Patent Publication Number: US-6662576-B1

Title: Refrigeration system with de-superheating bypass

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a high efficiency refrigeration system and more specifically, to a refrigeration system utilizing a bypass path to perform refrigerant de-superheating outside the condenser thereby increasing the overall system efficiency. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 is a block diagram of a conventional refrigeration system, generally denoted at  10 . The system includes a compressor  12 , a condenser  14 , an expansion device  16  and an evaporator  18 . These components are connected together via copper tubing such as indicated at  20  to form a closed loop system through which a refrigerant such as R-12, R-22, R-134a, R- 407 c, R-410a, ammonia, carbon dioxide or natural gas is cycled. 
     The main steps in the refrigeration cycle are compression of the refrigerant by compressor  12 , heat extraction from the refrigerant to the environment by condenser  14 , throttling of the refrigerant in the expansion device  16 , and heat absorption by the refrigerant from the space being cooled in evaporator  18 . This process, sometimes referred to as a vapor-compression refrigeration cycle, is used in air conditioning systems, which cool and dehumidify air in a living space, in a moving vehicle (e.g., automobile, airplane, train, etc.), in refrigerators and in heat pumps. 
     FIG. 2 shows the temperature-entropy curve for the vapor compression refrigeration cycle illustrated in FIG.  1 . The refrigerant exits evaporator  18  as a saturated vapor (Point 1), and is compressed by compressor  12  to a very high pressure. The temperature of the refrigerant also increases during compression, and it leaves the compressor as superheated vapor (Point 2). 
     A typical condenser comprises a single conduit formed into a serpentine-like shape with a plurality of rows of conduit lying in a spaced parallel relationship. Metal fins or other structures which provide high heat conductivity are usually attached to the serpentine conduit to maximize the transfer of heat between the refrigerant passing through the condenser and the ambient air. As the superheated refrigerant gives up heat in the upstream portion of the condenser, the superheated vapor becomes a saturated vapor (Point 2a), and after losing further heat as it travels through the remainder of condenser  14 , the refrigerant exits as saturated liquid (Point 3). 
     As the saturated liquid refrigerant passes through expansion device  16 , its pressure is reduced, and it becomes a liquid-vapor mixture comprised of approximately 20% vapor and 80% liquid. Also, its temperature drops below the temperature of the ambient air (Point 4 in FIG.  2 ). 
     Evaporator  18  physically resembles the serpentine-shaped conduit of the condenser. Air to be cooled is exposed to the surface of the evaporator where heat is transferred to the refrigerant. As the refrigerant absorbs heat in evaporator  18 , it becomes a saturated or slightly superheated vapor at the suction pressure of the compressor and reenters the compressor thereby completing the cycle (Point 1 in FIG.  2 ). 
     FIG. 3 shows the temperature-entropy curve for the vapor compression refrigeration cycle, in which the de-superheating process in the condenser is indicated explicitly. The pressure of the discharge vapor from the compressor has to be raised such that the phase-change temperature (known as the saturation temperature) at the saturation pressure can be large enough to reject heat at the condenser. This requires that the discharge vapor from the compressor is superheated as the entropy increases slightly over the compressor as shown in FIG.  2 . Typically one-third of a condenser is utilized for the de-superheating process in most air-conditioning and refrigeration systems. 
     This is a source of significant inefficiency in conventional refrigeration systems as the condenser must be larger and more costly than needed for the heat transfer function involving the phase-change of the refrigerant. Conversely, for a condenser of a given size, if the first one-third does not need to be devoted to de-superheating, greater subcooling could be achieved. 
     An additional benefit which could be achieved by performing the de-superheating step outside the condenser would be an improved energy-efficiency ratio (EER). This is defined as Qv/Wc, where Qv is the heat absorption by the evaporator of the system and Wc is the work done by the compressor. By increasing subcooling for a given size condenser, a greater quantity of liquid in the refrigerant would enter the evaporator. This would increase the cooling capacity Qv, thus the EER would also increase. Furthermore, as the condenser becomes more efficient, the condenser pressure decreases, reducing the required pressure lift across the compressor, thereby reducing the compressor work and accordingly increasing the EER. 
