US2887857A

US2887857A - Jet pumps in refrigeration system

Info

Publication number: US2887857A
Application number: US518633A
Authority: US
Inventors: Hugh J Scullen
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-06-28
Filing date: 1955-06-28
Publication date: 1959-05-26
Anticipated expiration: 1976-05-26

Description

H. J. SCULLEN 2,887,857

JET PUMPS IN REFRIGERATION SYSTEM 3 Sheets-Sheet 1 May 26, 1959 Filed June 28, 1955 INVENTOR. //z .f' jazz/Z677 BY v 7'07P/VLVS May 26, 1959 H. J. SCULLEN JET PUMPS IN. REFRIGERATION SYSTEM 3 Sheets-Sheet 2 Filed June 28; 1955 May 26, 1959 H. J. SCULLEN JET PUMPS IN REFRIGERATIONSYSTEM 3 Sheets-Sheet 3 Filed June 28, 1955 R m m m IVE/S The present invention relates generally to refrigera tionsystems operable at low temperatures. More specifically, the invention relates to a refrigeration system employing refrigerant-powered booster or sion stages.

In refrigeration systemsvadapted to operate at low tempre-comp'resperatures, that is, at temperatures'below about-.20 or 40 F., it has been necessary .to employ compressors capable of drawing'a vacuum on the evaporator coils. In the usual case, in the small capacitysystems this has meant the use of one or more stages of positive displacement type compressors equipped with efficient metal-tometal sealing means to prevent the entry to the system of air and moisture. With this type of compressor, however, there are practical limits, imposed by the operating characteristics or efliciency of their. valves, tothe vacuum that can be drawn and to the number of serially arranged stages which can be beneficially employed.

It is an object of this invention, therefore, to provide a refrigeration system employing one or more refrigerantpowered booster compression stages to enable mechanical compressors to reach the desired low evaporator pressures and temperatures. Y t 1 Another object is to provide a refrigeration system which incorporates one or more pre-compressionor booster stages powered by high pressure refrigerant to extend the normal operating (temperature) range of. 'a given number of primary compression stages.

. Still another object is to provide a refrigeration sys tern in which one or more expensive primary refrigerati on stages are replaced by inexpensive, refrigerantpowered jet pumps.

Still other objects I and advantages of the present invention will be apparent, or will become'apparent, in the more detailed description of the invention to follow and in the accompanying drawings, in which: 1 w .Figure l is a more or less: diagrammatic flow sheet illustrating an operative elementary refrigeration system employing a single primarystage of compression and'a single refrigerant-powered precompression stage;

Fig. 2 is a view similar to that of Fig. 1 showing a more complete refrigeration system including a single primary Patented- May 26, 1959 les sfeflicient, when operated at other than their normal design temperature; e

m Fig. 4 is aflow diagram of a complete. refrigeration system of. a type usually employing two primary compression stages, the figure in this case illustrating one such primary. stage replaced by two refrigerant-powered j'et booster'pumps operating in series flow relation, with one of the booster pumps being powered in part, at least, by flash gas and flash gas condenser vapors and, in part, by high pressure refrigerant from the preceding booster; Fig.5 is.;alcomplete flow diagram and wiring diagram of a refrigeration system adapted to operate at extremely low temperatures of 125 F. to 200 F. or lower, Fig. 5 in, this case showing three primary stages of compression, assisted or boosted by a single refrigerant-powered jet pump booster unit, the latter deriving its power from an auxiliary compressor arranged to deliver its full output to the nozzle inlet of the jet booster unit; and

" Fig. 6 is a schematic representation in section of a typical jet pump of the type employed in the refrigeration systems of Figs. 1 to 5.

,As .is indicated above, the present invention provides a refrigeration system wherein one or more refrigerantpowered booster units are employed to improve the vacuum-producing capacity of one or more primary stages of mechanical compression. The booster units are particularlyeffective in low temperature refrigeration systems wherein fiash gas or refrigerant vapors of intermediate pressure (which normally are recycled anyway) are'ffavailable to power the booster unit. Such a low temperature refrigerating system, employing a flash gas separator (or expansion vessel) and/or a refrigerantcooled flash gas condenser is disclosed in my copending application, Serial No. 26l,3l3, filed December 12., 1951, now US. Patent No.-2,714,80'6, August 9, 1955.

