US2714806A - Refrigerating system - Google Patents

Description

Aug. 9, 1955 H. J. scULLEN REFRIGERATING SYSTEM 2 Sheets-Sheet l INVENTOR.

Filed DSG. l2, 1951 nited States Patent O This invention relates generally to a refrigerating system which is particularly adapted, among other uses, for maintaining low temperatures.

An object of this invention is to provide a new refrig erating system of the character described.

A further object is to provide such a system in which temperatures of the order of 150 degrees below zero or less may be maintained.

A further object is to provide such a system which will function to maintain a range of temperatures from degrees Fahrenheit or above zero to 150 degrees below zero I or below.

Another object is to provide such a system in which the heat is radiated from the system at usual radiating temperatures.

Another object is to provide such a system in which the pressure of the liquid refrigerant is reduced in a plurality of steps.

Another object is to provide such a plural step liquid refrigerant pressure reducing system with means for eliminating flash gas produced during the pressure reducing operations whereby a higher percentage of liquid is supplied to the evaporator.

Another object is to provide such a system in which the concentration of the circulating lubricant is maintained sufficiently low to provide proper operation of the system.

Another object is to provide means for removing wax from the circulating lubricant.

Another object is to maintain such a system using capillary tubes fiow controlling devices at high operating efficiencies.

Another object is to provide such a system which uses plural stages of compression of the refrigerant removed from the evaporator.

Another object is to provide an automatic control of such compression stages so that the temperature of the r cooled space may be widely varied.

Another object is to provide such a control for the compression stages which will insure a desired operating relation therebetween.

Other objects will be apparent from the description, the appended claims and the drawings in which drawings:

Figure 1 is a schematic View of a refrigerating system embodying the invention;

Fig. 2 is a detailed View of Fig. l showing the thermal heat bridges which were omitted in Fig. l for simplicity and for simplicity omits the showing of the compressor by-pass connections;

Fig. 3 is a detailed View of the reservoir of Fig. l;

Fig. 4 is a detailed view of a modified form of reservoirs;

Fig. 5 is a View taken substantially along the line 5-5 of Fig. 4;

Fig. 6 is a schematic view of a modified form of system embodying the invention; and

Fig. 7 is a still further modified form of systems embodying the invention.

l' ice While there is shown herein three forms of the invention, in accordance with the patent statutes, these forms are to be taken as illustrative rather than limitative as various modifications thereof may be made within the scope of the invention which is claimed in the appended claims.

The numeral 2 designates an evaporator which might comprise coils wrapped around a metallic tank intermediate the tank and insulation which surrounds the tank. Vaporized refrigerant leaves the evaporator 2 through a suction line 6 to the inlet 8 of a reciprocating first stage compressor 10. The vaporized refrigerant passes from the compressor 10 through its outlet 12 and an oil separator 14 'to the inlet 18 of the second stage compressor 20 L' by means of conduit 21. The outlet 22 of the compressor is connected by conduit 23 through an oil separator 24 to the inlet 26 of a third stage compressor 2S having its outlet 30 connected by conduit 31 through another oil separator 32 to the inlet 34 of a water-cooled condenser 36, the outlet 38 of which is connected through a silica gel dryer 40, filter 42 and a solenoid valve 44 to the inlet 48 of a thermostatic expansion valve and through branch conduit 52 and check valve 53 to a second thermostatic expansion valve 54. The outlet 51 of an expansion valve 50 is connected to the inlet of a capillary restrictor tube 46, the outlet of which is connected through silica gel dryer 55 to the inlet of 56 of a heat exchanger 58. The outiet dfi or exchanger 58 is connected through a filter 61 and conduit 62 to the inlet end of a capillary tube 64 the outlet end of which is connected to an inlet 66 of an expansion tank or container 68.

The expansion tank 68 has a liquid outlet 70 adjacent its bottom which is connected to the inlet end of a capillary tube 72 the outlet end of which is connected to the inlet 74 of the main evaporator 2 which is in heat exchange relation with the walls of an inner liner 76 shown fragmentarily and which is protected from ambient air by insulation as shown by the dash line 78. The expansion tank 63 has a second outlet 8f) adjacent its top which is connected by a conduit 82 through a capillary tube 84 and check valve 86 to the conduit 21 intermediate the oil separator 14 and inlet 13 of compressor 20 whereby vaporous refrigerant may iiow back to the compressor 20 without passing through the evaporator :2. The capillary tubes 72 and 84 are arranged in heat exchange relation with the conduits 6 and 21 respectively.. The tube 72 is located in the insulation 78 while the tube 84 and most of the conduit 82 is located outside of the insulation 78 in the ambient air.

The expansion valve S0 is the type known as the equalizer type in which the pressure element is connected by a fiuid pressure conveying conduit 87 to the conduit 82 intermediate the tank 68 and the restrictor tube 84. The expansion valve 5@ also has a temperature controlling element 38 which is clamped to, or otherwise secured, in heat exchange relation with the conduit 6 externally of the insulation 78. The element 88 and adjacent portion of the conduit 6 are covered with insulation 90.

The expansion valve 54 is of the same type as the expansion valve 50 and its outlet 92 is connected to the inlet end of a capillary tube 94, the outlet of which is connected to a second inlet 96 of the heat exchanger 58. A second outlet 98 of this exchanger 58 is connected through a conduit 100 to conduit 23 and therethrough to the inlet 26 of the third stage compressor 28. A fluid pressure conveying tube 102 connects the pressure element of the valve S4 to the conduit 100 and the temperature element 104 is secured in heat exchange relation to the conduit 10ft externally of the insulation 78. The element 104 and portion of conduit 100 to which it is in heat exchange relation are covered by insulation 106.

under control of a pressure operated water regulating valve `126 Whose control element 128 is connected by conduit 129fto the discharge conduit 31 whereby valve 126 is responsive to the discharge pressure of the compressor 28 and acts in the usual manner to increase the flow of coolant water upon an increase in discharge pressure.

