser I8 in turn is joined at its outlet to a refrigerant receiver 20.

Extending from receiver 20 is a conduit 2 l which at its other end is joined to the inlet end of an evaporator 22. Conduit 2I contains an expansion valve 23 which is connected by a tube 24 to a thermostatic bulb 25. Joined to conduit 2i on either side of valve 23 is a by-pass 26 containing a check valve 21. A conduit 28 extends from the outlet end of evaporator 22 to the low pressure side of compressor I4, and conduit 28 is in heat transfer relationship with bulb 25. A conduit 30 extends from a junction Il on conduit I6 to a junction 3I located at a central area in evaporator 22. Conduit 30 contains a flow control valve 32 which is operated by an electric operator 34. In practice valve 32 would be a two position solenoid valve.

For reasons which will be explained hereinafter, it is important that the interior cross-sectional area of conduit 30, valve 32 and junctions I! and 3I, be at least as great as conduit It.

Also shown in Fig. 1 and indicated by the general reference numeral 36 is a control device composed of a casing 38 which houses a pair of thermal motors shown as expansible bellows members 40 and 42. Bellows 40 on its lower end is sealed by a cap 44 to which is secured a projection 45. Adjustably extending from projec tion is a threaded adjustable actuating member 48. Extending from the other end of bellows 40 is a tube which at its outer end carries a bulb 52 that is suitably. secured to one of the coils of evaporator 22. Bellows 42 is provided wiht a cap 54 from the center of which extends an upstanding guide rod 56 that passes through a tube 58. Tube 58 is provided with external threads 60 on its outer surface and is secured at its upper end in a bracket 6|, supported by casing 38. Surrounding tube 58 is coil spring 62, whose opposite ends engage washers S3, 64. A nut engages the threads 60 on tube 58 and is provided for adjusting the tension on spring 62. Atits other end bellows 42 is connected to a tube 66 which at its outer end carries a bulb I 68 that is positioned adjacent the evaporator 22 and responds tothe temperature of air flowing over the evaporator.

A floating lever I0 extends between the inner ends of bellows 4D and 42 and is pivotally secured at I2 to rod 56 and at 14 to projection 45. Lever 10 at its center is pivotally secured at I6 to a link I8 whose lower end is pivoted at to a second lever 82. At one end lever 82 is pivoted at 84 to a stand 85 that is mounted in the lower surface of the casing 38; At its other end lever 82 carries a threaded adjustable actuator 81.

Also mounted within casing 38 is a latch 38 which is pivoted at 90. Latch 88 has a first projection 92 which extends beneath the actuator 48, and a second projection 94. Secured at one end to latch 88 is a spring 96, which at its other end is secured to an adjustable eye bolt 98 that extends through a bracket I00 and carries an adjustable nut I 02 in contact with the upper surface of the bracket I00. Associated with latch 88 within casing 38 is a'second latching member I04 which is pivoted at I06. Latch I0 4 carries a hook-shaped projection I08 and an up-standing finger III! which is positioned in the path of the projection 84 of latch 88. Aspring H2 is secured at one end to casing 38 andat its other end to a portion of the latch member I04. A stop pin I I4 is supported by the casing 38 to engage a portion. of latch I04 adjacent the lower end of spring I I2.

Referring now to a portion of Fig. 1 in conjunction with Figs. 2 and 3, is shown a switching device designated by general reference numeral. I I6, which is carried by casing 38. The switching: device I I6 consists of a movable switch-actuating member H8 having a hook-shaped portion I20 at one end and a hammer-like contact member I22 at its other end. The actuator H8 is sup ported on a block I24 by a pivot I26. A curved opening I28 is provided in the actuator H8 and a pin I30 carried by block I24 extends through the opening I28. A spring I32 extends between pin I30 and a second pin I34 carried by the: actuator I I8 and is intended to provide an overcenter snap action to the actuator IIB when the latter moves between its two positions, as indicated by the full line and dotted line disclosures of Fig. 2. Carried by block I24 on either side of the hammer-like portion I22 are a pair of switches I38, I38 which in practice may be conventional snap switches. A branched conductor I40 extends from a source of power, not shown, to one side of each of the switches I36, I38 to supply current to these switches. A conductor I42 extends from switch I38 to one pole of the motor operator 34 of valve 32. A conductor I44 extends from the other pole Of motor 34 to ground, as shown in Fig. 1. Under certain circumstances it may be necessary in a refrigeration control device to provide means for controlling the flow of air over the evaporator 22 and under these conditions switch I36 is connected by a conductor I46 to an electrical control device which controls the flow of air and in Fig. 1 such a device might be a motor, not shown, which is provided to drive fan I48.