     FIG. 4 illustrates a modified temperature-entropy curve showing what would happen if the de-superheating step could be performed between the compressor and the condenser. Heat would be removed from the vapor discharged from the compressor, reducing the temperature of the vapor substantially while the saturation pressure is almost unchanged. Consequently, the vapor from the compressor could enter the condenser at or close to its saturation temperature and pressure. This is illustrated in the modified temperature-entropy curve of FIG. 4 between points  2   c  and  2   a . Up to now, however, no suitably cost effective technique has been available to eliminate the need for de-superheating in the condenser. 
     Therefore, a need clearly exists for a cost-effective way to achieve de-superheating at the inlet side of the condenser. The present invention seeks to meet this need. 
     SUMMARY OF THE INVENTION 
     According to the present invention, the de-superheating step is performed on the inlet side of the condenser, rather than in the condenser. To achieve this, a portion of liquid refrigerant exiting from the condenser is diverted into a bypass line from which it is re-injected into the primary refrigerant path at a location between the evaporator outlet and compressor inlet. In the bypass line, a secondary expansion valve is used to throttle the diverted liquid refrigerant from the condenser, thus decreasing the temperature substantially below the condenser outlet temperature. 
     The cooled refrigerant exiting the secondary expansion valve then passes through a heat exchanger which is thermally coupled to the primary refrigerant line between the compressor outlet and the condenser inlet. The heat exchanger removes heat from the refrigerant vapor exiting from the compressor, thus reducing its temperature. As a result, the refrigerant enters the condenser at or near its saturation temperature, and no portion of the condenser needs to be devoted to de-superheating. 
     Because the refrigerant pressure in the bypass line at the outlet of the heat exchanger is greater than the pressure at the evaporator outlet, a pressure differential compensating device is used to couple the outlet of the bypass line to the primary refrigerant line. The pressure differential compensating device can be either a vacuum generating device or a pressure-reducing device. 
     According to a first aspect of the invention, there is provided a refrigeration system including refrigerant compressing means, refrigerant condensing means, expansion means and evaporation means connected together to form a closed loop system with a refrigerant circulating therein, and a bypass line connected between the outlet of the condensing means and the inlet of the compressing means, the bypass line including a secondary expansion means, heat exchanging means to remove heat from the discharge vapor from the compressor between the outlet of the compressing means and an inlet of the condensing means, and a pressure differential accommodating means for mixing two vapors at two different pressures connecting the outlets of the evaporation means and the heat exchanging means to an inlet of the compressing means. 
     According to a second aspect of the invention, there is provided a refrigeration system comprised of a primary refrigerant path including a compressor, a condenser, a primary expansion device, and an evaporator connected together to form a closed loop system with a refrigerant circulating therein, and a bypass line connected between the outlet of the condenser and the inlet of the compressor, the bypass line including a heat exchanger thermally coupled to the primary refrigerant path between the compressor outlet and the condenser inlet to remove heat from the discharge vapor from the compressor, and a pressure differential accommodating device for mixing two vapors at two different pressures connecting the outlets of the evaporator and the heat exchanger to an inlet of the compressor. 
     Further according to the second aspect of the invention, the pressure differential accommodating means is a vacuum generating device with no moving parts such as a venturi tube, or a so-called “vortex tube” which is conventionally used to create two fluid steams of differing temperature from a single high pressure input stream. (Such a vortex generator is the subject of a copending U.S. provisional patent application entitled USE OF A VORTEX GENERATOR TO GENERATE VACUUM, Serial No. 60/356,059 filed in the names of Young Cho, Cheolho Bai, and Joong-Hyoung Lee on Feb. 11, 2002, the contents of which are hereby incorporated by reference.) 
