US2729950A

US2729950A - Hot gas defrosting system

Info

Publication number: US2729950A
Application number: US343108A
Authority: US
Inventors: Toothman Earl
Original assignee: EDWARD A DANFORTH
Current assignee: EDWARD A DANFORTH
Priority date: 1953-03-18
Filing date: 1953-03-18
Publication date: 1956-01-10
Anticipated expiration: 1973-01-10

Description

Jan. 10, 1956 E, TOOTHMAN 2,729,950

HOT GAS DEFROSTING SYSTEM Filed March 18, 1953 5 Sheets-Sheet l 1N VEN TOR. [4m 75cm/M4N BVM/M wrap/vir Jan. 10, 1956 E.'roo1-HMAN 2,729,950

HOT GAS DEFROSTING SYSTEM Filed March 18, 1953 3 Sheets-Sheet 2 Jan- 10, 1956 E. TooTHMAN HOT @As DEFROSTING SYSTEM 5 Sheets-Sheet 5 Filed March 18, 1955 INVENTOR. f4.0; Iyar/M4N BY L) from/if United States Patent O 2,729,950 HOT GAS DEFROSTING SYSTEM Earl Toothman, San Francisco, Calif., assignor of one-half to Edward A. Danforth, Palo Alto, Calif.

Application March 18, 1953, Serial No. 343,108 13 Claims. (Cl. 62-3) This invention relates to a hot `gas defrosting system.

This application is a continuation-impart of my copending application Serial No. 224,319, filed May 3, 1951, now Patent No. 2,693,683, granted November 9, 1954, entitled Defrostng Machine and of my copending application Serial No. 277,555, filed March 20, 1952, now Patent No. 2,693,678, granted November 9, 1954, entitled Automatic Defrosting System.

In a refrigeration system it is desirable to provide automatic defrosting means for periodically and automatically heating the evaporator coils of the system to defrost the same.

Various automatic defrosting systems have been proposed heretofore, some of which are in use. For example, electric heating means have been proposed heretofore wherein an electric heating element is inserted in or adjacent to the evaporator coils. A circuit is provided which is operated by a timer to energize the heating element at regular intervals and for a predetermined period of time. A disadvantage of electric defrostingV is that the heating element employed is rapidly corroded. Also there is` no satisfactory means of limiting pressure in an electric defrosting system; i. e., the heating element may overheat the evaporator coils and create too high a pressure.

Hot gas defrosting has been proposed heretofore and is, in fact, used extensively. Hot gas defrosting makes use of the heat contained in compressed gas from the compressor of the refrigeration system to heat and defrost the coils. Periodically `the condenser of the refrigeration system is by-passed and hot compressed gas from the compressor is sent to the evaporator coils to accomplish defrosting. The spent gas is then returned to the suction line of the compressor. Hot gas defrosting has the advantages that corrodible heating elements are avoided and that the compressor provides an automatic pressure control.

Difficulties are encountered, however, in hot gas defrosting. Thus during the refrigeration cycle and/or during the initial part of the defrosting cycle, gaseous refrigerant is condensed in the evaporator coils and tends to collect and lie in these coils. During the defrosting cycle hot gas from the compressor pushes this liquid refrigerant from the coils. lf it is returned to the suction line of -the compressor along with gaseous refrigerant, slugging will occur. Slugging imposes a severe strain on the return lines and compressor, and it may rip lines off a wall and/or blow the head off the compressor. Also, if only liquid refrigerant is returned to the compressor, no hot gas will be produced by the compressor.

To avoid such difficulties, it has been proposed to trap liquid refrigerant pushed out of the evaporator coils by the hot gas during the defrosting cycle, and to evaporate the trapped liquid refrigerant by means of heat which is stored in a body of liquid during the refrigeration cycle. This system is disadvantageous because the heat required to accomplish re-evaporation of liquid refrigerant, especially during the initial part of the defrosting cycle when a great quantity of such liquid is pushed out of the evaporator coils, may be in excess of the heat that can, in practice, be supplied by a body of preheated liquid. This is a particularly great diiculty in cold weather. Also, this system is diicult to balance for ICC summer and winter operation, and the liquid storage means or reservoir and the means for heating the liquid during the refrigeration cycle are relatively expensive.