As shown the compressors 10, and 28 are respectively driven by 3 phase motors 188, 190 land 192, however, it will be apparent that the number of phases is unimportant and also the compressors could be driven by other sources of power and controlled in the manner to be described. Electrical energy is supplied to the conductors .194, 196 yand 198 through the line switch ILS-1. The conductors 194, 196 and 198 are connected through line switch l'motor starters 200, 202 and 204 to the motors 188, 190 and 192 respectively. Single phase control power is obtained from the 3 phase source through a transformer 206 having its primary winding 207 connected between any two of the conductors which in the shown 'instance is connected between conductors 194 and 196. A 4secondary winding 208 of transformer `206 has one terminal connected by conductor 210 to one terminal 212 of the operating coil 214 Vof the motor starter 204. The other terminal of the coil 214 is connected by conductor 216 through a pressure switch 130, thermostatic switch 132 and manual switch 134 to conductor 136 which is connected to the other terminal of the winding 208. The switch y130 has a usual set of contacts 138 which are controlled by a pressure responsive element 140 connected by a pressure conveying conduit 142 to the discharge port or outlet 30 of compressor 28. Increase in pressure at the discharge 30 of the compressor 28 above a predetermined pressure acts to open the contacts 138.

The thermostatic switch 132 has a pair of lcontacts 144 which are controlled by means of a temperature sensitive element 146 having the usual bulb 148. The bulb 14S is secured to the wall of the cabinet storage chamber liner 76 on the .side thereof .adjacent the insulation and intermediate a pair of turns of the evaporator 2 which is secured 'in heat exchange relation therewith. Upon increase in temperature above the predetermined desired temperature, :the contacts 144 close. The motor starter 204 has main normally open contacts 218, 220, '222 closed upon energizatiton -of the `c'oil 214 which control the connection of -t-he motor 192 tothe conductors 194, 196 and 198. The motor starter 204 has a fourth contact 224 which is Iclosed upon energization of the coil 214 to complete a'circuit from the lconductor 21.0 to a conductor 226`which is connected to one terminal 22-8 of the energizing winding 230 of the motor starter 202. A branch conductor 227 of conductor 226 is connected to one terminal of the energizing coil of the solenoid valve 44 while the conductor l136 is vconnected to the other terminal of this coil so that the valve 44 will open and close upon opening and closing of the contact 224.

The starter 202 is like the starter 204 and has contacts controlling the energizat-ion'of the motor x190 and a fourth contact 232 closed upon energization of the coil 230. The other terminal of the coil 230 is 'connected through a pressure switch `r150 and manual switch 152 to the conductor 136. The switch '150 is like the Aswitch 130 but which has its element 1'54 connected to the conduit '23. Closure of the contacts 232 4connects'the conductor '226 to a conductor 234 which is connected to one terminal of the operating coil '236 of the motor starter 200. The motor starter 200 is like the starter 202 Iand -204 except that it needs no fourth contact or if present such lcontact is not used. Such starter `200 does have the main `concheck valves 246 and 248.

tacts which close as a consequence of the energization of the coil 236 to energize motor 188. The other terminal of the coil 236 is connected through a pressure switch 154 and manual switch 156 to the conductor 136.

The restrictors 46 and 94 maintain the expansion valves 50 and 54 at high enough temperature with respect to ambient temperature to avoid the difficulties which might otherwise occur due to frictional effects of congealing oil and sweating of the valves.

It is believed that the remainder of the construction may best be understood by a description of the operation of the system which is `as follows:

Assuming that the system has been standing idle for a considerable period ottime and the system parts are all at, or substantially at, ambient temperature and the thermostatic switch 132 is set to maintain a low temperature as for example 150 degrees Fahrenheit below zero. Under these conditions the pressure switches 1.50 and 154 will be open while switches and 132 will be closed. The manual switches 134, 152 and 156, if not `already closed, will be closed. Closure of line switch LS-l will energize the conductors 194, 196 and. 198 and the tra-n.)- former 206. Control current will now ow from conductor 210 through coil 214 and switches 130, 132 and 134 to cause coil 214 to close contacts 218, 220, 222 and l224. Closure of contacts 218-222 causes motor 192 'to start the compressor 28. Closure of Contact 224 causes the valve 44 to open and to energize conductor 226 to prepare for energization of coil 230 upon closure of switch as will be described below. Upon operation of the compressor 28 suction vapor will flow from the main evaporator 2 through the other two compressors which under pull down conditions as described will not be yoperating since the pressures in the evaporator y2 will be so high as to maintain the pressure switches 150 and 154 open. .In many compressors refrigerant can flow therethrough in a direction from the inlet to the outlet whenever the .inlet pressure is greater than the outlet pressure even though the compressor is not ruiming. ln some instances it may be desirable to provide for by-passing the refrigerant around non-running compressors and for this purpose there is provided by-pass lines connecting the conduits 6 and 21, and 21 and 23 in which are provided A solenoid valve, connected to be opened when the compressor ywith which it is associated is running, may be used in place of the check` valve.