The operation of the refrigeration system I8 in conjunction with the control device 36 will now be explained. With the parts in the position shown, it will be assumed that the refrigerating system I has not been in operation but is about to be started. The prime mover I2, which, as previously explained, may be either an electric motor or an internal combustion engine, by means, not shown but explained in part in conjunction with the unit shown in Fig. 4, will be placed in operation by a call for refrigeration in an enclosed space surrounding the evaporator 22. When started, the prime mover will intermittently operate the compressor for a sufficient period of time to bring the temperature in the space adjacent evaporator 22 down to a level where the need of refrigeration is satisfied. Assuming, therefore, that prime mover I2 has been started and is now driving the compressor I4, and further assuming that fan I48 is in operation and is circulating air over the evaporator. Under these conditions the temperature of the air and the surface temperature of the evaporator will be substantially identical until the compressor has operated long enough to reduce the pressure within the evaporator to cause evaporation of refrigerant fluid present therein. With the surface temperature of the evaporator being equal to the ambient temperature, the expansion valve 23 under the influence of thermostatic bulb 25, which is in contact with conduit 28, will permit liquid refrigerant within the re ceiver 20 to flow into the evaporator 22 because of the low pressure created by the compressor. Except for the presence or flash gases which quickly separate themselves from the liquid, the liquid level within the evaporator is not ordinarily more than about one-third of the internal capacity of the evaporator. A middle portion of the evaporator will contain a mixture of liquid and as in What may be regarded as a saturated condition, and the remaining portion of the evaporator, which is generally not more than about one-third, will contain refrigerant in a gaseous condition which is continuously being removed by the compressor and when compressed, driven through the condenser where it is converted to liquid and returned to the receiver 20.

Considering now the control device 36, which is shown in Fig. 1, in its normally inoperative condition as it would exist immediately before the starting of the system I0, and with bulb 52 in contact with the evaporator, and bulb 68 in the path of the air stream flowing from fan I48. Under these conditions bulbs 52 and 68 are both subjected to substantially the same temperature conditions and, therefore, the thermal motors or bellows 40 and 42 would both be in a relatively expanded condition and lever I0 would most likely be slightly tilted, as shown in Fig. 1. From the present explanation it will be assumed that springs 86 and 62 have been appropriately biased, by means of the adjusting nuts I02 and 65 to maintain a differential pressure between the bellows 40 and 42. Now, considering that evaporation is taking place within evaporator 22, bulb 52 will begin to respond to a slightly lower temperature than bulb 68 and, therefore, bellows 40 will begin to contract at a slightly greater rate than bellows 42 although it should be clearly understood that both bellows will retract but no marked difference will be immediately evident because of the large volume of air flowing over evaporator 22 and in heat exchange relationship therewith. As the surface temperature of evaporator 22 descends towards the freezing temperature, spring 96 will urge the bellows 40 toward a retracted position and link 88 will slowly rotate in a clockwise direction on its pivot 90 bringing the projection 84 into contact with the projection IIO on the link I04. As the cooling operation continues, link I04 is rotated on its pivot I88 by the action of link 88 and against the resilience of spring I I2 so that by the time a freezing condition exists at the evaporator, the hook-shaped portion I08 of the link I04 has cleared the hookshaped end I20 of the switch actuator H8. The purpose of links 88 and I04 is to maintain the switch actuator I I8 in a locked condition to prevent operation of the switching device II6 until a freezing condition exists at the evaporator 22, and a normal differential exists between bellows 40 and 42.