In another hot gas defrosting system, heat is transferred directly from the hot gas to the cold refrigerant during the defrosting cycle, thereby avoiding the necessity of preheating a body of liquid during the refrigeration cycle to store up heat for use in re-evaporating liquid refrigerant during the defrosting cycle. In this system, however, the heat transfer means and the control means for controlling, adjusting and operating the hot gas defrosting system are unsatisfactory.

With both such hot gas defrosting systems, i. e., that system in which a body of liquid is preheated during the refrigeration cycle, and that system in which direct heat transfer between hot gas and cold refrigerant is ac complished during the defrosting cycle, still another difticulty has been encountered, as follows: The lubricant employed to lubricate the compressor of a refrigeration system inevitably and necessarily reaches the evaporator coils. Such lubricant is freely miscible with liquid re frigerants commonly used in refrigeration systems, e. g., Freon, which is the trademark of Kinetic Chemicals Co., a subsidiary of E. I. du Pont de Nemours Co., Wilmington, Delaware. Various grades of Freon are used, one of which, dichloro diuoromethane, is illustrative. During the defrosting cycle, when liquid refrigerant is pushed out of the evaporatorcoils the accumulated compressor lubricant is pushed out with the refrigerant. Heretofore no satisfactory means of returning this liquid lubricant to the compressor has been provided. Thus neither of the hot gas defrosting systems mentioned above provides a satisfactory means of returning the compressor lubricant to the compressor.

It is an object of the present invention to provide improved automatic defrosting means.

It is another object of the invention to provide irnproved automatic hot gas defrosting means.

Yet another object of the invention is to provide a hot gas defrosting system of the type in which hot gas is used for defrosting the coils and to re-evaporate condensed refrigerant, and wherein difliculties such as those mentioned above and previously encountered in hot gas de frosting systems are obviated.

Yet another object of the invention is to provide improved means for heat transfer in a hot gas defrosting ssytem, to more effectively reheat the spent refrigerant and re-evaporate condensed refrigerant.

A further object of the invention is to provide an improved control means for a hot gas defrosting system of the character described, particularly of the character wherein the hot gas is employed to heat and re-evaporate condensed refrigerant.

A further object of the invention is to provide an improved means of returning compressor lubricant to the compressor.

These and other objects of the invention will be apparent from the ensuing description and the appended claims.

One form of the invention is illustrated by way of example in the accompanying drawings wherein,

Figure 1 is a diagrammatic view of a complete refrgeration system incorporating the hot gas defrosting system of the present invention.

Figure 2 is a View in side elevation of a defrosting unit constructed in accordance with the present invention.

Figure 3 is a top plan view of the same..

Figure 4 is a vertical, longitudinal section taken along the line L-4 of Figure 3, showing the interior construction of the re-evaporator.

Figure 5 is a horizontal, transverse section taken along the line 5-5 of Figure 4.

Figures 6 and 7 are fragmentary views in end elevation as seen alongthe lines '6-'6 and '7-7, respectively, of Figure 2.

Referring now to Figure l of the drawingsa refrigeration .system is there shown including a compressor 10 having a crankc'ase 11.

VThe compressor 10 is supplied with gaseous .refrigerant through a suction line 12 and it delivers hot, compressed, .gaseous refrigerant through a .hot gas .line 13. The hot gas vline 13 divides at a T 14 .into a first branch 15, and into asecond branch 16. The second branchf16 is provided with a hand valve 17 and with a normallyclosed solenoid valve 18 which is operated by asolenoid 19 energized through'leads 20.

The branch is connected to a condenserZS which in turn is connected through a line 26 with .a receiver 27. The receiver`27 is connected by means of a line 28 containing Ian expansion valve.29 with .a.header.30, which distributes refrigerant to evaporatorcoils 31. yIt will be understood, of course, that more thanone set of'evaporator coils may be employed. A fan 32.is illustrated which is drivenv by a motor .'33 energized .through leads 34. The purpose of theffan v32 is tocirculate air overthe evaporator .coils .and to effect vrefrigeration vof a large space such'as a walk-.in cooler or other large refrigerated space. 'The defrosting' system of the present invention is,

however, also adapted .for use with smaller refrigeration systems Vsuch as household refrigerators.

The evaporator coils 31 are connected througha header I-35 ,to'a return'line 36 which is connected to la receiving vessel-40. `The .receivingvessel 40 forms a part of the defrostingsystem of thepresent invention, as described moreifully hereinafter. Refrigerant vapor passes from the receiving vesse`l^40 through a vapor line .41 which divides v at a T 42 into a branch 43 and the `above-mentioned suction'line A 12. A normally open solenoid valve 44 is located in the suction line 12 and is operated .by a solenoid 45 which is energized through leads 46. As will be seen, "the receiving vessel 40 is also ,provided with a gauge 47.