As the compressor 28 operates, the temperature and corresponding pressure .in the evaporator 2 will drop until,

when the pressure in the evaporator `2 has reached approximately 20 pounds pressure, control will close to complete the energizing circuit vfor coil which then causes thefoontactstot the starter 202 to close to start compressor 20 and energize .the conductor 234 as a prepara tory circuit for -energization or" the .coil 236. `Continued operation 4of compressors 20 and 28 results in a further drop in temperature and pressure in the main evaporator' 2 until, at a .pressure of approximately l() inches of vacuum, the pressure control 1154 will close to complete the energizing circuit for coil 23.6 which then causes the contacts of the starter 200 to close to start compressor 10. Continued operation of compressors 28, l20 and 10 will result yin a .further lower-ing of temperature in the fevaporator 2 until the temperature of bulb 148 has been lowered to the cutout point of the thermostat 132, at which time the thermostat will lopen is contacts 144 to .de-energizing `coil 214 -which results in opening .of the 4contacts 218-224 which de-energize motor 192, valve 44 which :then closes Vand coils 230 and 236 which causes the motor starters 202 and 200 to open their contacts and de-energize the motors 18S `and `190.

As the temperature of the liner 76 increases to the cut-inpoint Iof the thermostat 132 its :con-tacts .again close initiating an operation of the compressor 28. As-

s'uming that the operating temperature of the thermostat 132 has not been changed, the pressures in the conduits 21 and 23 will be within the pressure range at which the pressure switches 150 and 154 will be closed resulting in energization of the motor starters 202 and 209 and the motors 188 and 190 controlled thereby resulting in immediate restarting of all of the compressors 10, 2t) and 28. This cycling condition will continue, assuming that no great heat loads have been placed in the cabinet, and the temperature of the cabinet will be maintained within the desired temperature range as determined by the differential operating temperature of the thermostat 132.

If the operating range of the thermostat 132 is adjusted to call for operation of the cabinet at a substantially higher temperature, then corresponding higher pressures will occur in the evaporator 2. An adjustment of the thermostat 132 to a temperature at which the operating evaporator pressure is above the pressure at which the switch 154 opens will cause the switch 154 to stand open and compressor 10 will not be operated. A still higher setting of the thermostat 132 will result in a higher operating evaporator pressure with the result that switch 150 will open and keep compressor from operating.

The temperature range of the system may be from minus 120 degrees Fahrenheit in which cycling under control of the thermostat 132 causes operation of all of the compressors 10, 20 and 28, an intermediate temperature as, for example, minus 60 degrees Fahrenheit at which compressors 20 and 28 only would operate, and a higher temperature of, for example, 0 degrees Fahrenheit at which only the third stage compressor 28 would operate. The above temperatures are illustrative as the exact temperatures which would cause such operation may be varied somewhat, depending upon the particular design,

by changing the pressure at which the switches 150 and 154 are set to open.

Because cabinets of this general type are desired to be operated in rooms normally maintained at temperatures for human comfort, and because the condenser 36, which is shown as liquid cooled but which could be air cooled, will be supplied with coolant which is of usual temperature generally in the neighborhood of 60 to 8O degrees Fahrenheit, the temperature and pressure of theliquid refrigerant supplied by the condenser 36 may be in the neighborhood of 8O to 100 degrees or even 120 degrees Fahrenheit under extreme conditions. If this liquid refrigerant were immediately allowed to expand into the evaporator 2, which may be operating as low as minus 140 degrees Fahrenheit to maintain temperatures of minus 120 degrees Fahrenheit within the liner 76, a considerable amount of this liquid would be turned into flash gas resulting from the heat abstracted from the liquid refrigerant in reducing its temperature from that of liquid supplied by the condenser 36 to the temperature of the liquid refrigerant in the evaporator 2. This would result in inefficient operation of the system since such flash gas would have to be compressed from the pressure appearing in the evaporator 2 to the discharge pressure of the compressor 28 requiring additional energy and larger compressors. In addition to the above ineticiencies, a certain amount of oil used to lubricate the compressors 10, 2t) and 28 will also be flowing through the refrigerating system. Normally the percentage of oil flowing through such a system is small in proportion to the liquid supplied to the evaporator and will flow back to the compressor with the circulating refrigerant and a balance between refrigerant and lubricant is maintained in the various portions of the refrigerating system. If a large amount of liquid goes into ash gas to provide cooling of the liquid refrigerant supplied to the evaporator 2, the amount of lubricant or oil remains the same but since the amount of liquid refrigerant is less the percentage of oil, with respect to liquid refrigerant supplied to the evaporator, becomes excessive. Such excessive concentrations d of oil cause further loss of efficiency and, in some cases, actual plugging of the orifices and other refrigerant supplying passageways and cases have been known in which the evaporator tubes themselves have been plugged.

The amount of fiash gas supplied to the evaporator 2 is reduced by the heat exchanger 58 which recondenses the liash gas formed as a consequence of 'the initial reduction in pressure of the liquid refrigerant passing through the valve and the restrictor 46. Again the accumulated flash gas formed as a consequence of the ow of refrigerant through the restrictor 64 and a portion of the circulating oil is removed through the conduit 82 so that little more than the flash gas formed as a consequence of the ow of refrigerant through the restrictor '72 passes into the evaporator 2. Thereby a big percentage of the ash gas is compressed from a higher pressure than that maintained in the evaporator 2 and also a desired portion of the lubricant is prevented from entering the evaporator 2 where it would cause undesirable results.

