Abstract:
A system ( 170 ) has a compressor ( 22 ). A heat rejection heat exchanger ( 30 ) is coupled to the compressor to receive refrigerant compressed by the compressor. A non - controlled ejector ( 38 ) has a primary inlet coupled to the heat rejection exchanger to receive refrigerant, a secondary inlet, and an outlet. The system includes means ( 172,  e.g., a nozzle) for causing a supercritical-to-subcritical transition upstream of the ejector.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Benefit is claimed of U.S. Patent Application Ser. No. 61/367,140, filed Jul. 23, 2010, and entitled “Ejector Cycle”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to refrigeration. More particularly, it relates to ejector refrigeration systems. 
         [0003]    Earlier proposals for ejector refrigeration systems are found in U.S. Pat. No.  1 , 836 , 318  and U.S. Pat. No. 3,277,660.  FIG. 1  shows one basic example of an ejector refrigeration system  20 . The system includes a compressor  22  having an inlet (suction port)  24  and an outlet (discharge port)  26 . The compressor and other system components are positioned along a refrigerant circuit or flowpath  27  and connected via various conduits (lines). A discharge line  28  extends from the outlet  26  to the inlet  32  of a heat exchanger (a heat rejection heat exchanger in a normal mode of system operation (e.g., a condenser or gas cooler))  30 . A line  36  extends from the outlet  34  of the heat rejection heat exchanger  30  to a primary inlet (liquid or supercritical or two-phase inlet)  40  of an ejector  38 . The ejector  38  also has a secondary inlet (saturated or superheated vapor or two-phase inlet)  42  and an outlet  44 . A line  46  extends from the ejector outlet  44  to an inlet  50  of a separator  48 . The separator has a liquid outlet  52  and a gas outlet  54 . A suction line  56  extends from the gas outlet  54  to the compressor suction port  24 . The lines  28 ,  36 ,  46 ,  56 , and components therebetween define a primary loop  60  of the refrigerant circuit  27 . A secondary loop  62  of the refrigerant circuit  27  includes a heat exchanger  64  (in a normal operational mode being a heat absorption heat exchanger (e.g., evaporator)). The evaporator  64  includes an inlet  66  and an outlet  68  along the secondary loop  62  and expansion device  70  is positioned in a line  72  which extends between the separator liquid outlet  52  and the evaporator inlet  66 . An ejector secondary inlet line  74  extends from the evaporator outlet  68  to the ejector secondary inlet  42 . 
         [0004]    In the normal mode of operation, gaseous refrigerant is drawn by the compressor  22  through the suction line  56  and inlet  24  and compressed and discharged from the discharge port  26  into the discharge line  28 . In the heat rejection heat exchanger, the refrigerant loses/rejects heat to a heat transfer fluid (e.g., fan-forced air or water or other fluid). Cooled refrigerant exits the heat rejection heat exchanger via the outlet  34  and enters the ejector primary inlet  40  via the line  36 . 
         [0005]    The exemplary ejector  38  ( FIG. 2 ) is formed as the combination of a motive (primary) nozzle  100  nested within an outer member  102 . The primary inlet  40  is the inlet to the motive nozzle  100 . The outlet  44  is the outlet of the outer member  102 . The primary refrigerant flow  103  enters the inlet  40  and then passes into a convergent section  104  of the motive nozzle  100 . It then passes through a throat section  106  and an expansion (divergent) section  108  through an outlet  110  of the motive nozzle  100 . The motive nozzle  100  accelerates the flow  103  and decreases the pressure of the flow. The secondary inlet  42  forms an inlet of the outer member  102 . The pressure reduction caused to the primary flow by the motive nozzle helps draw the secondary flow  112  into the outer member. The outer member includes a mixer having a convergent section  114  and an elongate throat or mixing section  116 . The outer member also has a divergent section or diffuser  118  downstream of the elongate throat or mixing section  116 . The motive nozzle outlet  110  is positioned within the convergent section  114 . As the flow  103  exits the outlet  110 , it begins to mix with the flow  112  with further mixing occurring through the mixing section  116  which provides a mixing zone. In operation, the primary flow  103  may typically be supercritical upon entering the ejector and subcritical upon exiting the motive nozzle. The secondary flow  112  is gaseous (or a mixture of gas with a smaller amount of liquid) upon entering the secondary inlet port  42 . The resulting combined flow  120  is a liquid/vapor mixture and decelerates and recovers pressure in the diffuser  118  while remaining a mixture. 