During'the refrigeration cycle, vand by virtue of an electrical timing system (not shown), the solenoid 19 is defenergized-(hence the valve 18 is closed) and the solenoid ISjis-energized (hence the valve 445 is open). Any suitable electrical timing system may be employed for thisjpurpose, several of which are well known. A circuit such'as that illustrated in my 'copending application Serial No. 277,555, now Patent No. 2,693,678, granted November 9, -1954, may be employed.

Itwill'be apparent that, during the refrigeration cycle, hot compressed gas delivered by the compressor 10 through the hot gas line 13 will'pass through the branch 15 -to'the condenser.25 wherein'it will Vbe condensed, as by means of-air cooling, water cooling orother suitable means. Condensed refrigerant will then pass throughthe..line..26 to"thefreceiver27*which acts as a storage vessel forliquid refrigerant. Liquid refrigerant `then passes through the y line 28 and is rexpanded by means of the expansionvalve 29. 'In vaccordance with well known, conventional .technique theexpension valve 29..may becontrolled and regulatedby'a feeler bulb ,(notshown) to maintain proper expansion and ow of refrigerant to the evaporatorcoils. The expanded refrigerant, now .largely or entirely in the form of cold vapor, ,passes through the header 30 into the evaporator coils 31. Spent refrigerant passes through the 'otherfheader 35 Vinto .the return. line 36, Vthence into the'receiving vessel 40. Refrigerant vapor then returns through the vapor line 41 to the suction line 12, thence to thecompressor where it is recompressed. Y

The defrosting.. system-of -thepresent .invention includes the above-mentioned .receiving vessel'40 and it `als'o'in- CIudesare-evapOratGr 5.0 -togethervvith various connecting lines and control means described in-detail hereinafter. 'Ihefdefrostingnsystem isoutlined inFi-gure lbythe'dotdash lines. The re-evaporator is armultiple comparty predetermined duration.

ment vessel includingan outer vessel 51, an intermediate vessel 52 and an inner vessel 53. A gas tight lid or cover S4 is provided and the entire re-evaporator, including the several vessels, are of gas tightV construction except for the intercommunicatinglines hereinafter described. As will be seen the arrangement 'of the

vessels

51, 52 and 53 is such as to provide an outer compartment or chamber 55 between the Aouter vessel l51 andthe intermediate vessel 52, an intermediate compartment or chamber 56 between the intermediatevesselSZ and the'inner vessel 53 and an inner compartment -or chamberl 57 'within the inner vessel 53. As will also be seen baflles 58 are provided within the 'innerchamber 57 which extend downwardly from-the top of the intermediate vessel 52 toa point close to but spaced somewhat above the bottom of such vessel.

The remaining elements of thedefrostingsystem of the present invention will be best understood 'in connection with the operation of thedefrosting system, which will now be described. It is assumed that the system has previously been regulated.

The defrosting vcycle is initiated by the timing system to occur at predetermined intervals, each cycle having a In a typical, large commercial installation the Vdefrosting cycle may have a duration-'of thirty minutes vand may be initiated once every twelve ,Y

hours. When the defrosting cycle is initiated, the valve Vltlopens yand vthe valve 44closes. Hot gas from the compressor 1l)v therefore vby-passes the condenser .25 and passes, instead, through the branchlirne 16. The compressed hot gas dividesat a T 59. A portion of the` hot gas passes through. a branch 60 and another portion through a branch 61. The portion of hot gas passing through'the branch 60 enters drip pan coils 62, then passes through a check valve 63 to the line 28 at a point'between the expansion valve 29and the header 30. `It will be'apparent that Vthe `hot gasis .not expanded and that it remains in a hot, compressed state until it reaches the evaporatorcoils. The drip pan coils 62 are an optional feature insofar as the defrostingy system of the present invention is concerned. If desired, .the hot gas may be supplied directly `to the evaporator coils 31 Without rst passing through the drip pan coils 62. However, the arrangement shown is preferred.