More specifically, liquid refrigerant in the system of Fig. l ows from the condenser 36 through the dryer 40 and filter 42 to the valves 50 and 54. Refrigerant flows through the valve 50 and restrictor 46 to the exchanger 58 wherein the flash gas is recondensed. The valve 50 cooperates with the restrictors 46, 64, 72 and 84 to control the refrigerant ow to the evaporator 2 as will be more specifically described hereinafter. The refrigerant then flows through the restrictor 64 to the reservoir 68. The resulting ash gas and some lubricant flows through the upper outlet 80, conduit 82 and restrictor 84 to the suction line 21 of the compressor Ztl. The liquid refrigerant and some oil collects in the bottom of the receptacle 68 and flows out through the lower outlet 70 and restrictor 72 to the evaporator 2. In order to reduce the amount of Hash gas produced as a consequence of the final reduction in refrigerant pressure, the capillary tube or restrictor 72 is arranged in heat exchange relation with the suction line 6 within the insulation 78 so that the cold gaseous refrigerant flowing from the main evaporator 2 to the inlet 8 of the first stage compressor 10 will abstract as much heat as possible from the incoming refrigerant. The vapor formed in cooling the space defined by the liner 76 and some oil passes through conduit 6 to the inlet 8 of Compressor 1t) and then back to the condenser 36 where the heat thereof is removed and the refrigerant is condensed to a liquid. The oil separators 14, 24 and 32 act to collect and return some of the circulating oil but are not effective to prevent some oil from circulating throughout the system.

Valve 54 in cooperation with the restrictor 94 controls flow of refrigerant to the exchanger S8. The liquid refrigerant so admitted to the exchanger 58 vaporizes to cool and recondense the ash gas in the refrigerant flowing between the inlet 56 and outlet 6i). The resulting vapor together with the flash gas formed as a consequence of refrigerant ow through restrictor 94 and any circulating oil then passes through the outlet 98 and conductors 100 and 23 to the inlet 26 of the compressor 28.

The valve 50 is of conventional construction but functions to provide an unusually high degree of superheat. This is because the equalizing or pressure connection 87 is responsive to the pressure of the refrigerant within the expansion tank 68, and its temperature responsive bulb 88 is in heat exchange relation with the suction line 6 intermediate the heat exchange relationship of the capillary tube 72 with the suction line 6 and the compressor inlet 8. Preferably the heat interchange between the capillary tube 72 and the suction line 6 raises the temperature of the gaseous refrigerant owing through the suction line 6 so that when leaving the insulation 78 it is substantially at the same temperature as the temperature of the refrigerant in the container 68 which is very considerably above that in the evaporator 2. A superheat of 50 degrees Fahrenheit lhas been -found satisfactory i-with compressors and restrictors as follows:

Compressor Capacity, C. F. `M.

Internal Diameter,

Restrictor Inches Length, feet when using 'F22 as the refrigerant. The proper heat exchange between the restrictor 7.2 and suction conduit 6 may be obtained by soldering about 3 `feet of the restrictor 72 to substantially the same 'length of 'the conduit 6.

`Initially under pull down conditions, the valve'50 will normally be in a fully open condition. v.As the temperature of the evaporator vlowers to an intermediate temperature, which for purposes of illustration will be assumed .to be '30 degrees Fahrenheit below zero, the valve 50 will commence to throttle the 'fluid 'flow to 'the restrictors. Such temperature could well 'be above or below this temperature depending upon design factors. As the intermediate temperature is reached the restriction to ow koffered by the restrictors when related to the temperature of the liquid refrigerant in the condenser 36 is suc'hithat the 'flow of refrigerant entering the evaporator 2 would result in a greater rate of 'flow of refrigerant entering the evaporator than being removed therefrom. Continued lowering of the evaporator 'temperature and consequently of the pressure of the refrigerant therein results in a progressively greater pressure differential between that of the evaporator 2 andthe condenser '36 'and an increased flow of refrigerant to the evaporator I2. Such increased flow results 'in a reduction in ,temperature of the bulb 88 since the superheated refrigerant 'vapor acting on the bulb 88 is ata lower temperature. There `may-'even ybe some ltendency for tsmall -amounts -of liquid lrefrigerant to flow into the conduit v16, fthus lowering of .the temperatureof :the bulb 88 still further. -As I"thelbulb :temperature decreases, v.the valve .50 moves ifurther toward the closed position and cooperates Vwith `the rrestrictors .to -limit the refrigerant ow .to theevaporatorl tomain- .tain the-desired amount of liquid therein. The inherent characteristic of a thermostatic expansion valve .of -decreasing the degree of superheat required .to .actuate the valve as a function of increase in evaporator temperature and pressure aids the valve in maintaining its open condition during pull down and acting as a throttling valve during lnormal low temperature running.

The restrictor "84 is varranged in heat exchange rela- Ation wit-h the f conduit 21 which is ynormally maintained 'at a higher temperature, though the pressure -of refriger- -ant therein is lower, than that ofthe container\.68. ormally the refrigerant `flowing through .the-restrictor 84 is vaporous and .any further superheating has :little effect on .the rate .of ow .through the restrictor. lf, rhowever, liquid refigerant flows Ainto :the container 68 .faster than it `flows out of the outlet 70 the level thereof will yrise .and finally flow .out into the conduit 82. .Such liquid refrigerant will pick up heat from the .ambient air surrounding the vportion ofthe conduit external .of the insulation 78 and vaporize substantially increasing the amount of vapor which the restrictor 84 is required to pass `and `increasingthe pressure drop'therethrough. 'This Aresults in an increase in Vpressure *in "the Vcontainer and an 'increased flow of liquid refrigerant `to lthe evaporator l2'through the restrictor 1'72. yIncrease in .pressure -in =the container .'68 will ztend to reduce ow of :refrigerant through the frestictor 64 and liquid may tend .to back -up inthe exchangerandeven to the extent l.that the inner tube connecting outlet 60 with inlet 56 will .completely 5 fill with liquid which is, of course, subcooled by :the evaporating refrigerant in the shell connecting .the inlet 96 and outlet 98. This will result in a tendency for the restrictor 46 to lpass less refrigerant. However, such :increases :in pressure will result in the `production of less l Hash gas and umore .cooling .byzthe exchanger 5 8 so .that the net Iresult will .the .increased pressure in the system for forcing `the normal .amount of refrigerant into the evaporator 2.

