Patent Publication Number: US-9903623-B2

Title: Ejector having an atomization mechanism and heat pump apparatus

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an ejector to which single-fluid atomization techniques are applied and a heat pump apparatus that uses the ejector. 
     2. Description of the Related Art 
     Atomization techniques are applied in various industrial fields, which include spray coating, spray drying, humidity control, agrochemical dispersion, and fire extinguishing, in addition to energy-related techniques, such as combustion techniques for liquid fuel. Performances desired for spray nozzles vary, depending on the application purposes of the spray nozzles. The atomization principle of a spray nozzle is variously studied, such as atomization using a turbulent flow, atomization including film thinning by widening a sprayed area, atomization using centrifugal force, or atomization using two-fluid interaction. However, a nozzle that can achieve a high flow rate, high performance in atomization, a high spray speed, a small spray angle, and flow contraction spraying at the same time through the application of the principle of single-fluid atomization has not existed. 
     An ejector is used for various apparatuses as a pressure reducer, which include a vacuum pump and a refrigeration cycle apparatus. As illustrated in  FIG. 18 , a refrigeration cycle apparatus  300  described in Japanese Patent No. 3158656 includes a compressor  102 , a condenser  103 , an ejector  104 , a separator  105 , and an evaporator  106 . The ejector  104  receives refrigerant liquid from the condenser  103  as a driving flow and sucks refrigerant vapor supplied from the evaporator  106  and boosts the pressure of the refrigerant vapor before discharging the resultant refrigerant to the separator  105 . The separator  105  separates the refrigerant liquid and the refrigerant vapor. The compressor  102  sucks the refrigerant vapor having the pressure that has been boosted by the ejector  104 . Thus, the compression work of the compressor  102  is reduced and the coefficient of performance (COP) of the refrigeration cycle is increased. 
     As illustrated in  FIG. 19 , the ejector  104  includes a nozzle  140 , a suction port  141 , a mixer  142 , and a pressure booster  143 . Near the outlet of the nozzle  140 , a plurality of communication ports  144  for communication between the inside and the outside of the nozzle  140  are provided. The refrigerant vapor is sucked into the ejector  104  from the suction port  141 . Part of the sucked refrigerant vapor is guided into the inside of the nozzle  140  through the communication ports  144 . 
     The nozzle  140  of the ejector  104  includes a diameter reduction portion near the outlet of the nozzle  140 . In the diameter reduction portion, the flow velocity of the refrigerant increases and the pressure decreases. As a result, the refrigerant supplied to the nozzle  140  as the driving flow changes into a gas-liquid two-phase state from the liquid-phase state in the diameter reduction portion. That is, the ejector  104  illustrated in  FIG. 19  is called a two-phase flow ejector. 
     SUMMARY 
     One non-limiting and exemplary embodiment provides single-fluid atomization techniques of liquid to increase the performance of an ejector, which depends on whether the momentum is efficiently transported between a driving flow and a suction flow. 
     In one general aspect, the techniques disclosed here feature an ejector including: a first nozzle to which a liquid-phase working fluid is supplied; a second nozzle into which a vapor-phase working fluid is sucked; an atomization mechanism that is arranged at an end of the first nozzle and atomizes the liquid-phase working fluid without changing a liquid-phase state of the liquid-phase working fluid; and a mixer that mixes the atomized working fluid generated in the atomization mechanism and the vapor-phase working fluid sucked into the second nozzle and generates a fluid mixture, the atomization mechanism including a plurality of orifices and a collision plate against which each of a plurality of jets ejected from the plurality of orifices collides, the collision plate including a first principal surface and a second principal surface as a collision surface against which the jet collides, each of the first principal surface and the second principal surface extending toward an outlet of the ejector, the plurality of orifices including a plurality of first orifices arranged on a side of the first principal surface of the collision plate and a plurality of second orifices arranged on a side of the second principal surface of the collision plate. 
     The techniques according to the present disclosure may enable the momentum of the liquid-phase working fluid, which is the driving flow, to be efficiently transported into the vapor-phase working fluid, which is the suction flow. Thus, the performance of the ejector increases. 
     It should be noted that general or specific embodiments may be implemented as a system, a method, an integrated circuit, a computer program, a storage medium, or any selective combination thereof. 
     Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an ejector according to Embodiment 1 of the present disclosure; 
         FIG. 2A  is a partial enlarged cross-sectional view of an atomization mechanism of the ejector illustrated in  FIG. 1 ; 
         FIG. 2B  is a plan view of the atomization mechanism of the ejector illustrated in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a mixer of the ejector illustrated in  FIG. 1 , which is taken along line III-III; 
         FIG. 4A  illustrates what matters when jets are caused to collide against only one surface of a collision plate; 
         FIG. 4B  illustrates advantages obtained when jets are caused to collide against two surfaces of the collision plate; 
         FIG. 5A  is a diagram illustrating the positional relation between the collision plate of the atomization mechanism and the inner wall surface of the mixer; 
         FIG. 5B  is another diagram illustrating the positional relation between the collision plate of the atomization mechanism and the inner wall surface of the mixer; 
         FIG. 6  is a plan view of an atomization mechanism according to a variation; 
         FIG. 7  illustrates advantages obtained by the atomization mechanism illustrated in  FIG. 6 ; 
         FIG. 8  is a plan view of an atomization mechanism according to another variation; 
         FIG. 9A  is a partial enlarged cross-sectional view of an atomization mechanism according to still another variation; 
         FIG. 9B  is a plan view of the atomization mechanism illustrated in  FIG. 9A ; 
         FIG. 9C  is a partial enlarged cross-sectional view of an atomization mechanism according to still another variation; 
         FIG. 10  illustrates the positional relation between collision plates of an atomization mechanism and the inner wall surface of a mixer according to still another variation; 
         FIG. 11  is a cross-sectional view of an ejector according to Embodiment 2 of the present disclosure; 
         FIG. 12A  is a partial enlarged cross-sectional view of an atomization mechanism of the ejector illustrated in  FIG. 11 ; 
         FIG. 12B  is a plan view of the atomization mechanism of the ejector illustrated in  FIG. 11 ; 
         FIG. 13  is a cross-sectional view of a mixer of the ejector illustrated in  FIG. 11 , which is taken along line XIII-XIII; 
         FIG. 14  is a plan view of an atomization mechanism according to still another variation; 
         FIG. 15  is a plan view of an atomization mechanism according to still another variation; 
         FIG. 16  is a plan view of an atomization mechanism according to still another variation; 
         FIG. 17  is a configuration diagram of a heat pump apparatus that uses the ejector; 
         FIG. 18  is a configuration diagram of a conventional refrigeration cycle apparatus; and 
         FIG. 19  is a cross-sectional view of an ejector used in the refrigeration cycle apparatus illustrated in  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION 
     When a driving flow is gas or a two-phase flow with high void fraction while a suction flow is gas, the momentum can be efficiently transported between the driving flow and the suction flow simply by mixing the driving flow and the suction flow. In contrast, when the driving flow is liquid while the suction flow is gas, the time taken to relax the velocity, which is the time taken for the velocity of the driving flow and the velocity of the suction flow to become approximately equal, is long and thus, the transportation of the momentum from the driving flow to the suction flow is hindered. As a result, it is difficult to expect high-efficiency driving of the ejector. 