In the evaporator.v coils 31 the hot gas accomplishes defrosting in the manner explained hereinabove. After passing through the coils, the hot gas passes through the header 35 into the return line 36, thence into the receiving vessel 4t). AAs explained above, during the refrigeration cycle and/or during the Vinitial portion of the defrosting cycle,v gaseous .refrigerant is condensed to liquid in the evaporator coils 31, and during the defrostingpe'riod hot gas pushes thefaccumuiated refrigerant from the coils. This liquid refrigerant is delivered, along with spent refrigerant vapor, to the receiving vessel 49. As also-explained hereinabove, during operation of the refrigeration system .lubricant from the compressor l10 passes into the systemfanda certain portion thereof (collects in the evaporator coils 31. lt is pushed out of the coils by the hot gas during ,the defrosting cycle and is introduced through the return line 36 into the receiving vessel 4i).

i 'It is a purpose of the receiving vessel 40 to separate spent refrigerant yvapor from liquid refrigerant which are shown, respectively, at 40a and 4Gb. lt is also a purpose ofthe receiving Vvessel tlito serve as a reservoir for holding liquidrefrigerant. lt is a purpose of the re-evaporator 5() to re-evaporate liquid refrigerant and it is another purpose of Vthis re-evaporator to convert the compressor lubricant contained in the liquid refrigerant to a form such that it canhe returnedto the compressor without difficulty. These functions are carried out in the manner and by the means whichwill now be described.

Hotgas passing through the branch line 61 and through a hand Yvalve -tcontained in the vline 61 enters the intermediate chamber '56 of the re-evaporator 50. As will .be seen the 'line or pipe 61 extends only a short distance into `arenoso the upper end of the intermediate compartment 46 and is located on one side of the bafes 58. A pipe 65 is provided which is connected at one end to the intermediate chamber 56 and at its other end to the outer chamber 55. As will be seen the pipe 65 extends only a short distance into the upper end of the intermediate chamber 56 and is located on the opposite side of the bafiles 58 with respect to the pipe 61. As will also be seen, the other end of the pipe 65 communicates with the outer chamber 55 near the bottom thereof and at the left as viewed in Figure l. Spent refrigerant vapor coming from the receiving vessel through the line 41 passes into the pipe 43 which contains a manually operated control valve 70 and to which is connected a pressure gauge 71. Refrigerant vapor then passes through a pipe 72 into the outer chamber 55 of the heat exchanger 50. Preferably, as indicated, the pipe 72 connects with the outer chamber near the bottom thereof and adjacent the pipe 65. Liquid refrigerant, together with compressor lubricant contained therein, are removed from the receiving vessel 49 through a pipe 73. The pipe 73 extends into the inner chamber 57 of the re-evaporator 50, to a point near the bottom of the chamber. At its lower end, within the chamber 57, the pipe 73 is formed with small holes 74 to provide, in effect, a restricted orifice or nozzle for spraying liquid refrigerant. A pipe 75 is provided one end of which extends into the upper end of the inner chamber 57. At its other end the pipe 75 is connected to the pipe 72. As will be seen, an expansion valve 76 is located in the pipe 73 and is connected by a coil 77 to a feeler bulb 78 which is attached to the pipe 75.

During the defrosting cycle, hot gas diverted through branch line 61 provides the heat necessary for reheating spent gaseous refrigerant and for re-evaporation of liquid refrigerant. The proportion of hot gas diverted for this purpose is controlled by the valve 64. The major portion of the heat given up by the hot gas for this purpose, is given up in the intermediate chamber 56from which heat hows to the inner chamber 57 and to the outer chamber 55 by conduction through the Walls separating these chambers. j

Refrigerant vapor from the receiving vessel 40 passes through pipes 41 and `72 into the outer chamber 55 0f heat exchanger `50` where it is heated indirectly by hot gas in the intermediate chamber 56 (i. e., by conduction through the walls of compartment 53), and where it is also heated by direct mixture with hot gas entering through pipe 65. The juxtaposition of the outlets of pipes 65 and 72 promotes such mixing of hot gas and spent refrigerant.

Meanwhile liquid refrigerant from receiving vessel 40 enters the inner chamber 57 through pipe 73 and nozzle 74. It is sprayed into the inner chamber by reason 0f the restricted character of the holes 74W and it is expanded to the vapor state by reason of the expansion valve 76.

It is also heated by heat absorbed from the hot gas in f intermediate chamber 56. The combined effects of expansion, spraying and heating the liquid refrigerant into inner chamber 57 are such that the liquid refrigerant is rapidly and completely vaporized and the lubricant is dispersed in the vapor in the form of small particles, i. e., as a mist. In this form the lubricant can be safely returned to `the compressor without slugging and without the necessity of trapping it and returning it to the crankcase.