     Further according to the second aspect of the invention, the pressure differential accommodating means is a pressure reducing device with no moving parts such as a capillary tube, an orifice, a valve, or a porous plug. The pressure reducing device is used in the bypass line which is maintained at a higher pressure than the evaporator. The pressure reducing device reduces the high pressure at the bypass line to the evaporator pressure so that two vapors can be mixed. 
     According to a third aspect of the invention, there is provided a method of increasing the efficiency of a refrigeration system comprised of a primary refrigerant path including a compressor, a condenser, a primary expansion device, and an evaporator connected together to form a closed loop system with a refrigerant circulating therein, the method comprising the steps of bypassing a portion of the refrigerant exiting the condenser into a secondary refrigerant line, passing the bypassed refrigerant through a heat exchanger thermally coupled to the primary refrigerant path between the compressor outlet and the condenser inlet to remove heat from the discharge vapor from the compressor, and passing the refrigerant exiting the heat exchanger and the refrigerant exiting the evaporator through a pressure differential accommodating device means that mixes two vapors at different pressures and feeding the refrigerant exiting the pressure differential accommodating device to an inlet of the compressor. 
     Providing a bypass path for performing de-superheating makes the condenser more efficient thereby reducing the condenser pressure, a phenomenon which decreases the pressure lift at compressor, and thus reduces the compressor work. Correspondingly, because de-superheating does not have to be done inside the condenser, the condenser becomes more efficient, and subcooling at the end of the condenser is increased. This increases the amount of liquid refrigerant after the throttling process through the main expansion valve. Thus, the heat absorption at the evaporator (often referred as the cooling capacity) increases. 
     The above-described benefits of the de-superheating bypass are achieved with diversion of 10-15% of the liquid refrigerant outflow from the condenser. At this level, reduced compressor work and increased cooling capacity are achieved. Since the EER (energy efficiency ratio) is defined as the ratio of the cooling capacity to compressor work, this increases the EER. 
     According to a fourth aspect of the invention, when more than 15%, for example, 30%, of the liquid refrigerant from the condenser is diverted to the bypass path, the cooling capacity is reduced due to the substantial decrease in the refrigerant mass flow rate circulating through the evaporator. By use of an adjustable valve in the bypass path, the bypass mass flow rate, and thus, the cooling capacity, can be varied according to the thermal load, whereby it is possible to operate an air conditioning or refrigeration system without frequent, highly energy-inefficient, ON-OFF operations of the compressor. This results in improved long-term seasonal energy efficiency ratio (SEER). 
     According to a fifth aspect of the invention, multiple evaporators can be employed, e.g., in a zoned cooling system. Thus, several small evaporators could be provided for separate rooms, with one condenser and one compressor. When all the rooms require cooling, the system can be operated with a 10% bypass rate to provide the maximum cooling capacity and the maximum efficiency. If the thermal load decreases, as when fewer rooms need to be cooled, the bypass rate can be increased to reduce the cooling capacity without the need to cycle the compressor on and off. This is quite beneficial because the repeated ON-OFF cycling of the compressor is a very energy-inefficient process. 
     The concepts of this invention are applicable to conventional single-refrigerant systems, and also to mixed-refrigerant systems using a combination of refrigerants selected to provide the desired combination of thermal and flammability characteristics. Such mixed-refrigerant systems may also include regenerative features which provide higher evaporator efficiency by increasing the percentage of liquid in the refrigerant as it enters the evaporator. Regenerative mixed refrigerant systems are disclosed, for example, in our U.S. Pat. No. 6,250,086 and 6,293,108, the contents of which are hereby incorporated by reference. 
     It is accordingly an object of this invention to provide an apparatus and method that eliminates the need for de-superheating to take place in the condenser of a refrigeration system. 
