Abstract:
High pressure drop and evaporator inefficiency due to the presence of lubricant in a refrigerant are avoided in a refrigeration system including a compressor ( 10 ) having an inlet ( 12 ) and an outlet ( 14 ). A gas cooler/condenser ( 16 ) receives compressed, lubricant containing refrigerant from the compressor outlet ( 14 ). Also included is an evaporator ( 48 ) for evaporating refrigerant and cooling another fluid and returning the refrigerant to the compressor inlet ( 12 ). A phase separator ( 36 ) is interposed between the gas cooler/condenser ( 16 ) and the evaporator ( 48 ) for receiving cooled refrigerant from the gas cooler/condenser ( 16 ). The phase separator ( 36 ) includes a chamber ( 62 ) having an inlet ( 34 ) connected to the gas cooler/condenser ( 16 ), an upper vapor outlet ( 38 ) connected to the compressor inlet ( 12 ), a liquid refrigerant outlet ( 40 ) and a lubricant outlet ( 78 ). A lubricant conduit ( 74 ) is connected to the lubricant outlet ( 78 ) and to the compressor inlet ( 12 ) for delivering lubricant separated in the phase separator ( 36 ) to the compressor ( 10 ) for lubrication purposes and a bypass conduit  42  is connected to the vapor outlet  38  and to the compressor inlet ( 12 ) to deliver the vapor stream to the compressor ( 10 ).

Description:
FIELD OF THE INVENTION 
     This invention relates to vapor compression refrigeration systems used for refrigeration and/or air conditioning purposes, whether or not employed as part of heat pump systems. 
     BACKGROUND OF THE INVENTION 
     State of the art refrigeration systems operating on the vapor compression cycle conventionally feed the evaporator with refrigerant that is in both the liquid phase and the vapor phase. In a typical system, the vapor phase refrigerant is about 30% of the total mass flow rate. Inasmuch as refrigerant vapor has a lower density than liquid refrigerant, a higher speed of the mixture is required when the mass flow rate is kept constant if the percentage of the mixture in the vapor phase is increased. This leads to a higher pressure drop inside the conduits in the evaporator than would be the case for a liquid or a two phase fluid where a lesser percentage of the total mass flow rate was in the vapor phase. 
     As is well known, high pressure drops are highly undesirable in systems operating on the vapor compression cycle. High pressure drops lead to heat exchange inefficiency,the requirement for oversized heat exchangers with flow paths of a larger total cross sectional area to minimize the pressure drop, increased compressed energy costs and the like. 
     To solve these difficulties, it has been proposed in, for example, U.S. Pat. No. 4,341,086 issued Jul. 27, 1982 to Ishii to employ a phase separator located downstream of an expansion device that in turn receives compressed refrigerant from the condenser or gas cooler of the system. The phase separator provides liquid refrigerant to the evaporator and provides for bypassing of the evaporator by the vapor phase. Consequently, the velocity of the refrigerant through the vapor is considerably reduced because only liquid phase refrigerant is entering it. In addition, there may be improved distribution of refrigerant on the inlet side of the evaporator leading to increased efficiency of the evaporator. 
     However, and as is also well known, it is conventional to employ a lubricant in the refrigerant to provide lubrication of the compressor during system operation. In the Ishii system, and those like it, the lubricant is frequently dissolved in the liquid refrigerant or of a density much more closely approaching the density of the liquid refrigerant than the refrigerant vapor and as a consequence is fed through the evaporator with the liquid refrigerant. The lubricant can adversely affect heat exchange within the evaporator and thus some of the advantages of phase separation taught by Ishii are lost. 
     U.S. Pat. No. 5,996,372 issued Dec. 7, 1999 to Koda et al. discloses the use of an accumulator intended for use in a refrigeration system and which provides a means for separating lubricant. However, the use of the accumulator at a particular location in a system to achieve maximum efficiency is not particularly well described. Moreover, the accumulator itself, with its provision for oil separation is unduly complicated and costly. 