Referring ,now to the accompanying drawings, it will be seen that Fig. 1 shows an elementary refrigeration system which incorporates few controls, only a length of flow-restricting capillary tubing 10 being interposed as a control: in the high pressure refrigerant inlet line 12 between the condenser 14 and the evaporator coil 16. The tubing 10 is wrapped around, and in heat-exchange relation with, the suction vapor line 18. A primary compressor 20 is arranged to draw low pressure refrigerant vapors from the refrigerant suction line 18 and to discharge high pressure, compressed refrigerant to the condenser 14 through line 22. The refrigerant vapors leaving'the evaporator 16 pass through suction line 18 to a jetbooster pump 24 wherein they are pre-compressed to a considerable degree and delivered through line 26 to the jinlet of the primary compressor 20. The jet pump compression stage and a pair of' serially-arranged, re-

frigerant-powered jet pump pre-compression or booster stages, the system also employing a flash gas separator or expansion vessel located between two lengths of flowrestricting capillary tubing with the hash gas collected in the expansionvessel being recycled to-power one of the, booster stages; j v

Fig. 3 is a :view similar to Figs. 1 and 2 showing-a still more complete low temperature refrigeration system, in

this case employing a refrigerant-cooled flash gas con-- v denser or heat-exchanger located between a pair of flowrestricting capillary tubes, a watery cooled primary condenser, a thermostatic expansion valve and othercontro'ls', the systemin this case being. adjustable. as to operating temperature, whereas, thO SGJOf Figs. 1 and 2'are com]- paratively constant temperature systems whichb'ecome 24lis powered by high pressure refrigerant vapor taken from high pressure line 22 through line 28.

The jet pump 24is of the injector or ejector type shown Fig. 6 which is essentiallya small 'high pressure jetjor nozzle 30 in axial alignment with a larger low'p'ressure nozzle, jet or venturi-like passageway 32. Both' nozzles are housed in a casing 34 provided with a small high pressure nozzle inlet 36, a larger suction inlet38 and a nozzle outlet 39. With this type of comp'ressor or'pump asmall quantity of high pressure nozzle gas is fed into the nozzle inlet 36 to aspirate low pressure gas from the evaporator through suction inlet 38. The pressurenozzle gas and the low pressure suction gas are mingled in the passageway 32 so as to exit as a single stream having a pressure higher than that ofthe suction gas but lower than that of the nozzle gas. Sucha device is of simple construction and is not appreciably more expensive than a valve or other similar n lffi a- "result of the operation of the jet pump 24 of Fig.1 is'a'net' increase in the amount of'refri'gerant' handled by the primary compressor 20. In some respects this may be considered a net decrease in overall operating efliciency, although in most cases the primary compressor 20 is capable of handling the increased volume without material increase in power requirements because the refrigerant is supplied to its inlet valves at a higher pressure than would be the case were it drawing'a vacuum directly on the evaporator coil 16. In more complex I ment compressors could be employed. As a result, the

net initial cost of the system is reduced since the total cost of the jet pump booster and a single compressor of simple design is considerably less than the cost of a single reciprocating compressor and its controls. When the primary compressor is a compressor of high volumetric elficiency the jet pump booster unit enables the system to develop much lower evaporator temperatures than without it. In this respect a single primary reciprocating compressor having a single jet booster unit is p capable of approaching the operating range of the much more expensive two stage systems. Thus, irrespective of the type of compressor employed in the primary conipression stages, the use of a single refrigerant-powered jet booster pump powered by high pressure refrigerant provides real initial cost and operating advantages in spite of a sometimes lowered overall efficiency. Where a low temperature refrigeration system is not intended for continuous use, the use of the system of Fig. 1' results in an overall reduction in cost.