A :portion of the restrictors 4.6 and 94 are located exiternal 'of the `insulation 78 as .are the valves .50 and 5'4. lRestrictor 46 provides a `sui'licient pressure drop between the outlet of the expansion valve y50 and the temperature maintainedin rthe heat exchanger 58 so that the temperature of ,the valve 50 is maintained high enough to .pre- 20 vent .excessive sweating and substantial drag in the operation-.of the valve which might otherwise occur due to low -temperature .of the oil therein. Smoother operation of the valve and more even ow of refrigerant therethrough is therebyvprovided. The valve 54 is similarly vmaintained for smooth operation and prevented from excessive sweating.

The valve 54 cooperates with the restrictor 94 in much the same way as .does the valve 5.0 with .the restrictors 46, `64 and 72 to maintain a desired refrigerant ow to the exchanger S8. Initially at pull down the pressure diiferenceacross the .compressor 28 is small and valve 54 will .be -wide open. As the pressure and temperature of .the low .pressure portions .of .the system decreases the pressure difference across the compressor 28 increases and the va1ve.54 acts to prevent excessive quantities of refrigerant Afrom owing to the exchanger 58 and flood back through the conduit 100. It should further be noted that the .temperature of the exchanger 58 will drop during pull down resulting in a reduced pressure of the re- 'frigerant flowing through the restrictor 64 which will tend to reduce refrigerant ow'through the restrictor 72 to the evaporator 2. Fluid ow to the restrictor 64 ,and 72 is further influenced by restrictor 84. The in- P herent tendency of the condenser 36 to reduce its operat- 'ing pressure as a consequence of a reduction in the pressure in the evaporator 2 also aids in maintaining .the

properow of refrigerant in the system.

Since capillary ltubes are essentially xed value re- 'strictors, and as such are designed for maximum system l eciency at one .desired operating condition -of the sys- `tem,their use has ybeen somewhat limited to systems operating within a relatively narrow temperature range. With the illustrated system the range over which eficient operation of the system is increased many fold both dueto the presence of the valves `50 and 54 which act to prevent excessive liquid being supplied to the exchanger '.58 and :evaporator 2 and .due to the compensating effect provided by vthe exchanger 8 and Vrestrictor v84 which .cooperate together to yprovide fora .greater flow to refrigerant to the evaporator 2 in part at least *due tothe variable pressure ldrops ,mentioned above resulting as a consequencetof liquidbuild up in the reservoir 68.

lIn Figure .2 there is shown .a detail .of the system of .'Fig. l in which/.thermal bridges 250, 252 and 254 have :been provided Ito .modify the actionof the valve `50 as a function of the temperature .of the discharge vapors of the compressors 10, and 28. For simplicity the showing of the yby-pass connections, including the check valves h :246;and 248,-have been omitted in Fig. 2. While :three '10 fbridges .250, 252 and 2541are,-shown and the presence `thereof .provides certain beneficial results, within the generic scopeof the invention, one-or more `are not-essenytial tothe functioning ofthe system. The bridges i250, 252 and 254 4are designed -to l`funct`ionduring `the operation Ofthe system when-the lvalve V"'50 Jis tending `\tothrot tle refrigerant ow. They are shown as being straps of suitable material such as copper, aluminum or other good heat conducting material and serve to transfer some heat from the discharge of the compressors 10, and 28 back to the conduit 6 adjacent the bulb 88. The exact location of the bridges on the conduit 6 is not to important except that they must be able to influence the temperature of bulb 88. In the event of abnormal discharge temperature of the compressors 10, 20 and/ or 28, the bridges 250, 252 and/or 254 will raise the temperature of the bulb 88 slightly above the temperature it would otherwise assume and tend to open the valve to provide for a greater iiow of refrigerant to the evaporator 2 which results in a cooler temperature of the refrigerant owing to the compressor inlets. In some instances it may be desirable to even raise the temperature of the bulb 88 sufficiently to permit: some liquid refrigerant t0 ow past the bulb 88 but such amount should not be great enough to flood liquid into any of the compressors. A similar bridge 256 may be provided between the conduits 31 and 100 to heat the bulb 104 whereby additional refrigerant will be admitted to the exchanger 58 and the temperature of the refrigerant flowing to the inlet 26 of the compressor 28 will be lowered due to the lower temperature of the refrigerant flowing from the conduit 100.

In Fig. 3 there is shown a detail of the reservoir 68 which not only functions as above described but which also functions to remove wax from the circulating refrigerant. The already rather cold liquid refrigerant and entrained oil enters the reservoir 68 at high velocity from the end of the capillary tube 64 which extends through the inlet 66. The refrigerant and entrained oil upon entering the interior of reservoir 68 rapidly expands and reduces in temperature and velocity and any wax in the oil tends to separate out as wax particles which then collect on the internal fine mesh screen 260.

Figs. 4 and 5 show a modified form of reservoir 68 in which the capillary tube 64 discharges tangentially into the reservoir 68 and the wax which may be formed as above tends to be thrown against and adhere to the internal walls of reservoir 68. The separation of wax at this .stage in a relatively large space prevents its formation in the rather small bore restrictor 72 or in the evaporator 2 where it might collect and plug the system.