The unusual conditions for which the lockin mechanism just described is provided, might exist where considerable pressure existed in evaporator 22 before starting, such as might be caused by a relatively hot load being present in the enclosed space to create a substantial back pressure on the compressor. When a substantial pressure exists in the evaporator before starting, the initial operation of the compressor might so materially reduce the temperature in the evaporator as to cause the temperature of the evaporator to quickly drop so that bulb 52 might momentarily record a very substantially lower temperature than bulb 88 and cause the linkage to make an'untimely movement of the switch operator [I8 to bring about defrosting when the same is not desired.

Assuming now therefrigerating system to be in normal operation, as air is circulated over the evaporator coil 22, moisturetherein will 001- lect on the cold surface of the evaporator and form a progressive layer of frost which will not only cover. the evaporator 22 but also bulb 52. As the frost layer grows, heat transfer from the air to the evaporator is'diminished and bulb 52 will register a gradually decreasing temperature, whereas bulb 68 will gradually register an increase in temperature since the layer of frost will preclude proper cooling of the air. When this condition has progressed to the point where the difierential between bellows 48 and 42 exceeds the predetermined setting, the floating lever I will rise in a generally horizontal direction and through its connection by link I8 to the lever 82, will cause lever 82 to rotate on its pivot 84 until member 8I engages actuator H8 of the switching device II6. fThe actuator II8 through pivot I26, and spring I32 through its connection between pins I38 and I34 will provide an over-center snap action to the actuator II8 moving the hammer-like portion I22 from its position in engagement with switch I38 into engagement with switch I36. When this occurs a circuit will be established from conductor I40 through switch I36 and conductor I42 to the motorizing device 34 of the valve 32 so that valve 32 will quickly move to a fully open position to initiate a defrosting operation.

As previously explained, the prime mover I2- will almost always be in operation whenever the temperature in the enclosed space is above a predetermined setting, and as the evaporator becomes frosted, such a condition will likely exist as will be evident by the fact that as previously explained bulb 68 is recording a higher than normal temperature. It will be assumed, therefore, that compressor I4 is in operation when valve 32 is opened. When valve 32 opens, hot compressed refrigerant will flow from the high pressure side of the compressor through conduit l6 and the junction l1 through conduit 30 and valve 32 to the junction 3| where it enters the evaporator 22 at an area between the opposite ends of the evaporator and above the liquid level therein. When the internal cross-sectional area of conduit 36 and its associated connections is atleast equal to the internal cross-sectional area of conduit I6, the volume of hot gas entering the evaporator is sufficient to reduce the pressure in the condenser I8 and substantially raise-the pressure in evaporator 22, allowance being made for the fact that these pressures will never beexactly equal ,because of the continuing operation of compressor I4. An initial portion of the hot compressed gas entering evaporator 22 will be condensed by the low temperature of the. evaporator and thereby be converted into a liquid state when it' will flow by gravity to the lower portion of the evaporator and join the liquid refrigerant therein. As the hot gas continues'to enter the evaporator, the suction effect of compressor I4 will draw a portion of the gas upwardly from the central area and back to the compressor.

Except in an instance which will be mentioned hereinafter, the expansion valve 23 will most likely be at least partially open at the time defrostingoccurs and when the pressure in evaporator 2211s raised bytheentryof. the hot gas,

liquid refrigerant-in the lower or initial part of the evaporator will flow by gravity back into the receiver20 so that in a relatively short time the evaporator will only contain gaseous refrigerant which will quickly defrost the entire area of the evaporator. In certain applications, and particularly where relatively low temperatures are desired in the space surrounding evaporator 22, the expansion valve 23 may be of a, type which will close on a rise of pressure within the evaporator and which would normally prevent the liquid refrigerant from returning to the receiver 20. When such an arrangement exists, a by-pass 26 is provided to circumvent the expansion valve 23 and check valve 21 will become operative to permit refrigerant to flow around the closed expansion valve. Thus in either instance the evaporator is quickly freed of any liquid refrigerant which might maintain a low temperature in the evaporator and is replaced by gaseous refrigerant. It will be apparent that when the hot gas is introduced into the evaporator at an area above the liquid level, it tends to separate the refrigerant therein into two phases so that none of the refrigerant existing in a liquid state is forced through the outlet end of the evaporator where it would cause injury to the mechanism of the compressor.

