Abstract:
An ejector has a primary inlet, a secondary inlet, and an outlet. A primary flowpath extends from the primary inlet to the outlet and a secondary flowpath extends from the secondary inlet to the outlet, merging with the primary flowpath. A motive nozzle surrounds the primary flowpath upstream of a junction with the secondary flowpath. The motive nozzle has a throat and an exit. In one group of embodiments, an effective area of the exit is variable. In others, the needle may extend downstream from a flow control portion or may have an upstream convergent surface of a flow control portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a divisional application of U.S. patent application Ser. No. 13/993,207, filed Jun. 11, 2013, now U.S. Pat. No. 9,285,146, entitled “Ejector”, which is the U.S. national stage of PCT/CN11/00001, filed Jan. 4, 2011, 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 (exit)  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. 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 and a secondary flowpath extends from the secondary inlet to the outlet, merging with the primary flowpath. 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 effective area of the exit and/or of a mixer is variable. 
     In one or more embodiments of any of the other embodiments the means is means for simultaneously varying the effective area of the exit and an effective area of the throat. 
     In one or more embodiments of any of the other embodiments, the means comprises a needle mounted for reciprocal movement along the primary flowpath between a first position and a second position and, in at least one position, spanning at least from the throat to the exit. 
     Another aspect of the disclosure involves an ejector comprising: a primary inlet; a secondary inlet; an outlet; a primary flowpath from the primary inlet to the outlet; a secondary flowpath from the secondary inlet to the outlet; a motive nozzle surrounding the primary flowpath upstream of a junction with the secondary flowpath and having: a throat and an exit; and a needle mounted for reciprocal movement along the primary flowpath between a first position and a second position. The needle comprises: a flow control portion; and a shaft, extending from the flow control portion. An actuator is coupled to the shaft to move the needle between the first and second positions. The needle shaft extends downstream from the flow control portion along the primary flowpath and is positioned for varying an effective area of the exit over at least a portion of a range of motion. 
     In one or more embodiments of any of the other embodiments, the needle is a second needle, and the actuator is a second actuator. The ejector includes: a first needle mounted for reciprocal movement along the primary flowpath between a first position and a second position and comprising: a flow control portion; and a shaft, extending from the flow control portion. A first actuator is coupled to the shaft of the first needle to move the first needle between its first and second positions. The first needle&#39;s shaft extends upstream from the first needle&#39;s flow control portion along the primary flowpath. 
     In one or more embodiments of any of the other embodiments, the needle flow control portion is, at least along a first zone, upstream convergent. 
     Other aspects of the disclosure involve methods for operating the system. 
     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. 3A  is an enlarged view of a portion of the ejector of  FIG. 3 . 
         FIG. 4  is schematic axial sectional view of a second ejector. 
         FIG. 4A  is an enlarged partial view of the ejector of  FIG. 3 . 
         FIG. 5  is a schematic axial sectional view of a third ejector. 
         FIG. 6  is a schematic axial sectional view of a fourth ejector. 
         FIG. 7  is a partial schematic axial sectional view of a fifth ejector. 
         FIG. 8  is a partial schematic axial sectional view of a sixth ejector. 
         FIG. 9  is a partial schematic axial sectional view of a seventh ejector. 
         FIG. 10  is a schematic axial sectional view of an eighth ejector. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     As is discussed further below, in addition to or separately from controlling an effective area of the throat, an effective area of the motive nozzle exit may be varied/controlled. The area ratio of a nozzle such as that of an ejector is ratio of exit area to throat area. With a conventional controllable ejector, using the needle to reduce throat area causes an associated increase in area ratio. A fifty percent reduction in throat area would cause a doubling in area ratio. If the area ratio is too large, the supersonic flow will be overexpanded. This results in a loss of efficiency which can be in the range of 20%. Thus, with an ejector having a controllable throat area, adding exit area control allows for an at least partial compensation. 