During off time of the refrigerating system the solenoid valve 44 will be de-energized and closed to prevent draining of the liquid refrigerant from the condenser 36 into the low pressure side of the system. Cheek valves 53 and 86 are provided to prevent draining of other intermediate pressure portions of the system back to the evaporator 2. This is necessary since during oft' time, the temperature of the thermostatic element 88 and 104 of the valves 50 and 54 will increase substantially above operating temperatures and cause the respective Valves S0 and 54 to remain open.

The system of Fig. 6, in which parts corresponding to those in Fig. l are identified by the same reference characters, is similar to the operation of the system of Fig. 1 except that the heat exchanger 58 of Fig. 1 hasbeen replaced by a second container 300 similar to the container 68 in which the flash gas, resulting as a consequence of the flow of liquid refrigerant through the restrictor 46, is removed through the conduit 302 and restrictor 304 to the conduit 23 which is in open communication with the inlet 26 of the compressor 28. The container 300 like container 68 is provided with an inlet 306 to which the outlet end of the restrictor 46 is connected and with a lower outlet 308 which is connected to supply liquid to the restrictor 64. The conduit 302 is connected to the upper outlet 310. A major portion of the conduit 302 is located externally of the insulation 78 and the restrictor 384 is arranged in heat exchange relation with the conduit 23. A check valve 312, similar to the 0` check valve 86, is provided to prevent reverse iiow of fluid through the restrictor 304 and conduit 302.

The operation of this system is similar to that of the system of Fig. l except that the flash gas which forms between the restrictor 46 and 64 is collected in container 308 and conducted back to the compressor 28 through conduit 302, along with some oil, rather than recondensed as in Fig. l. Restrictor 304 cooperates with the container 300, similarly as does the restrictor 84 and conduit 82 with the container 68, to provide for an increased pressure in the container 300 in the event that the container 300 fills and liquid tends to flow outwardly of the outlet 310 into the conduit 302.

The system of Fig. 7 is similar to that of Fig. l except that the second stage compressor 20, the restrictor 64, the container 68 together with its conduit 82 and restrictor 84 and certain associated parts have been omitted. This system is particularly adapted for applications wherein the temperature to be maintained within the shell 76 are not required to be as low as the minimum ternperatures desired within the shells 76 of the systems of Figs. l and 6.

It will be noted that while the valves 50 are shown in connection with both the systems of Figs. 1 and 7 and not with the system of Fig. 6, the valves could be used with the system of Fig. 6 or could be omitted from the systems of Figs. 1 and 7 if desired. As explained above during normal operation the valves 50 are maintained open and throttle refrigerant flow when necessary to prevent flood-back of the refrigerant from the evaporator 2.

While capillary tube type restrictors are shown and their use provides certain desirable operating features of the refrigerating system, the invention also contemplates the use of other types of liquid refrigerant feeding devices such as automatic or thermostatic expansion valves, low side iioat devices, etc. which may be used to regulate the liquid flow through a plurality of reducing stages in place of the shown restrictors either with or without the valves 50. ln such event the flash gas will be eliminated either by recondensing such gas or by removing it or a combination of the two methods.

What is claimed and is desired to be secured by United States Letters Patent is as follows:

l. In a refrigerating system for cooling a space, an evaporator having an inlet and an outlet and arranged in heat exchange relation with such space, at least three refrigerant compressors each having a suction connection, and a discharge connection and a connection for returning lubricant thereto, a condenser for refrigerant having an inlet and an outlet means providing a first fluid flow passageway from said discharge connection of one of said compressors to said condenser inlet, means providing a second fluid flow passageway connecting said condenser outlet to said evaporator inlet, a third fluid flow passageway connecting said discharge connection of a second of said compressors to said first compressor suction connection, a fourth iiuid fiow passageway connecting said evaporator outlet with said suction connection of a third of said compressors, a fifth uid fiow passageway connecting said third compressor discharge connection to said second compressor suction connection, a plurality of lubricant separators individually connected with said discharge connection of said compressors, said separation having a lubricant return connection connected to said lubricant connection of the one of said compressors with which it is individually associated, said second passageway including three ow controlling devices arranged in series therein, means including said first said compressor for substantially eliminating flash gas formed as a consequence of flow of liquid refrigerant through a rst of said devices, means including said first and said second compressors for substantially eliminating the flash gas formed as a consequence of ow of liquid refrigerant through a second of said devices, means responsive Vto the temperature of said space for controlling e'i nene the .operation .of said first compressor, means responsive to an operating condition of said first compressor for controlling the Aoperation of said second compressor, and means yresponsive to an operating condition of said second :compressor for controlling the operation of said third compressor.

2. The combination of claim l in which said devices are small bore tubes.

3. The combination of claim l in which at least one of said flash gas eliminating means includes a small 'bore tube.

A4. in .a refrigerating system for cooling a space, an evaporator in heat exchange relation with such space, a liquid refrigerant ,container normally maintained at atemperature elevatedwith respect to that of such space, a fluid conveying passageway connecting said container yto said evaporator and including a pair of How controlling devices serially larranged between said container and .said evaporator, and asecond refrigerant evaporatorconnected in parallel with said rst named evaporator and in heat exchange relation with said passageway intermediate said devices to cause condensation of the flash gas resulting from the passage of refrigerant through a first of said devices.

v5. The Acombination of claim 4 in which atleast one of said devices isa section of small bore tubing.

