Patent Publication Number: US-9851130-B2

Title: Electronics cooling using lubricant return for a shell-and-tube style evaporator

Description:
BACKGROUND 
     The present invention relates to a refrigeration chiller, and more specifically, to an apparatus for recovering lubricant and ensuring high viscosity lubricant for a refrigerant compressor. 
     The compressor is typically provided with lubricant, such as oil, which is utilized to lubricate bearing and other running surfaces. The lubricant mixes with refrigerant, such that the refrigerant leaving the compressor includes a good quantity of lubricant. This is somewhat undesirable, as in the closed refrigerant system, it can sometimes become difficult to maintain an adequate supply of lubricant to lubricate the compressor surfaces. In the past, oil separators have been utilized immediately downstream of the compressor. While oil separators do separate the lubricant, they have not always provided fully satisfactory results. As an example, the lubricant removed from such a separator will be at a high pressure, and may have an appreciable amount of refrigerant still mixed in with the lubricant. This lowers the viscosity of the lubricant. The use of a separator can also cause a pressure drop in the compressed refrigerant, which is also undesirable. 
     SUMMARY 
     In one embodiment, the invention provides a refrigeration system including a compressor having a suction port and a discharge port, the compressor configured to receive refrigerant from the suction port, compress the refrigerant, and discharge the compressed refrigerant through the discharge port. The refrigeration system also has a condenser connected to the discharge port and configured to receive the compressed refrigerant from the compressor and condense the compressed refrigerant and an expansion device connected to the condenser and configured to receive the condensed refrigerant from the condenser. Also included as part of the refrigeration system is a shell-and-tube style evaporator having an inlet port, a first outlet port, and a second outlet port, wherein the evaporator is configured to receive refrigerant from the expansion device through the inlet port, evaporate a portion of the refrigerant, and discharge the evaporated portion of the refrigerant through the first outlet port to the suction port, the second outlet being in fluid flow communication with a location in the shell-and-tube style evaporator to which lubricant migrates during operation of the refrigeration system, the migrated lubricant mixing with liquid refrigerant in the shell-and-tube style evaporator to form a lubricant-liquid refrigerant mixture. In addition, the refrigeration system has a heat sink and a lubricant return line connecting the second outlet port to the suction port, wherein the lubricant return line is in heat exchange relationship with the heat sink such that heat is rejected from the heat sink to the lubricant-liquid refrigerant mixture to evaporate the liquid refrigerant in the lubricant-liquid refrigerant mixture to induce flow of the evaporated refrigerant and the lubricant in the lubricant-liquid refrigerant mixture to the compressor. 
     In another embodiment the invention provides a refrigeration system including a compressor having a suction port and a discharge port, the compressor configured to receive refrigerant from the suction port, a variable-speed-drive device connected to drive the compressor to compress the refrigerant and discharge the compressed refrigerant through the discharge port, a heat sink in heat exchange relationship to the variable-speed-drive device, a condenser connected to the discharge port and configured to receive the compressed refrigerant from the compressor and condense the compressed refrigerant and an expansion device connected to the condenser and configured to receive the condensed refrigerant from the condenser. The refrigeration system additionally includes a shell-and-tube style evaporator having an inlet port, a first outlet port, and a second outlet port, wherein the evaporator is configured to receive refrigerant from the expansion device through the inlet port, evaporate a portion of the refrigerant, and discharge the evaporated portion of the refrigerant through the first outlet port to the suction port, the second outlet being in fluid flow communication with a location in the shell-and-tube style evaporator to which lubricant migrates during operation of the refrigeration system, the migrated lubricant mixing with liquid refrigerant in the shell-and-tube style evaporator to form a lubricant-liquid refrigerant mixture. In addition, the refrigeration system has a lubricant return line connecting the second outlet port to the suction port, wherein the lubricant return line is in heat exchange relationship with the heat sink such that heat is rejected from the heat sink to the lubricant-liquid refrigerant mixture to cool the variable-speed-drive device and to evaporate the liquid refrigerant in the lubricant-liquid refrigerant mixture to induce flow of the evaporated refrigerant and the lubricant in the lubricant-liquid refrigerant mixture to the compressor. 