Fig. 2 demonstrates a more complete single (primary) stage system incorporating two serially-arranged jet pump booster units 24, 46. A flash gas separator or expansion vessel 40 is interposed between the flow-restricting capillary tubing 10 and a second length of flow-restricting capillary tubing 42. The tubing 42 is connected in series with the vessel 40 by line 43 and the vessel 40 is connected in series with the restrictor tubing 10 by means of line 48 taken off the vessel below the level of the liquid therein. Flash gas evolved by the expansion of refrigerant This tends to lower the pressure in evaporator 16 and increase the flow through restrictor 10. Another result is that jets 24, 46 and compressor 20 deliver an increased supply of liquid refrigerant to vessel 40, sometimes causing the liquid level to rise in line 44 wherein the liquid refrigerant is vaporized at a greatly increased rate. If desired, line 44 could be placed in a position where it could be warmed or heated and in this way increase the energy driving jet 46. This in turn causes jet 46 to further lower the pressure in evaporator 16. Thus, the restrictor 10, vessel 40 and jet 46 combine to provide a control which is more quickly responsive to the load on the evaporator 16.

Fig. 3 illustrates a still more complete single stage refrigeration system which employs a water-cooled condenser 50, a refrigerant-cooled flash gas condenser or heat-exchanger 52, an electrically-operated thermostatic on-ofi valve 54, three flow-restricting capillary tubes 10, 56, 58 and a thermostatically-controlled expansion valve 88. The valves 54, 88 are located outside of the space being cooled so as not to bind, seize or otherwise operate inefiectually.

In this system the primary compressor 20 is protected by a pressure-responsive on-oif control 60 made respom sive to the pressures existent at the outlet of the cornpressor 20 by means of a passageway 62 connecting with compressor outlet line 22. High pressure refrigerant flows from the compressor 20 through an oil separator 51,

' having an oil return line 53, and thence through line 22 to'the condenser 50. The supply of coolant in the latter is controlled by a pressure-sensitive bellows 64 connected to the compressor outlet line 22 by means of a line 65, the bellows 64 operating a water supply valve 66 located in the condenser water inlet line 68. The water leaves in vessel 40 is taken off the top of the vessel through line 44 and thence to the high pressure nozzle inlet of the first jet booster unit 46. The jet booster 46 draws low pressure suction vapors from the evaporator outlet line 18, compresses them and delivers the gas to inlet of the second booster unit 24. The latter further compresses the vapors and delivers them to primary compressor 20. As before, the second booster unit 24 is driven 'by high pressure refrigerant taken from the outlet of compressor 20 through line 28.

As will appear in Fig. 2, the cooled, high pressure refrigerant leaving the condenser 14 passes through re-. strictor 42 at a controlled rate to enter the flash gas separator or collector 40. Residual 'heat in the refrigerant is dissipated by expansion in the vessel 40 and is conducted away in the form of vapor, the latter being taken off the top of the vessel through line 44, :as described above. By the use of such a vessel, colder, more completely liquid refrigerant reaches the evaporator and the condenser through line 70. From the condenser 50 cooled refrigerant flows through a silica gel drying tube 72 and a filter 74 to the electrically-controlled valve 54. The solenoid of the latter is controlled indirectly by an on-off thermostat (not shown) having a bulb located in the space being cooled, the thermostat serving to shut off the compressor motor and close valve to prevent draining of the condenser 50. From the valve 54 the condensed refrigerant passes through line 12, which in this case has two

branches

76, 78. A portion of the refrigerant flowing in line 12 enters branch 76 and passes through a check valve 80, a. thermostatically-controlled valve 82 having its hub 84 in heat exchange relation with a condenser return line 86, and thence through a length 56 of restrictor tubing to the cooling jacket of the flash gas condenser or heatexchanger 52. Thus arranged, the supply of refrigerant for cooling the flash gas condenser 52 is controlled by valve 82 and restrictor 56, the valve 82 increasing the flow of refrigerant in line 76 in response to higher temperatures in line 86. Refrigerant vapor generated in the cooling jacket is returned to the inlet side of primary compressor 20 through line 86.