     The present invention is directed to overcoming one or more of the above problems. 
     SUMMARY OF THE INVENTION 
     It is the principal object of the invention to provide a new and improved refrigeration system. More specifically, it is an object of the invention to provide such a system with a means for separating refrigerant into liquid and vapor phases before it is flowed to an evaporator along with provision for assuring that lubricant contained within the refrigerant is constantly circulated to prevent lack of lubrication of the compressor during operation. 
     An exemplary embodiment of the invention achieves the foregoing objects in a structure including a compressor having an inlet and an outlet. A heat exchanger is provided for receiving compressed, lubricant containing refrigerant from the compressor outlet and cooling the refrigerant. Also included is an evaporator for evaporating refrigerant and cooling another fluid and returning the refrigerant to the compressor inlet. A phase separator is interposed between the heat exchanger and the evaporator for receiving cool refrigerant from the heat exchanger. The phase separator includes a chamber having an inlet connected to the heat exchanger, an upper vapor outlet adapted to be connected to the compressor inlet for delivering a vapor stream thereto and a liquid refrigerant outlet at a first level in a lower part of the chamber and connected to the evaporator. The phase separator also includes a lubricant outlet at a second level in the lower part of the chamber which is different from the first level. A lubricant conduit is connected to the lubricant outlet and to the compressor inlet for delivering lubricant separated in the phase separator to the compressor to lubricate the same by discharging lubricant into the vapor stream. Also included is a bypass conduit connected to the vapor outlet and to the compressor inlet to deliver the vapor stream to the compressor. 
     In a highly preferred embodiment, the lubricant conduit terminates in an eductor located in one of the vapor outlet and the bypass conduit. 
     In an even more preferred embodiment, the lubricant conduit is a capillary conduit having one end located in the chamber and serving as the lubricant outlet and an opposite end located in the vapor outlet serving as the eductor. 
     In one embodiment, the lubricant outlet is located below the liquid refrigerant outlet. 
     In an even more preferred embodiment of the system, the same includes a suction line heat exchanger having first and second flow paths in heat exchange relation with one another. The first flow path connects the heat exchanger and the phase separator and the second flow path connects the bypass conduit and the evaporator to the compressor inlet. 
     Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of a refrigeration system made according to the invention; and 
     FIG. 2 is an enlarged sectional view of a phase separator made according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of a refrigeration system made according to the invention is illustrated in the drawings and will be described as a system operating with conventional refrigerant as, for example, R134a or any of the commercially and environmentally acceptable refrigerants sold under the trademark FREON®. However, it is to be understood that the system can be employed advantageously in other vapor compression systems using other refrigerants. It may also be used as part of a vapor compression system utilizing atranscritical fluid as a refrigerant as, for example, carbon dioxide. No limitation to any particular type of refrigerant, whether conventional or transcritical, is intended except insofar as expressed in the appended claims. 
     Referring to FIG. 1, the system includes a compressor  10  having an inlet  12  and an outlet  14 . The outlet  14  is connected to a heat exchanger  16 . In a system using conventional refrigerants, the heat exchanger  16  will be a condenser whereas if the system is employing transcritical refrigerants such as carbon dioxide, it will serve as a gas cooler. In the usual case, the gas cooler/condenser  16  will cool the compressed refrigerant received from the compressor outlet  14  by passing ambient air through the heat exchanger  16  in heat exchange relation with the compressed refrigerant. The refrigerant will thus be cooled and/or condensed and will exit an outlet  18  of the heat exchanger as a high pressure fluid. 