     It is also an object of the invention to increase the efficiency of known refrigeration systems by providing a cost-effective way of reducing the temperature and pressure of the discharge vapor from the compressor. 
     It is another object of the invention to increase the cooling capacity and EER of known refrigeration systems by providing a cost-effective way of reducing the temperature and pressure of the discharge vapor from the compressor. 
     A related object of the invention to allow use of smaller condensers in known refrigeration systems by providing a cost-effective way of reducing the temperature and pressure of the discharge vapor from the compressor. 
     An additional object of the invention is to provide a way of reducing the temperature and pressure of the discharge vapor from the compressor, which may be used in single-refrigerant systems and also in mixed-refrigerant systems, with and without regenerative features. 
     An additional object of the invention is to provide an improved refrigeration system in which the evaporator is connected to a substantially low pressure created by a vacuum-generating device thereby boosting the evaporator capacity. 
     An additional object of the invention is to provide an improved refrigeration system in which the mixing two different pressures using a vacuum generating device increases the suction pressure of the compressor, whereby the required pressure rise over the compressor is reduced, which, in turn, reduces the compressor work and increases the EER. 
     An additional object of the invention is to provide an improved refrigeration system in which the mixing two different pressure vapors are carried out using a vacuum generating device so that the pressure at the bypass line can be maintained at a higher pressure than the evaporator pressure. 
     An additional object of the invention is to provide an improved refrigeration system in which the mixing two different pressure vapors are carried out using a pressure-reducing device so that the pressure at the bypass line can be maintained at a higher pressure than the evaporator pressure. 
     Yet another object of the invention is to provide an improved refrigeration system in which de-superheating is performed outside the condenser in a bypass path to which refrigerant from the condenser outlet is diverted, into a bypass path, and in which the quantity of refrigerant diverted is controlled such that the cooling capacity can be adjusted to meet varying thermal requirements, whereby the system can be operated without the need for energy-inefficient repeated on and off cycling of the compressor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram of a conventional refrigeration system. 
     FIG. 2 shows a temperature-entropy curve for the conventional refrigeration system of FIG.  1 . 
     FIG. 3 shows a temperature-entropy curve for the refrigeration system of FIG. 1, where de-superheating process is indicated. 
     FIG. 4 shows a temperature-entropy curve for a refrigeration system in which de-superheating process is performed outside the condenser according to the present invention. 
     FIG. 5 shows a block diagram of an embodiment of the present invention in which a heat exchanger in a bypass line removes heat from the discharge vapor from the compressor, and a pressure differential accommodating device is used to mix two vapors at two different pressures. 
     FIGS. 6A and 6B illustrate the construction of a vortex generator which may be used as a pressure differential accommodating device according to the invention. 
     FIG. 7 illustrates the construction of a venturi tube which may be used instead of the vortex generator shown in FIGS. 6A and 6B. 
     FIG. 8 shows a block diagram of an embodiment of the present invention in which a heat exchanger in a bypass line removes heat from the discharge vapor from the compressor, and a pressure-reducing device is used at the bypass line to reduce the high pressure at the bypass line to a level at the evaporator so that two vapors at two different pressures can be mixed. 
     FIG. 9 is a block diagram showing application of the present invention to a zoned cooling system. 
     FIG. 10 is a block diagram showing application of the present invention to a mixed-refrigerant system. 
     Throughout the drawings, like parts are given the same reference numerals. 
    
    
     DETAILED DESCRIPTION 
     FIG. 5 illustrates in block diagram form, a first embodiment of the invention. The system of FIG. 5, generally denoted at  30 , is similar to that of FIG. 1, except that a secondary bypass path  32  is coupled between the outlet of condenser  14 , and the inlet of compressor  12 . Bypass path  32  includes a secondary expansion device  34 . A heat exchanger  36  thermally coupled between the outlet of compressor  12  and the inlet of condenser  14 , and a pressure differential accommodating device  38 , which mixes the refrigerant exiting the evaporator  18  and the heat exchanger  36  for return to the inlet of compressor  12 . Pressure differential accommodating device  38  is needed because, as shown, the pressure at the outlet of the evaporator may be lower than the pressure at the outlet of the heat exchanger. 