     When the driving flow is liquid while the suction flow is gas, a mixing chamber of the ejector is filled with a two-phase flow. A principal factor in the transportation of the momentum from the driving flow to the suction flow is spray resistance, which is caused by viscous resistance for example. When liquid is ejected into the mixing chamber filled with gas, a gas-liquid two-phase spray flow where droplets constitute a dispersed phase and gas constitutes a continuous phase is formed. In the two-phase flow where the dispersed phase and the continuous phase have relative velocity, the transportation of the momentum is ruled by the equation of motion of a droplet. According to the equation of motion of a droplet, as the contact area between the droplet and the gas increases, the transportation of the momentum can proceed in reduced time. That is, under the constraint that the size of the ejector is limited, as the total surface area of the droplets increases (as the diameter of each droplet decreases), the transportation of the momentum can proceed more efficiently. 
     When the sprayed driving flow (the spray flow) collides against the inner wall surface of the ejector, the performance of the ejector is reduced by decrease in the surface area, which is due to the coalescence of a plurality of droplets, and by consumption of the momentum as force. Also when the droplets collide against one another, the particle diameter increases because of the coalescence of the plurality of droplets. As a result, the total surface area of the droplets decreases and the performance of the ejector is reduced. Besides, also when drip occurs in a mechanism for ejecting the driving flow, the total surface area of the droplets decreases and the performance of the ejector is reduced. 
     On the basis of the above-described findings, the present inventors have conceived the techniques for suppressing collision of a droplet against the inner wall surface of an ejector, coalescence of droplets, and drip in a mechanism for ejecting a driving flow. 
     A first aspect of the present disclosure provides an ejector including:
         a first nozzle to which a liquid-phase working fluid is supplied;   a second nozzle into which a vapor-phase working fluid is sucked;   an atomization mechanism that is arranged at an end of the first nozzle and atomizes the liquid-phase working fluid without changing a liquid-phase state of the liquid-phase working fluid; and   a mixer that mixes the atomized working fluid generated in the atomization mechanism and the vapor-phase working fluid sucked into the second nozzle and generates a fluid mixture,   the atomization mechanism including a plurality of orifices and a collision plate against which each of a plurality of jets ejected from the plurality of orifices collides,   the collision plate including a first principal surface and a second principal surface as a collision surface against which the jet collides, each of the first principal surface and the second principal surface extending toward an outlet of the ejector,   the plurality of orifices including a plurality of first orifices arranged on a side of the first principal surface of the collision plate and a plurality of second orifices arranged on a side of the second principal surface of the collision plate.       

     According to the first aspect, the jets ejected from the orifices collide against the collision plate and a thin liquid film is generated. The liquid film is unstable, quickly atomized, and supplied to the mixer. In the mixer, the atomized working fluid is mixed with the vapor-phase working fluid and the fluid mixture is generated. The fluid mixture has a form of a fine spray flow. The contact area between the liquid-phase working fluid and the vapor-phase working fluid is increased by atomizing the liquid-phase working fluid. In the liquid film generated through the collision of the jets against the collision plate, the flow velocity in close proximity to a surface of the collision plate is low. The flow with the low flow velocity and the flow with the flow velocity that is reduced by a hydraulic jump phenomenon move around an end surface of the collision plate because of the surface tension of the liquid. According to the first aspect of the present disclosure, jets are caused to collide against the first principal surface and the second principal surface of the collision plate and thus, drip that can possibly occur on the end surface of the collision plate can be suppressed. Consequently, in the ejector according to the first aspect, the momentum of the liquid-phase working fluid, which is the driving flow, can be efficiently transported to the vapor-phase working fluid, which is the suction flow. That is, the present disclosure can provide an ejector with high performance. 
     In addition to the first aspect, a second aspect of the present disclosure provides the ejector, where, in a cross section including a central axis of the ejector,
         (a) an extension line of the first principal surface of the collision plate intersects an inner wall surface of the mixer, or   (b) when, on an opening plane on an outlet side of the mixer, r represents a distance from the central axis of the ejector to the inner wall surface of the mixer, an intersection point of the extension line of the first principal surface of the collision plate and the opening plane on the outlet side of the mixer is in a range from a boundary between the opening plane on the outlet side of the mixer and the inner wall surface of the mixer to a position away from the boundary by r/4. According to the second aspect, while the spray flow can be uniformly diffused all over the mixer, collision of the spray flow against the inner wall surface of the mixer can be avoided as much as possible. As a result, loss in the momentum and coalescence of a plurality of droplets, which the collision of the spray flow against the inner wall surface of the mixer causes, can be suppressed and the efficiency of the ejector can be enhanced.       

     In addition to the first or second aspect, a third aspect of the present disclosure provides the ejector, where the atomization mechanism includes a plurality of collision plates, each of which is the collision plate. The third aspect facilitates coping with increase in the flow rate of the ejector. 
     In addition to the second aspect, a fourth aspect of the present disclosure provides the ejector, where a plurality of collision plates, each of which is the collision plate, are provided in a direction from the central axis of the ejector toward the inner wall surface of the mixer, and in the collision plate arranged in a position closest to the inner wall surface of the mixer, the first principal surface is positioned nearer to the inner wall surface of the mixer than the second principal surface is, and the (a) or the (b) is satisfied. According to the above-described configuration, the advantages described with the second aspect can be obtained even when the plurality of collision plates are provided. 
