Abstract:
An ejector has a primary inlet ( 40 ), a secondary inlet ( 42 ), and an outlet ( 44 ). A primary flowpath extends from the primary inlet to the outlet. A secondary flowpath extends from the secondary inlet to the outlet. A mixer convergent section ( 114; 300; 400 ) is downstream of the secondary inlet. A motive nozzle ( 100 ) surrounds the primary flowpath upstream of a junction with the secondary flowpath. The motive nozzle has a throat ( 106 ) and an exit ( 110 ). An actuator ( 204 ) is coupled to the motive nozzle to drive a relative streamwise shift of the exit and convergent section.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Benefit is claimed of U.S. patent application Ser. No. 61/418,045, filed Nov. 30, 2010, and entitled “Ejector”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. 
    
    
     BACKGROUND 
     The present disclosure relates to refrigeration. More particularly, it relates to ejector refrigeration systems. 
     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 . 
     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 . 
     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. Thus, respective primary and secondary flowpaths extend from the primary inlet and secondary inlet to the outlet, merging at the exit. 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. 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. 
     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). 
     The exemplary ejector may be a fixed geometry ejector or may be a controllable ejector.  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. 
     SUMMARY 
     One aspect of the disclosure involves an ejector having a primary inlet, a secondary inlet, and an outlet. A primary flowpath extends from the primary inlet to the outlet. A secondary flowpath extends from the secondary inlet to the outlet. A mixer convergent section is downstream of the secondary inlet. A motive nozzle surrounds the primary flowpath upstream of a junction with the secondary flowpath. The motive nozzle has a throat and an exit. An actuator is coupled to the motive nozzle to drive a relative streamwise shift of the exit and convergent section. 
     In various implementations, the coupling may be effective to provide the relative streamwise shift along a range of motion between a relatively extended condition and a relatively retracted condition. Over at least a portion of the range of motion, the exit may be within the convergent section. A needle may be mounted for reciprocal movement along the primary flowpath between a first position and a second position. A needle actuator may be coupled to the needle to drive the movement of the needle relative to the motive nozzle. 
     Other aspects of the disclosure involve a refrigeration system having a compressor, a heat rejection heat exchanger coupled to the compressor to receive refrigerant compressed by the compressor, a heat absorption heat exchanger, a separator, and such an ejector. An inlet of the separator may be coupled to the outlet of the ejector to receive refrigerant from the ejector. 
     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 
         FIG. 1  is a schematic view of a prior art ejector refrigeration system. 
         FIG. 2  is an axial sectional view of a prior art ejector. 
         FIG. 3  is a schematic axial sectional view of an ejector. 
         FIG. 4  is a schematic axial second view of a second ejector. 
         FIG. 5  is a partial further schematic view of the ejector of  FIG. 4 . 
         FIG. 6  is a partial schematic sectional view of an alternate ejector. 
         FIG. 7  is a partial schematic sectional view of another alternate ejector. 
         FIG. 8  is a partial schematic sectional view of another alternate ejector. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 3  shows an ejector  200 . The ejector  200  may be formed as a modification of the ejector  38  and may be used in systems where conventional ejectors are presently used or may be used in the future. The convergent section  114  is shown having a length L C  and a half angle (e.g., conical half angle about the central longitudinal axis (centerline)  500 ) θ C . The mixing section  116  is shown having a length L M . The motive nozzle  100  protrudes into the convergent section of the mixer by an overlap or protrusion length L. The overlap may be controllable by means for controlling the relative streamwise positions of the motive nozzle exit and the convergent section. Exemplary means shifts the exit streamwise relative to the convergent section (e.g., via reciprocal linear motion  202 ). Exemplary means comprises an actuator  204 . An exemplary actuator  204  shifts the motive nozzle while the convergent section remains fixed relative to the environment. The exemplary actuator  204  shifts the motive nozzle and needle as a unit so that the needle actuator  134  still provides relative motion of the needle to the motive nozzle. An exemplary actuator comprises a step motor and transmission to provide linear movement (e.g., pinion and rack system that transfers the motor rotation into the liner reciprocal movement of the motive nozzle).  FIG. 4  shows a nozzle  220  lacking a needle and associated control hardware but having the overlap (protrusion) L P  as the only adjustable or controllable parameter. 