6. In a refrigerating system for cooling a space, an evaporator in heat exchange relation with vsuch space, a liquid refrigerant container normally maintained `at a temperaturetelevated with respect to that of suchspace, ,a Huid conveying passageway connecting said container to said evaporator and including a pair of flow controlling devices serially arranged between said container and said evaporator, means for cooling at least a portion of said passageway intermediate said devices to cause condensation of the flash gas resulting from the passage of refrigerant through a first-of said devices, a section of small bore tubing and a iiuid container serially arranged in the order recited in said passageway between said passageway cooled portion and the second of said devices, said container yhaving an inlet for receiving refrigerant passed by said first device and a pair of outlets, one of said outlets being at a flower elevation than the other thereof, said lower outlet being connected to supply .refrigerant to said second device, and means for removing refrigerant from the said other container outlet inby-pass relation to said-evaporator.

7. The combination of claim 6 in which a thermostatic expansion valve is provided intermediate said container and said first device to control flow of refrigerant to said first device from said container, said valve having la thermostatic Acontrol element and a pressure control element, Said thermostatic element being arranged to beresponsive to a function of the temperature of the refrigerant in said evaporator and said pressure element being responsive to the pressure in said passageway intermediate said first and said second `control devices.

8.1m a refrigerating system for cooling a space, an evaporator arranged in heat exchange relation with such space and having an inlet and an outlet, insulation around such space, a plurality of refrigerant compressors located externally of said insulation and said space and each provided'with a suction and a discharge port, a condenser located Aexternally of said insulation and said space vand having an inlet and an outlet and varranged to .be cooled whereby vaporous refrigerant may be condensed therein,

a first .conduit `connecting said discharge port of .one of said compressors to said condenserinlet, a second conduit connecting said discharge port of a second of'saidcompressors-to said first compressor suction port, a first ,and a second section of small ybore `iiuid liow controlling tubing arranged in series between saidcondenser .outlet and said evaporator inlet, a fluid .container serially arranged between said tubing section, said container having an fiulet for receiving refrigerant from said rst tubing section and liquid lrefrigerant to Asaid second tubing section, .a ithird section -ofismall bore fluid flow controlling tubing serially arranged between said container inlet and said first Vtubing section, means including said first compressor for eliminating flash gas from the refrigerant intermediate said first and said third tubing sections, said container having a second outlet located at an elevation higher than said container first outlet, fiuid ow passageway means including a fourth vsection .of Small bore fluid flow 'controlling tubing connecting said container second outlet with said second compressor suction port, a third conduit .connecting said discharge port of .a third of lsaid compressors with said second compressor inlet port, a fourth conduit connecting said evaporator outlet with said third compressor inlet port, at least a ,portion -of f said fourth ytubing section being arranged in heat exchange relation with :fluid in said third conduit, at least a portion lof said `second tubing section being arranged in heat exchange relation with yfluid in said fourth conduit, a `thermostatic expansion valve .arranged in series .between-said ;condenser.outle tand Said first itubing section, ,said valve having a pressure sensitive ielementand a temperature sensitive element, said second .and third tubing sections and ,at least a portion of Said first Atubing section andrsaid .container being located so as to .be protected from .ambient `temperatures by Sad insulation, a length of said fourth conduit and said third conduit .and saidfourth .tubing .section being exposed to ambient temperature, lsaid `temperature sensitive element ,being arranged in heat-exchange relation with .an intermediate portion of saidffourthconduit length, insulating covering said temperature element and l'said fourth conduit intermediate portion, valve means normally preventing fluid ow to Said first tubing section, means responsive to la function of ythe operating condition of said evaporator .for controlling said first compressor imeans rendering said valve means .in condition to permit fluid flow concurrently with the operating of saidfirst compressor, means ,responsivefto an .operating condition of said first compressor to control said Secondcompressor, and means responsive to an operating condition lof said second compressor to control said third compressor.

9.. The combination lof claim 8 -in which a second evaporator is .arranged in heat exchange .relation with the fluid passed bysaid first tubing section, said second evaporator having an outletcommunicatively connected to said firstcompressorinletland being supplied with a controlled quantity of refrigerant from .said condenser.

1.0. Ina refrigerating system, a high ipressure side including acompressorhaving an inlet andan outlet, alow pressure side, .a thermostatic expansion valve having `an nletandan outlet and a1temperature sensitive bulb, fluid flow means .connecting said valve inlet to said high side on the loutletside of said compressor, .fluid flow means connecting said valve outlet to said low side, uid flow means connecting .said low side to said high side on the inlet side of said compressor, said lbulbbeing in heat exchange ,relation with said last named fluid iiow means, andheat 4tra-nsfermeans between said bulb and saidhigh side adjacent said `compressor outlet.

.11. In a refrigerating system, a high pressure side `including a compressor, a low pressure side including an .evaporator and a compressor connected in serial arrangement, a space to be ,cooled .in heat exchange relationship with Said evaporator, a thermostatic expansion valve located outside said space so as .to operate at a higher temperature than prevails therein and having an inlet and an outlet 'anda temperature sensitive bulb, fluid flow means connecting said valve inlet to said high side on the outlet sideo'f -said compressor, uid flow means connecting said valve -outlet yto said ylow side on the inlet side of said evaporator and including apair of serially arranged, small bore, fflow restricting tubes and a refrigerant heat exchanger serially connected between said tubes, and iiuid flow means connection, in by-pass arrangement with-rea `first outlet adjacent its bottom .portion .for supplying '1755 Spect to said low side, said high side to the cooling cham- :2m/gene ber of the said refrigerant heat exchanger for supplying refrigerant thereto for cooling the refrigerant passing directly through said heat exchanger to the said evaporator inlet, the bulb of said thermostatic valve being in heat exchange relationship with said low side between th: outlet of said evaporator and the inlet of said compressor so as to respond to the temperature therein prevailing for the purpose of controlling the amount of cooled refrigerant supplied to said evaporator.