     In addition to any one of the first to fourth aspects, a fifth aspect of the present disclosure provides the ejector, where, when the atomization mechanism is viewed from a side of the outlet of the ejector as a plane, the plurality of first orifices are arranged on a first virtual circle and the plurality of second orifices are arranged on a second virtual circle concentric with the first virtual circle. According to the above-described arrangement, drip caused by the quid-phase working fluid moving around can be sufficiently suppressed. 
     In addition to any one of the first to fifth aspects, a sixth aspect of the present disclosure provides the ejector, where the first principal surface and the second principal surface of the collision plate are each a conical surface or a cylindrical surface. The collision plate shaped as described above enables the spray flow to be uniformly supplied toward the mixer. 
     In addition to any one of the first to fourth aspects, a seventh aspect of the present disclosure provides the ejector, where a plurality of collision plates, each of which is the collision plate, are provided in a direction from the central axis of the ejector toward the inner wall surface of the mixer, when the atomization mechanism is viewed from a side of the outlet of the ejector as a plane, the plurality of orifices are arranged on a plurality of virtual circles concentric with each other, and each of the collision plates is arranged between the virtual circles next to each other. The seventh aspect facilitates coping with increase in the flow rate of the ejector. 
     In addition to the seventh aspect, an eighth aspect of the present disclosure provides the ejector, where the first principal surface and the second principal surface of the collision plate are each a conical surface or a cylindrical surface, the conical surface or the cylindrical surface being concentric with the plurality of virtual circles. The collision plate shaped as described above enables the spray flow to be uniformly supplied toward the mixer. 
     In addition to any one of the first to fourth aspects, a ninth aspect of the present disclosure provides the ejector, where, when the atomization mechanism is viewed from a side of the outlet of the ejector as a plane, the plurality of first orifices are arranged on a first virtual straight line and the plurality of second orifices are arranged on a second virtual straight line parallel to the first virtual straight line. According to the above-described arrangement, drip caused by the liquid-phase working fluid moving around can be sufficiently suppressed. 
     In addition to any one of the first to fourth aspects, a tenth aspect of the present disclosure provides the ejector, where the atomization mechanism includes a plurality of collision plates, each of which is the collision plate, when the atomization mechanism is viewed from the outlet side of the mixer as a plane, the plurality of orifices are arranged on a plurality of virtual straight lines parallel to each other, and each of the collision plates is arranged between the virtual straight lines next to each other. The tenth aspect facilitates coping with increase in the flow rate of the ejector. 
     In addition to any one of the first to eighth aspects, an eleventh aspect of the present disclosure provides the ejector, where, in a cross section perpendicular to the central axis of the ejector, the inner wall surface of the mixer indicates a circle. Since the cross-sectional shape of the mixer is in similitude relation with the arrangement of the orifices in the atomization mechanism, in other words, the cross-sectional shape of the mixer is in similitude relation with the diffusion pattern of the spray flow, the volumetric efficiency of the ejector can be enhanced. 
     In addition to any one of the first, ninth, and tenth aspects, a twelfth aspect of the present disclosure provides the ejector, where, in a cross section perpendicular to a central axis of the ejector, the inner wall surface of the mixer indicates a polygon. Since the cross-sectional shape of the mixer is in similitude relation with the arrangement of the orifices in the atomization mechanism, in other words, the cross-sectional shape of the mixer is in similitude relation with the diffusion pattern of the spray flow, the volumetric efficiency of the ejector can be enhanced. 
     In addition to any one of the first to twelfth aspects, a thirteenth aspect of the present disclosure provides the ejector, where the plurality of first orifices and the plurality of second orifices are arranged at alternate positions along the collision plate. According to the thirteenth aspect, drip suppression effect can be obtained more sufficiently. 
     In addition to any one of the first to thirteenth aspects, a fourteenth aspect of the present disclosure provides the ejector further including a diffuser that restores static pressure by reducing velocity of the fluid mixture. Since the velocity of the fluid mixture is reduced in the diffuser, the static pressure of the fluid mixture can be restored. 
     A fifteenth aspect of the present disclosure provides an ejector including:
         a first nozzle to which a liquid-phase working fluid is supplied;   a second nozzle into which a vapor-phase working fluid is sucked;   an atomization mechanism that is arranged at an end of the first nozzle and atomizes the liquid-phase working fluid without changing a liquid-phase state of the liquid-phase working fluid; and   a mixer that mixes the atomized working fluid generated in the atomization mechanism and the vapor-phase working fluid sucked into the second nozzle and generates a fluid mixture,   the atomization mechanism including a plurality of orifices and a collision plate against which each of a plurality of jets ejected from the plurality of orifices collides,   the collision plate including a principal surface as a collision surface against which the jet collides, the principal surface extending toward an outlet of the ejector, where   in a cross section including a central axis of the ejector,
           an extension line of the principal surface of the collision plate intersects an inner wall surface of the mixer, or   when, on an opening plane on an outlet side of the mixer, r represents a distance from the central axis of the ejector to the inner wall surface of the mixer, an intersection point of the extension line of the principal surface of the collision plate with the opening plane on the outlet side of the mixer is in a range from a boundary between the opening plane on the outlet side of the mixer and the inner wall surface of the mixer to a position away from the boundary by r/4.   
               

     According to the fifteenth aspect, while the spray flow can be uniformly diffused all over the mixer, collision of the spray flow against the inner wall surface of the mixer can be avoided as much as possible. As a result, loss in the momentum and coalescence of a plurality of droplets, which the collision of the spray flow against the inner wall surface of the mixer causes, can be suppressed and the efficiency of the ejector can be enhanced. 
     A sixteenth aspect of the present disclosure provides a heat pump apparatus including:
         a compressor that compresses refrigerant vapor;   a heat exchanger through which refrigerant liquid flows;   the ejector according to claim  1  that generates a refrigerant mixture using the refrigerant vapor compressed in the compressor and the refrigerant liquid that flows out from the heat exchanger;   an extractor that receives the refrigerant mixture from the ejector and extracts the refrigerant liquid from the refrigerant mixture;   a fluid pathway that passes from the extractor and reaches the ejector through the heat exchanger; and   an evaporator that stores the refrigerant liquid and generates the refrigerant vapor to be compressed in the compressor by vaporizing the refrigerant liquid.       

     According to the sixteenth aspect, the refrigerant liquid supplied to the ejector is utilized as the driving flow and the refrigerant vapor from the compressor is caused to be sucked into the ejector. The ejector generates the refrigerant mixture using the refrigerant liquid and the refrigerant vapor. Since the work to be performed by the compressor can be reduced, the compression ratio of the compressor can be largely decreased and the efficiency of the heat pump apparatus, which is equivalent to or higher than that of a conventional heat pump apparatus, can be achieved. In addition, the heat pump apparatus can be made smaller in size. 