     With a traditional ejector, as operating conditions change, mixing conditions may change. If initial operation is at an optimal condition (e.g., a design target condition) changes in system conditions may increase friction and mixing losses and decrease pressure recoveries in the mixer and/or diffuser. The relative motive nozzle position may be controlled by the control system  140  to compensate for changes in system operating condition. The motive nozzle may be moved forward or backward (upstream or downstream) as needed responsive to sensed parameters (e.g., the outlet pressure or the pressure lift ratio). This may be combined with control of needle position if available. 
     The shift may be performed, for example, to maximize the ejector&#39;s performance, and therefore the system efficiency. One or more operational parameters of the ejector or the system may be sensed. The controller may be programmed to determine an ejector efficiency or a proxy therefor. Responsive to the sensed operational parameters or the calculated efficiency or proxy, the controller may be programmed to cause the actuator to drive the shift. 
     The controller may vary the motive nozzle position in order to maximize system coefficient of performance (COP). The system COP is highest when the pressure rise achieved by the ejector from the secondary inlet (suction port) to the outlet (exit port) is highest. The controller may dynamically sense (via pressure sensors) the actual pressure rise by measuring pressure at the ejector outlet and the ejector suction port and subtracting these two values. The controller then moves the motive nozzle position to find the peak pressure rise value. If L P  is too large (i.e., the motive nozzle is extended too far into the mixing section of the ejector), then the ejector performance will be poor and the pressure rise small. If L P  is too small (the nozzle is too far from the mixing section of the ejector), then the same is true. At the ideal motive nozzle location the pressure rise is maximized. 
     The process may be an iterative optimization (e.g., a back and forth iterative stepwise or continuous movement until a desired condition (e.g., an optimized condition) is reached. The optimization may be performed from the instantaneous position (e.g., a slight movement in each direction followed by choosing whichever direction improved performance and then repeating) or by a scan-like movement (e.g., across the entire range of motion or portion thereof and choosing the position that provided the best performance). 
       FIG. 5  shows a range of motion of the motive nozzle between a maximally retracted (withdrawn) position  100 ′ with a protrusion L PMIN  and a maximally inserted (extended) position  100 ″ with a protrusion L PMAX . An exemplary ratio of L C  to L M  is 0.05-60, more narrowly, 0.02-20, more narrowly, 0.2-10. An exemplary ratio of the overlap L P  to the length L C  is in the range of −0.5-1.5, more narrowly, 0.2-0.9. The range of motion may encompass such exemplary position. The range of motion ΔL may encompass that entire range of 0.2-0.9. More narrowly, the exemplary range of motion may include ratios of said overlap to said length including at least 0.4-0.7. An exemplary range of motion ΔL may thus be at least 0.3 (more narrowly, at least 0.5) of said length L C . Alternatively characterized, ΔL may be at least 0.1 of a mixer minimum diameter D MIX , more narrowly, at least 0.2 or 0.3-2.0. The exemplary angle θ C  is 1-75°, more narrowly, 5-45°, more narrowly, 10-30°. This may be measured as an overall half angle between the upstream end  220  of the convergent section and the downstream end  222  of the convergent section or as a median or modal angle. Thus, the angle of convergence need not be constant. Along the exemplary convergent section, not only does the wall  224  of the convergent section converge but the cross-sectional area of the annular space  226  between the wall  224  and the exterior surface  228  of the motive nozzle converge. 
       FIG. 6  shows a convergent section  300  having an upstream portion  302  and a downstream portion  304  of differing angles θ C1  and θ C2  and different respective lengths L C1  and L 2 . Exemplary θ 1  is larger than θ 2 . However, both may be in the ranges discussed above as may be the linear dimensions. Similarly, total protrusion of the motive nozzle into the convergent section  300  may be similar to that described above. 
       FIG. 7  shows an ejector wherein the convergent and constant area sections are effectively combined in a relatively long and shallow convergent section  400 . Exemplary ratios of L P  to L C  are −0.1-0.6, more narrowly, 0.1-0.4 or 0.2-0.4. Exemplary θ C  is 2-25°, more narrowly, 5-20° or 10-20°. 
       FIG. 8  modifies the  FIG. 6  configuration providing smoothly, continuously changing angle of convergence in the convergent section. Overall dimensions and ratios may be similar. 
     The system may be fabricated from conventional components using conventional techniques appropriate for the particular intended uses. 
     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 of the disclosure. For example, when implemented in the remanufacturing of an existing system or 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.