12. In a refrigerating system, a high pressure side including a compressor, a low pressure side including an evaporator and a compressor connected in serial arrangement, a space to be cooled in heat exchange relationship with said evaporator, a thermostatic expansion valve located outside said space so as to operate at a tempera-- ture higher than prevails therein and having an inlet, outlet and a temperature sensitive bulb, lluid flow means connecting said valve inlet to said high side on the outlet side of said compressor, iiuid ow means connecting said valve outlet to said low side on the inlet side of said evaporator and including a pair of serially arranged small bore, flow restricting tubes and a refrigerant heat exchanger serially connected between said tubes, fluid ow means connecting, in by-pass arrangement with respect to said low side and said compressor therein, said high side to the cooling chamber of the said refrigerant heat exchanger for supplying refrigerant for cooling the refrigerant passing directly through said heat exchanger to said evaporator inlet and including a thermostatic expansion valve located outside said space and a small bore, ow restricting tube connected in serial arrangement, the bulb of the first said thermostatic expansion valve being in heat exchange relationship with said low side between the outlet of said evaporator and the inlet of said compressor so as to respond to the temperature therein prevailing for the purpose of controlling the amount of cooled refrigerant to be supplied to said evaporator and the bulb of the second said thermostatic expansion valve being in heat exchange relationship with the effluent of the cooling chamber of the said heat exchanger for controlling the amount of refrigerant supplied to the said cooling chamber of said heat exchanger.

13. In a refrigerating system, an evaporator, a condenser, at least a pair of refrigerant compressors each having an inlet and an outlet, conduit means connectinsaid compressors in series between said evaporator and said condenser for transferring refrigerant from said evaporator to said condenser, means for conveying refrigerant to said evaporator from said condenser and including at least a pair of serially connected ow cor:- trolling devices, a ash gas collecting vessel located in said conveying means intermediate said flow controlling devices and through which refrigerant that is supplied to said evaporator necessarily iiows, a second conduit means, including a length of small bore tubing, connecting said flash gas collecting vessel with said first named conduit means and at a point which is intermediate said cornpressors, said length of small bore tubing also being arranged in heat exchange relation with said first named conduit means intermediate said compressors.

14. The combination of claim 13 in which said flash gas vessel has an inlet and a pair of outlets, said inlet of said vessel being connected to receive refrigerant from one of said flow devices, one of said outlets of said vessel being located in a low portion of said vessel and connected to discharge refrigerant to the other of said ow devices, the other of said outlets of said vessel being elevated with respect to said one outlet and connected to said second conduit means.

15. In a refrigerating structure, an insulated cabinet having an internal chamber insulated from the external surroundings, an evaporator in heat exchange relation withsaid chamber for removing heat therefrom, a condenslng unit located externally of said cabinet, uid flow means connecting said unit and said evaporator into a closed system and including a vapor conveying conduit for flow of refrigerant from said evaporator to said unit and a liquid conveying conduit for ow of refrigerant from sald unit to said evaporator, each of said conduits having portions external of said cabinet, said liquid conveymg conduit including a restricting device, at least a portion of said restricting device being located within the insulated portion of said cabinet, a thermostatically controlled expansion device located in said liquid conveymg conduit externally of said cabinet and having a pressure sensitive element and a temperature sensitive element, means for heating said vapor conveying conduit, said temperature sensitive element being arranged 1n heat exchange relation with a portion of said vapor conveying conduit intermediate said heating means and sald condensing unit, said restricting device acting to reduce the pressure of the fluid owing therethrough and havlng a portion thereof in which the pressure of the uid is substantially at or above the saturated pressure of the same fluid at the ambient temperature of said cabinet, and means connecting said pressure element to said closed system at said portion of said restricting device.

16. The combination of claim l5 in which said condensing unit includes a pressure increasing device and said heating means comprises a heat transfer connection between said vapor conveying conduit and the discharge side of said pressure increasing device.

17. In a refrigerating structure, an evaporator, a condensing unit having two pressure increasing stages, tluid flow means connecting said unit and said evaporator into a closed system, said system including a vapor conveying conduit for W of refrigerant from said evaporator to said unit and a liquid conveying conduit for ow of refrigerant from said unit to said evaporator, said liquid conveying conduit including a restricting device, a thermostatically controlled expansion device located in said liquid conveying conduit having a pressure sensitive element and a temperature sensitive element, means for heating said vapor conveying conduit, said temperature sensitive element being arranged in heat exchange relation with a portion of said vapor conveying conduit intermediate said heating means and said condensing unit, and fluid pressure conveying means connecting said pressure element to respond to the pressure in said unit intermediate said pressure increasing stages.

18. The combination of claim 17 in which control means is provided to control the periods during which said condensing unit is effective to transfer refrigerant, a valve in saidliquid conveying conduit, control means connected to actuate said valve between open and closed positions and normally effective to maintain said valve closed, said last named means being operable during periods in which said condensing unit is transferring refrigerant to open said valve.

References Cited in the tile of this patent UNITED STATES PATENTS 1,106,244 Schliemann Aug. 4, 1914 2,116,100 Cracknell May 3, 1938 2,318,318 Lodwig May 4, 1943 2,402,802 Carter June 25, 1946 2,453,095 McGrath Nov. 2, 1948 2,500,688 Kellie Mar. 14, 1950 2,520,045 McGrath Aug. 22, 1950 FOREIGN PATENTS 133,012 Switzerland July 16, 1929 656,641 France May 10, 1929

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