         [0006]    Upon entering the separator, the flow  120  is separated back into the flows  103  and  112 . The flow  103  passes as a gas through the compressor suction line as discussed above. The flow  112  passes as a liquid to the expansion valve  70 . The flow  112  may be expanded by the valve  70  (e.g., to a low quality (two-phase with small amount of vapor)) and passed to the evaporator  64 . Within the evaporator  64 , the refrigerant absorbs heat from a heat transfer fluid (e.g., from a fan-forced air flow or water or other liquid) and is discharged from the outlet  68  to the line  74  as the aforementioned gas. 
         [0007]    Use of an ejector serves to recover pressure/work. Work recovered from the expansion process is used to compress the gaseous refrigerant prior to entering the compressor. Accordingly, the pressure ratio of the compressor (and thus the power consumption) may be reduced for a given desired evaporator pressure. The quality of refrigerant entering the evaporator may also be reduced. Thus, the refrigeration effect per unit mass flow may be increased (relative to the non-ejector system). The distribution of fluid entering the evaporator is improved (thereby improving evaporator performance). Because the evaporator does not directly feed the compressor, the evaporator is not required to produce superheated refrigerant outflow. The use of an ejector cycle may thus allow reduction or elimination of the superheated zone of the evaporator. This may allow the evaporator to operate in a two-phase state which provides a higher heat transfer performance (e.g., facilitating reduction in the evaporator size for a given capability). 
         [0008]    The exemplary ejector may be a fixed geometry ejector ( FIG. 3 ) or may be a controllable ejector ( FIG. 2 ).  FIG. 2  shows controllability provided by a needle valve  130  having a needle  132  and an actuator  134 . The actuator  134  shifts a tip portion  136  of the needle into and out of the throat section  106  of the motive nozzle  100  to modulate flow through the motive nozzle and, in turn, the ejector overall. Exemplary actuators  134  are electric (e.g., solenoid or the like). The actuator  134  may be coupled to and controlled by a controller  140  which may receive user inputs from an input device  142  (e.g., switches, keyboard, or the like) and sensors (not shown). The controller  140  may be coupled to the actuator and other controllable system components (e.g., valves, the compressor motor, and the like) via control lines  144  (e.g., hardwired or wireless communication paths). The controller may include one or more: processors; memory (e.g., for storing program information for execution by the processor to perform the operational methods and for storing data used or generated by the program(s)); and hardware interface devices (e.g., ports) for interfacing with input/output devices and controllable system components. 
         [0009]    Various modifications of such ejector systems have been proposed. One example in US20070028630 involves placing a second evaporator along the line  46 . US20040123624 discloses a system having two ejector/evaporator pairs. Another two-evaporator, single-ejector system is shown in US20080196446. Another method proposed for controlling the ejector is by using hot-gas bypass. In this method a small amount of vapor is bypassed around the gas cooler and injected just upstream of the motive nozzle, or inside the convergent part of the motive nozzle. The bubbles thus introduced into the motive flow decrease the effective throat area and reduce the primary flow. To reduce the flow further more bypass flow is introduced. 
       SUMMARY 
       [0010]    One aspect of the disclosure involves a system having a compressor. A heat rejection heat exchanger is coupled to the compressor to receive refrigerant compressed by the compressor. A non-controlled ejector has a primary inlet coupled to the heat rejection exchanger to receive refrigerant, a secondary inlet, and an outlet. The system includes means (e.g., a nozzle) for causing a supercritical-to-subcritical transition upstream of the ejector. 
         [0011]    In various implementations, the means may consist essentially of a nozzle and a control valve. The nozzle may be a convergent nozzle or a convergent/divergent nozzle. The means may be non-branching and inline between the heat rejection heat exchanger and the ejector. The system may further include a separator having an inlet coupled to the outlet of the ejector to receive refrigerant from the ejector. The separator has a gas outlet coupled to the compressor to return refrigerant to the compressor. The separator has a liquid outlet coupled to the secondary inlet of the ejector to deliver refrigerant to the ejector. A heat absorption heat exchanger may be coupled to the liquid outlet of the separator to receive refrigerant. 
         [0012]    An expansion device may be immediately upstream of the heat absorption heat exchanger. The refrigerant may comprise at least 50% carbon dioxide, by weight. 
         [0013]    Other aspects of the disclosure involve methods for operating the system. 
         [0014]    The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic view of a prior art ejector refrigeration system. 
           [0016]      FIG. 2  is an axial sectional view of an ejector. 
           [0017]      FIG. 3  is an axial sectional view of a second ejector. 
           [0018]      FIG. 4  is a schematic view of a first refrigeration system. 
           [0019]      FIG. 5  is a view of a first refrigerant transitioning means. 
           [0020]      FIG. 6  is a pressure-enthalpy (Mollier) diagram of the system of  FIG. 4 . 
           [0021]      FIG. 7  is a view of a second transitioning means. 
           [0022]      FIG. 8  is a view of a third transitioning means. 