     In yet another embodiment the invention provides a refrigeration system including a compressor having a suction port and a discharge port, the compressor configured to receive refrigerant from the suction port, compress the refrigerant, and discharge the compressed refrigerant through the discharge port, a condenser connected to the discharge port and configured to receive the compressed refrigerant from the compressor and condense the compressed refrigerant and an expansion device connected to the condenser and configured to receive the condensed refrigerant from the condenser. The refrigeration system also has a shell-and-tube style evaporator having an inlet port, a first outlet port, and a second outlet port, wherein the evaporator is configured to receive refrigerant from the expansion device through the inlet port, evaporate a portion of the refrigerant, and discharge the evaporated portion of the refrigerant through the first outlet port to the suction port, the second outlet being in fluid flow communication with a location in the shell-and-tube style evaporator to which lubricant migrates during operation of the refrigeration system, the migrated lubricant mixing with liquid refrigerant in the shell-and-tube style evaporator to form a lubricant-liquid refrigerant mixture, a lubricant return line connecting the second outlet port to the suction port, a heat sink for an electronic device and a lubricant return heat exchanger connected to the lubricant return line. In addition, the refrigeration system has a coolant loop connecting the heat sink and the lubricant return heat exchanger and configured to circulate a coolant between the heat sink and the lubricant return heat exchanger such that heat from the electronic device is transferred to the heat sink, heat from the heat sink is transferred to the coolant, heat from the coolant is transferred to the lubricant-liquid refrigerant mixture in the lubricant return heat exchanger to cool the coolant, the heat sink, and the electronic device and to evaporate the liquid refrigerant in the lubricant-liquid refrigerant mixture to induce flow of the evaporated refrigerant and the lubricant in the lubricant-liquid refrigerant mixture to the compressor. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a refrigeration chiller. 
         FIG. 2  is a schematic illustration of an alternative embodiment of a refrigeration chiller. 
         FIG. 3  is a schematic illustration of yet another alternative embodiment of a refrigeration chiller. 
         FIG. 4  is a schematic illustration of yet another alternative embodiment of a refrigeration chiller. 
         FIG. 5  is a schematic illustration of a refrigeration chiller with a cooling loop. 
         FIG. 6  is a schematic illustration of a falling film shell-and-tube style evaporator. 
         FIG. 7  is a schematic illustration of a flooded shell-and-tube style evaporator. 
         FIG. 8  is a schematic illustration of a flowing pool shell-and-tube style evaporator. 
         FIG. 9  is a table titled “Minimum Refrigeration Capacity in Tons for Oil Entrainment up Suction Risers (Type L Copper Tubing)” 
         FIG. 10  is a schematic illustration of yet another alternative embodiment of a refrigeration chiller. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     Virtually all refrigeration chiller compressors employ or require the use of rotating parts to accomplish their compression purpose. Such rotating parts will, as is the case with virtually all rotating machinery, be carried in bearings, which will require lubrication. Typical also of most refrigeration chillers is the fact that at least some of the lubricant (typically oil) used to lubricate the bearings thereof will make its way into the refrigeration circuit as a result of its becoming entrained in the refrigerant gas that is discharged from the system&#39;s compressor. The embodiments described herein may employ at least one oil separator. The oil separator is able to remove some lubricant from a lubricant-refrigerant mixture, but is not able to remove all of the lubricant from the lubricant-refrigerant mixture. In a similar fashion, the oil separator is not able to remove only lubricant from the lubricant-refrigerant mixture, but rather, the oil separator removes lubricant with some refrigerant included therein. During the compression process, lubricant may be mixed with refrigerant resulting in a lubricant-refrigerant mixture. 
     A refrigeration system  12 , schematically illustrated in  FIG. 1 , includes a compressor  14 , a condenser  18 , an expansion device  22 , and an evaporator  26 , all of which are fluidly connected for flow to form a refrigeration circuit. The compressor may be, by way of example only, a centrifugal compressor, a screw compressor or a scroll compressor. The expansion device  22  may be, by way of example only, an expansion valve. The refrigeration system  12  further includes an oil separator  30  and a heat exchanger  34 . 
     All embodiments described herein include the evaporator  26  which may be one of a falling film shell-and-tube style evaporator (see  FIG. 6 ), a flooded shell-and-tube style evaporator (see  FIG. 7 ), a flowing pool shell-and-tube style evaporator (see  FIG. 8 ), or a variant of at least one of these evaporators. Additional information regarding the falling film shell-and-tube style evaporator can be found in U.S. Pat. No. 6,868,695, which is hereby incorporated by reference. Additional information regarding the flooded shell-and-tube style evaporator can be found in U.S. Pat. No. 4,829,786, which is hereby incorporated by reference. Additional information regarding the flowing pool shell-and-tube style evaporator can be found in U.S. Pat. No. 6,516,627, which is hereby incorporated by reference. For ease of describing the various embodiments herein, only the term evaporator will be used. The evaporator  26  serves to facilitate a vaporized refrigerant and lubricant-liquid refrigerant mixture adsorb heat from a medium to be cooled. In addition, the evaporator  26  allows lubricant to become concentrated in the lubricant-liquid refrigerant mixture that is not vaporized in the evaporator. 