       FIG. 3  shows an ejector  200  which may be formed as a modification of the ejector  38  (either an actual modification or a design modification) and may be used in place thereof. An exemplary means for varying the effective area of the exit comprises a valve element (needle) which, along at least a portion of its range of motion, extends through the exit. A first exemplary such needle (exit needle)  204  is shown coaxial with the needle  132  (throat needle) along a centerline  1000  of the ejector. A needle  204  has a tip portion  206  opposite and facing the tip portion  136  of the needle  132 . The needle  204  has a shaft  208  extending downstream from the tip. For moving the needle  204  to vary the effective area of the exit (e.g., the annular area between the needle and the inner surface of the motive nozzle at the exit or at a location close enough to the exit to produce the same or similar effect), an actuator  210  is coupled to the needle. Exemplary actuator  210  is a rotary actuator (e.g., a step motor). The exemplary actuator  210  is coupled to the needle valve via a geartrain. The exemplary geartrain includes a drive bevel gear  220  mounted to a shaft  222  of the actuator  210  to be driven thereby. Teeth of the drive bevel gear  220  are enmeshed with teeth of a driven bevel gear  224 . The exemplary shaft  222  and its axis of rotation are orthogonal to and intersecting the needle shaft and the centerline of the ejector. Back and forth reciprocal rotation by the actuator  210  drives back and forth reciprocal translation of the needle  204 . Although shown for ease of illustration as conical tip protuberances, the tips may be other than conical and may have similar maximum diameter to an adjacent portion of the shaft an may have known or yet-developed profiles. 
     The exemplary needle  204  has a downstream divergent tapering portion  240  ( FIG. 3A ). The exemplary range of motion extends from a maximally inserted/extended condition/position  204 ′ to a maximally withdrawn/retracted condition/position  204 ″. An exemplary range of motion is at least 25% of the divergent length L D  of the motive nozzle, more narrowly, 75-95%. Along at least a portion of this range of motion, the tapering portion is axially aligned with the exit so that insertion of the needle decreases the effective exit area (e.g., as approximated by the cross-sectional area of the annular space/gap between the exit and the portion  240 ). Similarly, retraction increases the effective exit area. The exemplary expansion (divergent) section  108  is shown having a characteristic half angle θ 2 . The exemplary portion  240  is shown having an exemplary half angle θ 1 . In the example, θ 2  is constant so that the expansion section  108  is conical. Similarly, at least over some part of the tapering portion  240 , θ 1  is constant to define a frustum of a cone. If based on an existing ejector or its motive nozzle, the angles and dimensions of the ejector and/or nozzle may be preserved. Exemplary θ 1  for such configuration is 0-30°, more narrowly 0-10°, or 2-10°, or 5-10°. Similarly exemplary θ 2  is 0-30°, more narrowly 0-10°, or 2-10°, or 5-10°. Other nozzle profiles including non-uniform angles θ 1 . and θ 2  are possible. 
     By way of example, the effective exit cross-sectional area reduction between the min and max conditions may be at least 5% of the max condition, more narrowly, at least 10% or 10-40%. These may be smaller than associate throat area reductions. 
       FIGS. 4 and 4A  show a single-needle ejector  300  which may be otherwise similar to the ejector  200  but which lacks the needle  132  and associated actuator, etc. Instead, the proportions of the needle  304  and the motive nozzle are such that, at least along a portion of the range of motion of the needle, the needle extends into the throat and spans a distance from the throat to the exit. Along at least this portion of the range of motion, the needle controls both the effective throat area and the effective exit area. 
       FIG. 5  shows an ejector  320  which may be otherwise similar but having a needle  322  which, along at least a portion of its range of motion, controls only an effective area of the throat and not the exit (e.g., by having the tapering portion end ahead of the exit). This may be achieved by a narrower and/or relatively short tapering portion  324 . An exemplary control over the throat area may have a similar range as the aforementioned control over exit area. For example, a difference in area between min throat and max throat conditions may be at least 10% of the max throat condition area, more narrowly, at least 20% or 35-100%.  FIG. 6  shows an ejector  340  wherein only the exit area is controlled by a needle  342  having a shorter, broader tapering portion  344  positioned to control only exit area and not throat area. 