     In addition to the sixteenth aspect, a seventeenth aspect of the present disclosure provides the heat pump apparatus, where pressure of the refrigerant mixture discharged from the ejector is higher than pressure of the refrigerant vapor sucked into the ejector and is lower than pressure of the refrigerant liquid supplied to the ejector. According to the seventeenth aspect, the pressure of the refrigerant can be efficiently boosted. 
     In addition to the sixteenth or seventeenth aspect, an eighteenth aspect of the present disclosure provides the heat pump apparatus, where saturated vapor pressure of a refrigerant at room temperature is negative pressure. 
     In addition to any one of the sixteenth to eighteenth aspects, a nineteenth aspect of the present disclosure provides the heat pump apparatus, where the refrigerant includes water as a principal ingredient. The load to the environment caused by the refrigerant whose principal ingredient is water is small. 
     Embodiments of the present disclosure are described below with reference to the drawings. The present disclosure is not limited to the below-described embodiments. 
     EMBODIMENT 1 
     As illustrated in  FIG. 1 , an ejector  11  includes a first nozzle  40 , a second nozzle  41 , a mixer  42 , a diffuser  43  and an atomization mechanism  44 . The diffuser  43  may be omitted. The first nozzle  40  is a tubular part arranged in a central portion of the ejector  11 . Refrigerant liquid, which is a liquid-phase working fluid, is supplied to the first nozzle  40  as a driving flow. The second nozzle  41  forms annular space around the first nozzle  40 . Refrigerant vapor, which is a vapor-phase working fluid, is sucked into the second nozzle  41 , The mixer  42  is a tubular part that communicates with both the first nozzle  40  and the second nozzle  41 . The atomization mechanism  44  is arranged at an end of the first nozzle  40  so as to face the mixer  42 . The atomization mechanism  44  has a function of atomizing the refrigerant liquid without changing the liquid-phase state of the refrigerant liquid. The atomized refrigerant generated in the atomization mechanism  44  and the refrigerant vapor sucked into the second nozzle  41  are mixed in the mixer  42 , and a refrigerant mixture, which is a fluid mixture, is generated. The diffuser  43  is a tubular part that communicates with the mixer  42  and includes an opening for discharging the refrigerant mixture to the outside of the ejector  11 . The inside diameter of the diffuser  43  is enlarged gradually from the upstream side toward the downstream side. In the diffuser  43 , the velocity of the refrigerant mixture is reduced and thus, the static pressure of the refrigerant mixture is restored. When the diffuser  43  is omitted, the static pressure of the refrigerant mixture is restored in the mixer  42 . The first nozzle  40 , the second nozzle  41 , the mixer  42 , the diffuser  43 , and the atomization mechanism  44  have a common central axis O. 
     As illustrated in  FIGS. 2A and 2B , the atomization mechanism  44  includes an ejection part  51  and a collision plate  53 , which is a collision surface formation part. The ejection part  51  is attached at the end of the first nozzle  40 . A plurality of orifices  51   a  and  51   b,  which are ejection openings, are formed through the ejection part  51 . The plurality of orifices  51   a  and  51   b  penetrate the ejection part  51  so as to allow communication between the first nozzle  40  and the mixer  42 . The refrigerant liquid is ejected from the first nozzle  40  to the collision plate  53  through the plurality of orifices  51   a  and  51   b.  That is, the ejection part  51  can generate a jet of the refrigerant liquid. Each of the plurality of jets ejected from the plurality of orifices  51   a  and  51   b  collides against the collision plate  53 . Thus, a fine spray flow is generated. 
     The collision plate  53  includes a first principal surface  53   p  and a second principal surface  53   q  as collision surfaces against which the jets ejected from the ejection part  51  collide. Each of the first principal surface  53   p  and the second principal surface  53   q  extends toward the outlet of the ejector  11 . The plurality of orifices  51   a  and  51   b  include the plurality of first orifices  51   a  and the plurality of second orifices  51   b.  The plurality of first orifices  51   a  are arranged on the side of the first principal surface  53   p  of the collision plate  53 . The plurality of second orifices  51   b  are arranged on the side of the second principal surface  53   q  of the collision plate  53 . The jets ejected from the first orifices  51   a  collide against the first principal surface  53   p  of the collision plate  53 . The jets ejected from the second orifices  51   b  collide against the second principal surface  53   q  of the collision plate  53 . As described above, the atomization mechanism  44  is structured so that jets collide against two principal surfaces of the collision plate  53 . The “principal surface” represents a surface with the largest area. 
     As illustrated in  FIG. 4A , when jets JF of the refrigerant liquid are caused to collide against only one surface of a collision plate  47 , a jet film jf is formed on the single surface of the collision plate  47 . The jet film jf flows along the collision plate  47  and is atomized while issuing from the end of the collision plate  47 . At the time, a gradient of the velocity is caused in the jet film jf. That is, the velocity of the jet film jf is low in a position close to the collision plate  47  and high in a position away from the collision plate  47 . The difference in the flow velocity and the surface tension allow the refrigerant liquid to move around an end surface of the collision plate  47 , and drip WD occurs and drops. The drip WD is one of causes that decrease the performance of the ejector. 
     As illustrated in  FIG. 4B , when jets JF of refrigerant liquid are caused to collide against two surfaces of the collision plate  47 , the jet film jf is formed on both the two surfaces of the collision plate  47 . Also in the example of  FIG. 4B , the refrigerant liquid moves around the end surface of the collision plate  47  and drip occurs. However, the drip from one of the two surfaces is involved in the jet film jf on the other surface and atomized. That is, the atomization mechanism  44  according to the present embodiment can efficiently generate a spray flow while suppressing the occurrence of drip. 
     As illustrated in  FIG. 2A , in the present embodiment, the collision plate  53  is a tubular part that extends toward the outlet of the ejector  11  from a surface of the ejection part  51 . The first principal surface  53   p  and the second principal surface  53   q  are each a conical surface. Specifically, the first principal surface  53   p  is formed so that the distance from the central axis O to the first principal surface  53   p  increases toward the outlet of the ejector  11 . The second principal surface  53   q  is formed so that the distance from the central axis O to the second principal surface  53   q  decreases toward the outlet of the ejector  11 . The collision plate  53  shaped as described above enables a spray flow to be uniformly supplied into the mixer  42 . The shape of the collision plate is not particularly limited. 