     All of the embodiments described herein include the condenser  18 . The condenser  18  utilized by the various embodiments may be a condenser or it may be a combination condenser/subcooler. If utilized, the subcooler portion serves to further cool the refrigerant. For ease of describing the various embodiments herein, only the term condenser will be used. 
     Returning now to the embodiment illustrated in  FIG. 1 , the compressor  14  includes a suction port  38 , and a discharge port  42 . First and second lubricant return lines  46 ,  50  provide lubricant to lubricate the compressor  14 . The compressor  14  is configured to receive refrigerant from the suction port  38 , compress the refrigerant, and discharge the compressed refrigerant from the discharge port  42 . In operation, the compressor  14  compresses refrigerant gas, heating it and raising its pressure in the process, and then delivers the refrigerant to the oil separator  30  and then to the condenser  18 . In the illustrated embodiment a screw compressor  14  is used, but use of other types of compressors  14 , such as a centrifugal compressor, in the refrigeration system  12  is contemplated. The illustrated embodiment includes the oil separator  30 , but an alternative embodiment may not include the oil separator  30 . 
     The condenser  18  is connected to the oil separator  30  and is configured to receive the compressed refrigerant and condense it. The gaseous refrigerant delivered into the condenser  18  is condensed to liquid form by heat exchange with a cooling fluid, such as water or glycol. In some types of refrigeration systems  10 , ambient air, as opposed to water, is used as the cooling fluid. The condensed refrigerant, which is still relatively hot and at relatively high pressure, flows from the condenser  18  to and through the expansion device  22 . 
     The expansion device  22  is connected to the condenser  18  and is configured to receive the condensed refrigerant from the condenser  18 . In the process of flowing through the expansion device  22 , the condensed refrigerant undergoes a pressure drop which causes at least a portion thereof to flash to refrigerant gas and, as a result, causes the refrigerant to be cooled. In some embodiments a restrictor is used in place of or in conjunction with the expansion device  22 . 
     The now cooler two-phase refrigerant is delivered from the expansion device  22  into the evaporator  26 , where it is brought into heat exchange contact with a heat exchange medium, such as water or glycol. The heat exchange medium flowing through a tube bundle  54 , having been heated by the heat load which it is the purpose of the refrigeration chiller to cool, is warmer than the refrigerant that is brought into heat exchange contact with and rejects heat thereto. The refrigerant is thereby warmed and the majority of the liquid portion of the refrigerant vaporizes. 
     The medium flowing through the tube bundle  54  is, in turn, cooled and is delivered back to the heat load which may be the air in a building, a heat load associated with a manufacturing process or any heat load which it is necessary or beneficial to cool. After cooling the heat load the medium is returned to the evaporator  26 , once again carrying heat from the heat load, where it is again cooled by vaporized refrigerant and the lubricant-liquid refrigerant mixture in an ongoing process. In some embodiments the lubricant migrates from the compressor  14  to the evaporator  26  using the same path as the refrigerant, and may mix with the refrigerant at an earlier point in the refrigeration cycle. 
     The evaporator  26  includes first and second outlet ports  28 ,  32 . The refrigerant vaporized in the evaporator  26  is drawn out of the evaporator  26  by the compressor  14  which re-compresses the refrigerant and delivers it to the oil separator  30  and then the condenser  18 , likewise in a continuous and ongoing process. 
     The lubricant entrained in the stream of refrigerant gas delivered from the compressor  14  to the oil separator  30  is separated in the oil separator  30 . Lubricant is then passed from the oil separator  30  to the first lubricant return line  46 . The first lubricant return line  46  passes through the heat exchanger  34  where it is brought into thermal contact with the lubricant in the second lubricant return line  50 . After leaving the heat exchanger  34 , the first lubricant return line  46  returns to the compressor  14  where the lubricant is used to lubricate the compressor  14 . Lubricant-liquid refrigerant mixture in the evaporator  26  leaves the evaporator  26  via the second outlet port  32 , usually on a bottom portion of the evaporator  26 . In an alternative embodiment the second lubricant return line  50  returns to the suction port  38 , as shown in  FIG. 2 . 
     The lubricant-liquid refrigerant mixture that has exited the evaporator  26  via the second outlet port  32  enters the second lubricant return line  50  at the saturated liquid temperature of the evaporator  26 . The second lubricant return line  50  passes through the heat exchanger  34  where it is in thermal contact with the lubricant in the first lubricant return line  46 , causing the refrigerant in the second lubricant return line  46  to evaporate. Lubricant that is drawn out of the second outlet port  32  exits the heat exchanger  34  in droplets, as opposed to slugs, by oil entrainment. The second lubricant return line  50  is downstream of the heat exchanger  34  and is sized and configured with regard to a saturated suction temperature and a refrigeration capacity of the refrigeration system  12 , according to recognized standards such as the table illustrated in  FIG. 7 . The table illustrated in  FIG. 7  is titled “Minimum Refrigeration Capacity in Tons for Oil Entrainment up Suction Risers (Type L Copper Tubing)” and can be found on page 1.20 of the 2010 ASHRAE Handbook (Refrigeration), which is published by the American Society of Heating, Refrigeration, and Air-Conditioning Engineers and has an ISBN number of 978-1-933742-81-6. After leaving the heat exchanger  34 , the lubricant-liquid refrigerant mixture in the second lubricant return line  50  returns to the compressor  14  where the lubricant is used to lubricate the compressor  14 . 