During defrosting the temperature of the evaporator will remain substantially constant at about 32F. until 'all of the frost is removed, whereafter it is rapidly heated by the hot gas. The heat of the hot gas will be rapidly transmitted to the bulb 62 which will then cause expansion of the fluid within the closed system composed of bulb 52 and tube 56 to cause bellows lllto expand, without necessarily causing retraction of bellows 42 because of the fact that bulb 66 is not in direct contact with the evaporator. As bellows 48 expands, the linkage forming lever 18, link 18 and lever 82 will return to a position approaching that shown in Figure 1 and the actuator 48 will engage actuator II8 to move the same downwardly in an over-center snap action to return the movable member I 22 to the position shown in Fig. 1, whereupon a new refrigerating cycle will commence. Bellows 42 will expand and contract in accordance with the change of temperature adjacent bulb 68, and its purpose is to maintain a differential with respect to bellows '46 so that the control device can be used under varying conditions.

The links 88 and I84 will oscillate slightly dur-' ing the normal operation of the control device, but hook I88 will not normally be permitted to rotate to a position where it will prevent movement of actuator .I I8 until the refrigeration system has been shut down and the parts of the control device 36 have assumed a position similar to that shown in Fig. 1.

Referring now to Fig. 4 is shown a practical commercial application of the refrigeration system shown in Fig. land which, at least insofar as defrosting is concerned, is controlled by the control device 36. The structure shown in Fig. 4 is a perspective view of a portable transport refrigeration unit which is fully disclosed and claimed in my Reissue Patent No. 23,000. In general, the structure is designated by the general reference character I 50 and consists of a casingv I52 that generally surrounds all of the operative portions of the mechanism but which is divided by a partition I64 that separates the operating mechanism, including the prime mover, compressor, condenser and receiver, from the v p ra or. and i a so itei ufilemem otor:-

ence character I55 designates an enjg ewhich throu h, a sta er oi e ator 5B oro ta...y. con: nected to a compressor lfiq E zgtendin irom the high pressureside oi compressor 16d is a con coi 16. wh h. onn ct t a. on ens r Suitably connected to condenser I54 are a pair o erc nnected reoei rten s 6 51m r ceive the compressed condensed refrigerant fluid A conductor I68 extends from receiverlfit to. an expansion valve I'll); Valve 110 is connected by a tube ill to a thermostatic bulbl'lZ. A by-pass [IA-extends around valve lflil and contains a check valve H5, Connected to the expansion valve n4 is a distribntorl'lli, havinga mu1 iplicity of capillary tubes designated severally at I86 which extend to oneend of each of several coils malging up a multiple: coil evaporator I52 Extending from conduit 1621s a hot gas line I84 carrying the solenoid valyetz having the electrical operator ,34.. The otherend of conduit 184 ;joins a manifold fllfi irom whichaplurality of small connecting tubes I38 each extend to a central point on one of the several multiple coils making up the composite evaporator 1.82. The outlet end of the multiple coils oi evaporator 1-82 areconnectedby small pipes tilt to 'a manifold I82 that is connected toa conduit 1.9.4 which extends in heat -e-xchange relationship with conduit 158 in the area inrear of partition I54 and until the conduit I931 joins the low pressure side of the compressor 160. p I

A siroccofan 19.6 is supported in rear of partition I54 and through a pulley 198 and a belt 200' is driven by engine .156. v

Mounted above evaporator 1.82 is an outlet air duct 202 which has itsinlet end in com. munication with the discharge of the .-fan 196, and is provided to discharge conditioned air into a compartment such as a storage room or the body of a cargo carrier, theair being drawn in.- wardly through the evaporator. Withinduct 2-92 is a damper .204 that is connected to a 206 winch .in turnis operated by .a solenoid operator 208. return spring 209 cooperates with the link .205 for moving the damper in an opposite direction. v a v t Extending =betweenp the multiplicity ,of coils making up the composite evaporator L82 :are ;a

plurality of fins 2H]. 7 Between two of the several fins a tube 212 which :has one end lprojecting beyondv the outer limits ofsthe fins and which at its other end carries a funnel-shaped member 214 that projects about :bulb 68 adjacent the intake side of the sirocco fan I96.