     The heat exchanger outlet  18  is connected to one flow path of a suction line heat exchanger  20  and enters the same at an inlet  22 . The suction line heat exchanger  20  is optional and is more apt to be used in a transcritical refrigerant system than in one employing conventional refrigerants. However, it may be employed in both. The high pressure refrigerant exits the suction line heat exchanger via an outlet  24 , still at high pressure but cooled further within the suction line heat exchanger  20 . In this regard. refrigerant vapor enters the suction line heat exchanger  20  at an inlet  26  to exit at an outlet  30 . The inlet  26  and outlet  30  are connected by a second flow path within the suction line heat exchanger  20  which is in heat exchange relation with the first flow path that extends between the inlet  22  and the outlet  24 . As illustrated, the flow is counterflow but cross flow or concurrent flow may be employed in some instances. 
     The cooled refrigerant exiting the outlet  24  of the suction line heat exchanger  20  is then passed to an orifice  32  and discharged into an inlet  34  of a phase separator  36 . The phase separator  36 , as will be explained in greater detail hereinafter, separates the incoming refrigerant into three different fractions. A first is a gas or vapor phase which exits at an outlet  38 . A second is a liquid phase which exits at an outlet  40 . The phase separator  36  also acts to separate the usual lubricant contained in the refrigerant from the liquid phase  40  and direct it to the outlet  38 . 
     The outlet  38  is connected to a bypass conduit  42  which includes a conventional expansion valve  44 . The liquid phase refrigerant  40  exits the phase separator  36  to enter an inlet  46  for one flow path of an evaporator  48 . The evaporator refrigerant flow path includes an outlet  50  which is joined to the bypass conduit  42  at a junction  52  and then to the inlet  26  for the suction line heat exchanger. The evaporator  48  additionally includes a second flow path in heat exchange relation with the one just described through which a fluid media passes to be cooled within the evaporator. In some instances, as in air conditioning systems, this fluid media will be ambient air. In other instances, the fluid media could be a liquid such as brine or the like. 
     The purpose of the phase separator  36  is, as mentioned previously, to separate liquid refrigerant and gaseous refrigerant and bypass the latter around the evaporator  48 . As is well known, to achieve a desired degree of cooling of the media cooled in the evaporator  48 , a given mass flow rate of refrigerant through the evaporator must occur. For a given mass flow rate of the refrigerant (quality being defined by the percentage of the refrigerant in the gaseous or vapor phase with the quality of 100 being a flow of gas or vapor with no liquid and a quality of zero being a flow of all liquid and no vapor or gas), the higher the quality, the greater the velocity of the fluid through the evaporator  48  because of the difference in densities between the vapor or gas on the one hand and the liquid on the other. All other things being equal, higher refrigerant velocities in the evaporator  48  mean a greater pressure drop across the evaporator  48 . As is well known, excessive pressure drops in refrigeration systems are to be avoided. Consequently, in order to avoid high pressure drops, it is necessary that the passages within the evaporator interconnecting the inlet  46  and outlet  50  be made larger for higher refrigerant quality flows. This, of course, increases the size of the evaporator  48  as well as increases the cost in terms of the materials that must be employed therein. 
     Through the use of the phase separator  36 , the vast majority of vapor and/or gaseous refrigerant bypasses the evaporator with the result being that the refrigerant quality passing through the evaporator  48  is lower than would otherwise be the case. This in turn reduces pressure drop and allows minimization of the size of the evaporator  48 . 
     The quality of refrigerant entering the evaporator from the phase separator can be closely regulated through the use of the expansion valve  44  which typically would respond to the temperature of the refrigerant at a desired point in the system. 
     One problem accompanies the use of such a system. As is well known, the refrigerants employed in systems of this sort typically include a lubricant for lubricating the compressor  10  during its operation. The lubricant typically will travel with the liquid phase refrigerant because of its relatively high density. In some instances, the lubricant may have a density greater than that of the liquid refrigerant while in others, it may be less than that of the liquid refrigerant. 
     When the mass flow of gas through the bypass conduit  42  is high, the flow of refrigerant exiting the evaporator  48  at the outlet  50  will typically be diminished which, in turn, will mean that the content of lubricant in the stream being returned to the compressor inlet  12  will be reduced. 
     Furthermore, it is desirable that a lubricant within the evaporator  48  be avoided entirely because of its poor thermal conductivity which, in turn, reduces efficiency of the evaporator  48 . 