     Routing the second lubricant return line  50  through the heat exchanger  34  will create a thermosiphon effect ensuring lubricant return and will result in liquid lubricant and superheated refrigerant vapor returning to the compressor  14  resulting in improved compressor  14  performance. Routing the first lubricant return line  46  through the heat exchanger  34  will reduce the temperature of the lubricant therein and improve the viscosity of the lubricant therein thus improving compressor lubrication, and also lowering sound. The heat exchanger  34  acts as a thermosiphon to ensure that the lubricant-liquid refrigerant mixture passes through the heat exchanger  34 . That is, the density of the refrigerant in the first lubricant return line  46  and the mixture that has adsorbed heat from the heat exchanger  34  is different due to the lubricant-liquid refrigerant mixture in the heat exchanger  34  having adsorbed heat and the refrigerant in the heat exchanger  34  being evaporated; this difference in density provides a motive force, i.e. a thermosiphon, to move the mixture through the heat exchanger  34 . 
     The embodiment illustrated in  FIG. 1  has several benefits. The heat exchanger  34  allows parasitic heat to be removed from the first portion of refrigerant, thus improving the viscosity of the lubricant-liquid refrigerant mixture. In addition, removing the parasitic heat allows the lubricant-liquid refrigerant mixture that has passed through the evaporator  26  to be superheated, thus improving the quality of the mixture to the compressor  14  and avoiding depressing the suction superheat to the compressors. Furthermore, removing the parasitic heat improves the flow and lowers the temperature of the lubricant passing through the heat exchanger  34  thus passing the cooled lubricant to the compressor  14  which improves compressor lubrication and lowers noise levels. Finally, removing the parasitic heat assists in creating a thermosiphon to the compressor which further minimizes any parasitic losses due to the cooling requirements. 
       FIG. 2  illustrates an alternative embodiment of the refrigeration system  12  illustrated in  FIG. 1  and the same components are assigned the same numerals of reference but will not be described again herein to avoid repetition. In describing the alternative embodiment illustrated in  FIG. 2 , only the differences between the embodiment illustrated in  FIG. 1  and the alternative embodiment will be described. 
     The compressor  14  illustrated in  FIG. 2  is driven by a variable speed drive (VSD), which requires cooling to function properly. An alternative embodiment may include the oil separator  30 . The gaseous refrigerant delivered into the condenser  18  is condensed to liquid form by heat exchange with a cooling fluid. The condensed refrigerant, which is still relatively warm and at relatively high pressure, flows from the condenser  18  to and through the expansion device  22 . 
     Before reaching the expansion device  22 , a first portion of refrigerant is directed to a VSD heat sink  66 . The VSD heat sink  66  serves to cool the VSD. Other components can be cooled in place of or in addition to the VSD heat sink  66 . Other components that may need cooling include, by way of example only, electronics, a load inductor or diodes. As the condensed first portion of refrigerant passes through the VSD heat sink  66 , the first portion of refrigerant absorbs heat from the VSD heat sink  66 , thus cooling the VSD. After leaving the VSD, the first portion of refrigerant passes through the heat exchanger  34 . 
     The first portion of refrigerant is in thermal contact with refrigerant that has passed through the evaporator  26  while the first portion is in the heat exchanger  34 . The refrigerant that has passed through the evaporator  26  absorbs heat from the first portion of refrigerant. In an alternative embodiment, the VSD heat sink  66  and the heat exchanger  34  are combined. After the first portion of refrigerant has shed heat to the refrigerant that has passed through the evaporator  26 , the first portion of refrigerant is combined with the refrigerant from the condenser  18  that did not pass through the VSD heat sink  66 . In the illustrated embodiment the first portion of refrigerant is combined with the refrigerant from the condenser  18  before the expansion device  22 . In yet another alternative embodiment (illustrated in phantom in  FIG. 2 ) the two are mixed together after refrigerant which did not pass through the VSD heat sink  66  passes through the expansion device  22 . In this alternative embodiment, the refrigeration line connecting the heat exchanger  34  to the point after the expansion device  22  where the two refrigerants are mixed may be sized to restrict the flow of refrigerant, and/or it may include an additional expansion device. 