The control device 361s also "utilized with the system disclosed in Fig. 4 and the casing 38 is suitably supported on any satisfactory. part .of the structure 150. The control bulb .52 secured to one of the composite icoils making up the evaporator "I82; and'the bulb 6B is 'positioned on the in-ta-ke side :of 1the1fan I96 so as to be in contact with the air :drawn through the evaporator I82. However, in the disclosure-of Fig. A, the multiplicity of coils making up evaporator 482, as well-as the multiplicity of fins 210', neces sitates the incoming air to pass in very close heat exchange relationship with the evaporator. In the event thattheievaporator becomes frosted to the extent that air'will'not satisfactorily pass through the small openingsathe fan 196 will tend to create :a .low pressure in rear of the evaporator and air will be drawnin through the tube 212 and discharged :directlvon the bulb 68 by the funnel-like structure 25". Also the switch ns. e ic .1 Jokes it f Q IF twentie a; 1 tion in that when th i ows i F .1" I35, the solenoid operator 208 which c trol s; the m v fii i'ito amp wi l. be energiz d. o. m nta th' dampe n moped po tion, as shown in Fig. During the period or defirgsp' is when the mb r 122 isin enga ment with switc I38, the circuit to the solenoid operator ZQflWiH. be ne si -d and the d mp s will be 0 d b the a n isprin .203 to pre ent or ma r a mimic or ulati o air, so as to prevent melted-moisture fvrom being drawn inw r ly b t 196, nd pos i lyb b own outwardly through the duct :92.

a In other. respects thesystem. show i Fisk 4 is substantially identi al with that shown i Fig. l, The engine I55 has a starter generator form ing an operative connection tothe compressor .5 ,..and the s me ner o 158 is capa le of energizing the enginein response to a ode; moo for refrigeration in accordance with an electrical system disclosed in ,my prior Patent No.

2,337,164. I v p I The evaporator structure or Fig. 9i diners from that disclosed Fig.1 only to the extent t t a -multiplicity .ore orator .co'ils ar pro id d; but it 1 1 h d thet p u it o short 911-. duits I :form connections betweenthe header {wand substantially the cen'tr point of the soy..- eral evaporator coils .132 so that in effect the comp i e p r or L 2 s defrosted inthosam manner as the evaporator schematically shown inE-igd, I V

erring w to ig- 5 s h n a ther n of ref-rigerationsystem in which there is a complete lreversal of flow of the refrige-rant fluid, The refrigerant 'system shown herein is also shown in mv copendin 'g" application ser. No. 13,6;,-9 52, fi1ed January -5 195.0. A refrigerant compressor here shown at z lt forms the means of circulating the retrigerant. The comirircool). 1 disclosed here; is operated by engine J56, such as is :shown Fig. ;'I o control the flow of re: lrigerant :relatiye to compressor 21-6 a control valve mdicated Eloy .eeneralreferenc numeral .218 is :provided. valve 2111.8 consist o a ca ing 22 having fluidconnection at the openings indicated at 222, .224; 22 6 and 228. An internal passage 231) :p'rdvides a hwpass connection with certain of the foregoing iop-enings; Within the interior of casing 220 are a pair of waives 23.2 and 139 which are adapted lto engage two 386135 of seats within the casin :notudesignated. Valves .232, 231 are "joined to aisinglestem 31 :5 Whose movement is .controlled by.=a",-piStOni2-3B within acham: bor -madamezendzoracasing.2210, v