The resulting mist, or suspension of lubricant in refrigerant vapor, is further heated by passage through

pipes

75 and 72 into the` outer chamber 55, where it is heated directly by mixture with hot gas and indirectly by conduction through the walls of vessel 52. j

Finally, heated, re-evaporated refrigerant, and lubricant dispersed therein, are returned to the compressor through pipe 79 and suction line 12.

At the conclusion of the defrosting cycle, the valve 18 is closed and the valve 44 is opened, thus renewing the refrigeration cycle.

The operation thus described `assumes that the system has been properly regulated. At the outset, after installation of the defrosting system of my invention, it is, of course, necessary to regulate the system to obtain optimum performance. It is an important advantage of my invention that such regulation can be easily accomplished and that, when it has been accomplished, the system will continue to operate efficiently for a long period of time.

The functions of the solenoid valves 18 and 44 have been explained; they automatically initiate and terminate the defrosting cycle. The hand valve 17 is a service valve which can be operated manually to allow servicing the solenoid valve 18 without shutting down the system.

In starting the refrigeration system of Figure l, the defrost cycle is initiated manually and valves 64 and 70 are closed. Then valve 70 is opened until gauge 71 reads about tive pounds per square inch gauge pressure. (Pressures hereinafter will be understood to be gauge pressures rather than absolute pressures.) The valve 64 is opened until no further frosting of pipe is observed. The setting of valve 70 will generally be such that gauge 71 registers about fifteen pounds during defrosting. This pressure is generally adequate for efficient operation of the compressor, and for eticient defrosting. However, if the suction line 12 is long, the valve 70 is preferably opened to produce a pressure reading of twenty to twentytive pounds on gauge 71.

The expansion valve 76 and its coil 77 and feeler bulb 78 may be of known construction and operation. As is well known, a volatile fluid, such as a small quantity of the refrigerant used in the refrigeration system, is used in the coil and it assumes the temperature of the feeler bulb, hence the corresponding pressure, and exerts a pressure on a diaphragm in the valve. In the system ot' the present invention, the valve 76 is selected and adjusted to open when a predetermined temperature differential exists between the fluid in the piper 75 and the uid in the pipe 73 ahead of the valve 76. Preferably, the predetermined temperature differential is about 8 to 10 F. By this means, liquid refrigerant is expanded and sprayed into the inner chamber 57, only to the extent that it can be evaporated by heat from hot gas in the chamber 56.

The recirculation of refrigerant vapor from chamber 57 through

pipes

75 and 72, and of refrigerant vapor from receiving vessel 40 through pipes 41, 43 and 72, to the outer chamber 55, provides an extra factor of safety; any liquid refrigerant remaining in the gas is vaporized, and the gas leaving re-evaporator 50 through pipe 76 is dry except for suspended lubricant.

The adjustments noted above may, of course, be varied in the light of existing circumstances. The valve 64 controls the amount of heat diverted from the evaporator coils to the re-evaporator. The Valve 70 controls the back pressure on the compressor, i. e., the pressure at the inlet of the compressor. The expansion valve 76 controls the rate of expansion and spraying of liquid refrigerant into the evaporator. By a modicnm of trial and error, optimum settings of these valves can be determined.

Another feature that may be noted is that external piping may be diminished in the case of the re-evaporator 5t). Thus, a direct opening may be provided between the chambers 56 and 55, instead of providing the external pipe 65. In such case, provision should be made for intimate mixing of warm gas from the chamber 56 with cold, and possibly wet gas from the receiving vessel 40 and inner chamber 57. j

As stated above the defrosting system of the present invention is that portion of the refrigeration system shown in Figure l which is enclosed or boxed in by the dot-dash lines. It is there shown in diagrammatic form, and the breaks in the

lines

12, 16, 28, 60 and 36 indicate that these lines may be of greater or lesser length, depending trapasso `improvement which comprises a hot gas defrosting system comprising means for by-passing said condenser during a defrosting cycle to pass hot gas from the compressor through the evaporator to defrost the same, a receiving vessel for receiving and holding liquid refrigerant expelled from the evaporator, means connecting said receiving vessel with said evaporator to conduct liquid refrigerant expelled from the evaporator to the receiving vessel, a re-evaporator, means for diverting a portion of the hot gas from said compressor to said re-evaporator to heat and evaporate liquid refrigerant, means for conducting liquid refrigerant from said receiving vessel to said evaporator, and control means effective to regulate the rate of delivery of hot gas and of liquid refrigerant to said re-evaporator to completely evaporate the liquid refrigerant therein, and means connecting` said reevaporator with said compressor to supply refrigerant vapor` to the compressor.