     After the refrigerant passes through the expansion device  22  it enters the evaporator  26  where heat is exchanged and lubricant is mixed as described with regard to the embodiment illustrated in  FIG. 1 . Warmed gaseous refrigerant leaves the first outlet port  28  and enters the suction port  38  of the compressor  14 . Lubricant-liquid refrigerant mixture leaves the evaporator  26  through the second outlet port  32  and passes through the heat exchanger  34 , where the lubricant is in thermal contact with the first portion of refrigerant. After absorbing heat from the first portion of refrigerant, refrigerant from the lubricant-liquid refrigerant mixture evaporates inducing the flow of the evaporated refrigerant and lubricant-liquid refrigerant mixture to the suction port  38  of the compressor  14 . In an alternative embodiment, the lubricant-liquid refrigerant mixture passes through a second expansion valve after leaving the evaporator  26  and before entering the heat exchanger  34  so that the pressure of the lubricant-liquid refrigerant mixture is reduced, thus evaporating refrigerant and cooling the mixture. In yet another alternative embodiment the second lubricant return line  50  returns the lubricant-liquid refrigerant mixture to an auxiliary suction port, as illustrated in  FIG. 1 . In yet another alternative embodiment the lubricant-liquid mixture that passes the heat exchanger  34  does not pass through the expansion device  22 , instead, the lubricant-liquid mixture that has passed through the heat exchanger  34  is passed directly to the evaporator  26 . 
     The heat exchanger  34  acts as a thermosiphon to ensure that the lubricant-liquid refrigerant mixture passes through the heat exchanger  34 . That is, the density of the refrigerant that has passed through the VSD heat sink  66  and the mixture that has adsorbed heat from the heat exchanger  34  is different due to the lubricant-liquid refrigerant mixture in the heat exchanger  34  having adsorbed heat and the refrigerant in the heat exchanger  34  being evaporated; this difference in density provides a motive force, i.e. a thermosiphon, to move the mixture through the heat exchanger  34 . 
     The embodiment illustrated in  FIG. 2  has several benefits. The heat exchanger  34  allows parasitic heat to be removed from the first portion of refrigerant, thus providing additional subcooling enhancing the performance of the evaporator  26 . In addition, removing the parasitic heat allows the lubricant-liquid refrigerant mixture that has passed through the evaporator  26  to be superheated, thus improving the quality of the mixture to the compressor  14  and avoiding depressing the suction superheat to the compressor  14 . Furthermore, removing the parasitic heat improves the flow and raises the temperature of the lubricant passing through the heat exchanger  34  thus passing the warmed lubricant to the compressor  14  which improves compressor lubrication. Finally, removing the parasitic heat assists in creating a thermosiphon to the compressor  14  which further minimizes any parasitic losses due to the VSD cooling requirements. 
       FIG. 10  illustrates an alternative embodiment of the refrigeration system  12  illustrated in  FIG. 1  and the same components are assigned the same numerals of reference but will not be described again herein to avoid repetition. In describing the alternative embodiment illustrated in  FIG. 10 , only the differences between the embodiment illustrated in  FIG. 1  and the alternative embodiment will be described. 
     The compressor  14  illustrated in  FIG. 10  compresses refrigerant which is then passed into the condenser  18 , where the refrigerant is condensed to liquid form by heat exchange with a cooling fluid. The condensed refrigerant, which is still relatively warm and at relatively high pressure, flows from the condenser  18  to and through the expansion device  22 . 
     Before reaching the expansion device  22 , a first portion of refrigerant is directed to the heat exchanger  34 . The first portion of refrigerant is in thermal contact with refrigerant that has passed through the evaporator  26  while the first portion is in the heat exchanger  34 . The refrigerant that has passed through the evaporator  26  absorbs heat from the first portion of refrigerant. After the first portion of refrigerant has shed heat to the refrigerant that has passed through the evaporator  26 , the first portion of refrigerant is combined with the refrigerant from the condenser  18  that did not pass through the heat exchanger  34 . In the illustrated embodiment the first portion of refrigerant is combined with the refrigerant from the condenser  18  before the expansion device  22 . In an alternative embodiment the two are mixed together after refrigerant which did not pass through the heat exchanger  34  passes through the expansion device  22 . 