     As a further alternative, a single needle may be actuated from upstream but extend through the motive nozzle throat so as to control effective properties of the divergent section  108  and the exit  110 .  FIG. 7  shows a motive nozzle of an ejector  400  which may be otherwise similar to the ejector  38  but with a different needle. The exemplary needle  402  has a relatively narrow upstream portion  404  which forms a main body of the needle. Downstream of the upstream portion  404  is a divergent (downstream divergent) portion  406 . Downstream of divergent portion  406  is a convergent (downstream convergent) portion  408  which extends to a downstream tip  410 .  FIG. 7  also shows a range of motion between an upstream-most maximally retracted position  402 ′ and a downstream-most maximally extended position  402 ″. It can be seen that, over some portions of the range of motion, the needle  402  controls both the effective throat area (e.g., the area of the annular space between the throat  106  and the needle) and the effective exit area. The exemplary divergent portion  406  has a half angle which may have the same magnitude as θ 1 . The narrow portion of the needle at the upstream end  412  of the tapering portion (which forms a junction with the straight portion) may have a diameter less than 75% (more narrowly less than 50%) of the maximum needle diameter (e.g., the diameter at the junction  414  between  408  and  406 ), with a lower boundary limited by strength of material (e.g., of the stainless steel used in needles). This may also be less than 50% of the throat diameter, more narrowly less than 25%. An exemplary such configuration is estimated to eliminate a quarter to three quarters of the losses associated with throat control. 
       FIG. 8  shows motive nozzle of an ejector  430  which may be otherwise similar to the ejector  38  or the ejector  400 . For example, relative to ejector  38 , the ejector  430  may add similar divergent and convergent portions  406  and  408  to its needle  432 , respectively, as does the ejector  400  while retaining a relatively broader proximal main shaft portion  438 . The needle (shown with broken line illustrations of a retracted condition and an extended condition) has a convergently downstream tapering portion (downstream convergent)  440  extending downstream from a junction  442  with the shaft portion  438  to a junction  446  with the portion  406 . This junction  446  establishes a local waist in the needle. The local waist may be, in at least part of the range of motion, near the throat  106 . With the exemplary arrangement, retraction from the solid line position may have a similar effect to retraction of the needle of  FIG. 7  on both effective throat and exit areas. However, a further insertion also has the same effect on exit area as in  FIG. 7  but tends to reduce effective throat area as a greater proportion of the throat is occupied by the portion  440 . In an exemplary redesign from a convention needle, the tapering portion  440  may be preserved from near the tip of the baseline needle. An exemplary half angle of taper is about 5°, more broadly 2-15°. A minimum diameter at the neck/junction  446  between the portions  440  and  406  is may correspond to that of the end  412  of  FIG. 7 . 
       FIG. 9  shows another modification in a motive nozzle of an ejector  456  wherein the  FIG. 8  protuberance is replaced in a needle  462  (shown retracted but with a broken line illustration of an extended condition) by a relatively narrow counterpart including a proximal portion  464  extending from the tapering portion  440  to create a stepped axial cross-section. A distal tapering portion  466  extends to a tip  468 . Over much of its range of motion, with the portion  464  at the exit, there will be little effect on the effective exit area. However, with retraction, the tapering portion  466  will pass through the exit occupying lesser and lesser fractions of the exit and thereby increasing effective exit area. A diameter of the portion  466  may be similar to that of the junctions  412 ,  446 . Length of the portion  464  may be effective to provide simultaneous control of throat and exit areas along at least part of its range of motion. 