     The pressure differential accommodating device  38  can be either a vacuum generating device such as a vortex generator or a venturi tube or a pressure reducing device. The construction of a vortex generator is shown schematically in FIGS. 6A and 6B. 
     The design of the vortex generator, generally denoted at  40 , is derived from the so-called vortex tube, a known device which converts an incoming flow of compressed gas into two outlet streams—one stream hotter than and the other stream colder than the temperature of the gas supplied to the vortex tube. A vortex tube does not contain any moving parts. Such a device is illustrated in our U.S. Pat. No. 6,250,086, which is hereby incorporated herein by reference. 
     As illustrated in FIGS. 6A and 6B, vortex generator  40  is used to mix two vapors at different pressures into one stream. The present invention uses the vortex generator as a mixing means. It is comprised of a tubular body  60 , with an axial inlet  52  and a tangential inlet  54  at an inlet end  62 , and an outlet  58  at an opposite outlet end  64 . The interior construction of tube  60  at the inlet end is such that a high-pressure gas stream entering tangential inlet  54  travels along a helical path toward the outlet  58 . This produces a strong vortex flow in tube  60 , and a radial pressure differential due to the centrifugal force created by the vortex flow forces the vapor radially outward and produces high pressure at the periphery and low pressure at the axis. The low pressure allows fluid drawn in through axial inlet  52  to mix with the high-pressure helical stream and to exit with it through outlet.  58 . 
     Further information concerning vortex generator  40  may be found in the Cho, Bai, Lee application Ser. No. 60/356,059 mentioned above. 
     In the system illustrated in FIG. 5, the high-pressure tangential flow is provided through tube  54  from heat exchanger  36 , and the incoming stream at axial inlet  52  is provided from the outlet of evaporator  18 . Using a vacuum-generating device based on the vortex generator makes it possible to combine the refrigerant exiting from evaporator  18  and the higher pressure refrigerant exiting from heat exchanger  36  without the need for a costly pump having moving parts. 
     Other devices which rely on geometry and fluid dynamics may also be used to generate a vacuum which permits mixing the refrigerant streams exiting from evaporator  18  and heat exchanger  36 . For example, a device operating on the principle of a venturi tube may also be used. In such a device, as illustrated in FIG. 7 at  69 , a high pressure fluid stream (here, the refrigerant exiting from heat exchanger  36 ), enters axially into an elongated tube  70  having an interior diameter  72  which decreases gradually to a point of minimum diameter  74  and thereafter increases gradually toward an outlet end  76 . As the cross-sectional area decreases, the vapor stream is accelerated. According to Bernoulli&#39;s principle, the pressure decreases, and reaches a minimum at the so-called “throat corresponding to the point of minimum diameter  74  where a vacuum is created. 
     A radial inlet  78  is provided at the low-pressure point. This is connected to the outlet of evaporator  18  (see FIG.  5 ), thereby permitting mixing of the evaporator outflow with the axial stream from heat exchanger  36 . 
     Referring again to FIG. 5, in operation, a portion of the liquid refrigerant exiting from condenser  14  is diverted into bypass path  32 , for example, by a suitable valve (not shown). The diverted refrigerant passes through secondary expansion device  34  and then through heat exchanger  36  which performs the de-superheating function conventionally performed by the upstream portion of the condenser. 
     By proper selection of system parameters, in particular, the mass flow rate of refrigerant diverted to the bypass path, the refrigerant can be made to enter condenser  14  at or close to the saturation temperature, and the entire flow path through the condenser can be devoted to the phase-change operation by transfer of heat to the environment, whereby maximum condenser efficiency can be achieved. It has been found that this requires diversion of 10-15% of the liquid refrigerant outflow from the condenser to the bypass path. 