     After the refrigerant passes through the expansion device  22  it enters the evaporator  26  where heat is exchanged and lubricant is mixed as described with regard to the embodiment illustrated in  FIG. 1 . Warmed gaseous refrigerant leaves the first outlet port  28  and enters the suction port  38  of the compressor  14 . Lubricant-liquid refrigerant mixture leaves the evaporator  26  through the second outlet port  32  and passes through the heat exchanger  34 , where the lubricant is in thermal contact with the first portion of refrigerant. After absorbing heat from the first portion of refrigerant, refrigerant from the lubricant-liquid refrigerant mixture evaporates inducing the flow of the evaporated refrigerant and lubricant-liquid refrigerant mixture to the suction port  38  of the compressor  14 . In an alternative embodiment, the lubricant-liquid refrigerant mixture passes through a second expansion valve after leaving the evaporator  26  and before entering the heat exchanger  34  so that the pressure of the lubricant-liquid refrigerant mixture is reduced, thus evaporating refrigerant and cooling the mixture. In yet another alternative embodiment the second lubricant return line  50  returns the lubricant-liquid refrigerant mixture to an auxiliary suction port, as illustrated in  FIG. 1 . In yet another alternative embodiment the lubricant-liquid mixture that passes the heat exchanger  34  does not pass through the expansion device  22 , instead, the lubricant-liquid mixture that has passed through the heat exchanger  34  is passed directly to the evaporator  26 . 
     The embodiment illustrated in  FIG. 10  has several benefits. The heat exchanger  34  allows parasitic heat to be removed from the first portion of refrigerant, thus providing additional subcooling enhancing the performance of the evaporator  26 . In addition, removing the parasitic heat allows the lubricant-liquid refrigerant mixture that has passed through the evaporator  26  to be superheated, thus improving the quality of the mixture to the compressor  14  and avoiding depressing the suction superheat to the compressor  14 . Furthermore, removing the parasitic heat improves the flow and raises the temperature of the lubricant passing through the heat exchanger  34  thus passing the warmed lubricant to the compressor  14  which improves compressor lubrication. Finally, removing the parasitic heat assists in creating a thermosiphon to the compressor  14  which allows for more efficient operation of the compressor  14   
       FIG. 3  illustrates an alternative embodiment of the refrigeration system  12  illustrated in  FIG. 1  and the same components are assigned the same numerals of reference but will not be described again herein to avoid repetition. In describing the alternative embodiment illustrated in  FIG. 3 , only the differences between the embodiment illustrated in  FIG. 1  and the alternative embodiment will be described. 
     The refrigerant system  12  illustrated in  FIG. 3  uses the VSD and the VSD heat sink  66  as described in relation to the embodiment illustrated in  FIG. 2 . In the refrigeration system  12  illustrated in  FIG. 3  all refrigerant that is compressed by the compressor  14  is sent to the condenser  18 . After leaving the condenser  18 , the refrigerant passes through the expansion device  22  and enters the evaporator  26  where it mixes with a lubricant, as described in relation to the embodiment illustrated in  FIG. 1 . The lubricant-liquid refrigerant mixture is taken from the second outlet port  32  of the evaporator  26  and is fed through the VSD heat sink  66 , thus cooling the VSD and evaporating refrigerant in the lubricant-liquid refrigerant mixture. The VSD heat sink  66  acts as a thermosiphon to aid in the passage of the mixture through the VSD heat sink  66 . After passing through the VSD heat sink  66 , the lubricant-liquid refrigerant mixture is combined with the lubricant-liquid refrigerant mixture that passed through the first outlet port  28  of the evaporator  26 , and both are returned to the suction port  38  of the compressor  14 . In an alternative embodiment, the lubricant-liquid refrigerant mixture that passes through the second outlet port  32  is also passed through a second expansion valve before it is fed through the VSD heat sink  66 . In yet another alternative embodiment the refrigeration system  12  includes an oil separator which receives refrigerant directly from the compressor discharge port  42 , separates lubricant from the refrigerant, and returns the separated lubricant to the compressor  14 . In an alternative embodiment an oil separator and associated lines is combined with the system illustrated in  FIG. 3 . In yet another alternative embodiment the second lubricant return line  50  returns the lubricant-liquid refrigerant mixture to an auxiliary suction port, as illustrated in  FIG. 1 . 
     The embodiment illustrated in  FIG. 3  has several benefits. The refrigeration system  12  removes parasitic heat from the VSD heat sink  66 , thus improving the quality of the lubricant and refrigerant that is returned to the compressor  14 . In addition, the refrigeration system  12  inhibits the return of liquid refrigerant return to the compressor  14 , which can reduce the superheat. The refrigeration system  12  utilizes the heat provided by the VSD to vaporize the refrigerant from the lubricant-liquid refrigerant mixture passing through the VSD heat sink  66 , which improves flow and quality of the lubricant and raises the temperature of the lubricant returning to the compressor  14  which improves compressor  14  lubrication. Finally, removing the parasitic heat assists in creating a thermosiphon to the compressor  14  which further minimizes any parasitic losses due to the VSD cooling requirements. 