conduit 12:4:2 extends from the ,high pressure side -ofmompressor 12k? to the op ni g .224. .A conduit 244 extends zf-rom ooenmglzz of the valve teasing 1129' to a T 124.6; This conduit lconstitutes a; schematic showing :of a:multiple coil cone denser an'd iSFhBI. indicated zbyqreferenoe numeral '2'48'. jnsconduit 25Davhioh;-c.ontains..a checkvalve .252 extends from EI'CZdfi-to a .T 254. Joined {to the side 50f '21 22 521 iisca rconduit :2 5B which extends to a connectiori :258bn aieceiver 2260; .At the other end of receiver 32-60331 connection 12-52 joins the receiver to abon'duit .2514, which contains a sight g-lass :2SB ,1-a'nd extends itO all .268. A can. duit 210 extends fnomir 288.1 0 zane 2.1-2 :and contains-2a; dehydrator :an'd filter 2314. The waive 2251. 2 515 ciontirolled'bya ithermost atic ibulb 2:16; A coiidizititlirextends iro'm' valve 212 to a T 288 and contains a check valve 28 2,' A single conduit 284 extends from one side of T 288 to the opening 226 in the valve casing 228. The conduit 284 constitutes a, schematic showing of a multiple coil evaporator designated at 286. It will be noted that portions of conduits 218, 284 are in contact with each other to .form, a heat exchanger designated at 288. A conduit 298 extends between another side of T 288 to T 254 and contains a check valve 292. A conduit 294 extends from the center of T 246 to an expansion valve 296 and contains a check valve 298. Expansion valve 296 is provided with a thermostatic bulb 388. A conduit382 extends between one side'of valve 296 and the center of T 268. A conduit 384 extends from the opening 228 in the valvecasing 228 to a T 386. Another conduit 388 extends from T 386 to the inlet side of a control device indicated by the general'reference numeral 318, which will be briefly described hereinafter. A conduit 312 extends from the outlet side of the control device 318 to the low pressure side of the compressor 216.

The control device 318 is a pressure operated governor controlled unloading valve which is fully disclosed and claimed in my copending application Ser. No. 31,591 filed June '7, 1948, now Patent No. 2,581,956, granted January 8, 1952.

To control the movement of the piston 238 within chamber 248, a solenoid operated valve indicated at 314 is mounted in 'a conduit 316 which extend from the high pressure side of the compressor 216 to T386. The valve body is also connected to the'chamber 248 by a short conduit 318. q v

The operation of the fluid circuit will now be explained. With the parts in the position shown, the system 'is set for the normal refrigeration cyclewith coil 286 serving as an evaporator and coil 243 serving as a condenser. Under these conditions, liquid refrigerant in the receiver 268 leaves by the connection 262, through conduit 264, T 268,-c0nduit 218, to the expansion valve 212. Assuming the bulb 216 is calling for refrigeration, the liquid passes through conduit 218 to T 288. Assuming the compressor 216 to be in operation, the fluid will enter the evap orator conduit 284 because of the lowered pressure within said conduit. When evaporated, the refrigerant gas will pass from conduit 284 into the valve body 228 through theopening 226 and thence through opening 228 to the.conduits,384, 388 to the control device 318, whose operation will be explained hereinafter, and thence through the conduit 312to the low pressure side of compressor 216. When compressed, the gas passes through conduit 242 to the opening 224 of the valve 228, from whenceit passes through condenser conduit 244 to the T 246 and conduit 258, to the T 254, from whence itpasses through the conduit 256 and connection 258 into receiver 268.

As to other valves in the system, it will be noted that check valve 298 and, 292 will permit free flow only in the direction indicated by the arrows and, therefore, these valves will prevent the condensed refrigerant from passing through these valves. While valve 292 would permit the passage of refrigerantfrom conduit 218 into conduit 288, the lowered pressure in the evaporator will cause the refrigerant to follow the path of least resistance to the compressor. The bulb 388 of the valve 296 is in contact with'conduit 304 and this conduit will be quite cold duringthe refrigerating cycle, therefore, the expansionvalve 296 is closed, but whetheritis closed orno't is not *iii highlyimportantsince there would be a substantially balanced condition in the Ts 268 and 246. It.should also be understood that the ex-.

pansion'va'l've' 212, controlled by bulb 216 in contact with the return portion of conduit 284 will control the flow of refrigerant into the evaporator 286 in a conventional manner to maintain proper refrigerating conditions.

Assuming now that with the system in actual operation .as described. above, and the control device 36 requires reversal of flow to defrost the evaporator, the action of the control device would be the same as previously explained and valve 32 would be replaced by the solenoid operated control valve 314. When energized, the control device 314 opensconduit 316 and high pressure gas from the compressor passes through this conduit into the conduit 318 to push the piston 238 to the left within chamber 248, to thereby shift valves 232, 234 to the left to terminate communication between openings 222, 224 and openings 228, 228 into open communication between openings 224, 226, and by passage 238 between the openings 226, 228. When this occurs, the refrigerant circuit will be established as follows: The high'pressure gas, which is in a heated condition, passes from the compressor 216 through conduit 242 to the opening 224 of valve 228, thence throughopening 226 to the conduit 284, which is now acting as a condenser, passing downwardly to the T 288. v The check valve 282 will prevent reverse passage of the fluid, which may include liquid as well as gas. However, the fluid can pass from the T 288 through the conduit 288, past the valve 292 to the T 254 and thence through conduit 256 and connection 258 into the receiver 268, because the valve 252wi1l check further travel in the direction of T 246.