2. In a refrigeration system comprising a compressor for compressing a gaseous refrigerant to produce hot compressed gas, a condenser for condensing the hot gas to produce liquid refrigerant, an evaporator and means for expanding liquid refrigerant into said evaporator, the improvement which comprises a hot gas defrosting system comprising means for by-passing said condenser during` a defrosting cycle to pass hot gas from the compressor through the evaporator to defrost the same, a receiving `vessel for receiving andholding `liquid refrigerant expelled from the evaporator, means connecting said receiving vessel from said evaporator to conduct liquid refrigerant expelled from the evaporator to the receiving vessel, a re-evaporator, means for diverting a portion of the hot gas from said compressor to said re-evaporator to heat and evaporate liquid refrigerant, means for conducting liquid refrigerant from said receiving vessel to said re-evaporator, means for also conducting cold refrigerant vapor from said evaporator to said re-evaporator, and control means effective to regulate the rate of delivery of hot gas, of cold refrigerant vapor and of liquid refrigerant to said re-evaporator to completely evaporate liquid refrigerant, to warm the cold refrigerant .vapor andro vaporize liquid refrigerant suspended in `the cold vapor,` and means connecting said re-evaporator with said compressor to supply refrigerant vapor to the compressor.

3. A hot gas defrosting system compirsing a receiving vessel for receiving cold refrigerant vapor and liquid refrigerant from the evaporator of a refrigeration system during a defrosting cycle, a re-evaporator for heating said cold refrigerant vapor and for evaporating said liquid refrigerant, means for by-passing the condenser of said refrigeration system during sucl'L defrosting cycle and for passing hot gas from the compressor to the evaporator to defrost the same, hot gas supply means for simultaneously diverting a portion of such hot gas to said reevaporator to supply the heat necessary for such heating and re-evaporating, means connecting said receiving vessel with said 1re-evaporator to supply refrigerant vapor thereto, means also connecting said receiving vessel with said re-evaporator to supply liquid refrigerant thereto, control means for each said connecting means to control the rate of supply of refrigerant vapor and of liquid re frigerant to said re-evaporator, and control means for said hot gas supply means to control the rate of supply of hot gas to said re-evaporator;` said various control means being adjustable to maintain the supply of refrigerant to the suction inlet of the compressor in a completely dry condition except for suspended lubricant and at a substantially constant pressure adequate for eiiicient operation of the compressor and for rapid. eflicient defrostin Y,

4. A hot gas defrosting system comprising a receiving vessel for receiving cold refrigerant vapor and liquid refrigerant from the evaporator of a refrigeration system during a defrosting cycle, a re-evaporator for heating said Cold refrigerant vapor and for evaporating said liquid refrigerant, means for by-passing the `ciondenser of 4saidI refrigeration system during such defrosting' cycle and for passing hot gas from the compressor to the evaporator to defrost the same, hot gas supply means for simultaneously diverting a portion of such hot gas to said re-evaporator to supply the heat necessary for such heating and reevaporating, vapor supply means connecting said receiving vessel with said re-evaporator to supply refrigerant vapor thereto, liquid supply means also connecting said receiving vessel with said re-evaporator to supply liquid refrigerant thereto, an adjustable control valve for said vapor supply means to control the rate of supply of refrigerant vapor to said re-evaporator, an expansion valve for said liquid supply means for regulating the supply of liquid refrigerant to and for expanding it into said re-evaporator, and an adjustable control valve for said hot gas supply means to control the rate of supply of hot gas to said reevaporator; said various control means being operable to maintain the supply of refrigerant to the suction inlet of the compressor in a completely dry condition except for suspended lubricant and at a substantially constant pressure adequate for eicient operation of the compressor and for rapid, efficient defrosting.