The main stream of refrigerant flowing in branch 78 1 passes through a thermostatically-controlled valve 88 having its bulb 90 in heat-exchange relation with the suction gas line 18. Valves 82, 88 are of the equalizer type and each have their pressure elements connected by a by-pass passageway 92 to a point beyond the restrictors 56, 58. In the case of valve 88, the passageway 92 may a portion of the energy of the flash gas evolved in the be connected to any point intermediate restrictors 58 and 10. The main stream of refrigerant flows from valve 88 through restrictor 58, a silica gel dryer 94, flash-gas condenser 52, a filter 96, and thence through line 44 to restrictor tube 10 and into the evaporator coil 16. Any residual superheat or flash gas in the refrigerant is condensed in the condenser or heat-exchanger 52 so that only cold, liquid refrigerant enters restrictor 10. Since the restrictor 10 and bulb of valve 88 are responsive to temperatures in suction line 18 the supply of refrigerant in evaporator 16 is maintained at a correct level determined by the setting of valves 54 and 88 and the size and length of restrictors 58, 10.

In the system of Fig. 3, the jet pump 24 is connected between lines 18, 26, as before, and is powered by high pressure refi-igerant supplied by the primary compressor 20 through line 28. The use of the jet pump 24 in this system makes the primary compressor 20 operate over a narrower range of pressure thereby improving its volumetric efliciency and making possible lower temperatures in evaporator 16. If compressor 20 is an eificient reciproeating compressor the system of Fig. 3 can produce temperatures in the evaporator 16 substantially as low as a similar system employing two full primary stages of compression. The cost of the system of Fig. 3 is lower because of the elimination of one expensive compressor, its seals and its controls. If compressor 20 is an inexpensive type the resulting system can produce temperatures as low or lower than that obtainable with a system employing a single, high efliciency reciprocating primary compressor without a jet booster.

In Fig. 4 there is illustrated a refrigenation system capable of producing extremely low temperatures yet it employs but a single primary compressor 20. The primary compressor 20 is in this case assisted by two seriallyarranged jet booster units 100, 102 similar to those described above. The second booster jet unit 102 is powered by high pressure refrigerant taken off the outlet line 22 of compressor 20 through line 104 and the first jet booster unit 100 is powered by high pressure refrigerant taken off the inlet line 112 of the primary compressor 20 through line 108. It should be noted, however, that vapors from the flash gas separator 40 are recycled between the booster units, and the refrigerant vapors from the cooling jacket of head-exchanger 52 are recycled to the inlet line 112 of the primary compressor 20. In this arrangement, the recycle vapors of both the vessel 40 land the condenser 52 are available, .through line 108, at least in part, to power the first booster unit 100. I

Thus, suction gas leaves the evaporator 16 through line 18, passes through the first jet booster 100, and from "thence it is conducted to the inlet line 110 of the second jet booster 102. From the second jet booster' the now considerably compressed refrigerant passes through line 106.to the inlet line 112 of the primary compressor 20. The primary compressor 20 under the control of the "pressure responsive element 60 supplies refrigerant through lines and valves, a condenser 50, a flash gas lcondenser 52, and an expansion vessel 40 all similar to the corresponding elements of the system of Fig. 2. In the system of Fig. 4, however, the flash gas separating Iexpansion vessel or reservoir 40 is connected in series with ,the flash gas condenser 52 in order to achieve a similar type of control. Cooled refrigerant from the refrigerantcooled flash gas condenser 52 passes through dryer 94, filter 96, line 114, a flow-restricting capillary tube 116 and line 118 into vessel 40 wherein expansion occurs with still further cooling of the liquid. Vapors liberated in this expansion pass out of the top of vessel 40 through line 120 through a length of flow-restricting capillary tubing 122 Wrapped in heat-exchange relation with the outlet line 110 of the first jet booster 100 then through acheck valve 124 and thence into line 110. The higher the temperatures in line 110, indicating high demand in evaporator 16, the greater will be the pressure in vessel .40 and thegreater will be the flow of liquid refrigerant from vessel 40 to evaporator 16. The effect of vessel 40 thus is to supply refrigerant under more precise control to the evaporator coil 16 thereby making possible still lower evaporator temperatures. The combination of the flash gas condenser 52, expansion vessel 40 and the two jet booster stages enables the system of Fig. 4 to reach temperatures substantially as low as a similar system -employing two or three full stages of primary compression. The initial cost of the system of Fig. 4, however,

is much less since one or two compressors, their motors and their motor controls have been replaced by the two inexpensive jet pumps which have no moving parts and which require no controls. The primary compressor 20, as in the systems of Figs. 1 to 3, could be of the rotary type adapted to operate efiicierrtly at high capacity over a narrow pressure range.