       FIG. 4  illustrates an alternative embodiment of the refrigeration system  12  illustrated in  FIG. 1  and the same components are assigned the same numerals of reference but will not be described again herein to avoid repetition. In describing the alternative embodiment illustrated in  FIG. 4 , only the differences between the embodiment illustrated in  FIG. 1  and the alternative embodiment will be described. 
     The refrigerant system  12  illustrated in  FIG. 4  uses the VSD and the VSD heat sink  66  as described in relation to the embodiment illustrated in  FIG. 2 . In the refrigeration chiller illustrated in  FIG. 4  refrigerant is compressed and passed to the oil separator  30 , where lubricant is removed from the refrigerant and the lubricant is then passed to the first lubricant return line  46 . The lubricant in the first lubricant return line  46  then passes through the heat exchanger  34 , where the lubricant in the first lubricant return line  46  is in thermal contact with the lubricant in the second lubricant return line  50 . The lubricant in the first lubricant return line  46  transfers heat to the lubricant in the second lubricant return line  50 . The lubricant in both the first and second lubricant return lines  46 ,  50  is then returned to the compressor  14 . 
     The refrigerant from the oil separator  30  is then passed to the condenser  18 . After leaving the condenser  18 , the refrigerant passes through the expansion device  22  and enters the evaporator  26  where it mixes with a lubricant, as described in relation to the embodiment illustrated in  FIG. 1 . Lubricant-liquid refrigerant mixture is taken from the bottom of the evaporator  26  and exits the second outlet port  32 , the lubricant-liquid refrigerant mixture then entering the second lubricant return line  50 . The second lubricant return line  50  passes through the heat exchanger  34  where the lubricant-liquid refrigerant mixture in the second lubricant return line  50  receives heat from the lubricant in the first lubricant return line  46 . The lubricant-liquid refrigerant mixture in the second lubricant return line  50  then passes through the VSD heat sink  66  where the lubricant-liquid refrigerant mixture receives heat from the VSD heat sink  66 . The refrigerant from the lubricant-liquid refrigerant mixture in the second lubricant return line  50  is vaporized as it passes through at least one of the heat exchanger  34  and the VSD heat sink  66 , thus creating a thermosiphon effect. After passing through the VSD heat sink  66 , the lubricant-liquid refrigerant mixture returns to the compressor  14 . In an alternative embodiment, the lubricant-liquid refrigerant mixture in the second lubricant return line  50  may pass through a second expansion valve before entering the heat exchanger  34 . Lubricant-liquid refrigerant mixture leaves the evaporator  26  through the first outlet port  28  and is passed to suction port  38  of the compressor  14 . In an alternative embodiment the second lubricant return line  50  returns to the suction port  38 , as shown in  FIG. 2 . 
     The heat exchanger  34  acts as a thermosiphon to ensure that the lubricant-liquid refrigerant mixture passes through the heat exchanger  34 . That is, the density of the refrigerant in the first lubricant return line  46  and the mixture that has adsorbed heat from the heat exchanger  34  is different due to the lubricant-liquid refrigerant mixture in the heat exchanger  34  having adsorbed heat and the refrigerant in the heat exchanger  34  being evaporated; this difference in density provides a motive force, i.e. a thermosiphon, to move the mixture through the heat exchanger  34 . 
     The refrigeration system  12  illustrated in  FIG. 4  provides several benefits. The lubricant in both the first and second lubricant return lines  46 ,  50  improves compressor  14  lubrication. The thermosiphon effect that is created by routing the second lubricant return line  50  through at least one of the heat exchanger  34  and the VSD heat sink  66  ensures lubricant is returned to the compressor  14 . The routing of the second lubricant return line  50  through the VSD heat sink  66  also ensures that superheated refrigeration vapor returns to the compressor  14  resulting in improved compressor performance and reliability. Another benefit of the refrigeration chiller is that the second lubricant return line  50  being routed through the heat exchanger  34  reduces the fluid temperature and improves the viscosity of lubricant delivered to the compressor  14  thus facilitating lubrication and lowering sound levels. Finally, removing the parasitic heat assists in creating a thermosiphon to the compressor  14  which further minimizes any parasitic losses due to the VSD cooling requirements. 
     A refrigeration system  12  with an electronics cooling loop  70  is schematically illustrated in  FIG. 5 . The refrigeration system  12  is similar to the refrigeration system  12  illustrated in  FIG. 3 . Thus the same components are assigned the same numerals of reference but will not be described again herein to avoid repetition. In describing the alternative embodiment illustrated in  FIG. 5 , only the differences between the embodiment illustrated in  FIG. 1  and the alternative embodiment will be described. 