5. In a hot gas defrosting system comprising means for automatically bypassing the condenser of a refrigeration system to supply hot gas to the evaporator of such system and thereby defrost the same, and means for returning refrigerant from the evaporator to the compressor, the improvement which comprises a multiple compartment vessel for heating cold refrigerant vapor and for reevaporating liquid refrigerant expelled from said evaporator, said vessel comprising a first hot: gas chamber, a second liquid refrigerant chamber and a third refrigerant vapor chamber, said liquid refrigerant and refrigerant vapor chambers being in heat exchange relation with said hot gas chamber to absorb heat therefrom, means for diverting a portion of the hot gas from the compressor to said hot gas chamber during the defrosting cycle and means for separating the bulk of liquid refrigerant expelled from the evaporator from cold refrigerant vapor and for supplying the separated vapor to said vapor chamber and for spraying the separated liquid into said liquid refrigerant chamber.

6. In a hot gas defrosting system comprising means for automatically by-passing the condenser of a refrigeration system to supply hot gas to the evaporator of such system and thereby defrost the same and means for returning refrigerant from the evaporator to the compressor, the im provement which comprises a multiple compartment vessel for heating cold refrigerant vapor and for re-evaporating liquid refrigerant expelled from said evaporator, said Vessel comprising a rst hot gas chamber, a second liquid refrigerant chamber and a third refrigerant vapor chamber, said liquid refrigerant and refrigerant vapor chambers being in heat exchange relation With said hot gas chamber to absorb heat therefrom, means for diverting a portion of the hot gas from the compressor to said hot gas chamber, means for separating the bulk of liquid refrigerant expelled from the evaporator from cold refrigerant vapor, means for supplying the separated vapor to said vapor chamber, and means for expanding the separated liquid and for spraying it into said liquid refrigerant chamber.

7. In a hot gas defrosting system comprising means for automatically by-passing the condenser of a refrigeration system to supply hot gas to the evaporator of such system and thereby defrost the same and means for returning refrigerant from the vaporator to the compressor, the improvement which comprises a multiple compartment vessel for heating cold refrigerant vapor and for re-evaporating liquid refrigerant expelled from said evaporator, said vessel comprising a first hot gas chamber, a second liquid refrigerant chamber and a third refrigerant vapor chamber, said liquid refrigerant and refrigerant vapor chambers being in heat exchange relation with said gas chamber te 1 1 absorb heattherefrom,l means for diverting a portion'of the l'o'tg'as' from 'the compressor-'t said'hot gas chamber, means 'for onducting VVp'artiallyspent gas from said hot gas 4hainber to said liquid refrigerant chamber, means for separating-the bulk of liquid refrigerant expelled from the evaporator from cold refrigerantyapor, means for supplying thelseparated vapor to said vapor chamber, means forexpanding the separated liquid and for spraying it into said lliquidrefri'gerant chamber, and means for conducting 'the reheated vapor from `said vapor chamber and the 'r evaporated refrigerant from said liquid refrigerant chamber to the inlet of said compressor.

-v8. Ahot -g`as defrosting system comprising a vaporizing chamber for expansion and vaporization of liquid refrigerant expelled `from theevaporator of a refrigeration systern, reheating chamber for reheating cold refrigerant `vapor expelled from such evaporator and for vaporizing any Iresidue 'of liquid refrigerant contained in such vapor, heating means lsupplied withhot gas from the compressor 'fv` such refrigeration system for heating said vaporizing y chamber, means communicating said heating means with said reheatin'g chamber to conduct partly spent hot gas `from said heating means to said'reheating chamber to thereby heat'said chamber, means for conducting vaporized'refrigerant 'and reheated refrigerant vapor to said compressor, means fory conducting cold refrigerant Vapor Y expelled from said evaporator into said reheating chamberandmeans for expanding liquid refrigerant expelled from said evaporator into saidliquid refrigerant chamber.

."9. A hot gas defrosting system comprising a vaporizing 9 ,expelled from said evaporator into said reheating chamber and means for expanding and spraying liquid refrigerant expelled' from said evaporator into said liquid refrigerant chamber.