     FIG. 2 illustrates one construction of the phase separator  36  that is designed to both assure a constant stream of lubricant to the compressor inlet  12  while minimizing or eliminating the passage of lubricant to the evaporator  48 . While it is illustrated as one that is useful in systems where the lubricant has a greater density than the liquid refrigerant, as explained in greater detail hereinafter, it is useful where the converse is true, i.e., the lubricant has a lesser density than that of the liquid refrigerant. 
     The phase separator includes a housing  60  defining a chamber  62 . The chamber  62  may be of any desired configuration so long as the desired separation can be achieved therein. The inlet  34  will typically, but not always, be toward the upper end of the chamber  62  while the vapor or gas outlet  38  will be at the upper end of the chamber  62  or at least near the upper end of the chamber  62 . 
     On the other hand, the outlet  40  will be near the lower end of the chamber. 
     As illustrated in FIG. 2, a body of separated lubricant  64  has an upper level at  66 . Above the lubricant  64  is a body  68  of liquid refrigerant having an upper level  70  which is below the vapor or gas outlet  38 . The outlet  40  includes a standpipe or the like that extends inwardly into the chamber  64  to a point above the lubricant level  66  and below the liquid refrigerant level  70  so as to provide an outlet opening  72  within the body  68  of liquid refrigerant for withdrawing the same from the phase separator and passing it to the inlet  46  of the evaporator  48 . 
     Also included is a capillary tube  74  having an upper end  76  and a lower end  78 . It will be observed that the lower end  78  of the capillary tube  74  is below the lubricant level  66  and within the body of lubricant  64 . Conversely, the upper end  76  of the capillary tube  74  extends into the outlet  38 . 
     In operation, refrigerant exiting the orifice  32  will enter the chamber  62  in the direction shown by an arrow  80 . Because of the difference in densities, the refrigerant will separate into gaseous refrigerant above the level  70  and liquid refrigerant below the level  70 . In addition, for the situation where the refrigerant  68  is less dense than the body  64  of lubricant, the lubricating oil will separate out at the level  66 . This level is, as mentioned previously, above the lower open end  78  of the capillary tube  74 . Consequently, refrigerant vapor passing through the outlet  38  will pass by the upper end  76  of the capillary tube  74  and draw lubricant through the capillary tube  74  out of the end  76  where it is discharged into the vapor stream passing from the outlet  38  ultimately to the junction  52 . From there it will pass with refrigerant through the suction line heat exchanger  20  and ultimately to the inlet  12  of the compressor  10 . It will be immediately appreciated that the upper end  76  of the capillary tube  74  serves as an eductor for lubricant into the vapor stream as long as vapor is passing from the inlet  34  to the outlet  38  and to the compressor inlet  12 . When such is not occurring, lubricant will not be educted through the end  76  but during such a situation, the compressor  10  will not be operating. 
     In some instances, the lubricant may have a lesser density than the density of the liquid refrigerant. The phase separator of the invention is useful in that situation as well. It is only necessary to locate the open upper end  72  at a lower position within the chamber  62  than the end  78  of the capillary tube  74  such that the latter will be located within the body of lubricant holding on the body of liquid refrigerant and the outlet  40  will have the end  72  disposed in the body of liquid refrigerant. 
     It will accordingly be appreciated that the invention provides a system whereby high pressure losses encountered in the evaporator  48  are limited through the use of the bypass line  42 . At the same time, adequate lubrication of the compressor  10  is achieved as a result of the eduction of lubricant from the phase separator  36  into the vapor stream that is being passed to the compressor inlet  12 . Further, the system avoids or minimizes the passage of lubricant into the evaporator  48  whereat it would have interfered with the operation of the evaporator  48 . Consequently, system efficiency is maximized, both through the elimination of inordinately high pressure drops within the evaporator  48  and the avoiding of the passing of lubricant to the evaporator  48 .