     As illustrated in  FIG. 2A , the central axis of the first orifice  51   a  is inclined with respect to the first principal surface  53   p  of the collision plate  53  and intersects the collision plate  53 . The central axis of the second orifice  51   b  is inclined with respect to the second principal surface  53   q  of the collision plate  53  and intersects the collision plate  53 . Each of the axis of the first orifice  51   a  and the axis of the second orifice  51   b  may be inclined with respect to an inner wall surface  42   p  of the mixer  42 . The opening shape, that is, the cross-sectional shape of each of the orifices  51   a  and  51   b  is not particularly limited. The opening shape of each of the orifices  51   a  and  51   b  is, for example, a circle, an ellipse, or a rectangle. The sizes of the droplets can be made uniform by suitably specifying the shape, the number, the arrangement, and the like of the orifices  51   a  and  51   b.    
     As illustrated in  FIG. 2B , the plurality of first orifices  51   a  are arranged at equiangular intervals along the first principal surface  53   p  of the collision plate  53 . That is, the plurality of first orifices  51   a  are arranged on a first virtual circle C 1 . Similarly, the plurality of second orifices  51   b  are arranged at equiangular intervals along the second principal surface  53   q  of the collision plate  53 . That is, the plurality of second orifices  51   b  are arranged on a second virtual circle C 2 , which is concentric with the first virtual circle C 1 . Pairs of the first orifices  51   a  and the second orifices  51   b  are positioned at respective equal angles around the central axis O. The first principal surface  53   p,  which is a conical surface, is concentric with the first virtual circle C 1  and the second virtual circle C 2 . The second principal surface  53   q,  which is a conical surface, is also concentric with the first virtual circle C 1  and the second virtual circle C 2 . According to the above-described arrangement, drip caused by the refrigerant liquid moving around can be sufficiently suppressed. The plurality of first orifices  51   a  are arranged so as to have axial symmetry and the plurality of second orifices  51   b  are arranged so as to have axial symmetry. Accordingly, lack of uniformity in the diameters of the droplets in the spray flow can be suppressed. The number of the first orifices  51   a  may be the same as or different from the number of the second orifices  51   b.    
     As illustrated in  FIG. 3 , in a cross section perpendicular to the central axis O of the ejector  11 , the inner wall surface  42   p  of the mixer  42  indicates a circle. In the present embodiment, the first principal surface  53   p  and the second principal surface  53   q,  which are the collision surfaces, are each a conical surface. Accordingly, the spray flow diffuses conically in the mixer  42 . Since the cross-sectional shape of the mixer  42  is in similitude relation with the arrangement of the orifices  51   a  and  51   b  in the atomization mechanism  44 , in other words, the cross-sectional shape of the mixer  42  is in similitude relation with the diffusion pattern of the spray flow, the volumetric efficiency of the ejector  11  can be enhanced. 
     In the present embodiment, the mixer  42  is made up of a portion where the cross-sectional area, that is, the inside diameter gradually decreases and a portion where the cross-sectional area or the inside diameter remains unchanged. As described below, only the portion where the cross-sectional area gradually decreases may constitute the mixer  42 . 
     As described above, to enhance the performance of the ejector  11 , it is desirable that the spray flow generated in the atomization mechanism  4  be caused to avoid colliding against the inner wall surface  42   p  of the mixer  42  as much as possible. In addition to the inclination of the collision surface positioned farthest from the central axis O, which is the first principal surface  53   p,  the positional relation between the collision surface and the inner wall surface  42   p  of the mixer  42  is important. The present embodiment employs a structure, which is described below. 
     As illustrated in  FIG. 5A , in a cross section including the central axis O of the ejector  11 , an extension line L 1  of the first principal surface  53   p  of the collision plate  53  intersects the inner wall surface  42   p  of the mixer  42 . An intersection point K 1  of the extension line L 1  and the inner wall surface  42   p  is positioned slightly more on the upstream side, compared with the boundary K between an opening plane  42   q  on the outlet side of the mixer  42  and the inner wall surface  42   p  of the mixer  42 . The spray flow diffuses slightly more inside than the extension line L 1 , that is, toward the side closer to the central axis O, because of interference with a liquid pool formed on the end surface of the collision plate  53 . Accordingly, the configuration illustrated in  FIG. 5A  enables the spray flow to avoid colliding against the inner wall surface  42   p  of the mixer  42  as much as possible while the spray flow is uniformly diffused all over the mixer  42 . As a result, loss in the momentum and coalescence of a plurality of droplets, which the collision of the spray flow against the inner wall surface  42   p  of the mixer  42  causes, can be suppressed and the efficiency of the ejector  11  can be enhanced. 
     As illustrated in  FIG. 5B  for another example, in the cross section including the central axis O of the ejector  11 , an intersection point K 2  of the extension line L 1  of the first principal surface  53   p  of the collision plate  53  and the opening plane  42   q  on the outlet side of the mixer  42  is positioned in a range from the boundary K between the opening plane  42   q  on the outlet side of the mixer  42  and the inner wall surface  42   p  of the mixer  42  to a position away from the boundary K by r/4, where, on the opening plane  42   q  on the outlet side of the mixer  42 , r represents the distance from the central axis O of the ejector  11  to the inner wall surface  42   p  of the mixer  42 . The configuration illustrated in  FIG. 5B  also enables the spray flow to avoid colliding against the inner wall surface  42   p  of the mixer  42  as much as possible while the spray flow is uniformly diffused all over the mixer  42 . 
     In the cross section including the central axis O of the ejector  11 , the extension line L 1  of the first principal surface  53   p  of the collision plate  53  may intersect the boundary K. The angle between the extension line L 1  that satisfies the condition depicted in  FIG. 5A  and the inner wall surface  42   p  of the mixer  42  is equal to or smaller than, for example, 10°. The angle between the extension line L 1  that satisfies the condition depicted in  FIG. 5B  and the inner wall surface  42   p  of the mixer  42 , which is specifically an extension line of the inner wall surface  42   p,  is equal to or smaller than, for example, 10°. 