l0. A het gas defrosting system comprising a reevaporator and' reheater for re-evaporating liquid refrigerant and rehearing cold refrigerant expelled from the evaporator of a refrigeration system, said re-evaporator and reheater comprising aiirst hot gas chamber, and a second liquid refrigerant chamber and a third refrigerant vapor chamber in heat exchange relation with said rst chamber; a' receiving vessel communicating with said levaporator receive liquid refrigerant and refrigerant vapor expelled therefrom; hot gas supplyrneans'for diverting a portion of the hotgas from the compressor ofsaid refrigeration system to said first chamber during the defrosting cycle, said hot gas supply means comprising an adjustable valve for adjusting and controlling the rate of supply of hot gas to said rst chamber; a conduit communicating said first chamber with said third chamber to'supply partly spenthotf gas thereto; means communicating said receivingvessel with said second chamber, such means including'an expansion valve and a nozzle for expanding liquid refrigerant and spraying it into said second chamber; vapor -supply means communicating said receiving vessel and said second chamberwith said third chamber to supply cold vapor from both such sources to saidthird chamber; feeler means for sensing the temperature of vapor expelled from said second chamber, such feeler means controlling `said expansion valve to regulate the ratefoffexpansion ffliquid refrigerant into` said second chamber; andfmeans comlrmnicating said third chamber Vchamber to 'said outer chamber; means for'expan'di 12 with the Vinlet of said compressor to supply ther with a mixture of refefvaporated liquid fef'rige'rantand reheated refrigerant vapor expelled from 'theqevapora r togethervvith spent hot gas diverted to Vsaidfirst cham er.

-11. A rie-evaporator and reheater for a hot gas lefrotslting system comprising an outer vessel, an intermediate vessel and an inner vessel in nested arrangement to prof vide a 'relatively narrow outer Vannular chamber betiveen the outer and intermediate vessels, an intermediate annular chamber between the intermediate and innerV yves: sels and an inner chamber with said inner vessel; means for introducing hot gas from the compressor fof `aireI frigeration system into said intermediate chamber; means for circulating'y partly spent hot gas from said intermediate spraying liquid refrigerant into said inner chamber; means for conducting cold refrigerant vapor expelled Ifrornthe evaporator of such refrigerationsys'tem, together With lreevaporated liquid refrigerant fr'ornfsaid 'innerfclianiben to said outer chamber; and means for conducting the resulting mixture of reh'eated refrigerant vaporg/ l orated liquid refrigerant and partly spent 'hot-gas tothe inlet of said compressor. p'

l2. A re-evaporator and reheater for a hot gas defrost# ing system comprising an'outer vessel, an intermediate vessel and an inner vessel inrnested arrangement to; f vide a relatively narrow outer annular chamber between the outer and intermediate vessels,V an intermediate an'nfV Y lar chamber between the intermediate and inner vessels and an inner chamber Within said inner vessel;` meansy fr introducing hot' gas from the compressor of a refrigeration system intos'aid intermediate chamber; means fo'r eirciilating partly spent hot gas from said` intermediatefcharn; ber to said outer chamber; means for expanding and spraying liquid refrigerant into said inner chamber; me for conducting cold refrigerant vapor expelled'frf f t evaporator of such refrigerationsystem, togetherw href evaporated liquid refrigerant from said :inner chamber, to said outer chamber; and means for conducting the fe# sulting mixture of rehea'ted refrigerant vapor,V rel I orated liquid refrigerant and-partly spent hotg'a's' tothe inlet of said compressor; said-reevaporator aridrehe'a'ter also comprising control valves to adjust and -4eoritro1 e rate of supply of hot gas to said intermediate chamber, of refrigerant vapor to said outer chamber and of expanded liquid refrigerant to said inner chamber. Y t y g y 13. A refrigeration system comprising fa compress r,a condenser and an evaporator and means interconne fng the same to provide a closed circuit whereinrefrrger `t" vapor is compressed in the compressor, coruprefsfs'edV frigerant'gas iscondensed in the condenser,fcondertv 'd refrigerant is evaporated in the evaporator and refrigerant vapor is returned from the evaporator to thesuctionf the compressor; 'said system also' comprising hot gas defros'tir'fg rneansrfor defrostingthe evaporator including afhot s defrosting )circuit for supplying hot refrigerantjgas'from the compressor to the evaporator to heat and defr ft' e same, means for returningl spent gas from the evaporatdr to the suction ofthe compressor and a'heat exchanger heated by vhot gas from the compressor, saidhetfex-` changeribeing interposedbetweenthe evaporator andthe suction of the Vcompressor for heating the spent gas and forevaporating liquid' refrigerant removed from'tlreev f orator With'said spent gas; said defrosting means' al'solrncluding'a trap interposed between said e \`fa1'iojratc r -and heat exchanger for entrapping liquid refrigerant'and cornprwsf` sor lubricant, and means' for conducting such liqni" fr said trap and expanding and spraying it into vsaidfheat exchanger.

La Porte infiel@ ,12,3 La Porte July 14, 1953