While the refrigeration systems of Figs. 1 to 4 have employed one or more refrigerant-powered jet booster pumps as partial or complete replacements for one or more primary stages of compression, primarily with a view to obtaining low temperature performance at a more modest initial equipment cost, the jet booster pumps also can be used solely to drive the evaporator operating temperatures to new low levels. In Fig. 5 there is illustrated a complete flow and wiring diagram of a low temperature refrigeration system operative at temperatures of to 200 F., the system employing three primary stages of compression, a single jet booster unit, and a fourth compressor employed solely to power the jet booster. Since three stages of positive displacement type compressors will operate at or near the limit of the vacuum-producing ability of this type, any further decrease in evaporator temperature will not be commensurate with the cost of adding further stages. The reason for this is that three such stages are capable of operating near the limit of the efliciency of the type of spring-actuated valves usually employed in such compressors. When, however, a fourth compressor is connected into the system as shown so as to power a jet booster, a significant increase in vacuum-v producing ability is realized since the jet pump operates without the limitations of valves, manifolds, etc. and is capable of producing a higher vacuum.

In the system of Fig. 5, many of the elements correspond -to those of the systems of Figs. 1 to 4 and are given the same identifying numerals. As 'shown, the space being cooled is enclosed in a dotted line 130. The third or final stage compressor 20 delivers highly compressed refrigerant through oil separator 51 to line 22 through which it flows to a water-cooled condenser where it is condensed and liquefied. The liquefied refrigerant then flows through the drier 72, filter 74, solenoid valve 54 and valves 82, 88 before entering the flash gas condenser or heat-exchanger 52. As inthe system of Fig. 4, a flash gas expansion vessel is connected in series with the condenser 52 although in this case the flash gas and condenser coolant vapors are recycled to the system directly, and are not employed to power the jet booster.

From the evaporator 16, refrigerant vapor passes into a jet booster pump 132 wherein it is pre-compressed and delivered through line 134 to a first primary compressor 136. The first stage jet booster 132, it should be noted, is powered entirely by high pressure refrigerant delivered through line 138 by a fourth compressor 139. The compressor 139 is connected to line 134 between the booster 132 and first primary stage compressor 136. With this arrangement the compressor 139 operates over only a small pressure differential, which differential is equivalent to the drop in pressure across jet 132. The first stage compressor 136 also operates under a much smaller pres- .sure differential, as do the second stage 146 and third stage 20. With this arrangement, jet 132 operates very effi- .ciently and greatly increases the vacuum drawn on the evaporator. The refrigerant is compressed by compressor 136 and delivered through line 140 to compressor 146. Together with the fiash gas returned through line 120, the partially compressed vapors are further compressed in second stage compressor 146 and delivered through line 26 and are compressed, along with the second stage vapors in third stage compressor 20. In a highly compressed condition, the refrigerant is again delivered to condenser .50 through line 22.

Control of the refrigeration system of Fig. 5 is effected by the electrical controls system shown at the top of Fig. 5 and including the main on-off solenoid-controlled valve 54 and four pressure-sensitive bellows-type compressor motor controls 60 which control the four 3-phase compressor motors 158, 160, 162, 164 and protect the compressors against high pressure overloads. The compressor motors have, respectively, motor starters units 159, 166, 168 and 170. A thermostatically-operated switch 172 is provided in series with the third stage motor starter 170 to start and stop all four of the compressors, the switch 172 being operated by a temperature-responsive bulb 174 positioned in close proximity to evaporator coil 16. Thus provided, thermostat switch 172 will start and stop the compressors in response to fluctuations of the temperature obtaining in the cooled space 130. Since the solenoid of valve 54 is in series with switch 172, it will effect corresponding on-off control of the supply of refrigerant to the valves 82, 88.