     More particularly, providing a bypass path for de-superheating makes the condenser more efficient thereby reducing the condenser pressure, which, in turn, decreases the pressure lift at compressor, thus reducing the compressor work. The coefficient of performance (“COP”) of a refrigeration system, sometimes termed the energy-efficiency ratio (EER), is defined as Q v /W c , where Q v  is the heat absorption by the evaporator of the system and W c  is the work done by the compressor. As will be appreciated, a decrease in W c  increases the COP and the EER. 
     Correspondingly, because de-superheating does not have to be done inside condenser  14 , the condenser becomes more efficient, and subcooling at the end of the condenser is increased. This increases the amount of liquid refrigerant after the throttling process through the main expansion valve  16 . Thus, the heat absorption at evaporator  18  (often referred as the cooling capacity) increases. 
     Referring still to FIG. 5, by proper design of the vacuum generating device such as vortex generator  40  illustrated in FIGS. 6A and 6B, or venturi tube  69  illustrated in FIG. 7, the pressure at the low pressure inlet can be made lower than the inlet pressure at main evaporator  18 . As a consequence, a pressure drop may be imposed across the evaporator. This is advantageous in that the lower evaporator outlet pressure means that the evaporator temperature differential is greater, resulting in enhanced evaporator capacity. 
     Of even more significance, after the mixing of the two vapor streams from heat exchanger  36  and evaporator  18 , the pressure of the combined stream can have a higher pressure than the evaporator inlet pressure. This means that the suction pressure at the compressor inlet is increased, which reduces the required pressure lift across the compressor. The reduced compressor work can provide a beneficial increase in the EER. 
     FIG. 8 shows a system, generally denoted at  44 , which is similar to system  30  shown in FIG. 5, but which uses pressure reducing device  48  to reduce the high pressure at the bypass line to a pressure level of the evaporator so that the two vapors can be mixed between the evaporator and the compressor. Pressure reducing device  48  can be any mechanism which reduces pressure via friction of sudden pressure drop such as a capillary tube, an orifice, a valve, a porous plug, or the like. A conventional Tee function  46  may be used to mix the vapor exiting evaporator  18  with that exiting pressure reducing device  48 . 
     FIG. 9 illustrates a zoned air conditioning system embodying the principles of this invention, generally denoted at  90 . This differs from system  30  illustrated in FIG. 5 in that bypass path  92  includes an adjustable control valve  94 , and the evaporator  96  is formed of several parallel-connector evaporator units  98   a  and  98   b  located to serve different rooms, and respectively connected to the main expansion device  16  by ON-OFF valves  100   a  and  100   b . System  90  is thus configured to provide two separate cooling zones, but as will be appreciated, more zones can be provided if desired. 
     The outlets of evaporator units  98   a  and  98   b  are at the same pressure, and are therefore connected in common to the input of pressure differential accommodating device  38 . 
     In operation, when cooling in both zones is required, valves  100   a  and  100   b  are opened, and refrigerant flows through both evaporators  98   a  and  98   b . Valve  94  is adjusted to divert between 10 and 15 percent of the refrigerant from condenser  14  into bypass path  92  to achieve maximum cooling and efficiency. Thus, all of the benefits of the de-superheating bypass described in connection with FIG. 5 are also realized in system  90 . 
     As an additional feature of system  90 , however, if cooling is required, e.g., only in the zone served by evaporator unit  98   a , valve  100   a  is opened, valve  100   b  is closed, and valve  94  is adjusted to divert the refrigerant which would otherwise flow through evaporator  98   b  into bypass path  92 , along with the refrigerant required for de-superheating. 
     To vary the bypass mass flow rate, valve  94  in bypass line  92  should be continuously adjustable or adjustable in steps, to provide the desired number of different flow rates. For example, 10% diversion could be provided for maximum performance, with 20%, 30%, and 40% diversion for reduced cooling capacity. Valves providing the above-described capability are commercially available and any suitable or desired valve of this type may be employed. 