s From receiver 288, refrigerant will pass through connection 262, conduit 264 to T 268, and thence through conduit 382 to the expansion valve 286. Valve 286 is controlled by the bulb 388 which is in contact with conduit 384 and, as will be explained hereinafter, this conduit will conduct heated gases so that in a few moments after reversal of flow, valve 296 will open under the influence of heat to permit the refrigerant to enter conduit 294 passing through the check valve 288 to T 246 and into the conduit 268, which now has become an evaporator or an absorber of'heati In tracing the circuit fromT 268, it should be understood that the fluid will follow the path of least resistance and will enter conduit 284 rather than conduit 218, where it would eventually meet the resistance of the high pressure fluid leaving T 2138. Returning now to the valve 218, the fluid leaving conduit 244 will enter opening 222 ofthe valve body 228 and pass through the. passage 238 to the opening 228 and thence through conduits 384, 388 to the control device 318, frornwhe nce it passes through conduit 312 to. the low pressure side of compressor 216 whence it is recirculated in the manner just described.

' The control device 318, while only schematically shown here, is fully described in'Patent 2,581,956, serves to prevent overloading the compressor such as might occur when the unit is initially started, or immediately after the valve 218 is switched from the refrigeration circuit to the defrosting cycle.

The apparatus shown in Fig, 5 is provided with a fan 314 that is operated-from an independent source of power in a manner similar to fan 186 '75 of Fig.4 and is here shown as being positioned end of the second lever moves' relative to the first lever, a movable switch actuator extending between one end of the first lever and the free end of the second lever for actuation by the movement of one of said-levers, and adjustable switch engaging means on said levers for adjusting the distance between-said levers and said switch actuator. I

6; In a refrigeration-plant, in combination, a condenser having an inletand an outlet,-- an evaporator coil having an inlet and an outlet at its opposite ends, a first conduit connecting the outlet of the condenser and the inlet of the evaporator for conducting liquid refrigerant from' the condenser to the evaporator, a second conduit forming communication between the condenser adjacent its inlet end-and the evaporator at a situs of the latter between its opposite ends, a two-position valve in said last named conduit and when opened permits hot gas to flow into the evaporator to defront the surface thereof, a compressor connected between the outlet end of the evaporator and the inlet of the second conduit adjacent the inlet of the condenser, said compressor being continuously operated when the valve is in an open position for circulating hot gas through the evaporator, and a condition responsive control device operatively connected to said valve and responsive to a condition of the evaporator indicating a need of defrosting the evaporator for opening the valve when the value of the'condition varies beyond a predetermined range.

7. In combination with a cold diffuser, a first control device which when operative permits air to pass in heat exchange contact with the cold diffuser, a second control device which when operative effects defrosting of the cold diffuser, switching means operatively connected to both of said control devices and adapted to alternately energize one or the other of said devices, and means for operating said switching means including a first lever, a pair of opposed thermal motors connected to the opposite sides of the outer ends of said lever, one of said motors being responsive to the surface temperature of the cold diffuser and the other ,of said motors being responsive to the air temperature only adjacent said cold diffuser, a second lever, means pivotally anchoring one end of the second lever to permit free movement of its other end, a link pivotally joining both of said levers, and a snapacting switch actuator extending between the free end of the second lever and one end of the V first lever to alternately energize said control devices in response to the combined action of both of said thermal motors.

8. A refrigeration control device, comprising a casing, a first lever within said casing, a pair of oppositely extending thermal motors within said casing and connected to opposite sides of the outer ends of the lever, a second lever extending in parallel spaced relation to the first lever, means for pivotally anchoring one end of the second lever to the casing, a link pivotally joining the center portion of each of said levers, a movable switch actuator extending between one end of the first lever and the free end of the second lever for actuation by movement of one of said levers, and latching means within said casing cooperablewith said switch actuator and one end of the first lever to prevent movement of said switch by the expansion of one of said thermal motors.