Electrical energy is supplied to the controls system through 3-phase leads 176, 178, 180 with a main line switch LS-l being provided to shut the entire system down when desired. Motors 158, 160, 162, 164 are connected in parallel across leads 176, 178 and 180 while their starters 159, 166, 168 and 170 are in series across the secondary of the transformer 188. Lower voltage control power is supplied to the operating coils 181, 182, 184, 186 of, respectively, starters 159, 166, 168, 170 and to the other switches, valves, etc. by the transformer 188 having the terminals of its primary coil 190 connected across leads 176, 178. One terminal 192 of the secondary coil 194 is connected to the operating coil 186 of motor starter 170 and the other terminal 196 is connected to a common control lead 198. Each of the serially-connected motor starter coils 181, 182, 184, 186 have one of their terminals connected to lead 198 through a normallyclosed manual cut-off switch 200 and its respective pressure control switch 60 and the other of its termnials' connected to the preceding starter coil by a lead 202. Thus arranged, the de-energization of one starter coil will deenergize all starter coils.

With the system shut down the thermostatic switch 172 and motor controls 60 will be closed so that upon closure of main line switch LS1 and the individual switches 200, starters 159, 166, 168 and 170 will be energized to start all of motors 158, 160, 162 and 164. The compressors 139, 136, 146 and 20 immediately start to operate with both of compressors 136, 139 at first drawing vapor directly from the suction line 18 through jet 132. The jet booster 132 soon comes into full operation due to the plentiful supply of vapor in the evaporator and suction line. As the evaporator temperature reaches its control point, however, the supply of refrigerant in the evaporator is reduced and a vacuum will exist on the suction inlet of the jet. Under these conditions'the booster powering compressor 139 will be recirculating a relatively large quantity of refrigerant as compared to the small quantities being aspirated from the vacuumized evaporator. However, it is this type of large ratio operation, not restricted by limitations of valves, which enables the jet pump to operate most effectively in lowering evaporator pressures and temperatures. The inlet valves of the first primary compressor 136, therefore, will always operate at a considerably higher pressure than if the compressor were directly connected to the evaporator.

When, as illustrated in Fig. 5, the three primary compressors are of the reciprocating type, the single jet booster unit 132 and its power-supplying compressor 139 make it possible for the system to operate at much lower'temperatures due to the ability of the jet pump to draw a high vacuum. Any of the primary compressors of Fig. could be a rotating-vane or gear-type of positive-displacement compressor or even one of the high speed centrifugal turbine types of compressors which do not operate on the positive displacement principle. Since the system of Fig. 5 can produce evaporator temperatures well below the normal 3-stage limits it can be appreciated that the cost of such a system is much less than that of more com- 8 plicated systems designed for the same extreme low temperature operating range.

What is claimed is:

1. In a refrigeration system including an evaporator, having an inlet and an outlet and means including at least one refrigerant compressor and a condenser arranged to supply compressed refrigerant to said evaporator inlet, the improvement which comprises an expansion vessel connected between said condenser and said evaporator inlet, a length of flow restricting capillary tubing connecting said vessel with said evaporator inlet and in heat exchange relation with said evaporator outlet, a refrigerant-powered jet pumping means having a nozzle outlet connected to the inlet of said compressor, a suction inlet in communication with said evaporator outlet, and a nozzle inlet, and passageway means for conducting refrigerant vapor liberated in said expansion vessel to the said jet nozzle inlet of said pumping means.

2. In a refrigeration system including an evaporator, a flash gas condenser arranged to supply cooled refrigerant to said evaporator and having a refrigerant-cooled cooling jacket, a main refrigerant condensing means arranged to supply condensed refrigerant to said flash gas condenser, and at least one mechanical refrigerant compressor adapted to supply high pressure refrigerant to said main refrigerant condensing means, the improvement which comprises a refrigerant-powered jet pumping means having a suction inlet communicating with said evaporator, a nozzle outlet communicating with the inlet of said compressor, and a nozzle inlet, and a passageway means connected on one end with the refrigerant-cooled cooling jacket of said flash gas condenser and on the other end with the nozzle inlet of said jet pumping means.