     As illustrated in  FIG. 6 , in an atomization mechanism  44 B according to a variation, the first orifices  51   a  and the second orifices  51   b  are arranged at alternate positions along the collision plate  53 . In other words, the first orifices  51   a  and the second orifices  51   b  are alternately arranged around the central axis O. As illustrated in  FIG. 7 , jets JF 1  ejected from the first orifices  51   a  collide against the first principal surface  53   p  and a liquid film, which is a spray flow, is formed. At the time, the drip described with reference to  FIG. 4A  can easily occur on the end surface of the collision plate  53 . However, since a liquid film is also present on the second principal surface  53   q  of the collision plate  53 , the drip can be suppressed in the present embodiment (see  FIG. 4B ). The drip can easily occur in regions  48  near both ends of the liquid films. However, when a jet JF 2  ejected from the second orifice  51   b  is present between the jets JF 1  next to each other, the liquid is unlikely to move in a width direction on the end surface of the collision plate  53 . Thus, drip suppression effect can be obtained more sufficiently. When the first orifices  51   a  and the second orifices  51   b  are alternately arranged, confluence of the liquid films can be suppressed by the effect of the dynamic pressure and the surface tension. 
     As illustrated in  FIG. 8 , in an atomization mechanism  44 C according to another variation, the opening shape of each of the orifices  51   a  and  51   b  is a rectangle. That is, the atomization mechanism  44 C includes the orifices  51   a  and  51   b  like slits. Also in the present variation, the first orifices  51   a  and the second orifices  51   b  are alternately arranged around the central axis O. 
     As illustrated in  FIGS. 9A and 9B , in an atomization mechanism  44 D according to still another variation, a plurality of collision plates, each of which is the collision plate  53 , are provided and the number of the collision plates  53  is two in the present variation, Specifically, the plurality of collision plates  53  are arranged in directions extending from the central axis O of the ejector  11  toward the inner wall surface  42   p  of the mixer  42 . The plurality of orifices  51   a  and  51   b  are arranged on a plurality of virtual circles, which are concentric with one another and are not illustrated. Each collision plate  53  is arranged between the virtual circles next to each other. The tubular collision plates  53  are also concentric with the virtual circles. As described above, each of the first principal surface  53   p  and the second principal surface  53   q  of the collision plate  53  may be a conical surface. The present variation facilitates coping with increase in the flow rate of the ejector  11 . Furthermore, the orifices  51   a  and  51   b  that each have a small cross-sectional area can be employed without difficulty. 
     The first orifices  51   a  and the second orifices  51   b  may be alternately arranged around the central axis O. 
     In the atomization mechanism  44 D, in the collision plate  53  arranged closest to the inner wall surface  42   p  of the mixer  42 , the first principal surface  53   p  is positioned nearer to the inner wall surface  42   p  of the mixer  42  than the second principal surface  53   q  is. The first principal surface  53   p  closest to the inner wall surface  42   p  of the mixer  42  satisfies the conditions described with reference to  FIGS. 5A and 5B . That is, the extension line L 1  of the first principal surface  53   p  intersects the inner wall surface  42   p  of the mixer  42 , or the intersection point K 2  of the extension line L 1  of the first principal surface  53   p  and the opening plane  42   q  on the outlet side of the mixer  42  is positioned in a range from the boundary K to the position away from the boundary K by r/4. According to the above-described configuration, the advantages described with reference to  FIGS. 5A and 5B  can be obtained even when the plurality of collision plates  53  are provided. 
     As illustrated in  FIG. 9C , in an atomization mechanism  44 E according to still another variation, the second orifices  51   b  are omitted from the atomization mechanism  44 D described with reference to  FIGS. 9A and 9B . That is, when the number of the collision plates  53 , the number of the first orifices  51   a,  and the like are suitably set, an even spray flow can be supplied to the mixer  42  without causing jets to collide against two surfaces of each collision plate  53 . 
     As illustrated in  FIG. 10 , an atomization mechanism  44 F according to still another variation is also provided with the plurality of collision plates  53  and the number of the collision plates  53  is two in the present variation. The first principal surface  53   p  and the second principal surface  53   q  of the collision plate  53  are each a cylindrical surface. That is, the first principal surface  53   p  and the second principal surface  53   q  are parallel to the central axis O. The extension line L 1  of the first principal surface  53   p  closest to the inner wall surface  42   p  of the mixer  42  satisfies the conditions described with reference to  FIGS. 5A and 5B . In the example illustrated in  FIG. 10 , the extension line L 1  intersects the boundary K. Such a configuration can also bring the above-described advantages. 
     In the example illustrated in  FIG. 10 , the cross-sectional area of the mixer  42  gradually decreases toward the opening plane  42   q  on the outlet side. Such a structure can also be desirably employed in the ejector of the present disclosure. 
     EMBODIMENT 2 
     As illustrated in  FIGS. 11, 12A, and 12B , in an ejector  61  according to Embodiment 2, an atomization mechanism  46  has a rectangular shape in a plan view. Specifically, the atomization mechanism  46  includes an ejection part  71 , which is shaped like a rectangular solid, and a collision plate  73 , which is shaped like a flat plate. A plurality of orifices  71   a  and  71   b  are formed through the ejection part  71 . The collision plate  73  includes a first principal surface  73   p  and a second principal surface  73   q  as collision surfaces against which the jets ejected from the ejection part  71  collide. Each of the first principal surface  73   p  and the second principal surface  73   q  extends toward the outlet of the ejector  61 . The first principal surface  73   p  and the second principal surface  73   q  are each a flat surface. The first principal surface  73   p  is slightly inclined with respect to the second principal surface  73   q.  The plurality of orifices  71   a  and  71   b  include the plurality of first orifices  71   a  and the plurality of second orifices  71   b.  The plurality of first orifices  71   a  are arranged on the side of the first principal surface  73   p  of the collision plate  73 . The plurality of second orifices  71   b  are arranged on the side of the second principal surface  73   q  of the collision plate  73 . The jet ejected from the first orifice  71   a  collides against the first principal surface  73   p  of the collision plate  73 . The jet ejected from the second orifice  71   b  collides against the second principal surface  73   q  of the collision plate  73 . 