9. A method of controlling the defrosting of acold diffuser on whicha progressive layer of frostis deposited from abody of circulated air, comprising mechanically measuring the direct surface temperature of a portion of the diffuser, mechanically measuring the temperature of the air after the same has passed in contact with the diffuser there being a normal differential between said measurementswhich increases with the progressive deposition of the frost layer, mechanically combining the two measurements to,-f orm-a single measurement of the increase of the differential between the first named measurements, utilizing said last named measurement to mechanically terminate normal operation of the cold diffuser and introduce'a heating fluid to pass in heat exchange relationship with the cold diffuser when said measurement exceeds a predetermined limit, and thereafter utilizing said last named measurement to mechanically terminate flow of heating fiuid and initiate normal ;operat ion 'of the diffuser when the differential is less than the predetermined limit.

10. In a refrigerant plant embodying a cold diffuser formed of a plurality of closely spaced tube sections through which a refrigerant medium is circulated, a fan positioned on one side of the diffuser for drawing air through the spaces between said tube sections, defrosting means operably associated with said diifuser, control means for controlling said defrosting means including a temperature responsive element positioned between the diffuser and the fan and responsive to the temperature of air passing between the tube sections, said diffuser being adapted to receive a, progressive layer of frost on its outer surface to the extent of impeding the passage of air between the tube sections, in combination with said diffuser of a tube extending transversely between the tube sections having an inner end terminating adjacent said temperature sensitive element and forming a bypass for air between the tube sections to direct impeded air over the temperature responsive element when the frost layer eifectively blocks passage between the tube sections.

11. In an air conditioning unit embodying a refrigerant condenser having an inlet and an outlet, a liquid receiver connected to the outlet of the condenser, an evaporator coil having an inlet and an outlet at its opposite ends, a first conduit connecting the receiver with the inlet end of the evaporator, a valve in said conduit for controllin the flow of liquid refrigerant from the receiver to the evaporator, a compressor connected between the outlet end of the evaporator and the inlet of the condenser, said evaporator being adapted to receive a progressive layer of frost on its outer surface, in combination with said unit of means for defrosting said evaporator consisting of a second conduit having an inlet extending from the junction of the compressor with the condenser and an outlet connected with the evaporator at a situs spaced outwardly a substantial distance from the inlet end of the evaporator to admit gaseous refrigerant into the evaporator between its opposite ends and divide the contents of the evaporator into two bodies, and a valve in said conduit betwen its opposite ends, said compressor being in continuous operation when said last named valve is open to permit the flow of compressed superheated gases into the evaporator.

12. In a refrigeration plant embodying a cold difiuser formed of a plurality of relatively closely agee'em ea spaoedtube sections: through which a cooling medium' is circulated; a: fan on oneside of said difiuser -for drawing air-through the spacesbetweensaid tube sections; defrosting-means open ably associated with said diffuser, control means for controliing said defrosting means comprising a temperature responsive member positioned between the difiuser and the fan' and responsive to the temperature of airpassing between the tube-sections, said diffuser being adapted to 'receive a; progressive layer of frost on its-outer 'surface-to the extent ofimpeding the passage of air between the tubesections, in combination with said difluser oia normally open tubehaving one-end terminating adjacent said'temperature responsive member-and forming a by-pass for air-betweenthe tube sections to direct impeded 'ain'into contact with the temperature responsive member whenthe layer-effectively blocks passage between the tube sections.

' FREDERICK M; JONES.

References: ()itedinthe file 0i? this? patent:

UNITED STATES PATENTS Number Name 1 Date Church-et'al. Dec. 4, 1894 Shipley June.9,z1931 Swezy Jan. 17,1933 Keighley .Nov. 26, 1935 Ruppricht Aug. 4; 1936 Phillip ..Apr. 19; .1938 Shively Apr; 26,; 1938 Hansen June 16,1942 Sunday, .Sept. 4,,1945 Newton Dec. 30,1947 Jones July 12,1949 Newton Sept. 5, 1950 Clark- Mar. 27, 1951

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