     As previously indicated, maximum efficiency and cooling capacity are achieved by diversion of 10-15% of the refrigerant mass flow to bypass path  92 . As the amount of refrigerant diverted is increased beyond 15%, for example, up to 30% or more, the cooling capacity is reduced due to the substantial decrease in the refrigerant mass flow rate circulating through evaporator  96 . Thus, by diverting the refrigerant not needed in the idle evaporator, the cooling capacity can be made to vary according to the thermal load, without the need for repeated on-off cycling of the compressor or resort to costly variable speed compressors. 
     This is particularly advantageous in that cycling the compressor on and off consumes a large quantity of energy. Eliminating this inefficiency results in significantly improved long-term energy efficiency, a parameter sometimes measured in terms of seasonal energy-efficiency ratio (SEER), which takes account of ON/OFF operation of the compressor on the efficiency of the system. SEER is defined as the ratio of the sum of Q v  (heat absorbed by the evaporator) times the hours of operation to the sum of W c  (compressor work) times the hours of operation. 
     As will also be appreciated, variable cooling capacity can be provided in a single-zone system such as illustrated in FIG.  5 . Here, additional refrigerant would be diverted to bypass path  32  to accommodate a decrease in required cooling capacity, and the system could operate without the need for frequent compressor on-off cycling. 
     In the constructions described above, it has been assumed that a single refrigerant circulates through the system. Desuperheating bypass can also be used in conjunction with mixed refrigerants in regenerative systems to achieve highly beneficial results. 
     FIG. 10 illustrates use of de-superheating bypass in a simple mixed-refrigerant system, employing, for example, a mixture of refrigerants R-32, R-125, and R-134a. This is a commonly used beneficial combination as the R-32 component is flammable, but possesses excellent thermal characteristics, while the R-125 and R-134a components exhibit less desirable thermal characteristics than R-32 but are non-flammable. In the interest of simplicity, various possible regenerative paths as illustrated in our above-identified U.S. Patents have been omitted from the illustrative system of FIG.  10 . 
     The system, generally denoted at  106 , comprises a compressor  12 , an expansion device  16 , an evaporator  18 , a heat exchanger  36 , and a pressure differential accommodating device  38  in a bypass path  110  as in system  30  (see FIG.  5 ). The condenser, however, is split into two stages  14   a  and  14   b , and a liquid-vapor (LV) separator  108  of any suitable or desired type is provided between the two condenser stages. 
     LV separator  108  functions to separate the incoming vapor stream exiting from condenser stage  14   a  into a first vapor component which passes to the inlet of condenser stage  14   b , and a second lower temperature liquid component a portion of which passes through a valve  112  to the inlet of heat exchanger  36 . 
     The second component exiting from LV separator  108  is rich in the R-134a refrigerant due to its high condensation and boiling point relative to the other refrigerant components. Aside from the advantages of performing the de-superheating step outside condenser stage  14   a  as described above, the R-134a-rich composition of the refrigerant in the bypass path to the condenser in liquid form has the added benefit of reducing the condenser pressure. 
     As indicated above, the system illustrated in FIG. 10 is representative of the application of the principles of this invention to mixed-refrigerant regenerative systems. It should be understood, however, that de-superheating bypass is applicable to other mixed-refrigerant regenerative system configurations as well. 
     In describing the invention, specific terminology has been employed for the sake of clarity. However, the invention is not intended to be limited to the specific descriptive terms, and it is to be understood that each specific term includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
     Similarly, the embodiments described and illustrated are also intended to be exemplary, and various changes and modifications, and other embodiments within the scope of the invention will be apparent to those skilled in the art in light of the disclosure. The scope of the invention is therefore intended to be defined and limited only by the appended claims, and not by the description herein.