     As illustrated in  FIG. 12B , the plurality of first orifices  71   a  are arranged at equal intervals along the first principal surface  73   p  of the collision plate  73 . That is, when the atomization mechanism  46  is viewed from the outlet side of the ejector  61  as a plane, the plurality of first orifices  71   a  are arranged on a first virtual straight line G 1 . Similarly, the plurality of second orifices  71   b  are arranged at equal intervals along the second principal surface  73   q  of the collision plate  73 . That is, the plurality of second orifices  71   b  are arranged on a second virtual straight line G 2  parallel to the first virtual straight line G 1 . The first principal surface  73   p  is parallel to the first virtual straight line G 1  and the second virtual straight line G 2 . The second principal surface  73   q  is also parallel to the first virtual straight line G 1  and the second virtual straight line G 2 . According to the above-described arrangement, drip caused by the liquid-phase working fluid moving around can be sufficiently suppressed. 
     The cross-sectional view in  FIG. 11  includes the central axis O of the ejector  61  and is perpendicular to the direction in which the orifices  71  a are arranged and/or the direction in which the orifices  71   b  are arranged. 
     As illustrated in  FIG. 13 , in a cross section perpendicular to the central axis O of the ejector  61 , an inner wall surface  42   p  of a mixer  42  indicates a polygon. Specifically, the shape indicated by the inner wall surface  42   p  in the cross section is a rectangle. In the present embodiment, each of the first principal surface  73   p  and the second principal surface  73   q,  which are the collision surfaces, is a flat surface. Accordingly, the spray flow diffuses rectangularly in the mixer  42 . Since the cross-sectional shape of the mixer  42  is in similitude relation with the arrangement of the orifices  71   a  and  71   b  in the atomization mechanism  46 , in other words, the cross-sectional shape of the mixer  42  is in similitude relation with the diffusion pattern of the spray flow, the volumetric efficiency of the ejector  61  can be enhanced. 
     As illustrated in  FIG. 14 , in an atomization mechanism  46 B according to a variation, the first orifices  71   a  and the second orifices  71   b  are arranged at alternate positions along the collision plate  73 . As described with reference to  FIGS. 6 and 7  in the first embodiment, according to the above-described configuration, drip suppression effect can be obtained more sufficiently. 
     As illustrated in  FIG. 15 , in an atomization mechanism  46 C according to another variation, the opening shape of each of the orifices  71   a  and  71   b  is a rectangle. That is, the atomization mechanism  46 C includes the orifices  71   a  and  71   b  like slits. 
     As illustrated in  FIG. 16 , an atomization mechanism  46 D according to another variation includes a plurality of collision plates, each of which is the collision plate  73 , and the number of the collision plates  73  is three in the present variation. The plurality of orifices  71   a  and  71   b  are arranged on a plurality of virtual straight lines, which are parallel to one another and are not illustrated. Each collision plate  73  is arranged between the virtual straight lines next to each other. The present variation facilitates coping with increase in the flow rate of the ejector  61 . Furthermore, the orifices  71   a  and  71   b  that each have a small cross-sectional area can be employed without difficulty. 
     The configurations in the embodiments and the variations described above may be combined as long as no technical contradiction arises. 
     EMBODIMENT OF HEAT PUMP APPARATUS USING EJECTOR 
     As illustrated in  FIG. 17 , a heat pump apparatus  200  of the present embodiment, which is a refrigeration cycle apparatus, includes a first heat exchange unit  10 , a second heat exchange unit  20 , a compressor  31 , and a vapor pathway  32 . The first heat exchange unit  10  and the second heat exchange unit  20  constitute a heat-radiation-side circuit and a heat-absorption-side circuit, respectively. The refrigerant vapor generated in the second heat exchange unit  20  passes through the compressor  31  and the vapor pathway  32  and is supplied to the first heat exchange unit  10 . 
     The heat pump apparatus  200  is filled with a refrigerant whose saturated vapor pressure at room temperature, which is 20° C.±15° C. according to JIS Z8703 of Japanese Industrial Standards (JIS), is negative pressure, that is, pressure lower than atmospheric pressure in absolute pressure. An example of such a refrigerant is a refrigerant that includes water, alcohol, or ether as the principal ingredient. During operation of the heat pump apparatus  200 , the pressure inside the heat pump apparatus  200  is lower than the atmospheric pressure. The pressure at the inlet of the compressor  31  is, for example, in a range from 0.5 kPaA to 5 kPaA. The pressure at the outlet of the compressor  31  is, for example, in a range from 5 kPaA to 15 kPaA. Another example of the refrigerant usable includes water for preventing freezing or the like as the principal ingredient and includes ethylene glycol, Naiburain (trademark), an inorganic salt, or the like mixed to make up 10% to 40% when converted to mass percentage. The “principal ingredient” represents the ingredient that is included the most at the mass ratio. 
     The first heat exchange unit  10  includes the ejector  11 , a first extractor  12 , a first pump  13 , and a first heat exchanger  14 . The ejector  11 , the first extractor  12 , the first pump  13 , and the first heat exchanger  14  are annularly connected in the named order through pipes  15   a  to  15   d.    
     The ejector  11  is connected to the first heat exchanger  14  through the pipe  15   d  and is connected to the compressor  31  through the vapor pathway  32 . The ejector  11  is supplied with the refrigerant liquid that flows out from the first heat exchanger  14  as the driving flow and supplied with the refrigerant vapor compressed in the compressor  31  as the suction flow. The ejector  11  generates a refrigerant mixture with a small quality, that is, dryness, and supplies the refrigerant mixture to the first extractor  12 . The refrigerant mixture is a refrigerant in a liquid-phase state or a gas-liquid two-phase state, where the quality is very small. The pressure of the refrigerant mixture discharged from the ejector  11  is, for example, higher than the pressure of the refrigerant vapor sucked into the ejector  11  and lower than the pressure of the refrigerant liquid supplied to the ejector  11 . 
     The first extractor  12  receives the refrigerant mixture from the ejector  11  and extracts the refrigerant liquid from the refrigerant mixture. That is, the first extractor  12  serves as a gas-liquid separator, which separates the refrigerant liquid and the refrigerant vapor. Basically, only the refrigerant liquid is taken out from the first extractor  12 . The first extractor  12  is made up of, for example, a pressure-resistant container with heat insulating properties. As long as the refrigerant liquid can be extracted, the structure of the first extractor  12  is not particularly limited. The pipes  15   b  to  15   d  constitute a fluid pathway  15 , which passes from the first extractor  12  and reaches the ejector  11  through the first heat exchanger  14 . The first pump  13  is provided between the liquid outlet of the first extractor  12  and the inlet of the first heat exchanger  14  in the fluid pathway  15 . The first pump  13  presses and sends the refrigerant liquid stored in the first extractor  12  to the first heat exchanger  14 . The discharge pressure of the first pump  13  is lower than the atmospheric pressure. The first pump  13  is arranged at a position where the available net positive suction head (NPSH), which takes account of the height from the suction port of the first pump  13  to the level of the refrigerant liquid in the first extractor  12 , is larger than the required NPSH. The first pump  13  may be arranged between the outlet of the first heat exchanger  14  and the liquid inlet of the ejector  11 . 