3. In a refrigeration system including an evaporator, a condenser arranged to supply condensed refrigerant to the inlet of said evaporator, and at least one refrigerant compressor arranged to supply high pressure refrigerant to said condenser, the improvement which comprises a first and a second serially-connected refrigerant-powered jet pumping means, the suction inlet of the first said jet pumping means being in communication with the outlet of said evaporator, the nozzle outlet of said second pumping means being in communication with the inlet of said compressor, a high pressure nozzle inlet means for each said jet pumping means, passageway means extending from the outlet of said compressor to the nozzle inlet of one of said jet pumping means, and passageway means extending from the nozzle outlet of said one of said jet pumping means to the nozzle inlet of the other jet pump ing means.

4. In a multiple-stage refrigerating system including an evaporator and a refrigerant compressor arranged to supply condensed refrigerant to said evaporator, the improvement which comprises a refrigerant-powered jet pumping means serially-connected to deliver refrigerant to the suction inlet of said compressor, said jet pumping means having a suction inlet in communication with said evaporator, a nozzle outlet in communication with the said inlet of said compressor, and having a nozzle inlet, and a second refrigerant compressor having a suction inlet in communication with the inlet of the first mentioned compressor and with said nozzle outlet of said jet pumping means and having a refrigerant outlet in communication with the said nozzle inlet of said jet pumping means.

5. In a refrigeration system, the combination comprising an evaporator having an inlet and an outlet, a refrigerant expansion vessel having an outlet for cooled liquid refrigerant in communication with the inlet of said evaporator and having an outlet for refrigerant vapors, and an inlet for condensed refrigerant, means including a mechanical refrigerant compressor and a condenser for supplying condensed refrigerant to said condensed refrigerant inlet of said vessel and a suction inlet communicating with said outlet of said evaporator, a refrigerantpowered jet pumping means serially-arranged with a suction inlet in communication with the said outlet of said evaporator and a nozzle outlet in communication with the said inlet of said compressor and having a nozzle inlet for the reception of high pressure refrigerant, passageway means connecting the outlet of said compressor with the said nozzle inlet of said pumping means, and passageway means connecting the said outlet for refrigerant vapors of said expansion vessel with the said suction inlet of said jet pumping means.

6. In a refrigeration system, the combination comprising an evaporator having an inlet and an outlet, a refrigerant-cooled, jacketed heat-exchanger for supplying cooled liquid refrigerant to said evaporator inlet, means including a mechanical refrigerant compressor having an outlet and a condenser for supplying condensed refrigerant to said heat-exchanger and its jacket and an inlet communicating with the outlet of said evaporator, a pair of refrigerant-powered jet-type pumping means in series flow arrangement, a first of said serially-arranged pumping means having a suction inlet communicating with the outlet of said evaporator, the second of said serially-arranged pumping means having a nozzle outlet communicating with the said inlet of said compressor, each said pumping means having a nozzle inlet for receiving high pressure refrigerant, passageway means connecting the outlet of said compressor with the nozzle inlet of said second jet pumping means, passageway means connecting the said nozzle inlet of said first jet pumping means with the said outlet of said second jet pumping means, and passageway means connecting the jacket of said heat-exchanger with a point intermediate said first and second jet pumping means.

7. In a refrigeration system including an evaporator, having an inlet and an outlet and means including at least one refrigerant compressor and a condenser arranged to supply compressed refrigerant to said evaporator inlet, the improvement which comprises an expansion vessel connected between said condenser and said evaporator inlet, restriction means connecting said vessel with said evaporator inlet, a refrigerant-powered jet pumping means having a nozzle outlet connected to the inlet of said compressor, a suction inlet in communication with said evaporator outlet, and a nozzle inlet, and passageway means for conducting refrigerant vapor liberated in said expansion vessel to the said nozzle inlet of said jet pumping means.

References Cited in the file of this patent UNITED STATES PATENTS 2,195,604 Taylor Apr. 2, 1940 2,513,361 Rausch July 4, 1950 2,683,361 Ridgley July 13, 1954 FOREIGN PATENTS 660,771 Great Britain Nov. 14, 1951