     The refrigeration system  12  with an electronics cooling loop  70  includes the heat exchanger  34 . Lubricant-liquid refrigerant mixture is taken from the bottom of the evaporator  26  and is fed through the heat exchanger  34  where the mixture adsorbs heat. The heat exchanger  34  acts as a thermosiphon to ensure that the lubricant-liquid refrigerant mixture passes through the heat exchanger  34 , that is, the density of the refrigerant in a refrigerant return line  74  and the mixture that has adsorbed heat from the heat exchanger  34  is different due to the lubricant-liquid refrigerant mixture in the heat exchanger  34  having adsorbed heat and a portion of the refrigerant in the heat exchanger  34  being evaporated; this difference in density provides a motive force, i.e. a thermosiphon, to move the mixture through the heat exchanger  34 . After passing through the heat exchanger  34 , the lubricant-liquid refrigerant mixture is combined with the refrigerant in the refrigerant return line  74  and both are returned to the suction port  38 . In an alternative embodiment the lubricant-liquid refrigerant mixture is passed through a second expansion valve before it is fed through the heat exchanger  34 . In yet another alternative embodiment the heat exchanger  34  is arranged such that gravity provides the motive force to take lubricant-liquid refrigerant mixture from the evaporator  26 , pass it through the heat exchanger  34  and return it to the compressor  14 . In yet another alternative embodiment an oil separator, as described with regard to  FIG. 1 , is utilized with the embodiment illustrated in  FIG. 5 . In yet another alternative embodiment the second lubricant return line  50  returns the lubricant-liquid refrigerant mixture to an auxiliary suction port, as illustrated in  FIG. 1 . 
     The electronics cooling loop  70  contains a coolant, such as glycol. The electronics cooling loop  70  includes a circulation pump  76 , the heat exchanger  34 , and a heat sink  78 . The circulation pump  76  serves to circulate coolant in the cooling loop  70 , the heat exchanger  34  serves to facilitate the exchange of heat between the coolant in the coolant loop  70  and the lubricant-liquid refrigerant mixture from the evaporator  26 , and the heat sink  34  serves to adsorb heat from components that need cooling, such as, by way of example only, electronics, a load inductor, diodes or a variable speed drive. In one embodiment the heat exchanger  34  is a brazed plate heat exchanger. In the illustrated embodiment the coolant flows from the circulation pump  76  to the heat sink  78 , from the heat sink  78  to the heat exchanger  34 , and from the heat exchanger  34  to the coolant pump  76 . In an alternative embodiment, the coolant flows in the opposite direction. 
     The refrigeration system  12  with an electronics cooling loop  70  has several benefits. Lubricant-liquid refrigerant mixture that would ordinarily be trapped in the evaporator  26  is removed from the evaporator  26  and returned to the compressor  14  which helps to ensure adequate compressor lubrication. In addition, the lubricant-liquid refrigerant mixture that returns to the compressor  14  is of higher quality (in this case quality refers to the ratio of vapor to liquid refrigerant) because the heat adsorbed by the lubricant-liquid refrigerant mixture serves to evaporate refrigerant from the lubricant-liquid refrigerant mixture, in addition to inducing flow to the compressor. Beneficial component cooling is accomplished by the cooling loop  70 . The coolant loop  70  is also able to adsorb some heat from the components even when the compressor  14  is shut down, thus prolonging the time that the components may be run after the compressor  14  is not operating. In addition, the coolant loop  70  contains a liquid coolant and does not rely on refrigerant, so there is always liquid present in the cooling loop  70 . Yet another benefit of the refrigeration system  12  with electronics cooling loop  70  is that the heat sink  78  and/or electrical components to be cooled do not need to be in close proximity to the compressor  14 . 
     It is to be noted that by the development of the thermosiphonic flow from the heat exchanger  34  to the suction port  38 , as a result of the density differences between the refrigerant in the refrigerant return line  74  and the lubricant-liquid refrigerant mixture that has adsorbed heat from the heat exchanger  34 , and with the assistance of the motive force of gravity due to the arrangement of the evaporator  26  and the heat exchanger  34 , self-sustaining flow of the lubricant-liquid refrigerant mixture is established and maintained without the need for mechanical or electromechanical apparatus, valving or controls to cause or regulate the flow of lubricant-liquid refrigerant mixture. As such, the cooling arrangement of the present invention is reliable, simple and economical while minimizing the adverse effects on refrigeration system efficiency that are attendant in other refrigeration system oil cooling schemes. It is to be further noted that the rate of the flow of lubricant-liquid refrigerant mixture is proportional to the magnitude of heat exchange between the lubricant-liquid refrigerant mixture and the heat exchanger  34 , and by the arrangement of the evaporator  26  and the heat exchanger  34 . In an alternative embodiment, a restrictor is placed between the evaporator  26  and the heat exchanger  34  to limit flow of lubricant-liquid refrigerant mixture to a preset maximum flow. 
     Thus, the invention provides, among other things, a refrigeration system. Various features and advantages of the invention are set forth in the following claims.