           [0023]      FIG. 9  is a view of a fourth transitioning means. 
           [0024]      FIG. 10  is a view of a fifth transitioning means. 
           [0025]      FIG. 11  is a view of a sixth transitioning means. 
       
    
    
       [0026]    Like reference numbers and designations in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0027]      FIG. 4  shows an ejector cycle vapor compression (refrigeration) system  170 . The system  170  may be made as a modification of the system  20  or of another system or as an original manufacture/configuration. In the exemplary embodiment, like components which may be preserved from the system  20  are shown with like reference numerals. Operation may be similar to that of the system  20  except as discussed below with the controller controlling operation responsive to inputs from various temperature sensors and pressure sensors 
         [0028]    The ejector is a non-controllable ejector. Directly upstream of the ejector primary inlet is a means  172  for providing a supercritical-to-subcritical transition of refrigerant before entering the primary inlet. A first exemplary means comprises a convergent nozzle  180  ( FIG. 5 ) and a control valve  182 . The convergent nozzle  180  has an inlet  184  and an outlet  186  A flow cross-sectional (interior surface) area of the outlet is less than that of the inlet (e.g., 10-95%, more narrowly, 20-80% or 40-60%). The outlet cross-sectional area may be nominally the same as that of the ejector primary inlet and any intervening conduit/line. The inlet cross-sectional area may be the same as the conduit/line from the heat rejection heat exchanger. The exemplary valve (e.g., a needle valve or ball valve) may be directly upstream of the inlet  184  or downstream of the outlet ( FIG. 7 ). 
         [0029]      FIG. 6  is a Mollier diagram of the system of  FIG. 4  with the means of  FIG. 5 . The exemplary evaporator pressure is P3 and the discharge or high side gas cooler pressure is P1. The means  172  lowers the ejector inlet pressure to P4. The flow rate and inlet condition of the motive nozzle can be controlled by the means  172  to keep the ejector motive nozzle inlet pressure below critical. 
         [0030]    In operation, the expansion device  70  is controlled to maintain a desired superheat of refrigerant exiting the evaporator. A target superheat exiting the evaporator may be maintained. The superheat may be determined by input from a pressure transducer P and temperature sensor 
         [0031]    T downstream of the evaporator. Alternatively, the pressure can be estimated from a temperature sensor along the saturated region of the evaporator. To increase superheat, the expansion device is closed, to increase opened. 
         [0032]    A third exemplary means comprises a convergent-divergent nozzle  220  ( FIG. 8 ) in place of the convergent nozzle  180 . The convergent-divergent nozzle  220  has an inlet  224  and an outlet  226 , and a throat  228 , between the inlet and the outlet. A flow cross-sectional (interior surface) area of the throat is less than that of the smaller of the inlet and outlet (e.g., 10-95%, more narrowly, 20-80% or 40-60%). An exemplary flow cross-sectional (interior surface) area of the outlet is greater or less (depending on the outlet refrigerant velocity requirement; higher velocity demands the outlet area be greater, less for lower velocity) than that of the inlet (e.g., 20-175%, more narrowly, 50-150%). The outlet cross-sectional area may be nominally the same as that of the ejector primary inlet and any intervening conduit/line. The inlet cross-sectional area may be the same as the conduit/line from the heat rejection heat exchanger. 
         [0033]    Further variations on the means involve omitting the control valve  182  ( FIG. 9  for the nozzle  220 ). In such situations, the dimensions of the nozzle  180  or  220  are pre-selected to maintain the ejector inlet pressure below the critical pressure over the anticipated range of operating conditions. 
         [0034]    Yet further variations of the means modify the nozzle  220  to have a controllable flow cross-section. For a convergent-divergent nozzle  240  ( FIG. 10 ), this may involve a controllable throat cross-section (e.g., via a needle valve having a needle  242  and an actuator (not shown). The needle may be controlled to control the nozzle outlet pressure or system parameters such as flow rates and temperatures, etc. 
         [0035]      FIG. 11  shows yet a further variation on the means involving an orifice plate  250  having an orifice  252 . An exemplary orifice  252  is an orifice plate or Venturi tube. Yet further variations of the means involve a series of convergent and/or convergent-divergent nozzles with or without control valves. For example, there may be just a convergent nozzle before the ejector. 
         [0036]    The system may be fabricated from conventional components using conventional techniques appropriate for the particular intended uses. 
         [0037]    Although an embodiment is described above in detail, such description is not intended for limiting the scope of the present disclosure. It will be understood that various modifications may be made without departing from the spirit and scope or the disclosure. For example, when implemented in the remanufacturing of an existing system of the reengineering of an existing system configuration, details of the existing configuration may influence or dictate details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.