     The first heat exchanger  14  is made up of a known heat exchanger, such as a finned tube heat exchanger or a shell and tube heat exchanger. When the heat pump apparatus  200  is an air conditioner that cools air indoors, the first heat exchanger  14  is arranged outdoors and heats outdoor air using the refrigerant liquid. 
     The second heat exchange unit  20  includes an evaporator  21 , a pump  22 , which may be referred to as a second pump, and a second heat exchanger  23 . The evaporator  21  stores the refrigerant liquid and generates refrigerant vapor to be compressed in the compressor  31  by vaporizing the refrigerant liquid. The evaporator  21 , the pump  22 , and the second heat exchanger  23  are annularly connected through pipes  24   a  to  24   c.  The evaporator  21  is made up of, for example, a pressure-resistant container with heat insulating properties. The pipes  24   a  to  24   c  constitute a circulation passage  24  in which the refrigerant liquid stored in the evaporator  21  is circulated through the second heat exchanger  23 . The pump  22  is provided between the liquid outlet of the evaporator  21  and the inlet of the second heat exchanger  23  in the circulation passage  24 . The pump  22  presses and sends the refrigerant liquid stored in the evaporator  21  to the second heat exchanger  23 . The discharge pressure of the pump  22  is lower than the atmospheric pressure. The pump  22  is arranged at a position where the available NPSH, which takes account of the height from the suction port of the pump  22  to the level of the refrigerant liquid in the evaporator  21 , is larger than the required NPSH. 
     The second heat exchanger  23  is made up of a known heat exchanger, such as a finned tube heat exchanger or a shell and tube heat exchanger. When the heat pump apparatus  200  is an air conditioner that cools air indoors, the second heat exchanger  23  is arranged indoors and cools indoor air using the refrigerant liquid. 
     In the present embodiment, the evaporator  21  is a heat exchanger that directly vaporizes the refrigerant liquid inside, which is heated by circulating through the circulation passage  24 . The refrigerant liquid stored in the evaporator  21  comes into direct contact with the refrigerant liquid that circulates through the circulation passage  24 . That is, part of the refrigerant liquid in the evaporator  21  is heated in the second heat exchanger  23  and used as a heat source that heats the refrigerant liquid in a saturated state. The upstream end of the pipe  24   a  is desirably connected to the lower portion of the evaporator  21 . The downstream end of the pipe  24   c  is desirably connected to the middle portion of the evaporator  21 . The second heat exchange unit  20  may be structured so that the refrigerant liquid stored in the evaporator  21  is not mixed into another refrigerant liquid that circulates through the circulation passage  24 . For example, when the evaporator  21  has a heat exchange structure, such as the structure of the shell and tube heat exchanger, the refrigerant liquid stored in the evaporator  21  can be heated using a heating medium that circulates through the circulation passage  24  to be vaporized. The heating medium for heating the refrigerant liquid stored in the evaporator  21  flows to the second heat exchanger  23 . 
     The vapor pathway  32  includes an upstream portion  32   a  and a downstream portion  32   b.  The compressor  31  is arranged in the vapor pathway  32 . The upstream portion  32   a  of the vapor pathway  32  connects the upper portion of the evaporator  21  to the suction port of the compressor  31 . The downstream portion  32   b  of the vapor pathway  32  connects the discharge outlet of the compressor  31  to the second nozzle  41  of the ejector  11 . The compressor  31  is a cyclone compressor or a positive-displacement compressor. A plurality of compressors may be provided in the vapor pathway  32 . The compressor  31  sucks the refrigerant vapor from the evaporator  21  of the second heat exchange unit  20  through the upstream portion  32   a  and compresses the refrigerant vapor. The compressed refrigerant vapor flows through the downstream portion  32   b  and is supplied to the ejector  11 . 
     According to the present embodiment, the temperature and the pressure of the refrigerant are boosted in the ejector  11 . Since the work to be performed by the compressor  31  can be reduced, the compression ratio of the compressor  31  can be largely decreased and the efficiency of the heat pump apparatus  200 , which is equivalent to or higher than that of a conventional heat pump apparatus, can be achieved. In addition, the heat pump apparatus  200  can be made smaller in size. 
     The heat pump apparatus  200  is not limited to an air conditioner for air cooling purpose. A passage switcher, such as a four-way valve or a three-way valve, may be provided so that the first heat exchanger  14  functions as a heat-absorbing heat exchanger and the second heat exchanger  23  functions as a heat-radiating heat exchanger. In this case, an air conditioner where a cooling mode and a heating mode are switchable can be obtained. The heat pump apparatus  200  is not limited to an air conditioner and may be another apparatus, such as a chiller or a thermal storage. A heating target of the first heat exchanger  14  and a cooling target of the second heat exchanger  23  may be gas or liquid other than air, 
     A return passage  33  for returning the refrigerant from the first heat exchange unit  10  to the second heat exchange unit  20  may be provided. An expansion mechanism  34 , such as a capillary or an expansion valve, is provided in the return passage  33 . In the present embodiment, to transfer the refrigerant stored in the first extractor  12  to the evaporator  21 , the return passage  33  connects the first extractor  12  and the evaporator  21 . Typically, the lower portion of the first extractor  12  and the lower portion of the evaporator  21  are connected through the return passage  33 . The refrigerant liquid that flows from the first extractor  12  in the return passage  33  is reduced in pressure in the expansion mechanism  34  and returned to the evaporator  21 . 
     The return passage  33  may branch from any position of the first heat exchange unit  10 . For example, the return passage  33  may branch from the pipe  15   a  that connects the ejector  11  and the first extractor  12  or may branch from the upper portion of the first extractor  12 . Returning the refrigerant from the first heat exchange unit  10  to the second heat exchange unit  20  may be omitted. For example, the first heat exchange unit  10  may be structured so that a redundant refrigerant can be discharged when necessary, and the second heat exchange unit  20  may be structured so that the refrigerant can be added when necessary. 
     The ejector and the heat pump apparatus disclosed herein is useful particularly for an air conditioner, such as a home air conditioner or an industrial air conditioner.