       FIG. 10  shows an ejector  480  otherwise similar to the ejector  460  but having a needle  482  relatively longer intermediate portion  484 . A distal/downstream tapering portion  490  of the needle, tapering from the intermediate portion  484  to the tip  492  is positioned to control an effective area of the mixer during at least a portion of the range of motion of the needle. The mixer may be oversized when the nozzle areas are reduced. With the needle tip  492  penetrating into the mixer constant area portion, the flow area of the mixer also is reduced to at least partially compensate for reduced total flow. The needle intermediate portion  484  and tip  492  may induce shocks in the mixer and avoid shocks occurring in the diffuser. 
     The ejectors may be fabricated from conventional components using conventional techniques appropriate for the particular intended uses. 
     A controllable ejector, such as shown in  FIG. 2 , is generally used to control the high-side pressure (e.g., in a baseline system or in modifications herein). The high-side pressure is the refrigerant pressure that exists from the compressor exit  26  to the ejector inlet  40 . For transcritical cycles such as CO 2 , raising the high side pressure decreases the enthalpy out of the gas cooler and increases the cooling available for a given compressor mass flow rate. However, increasing the high side pressure also increases the compressor power. There is an optimum pressure value that maximizes the system efficiency at a given operating condition. Generally, this target value varies with the refrigerant temperature leaving the gas cooler. A high side pressure-temperature curve may be programmed in the controller. To raise the high-side pressure the throat area  106  is reduced. The controller does this by moving the needle  132  into the throat (to the right in  FIG. 2 ). 
     For the  FIG. 3  embodiment, there are two independent actuators which may be varied by the controller  140 . The upstream needle  132  would be controlled in the same way as the traditional ejector needle in  FIG. 2 ; that is, it would be used to control the high-side pressure. The downstream needle  204  is varied to control the area expansion ratio of the motive nozzle. The expansion ratio can be defined as the ratio of the exit area of the motive nozzle (at  110 ) divided by the throat (or other minimum) area of the motive nozzle (at  106 ). For a given system operating condition there is an optimum expansion ratio. Increasing the expansion ratio increases the depressurization of the refrigerant that occurs in the motive nozzle. Generally it is desirable, for optimum ejector efficiency, to depressurize the motive flow to a value that is similar to the pressure at the suction port  42 . As needle  132  is inserted into the throat (moves to the right) to raise the high-side pressure, the area ratio increases. To maintain the same area ratio, needle  204  is moved toward the throat (to the left). 
     It may also be desirable to vary the expansion ratio while holding needle  132  constant if the system operating conditions change. For example, if the system  20  is a container refrigeration system, then there may be several different cold-air set points. If the cold-air set point, is lowered then the evaporator  64  pressure will decrease. To optimize the ejector performance it may be desirable to increase the area ratio in order to lower the pressure of the refrigerant leaving the motive nozzle. To do this controller  140  may further insert needle  204  into the motive nozzle. 
       FIGS. 4-6  have a single downstream needle  304 , and  FIGS. 7-10  have a single upstream needle. The primary function of such needle is to vary the throat size to control the high-side pressure. By doing so it also varies the exit area. The area ratio as a function of throat size is pre-designed by the needle and motive nozzle geometry. The needle of  FIG. 8  may reduce the throat size either by moving to the right (downstream) or to the left (upstream) from the maximum throat area position. In this way, the change in area ratio with throat size will be different depending on which way the needle is moved. Therefore the controller may choose between two different area ratios for a given throat area. For example, if the throat is being reduced from the max. throat condition due to reduced load, the larger of two available area ratios may be chosen when there is a large overall pressure ratio (between gas cooler and evaporator) and the smaller area ratio may be chosen when there is a smaller overall pressure ratio. 
     The controller may estimate the pressure at the motive nozzle exit based on models and on the motive nozzle inlet conditions (measured pressure and temperature along line  36 ). The suction port pressure (along line  74 ) may also be measured. The controller may use this information to determine the desired area ratio. 
     Although embodiments are 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.