Patent Publication Number: US-2023142460-A1

Title: Outdoor unit for air-conditioning apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a U.S. National Stage Application of International Application No. PCT/JP2020/023211 filed on Jun. 12, 2020, the contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an outdoor unit, including a bellmouth, for an air-conditioning apparatus. 
     BACKGROUND 
     Patent Literature 1 discloses an outdoor unit, including a bellmouth, for an air-conditioning apparatus. The bellmouth is provided upstream of a main flow of air and has a contraction portion whose pipe diameter is reduced from the upstream side toward the downstream side of the main flow of air and that is formed by a bend surface, and a straight pipe portion connecting to the downstream side of the contraction portion. In Patent Literature 1, interference between the bellmouth and a heat exchanger is inhibited by changing the curvature radius of the contraction portion in a circumferential direction. 
     PATENT LITERATURE 
     
         
         Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2013-96622 
       
    
     In the bellmouth, contraction of flow of air in the contraction portion generates contracted flow in the straight pipe portion, and a vortex may thus be generated at an inner surface of the straight pipe portion. In addition, due to the change in the curvature radius of the contraction portion in the circumferential direction, the bellmouth in Patent Literature 1 has a part in which the length of the contraction portion along the direction of the main flow of air is shorter than the length of the straight pipe portion along the direction of the main flow of air. In the part in which the length of the contraction portion along the direction of the main flow of air is shorter, when air flowing in a direction different from the direction of the main flow of air flows into the bend surface of the contraction portion, a directing angle for directing, in the direction of the main flow of air, the air flowing thereinto in the direction different from the direction of the main flow of air is large. When the directing angle is large, it is not possible to direct, in the direction of the main flow of air, air flowing in a direction different from the direction of the main flow of air. Thus, air separation occurs at the straight pipe portion, resulting in generation of a vortex. Such a vortex generated at the straight pipe portion increases in size as the straight pipe portion becomes longer. The vortex at the straight pipe portion substantially narrows an air passage in the straight pipe portion. As a result, pressure loss may occur in the straight pipe portion of the bellmouth in Patent Literature 1 due to the air passage in the straight pipe portion being substantially narrowed. 
     SUMMARY 
     The present disclosure is made to solve the above problem, and an object of the present disclosure is to provide an outdoor unit for an air-conditioning apparatus capable of inhibiting pressure loss from occurring in a bellmouth. 
     An outdoor unit for an air-conditioning apparatus of an embodiment of the present disclosure includes: a heat exchanger; an axial flow fan configured to generate flow of air passing through the heat exchanger; a casing having an opening through which the air passes, the casing accommodating the heat exchanger, and accommodating the axial flow fan between the opening and the heat exchanger; and a bellmouth having an annular shape and provided around the axial flow fan inside the casing to guide the air into the opening of the casing. The bellmouth has a first tapered portion in which an inner diameter of an upstream side of the bellmouth from which the air flows in is larger than an inner diameter of a downstream side of the bellmouth, and a straight pipe portion extending straight from the first tapered portion to the downstream side of the flow of the air. The first tapered portion includes a first bend portion forming an inlet for the air, a second bend portion connecting to the straight pipe portion and having an inner diameter smaller than that of the first bend portion, and a connection portion connecting to the first bend portion and the second bend portion and having an inner surface extending straight. A length of at least a part of the first tapered portion along an axial direction of the straight pipe portion is larger than a length of the straight pipe portion along the axial direction of the straight pipe portion. 
     In the above configuration of the embodiment of the present disclosure, the first tapered portion includes the connection portion having the inner surface extending straight, and the length of at least a part of the first tapered portion along the axial direction of the straight pipe portion is larger than the length of the straight pipe portion along the axial direction of the straight pipe portion. That is, the first tapered portion, which is a contraction portion, has a straight inner surface, and the length of a passage in the first tapered portion in the direction of a main flow of air is larger than the length of a passage in the straight pipe portion in the direction of the main flow of air. Accordingly, this configuration enables flow of air in the first tapered portion to be smoothly contracted and enables, even when air flowing in a direction different from the direction of the main flow of air flows into the first tapered portion, the air to be smoothly directed, in the first tapered portion, in the direction of the main flow of air. As a result, with the configuration of the embodiment of the present disclosure, it is possible to inhibit the air passage in the straight pipe portion from being substantially narrowed due to generation of a vortex at the straight pipe portion and to thus provide an outdoor unit for an air-conditioning apparatus capable of inhibiting pressure loss from occurring in a bellmouth. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic top view of an example of the internal structure of an outdoor unit for an air-conditioning apparatus according to Embodiment. 
         FIG.  2    is an enlarged schematic view of a part of a section of a bellmouth in  FIG.  1   . 
         FIG.  3    is a schematic diagram illustrating the relationship between a first curvature radius and a first central angle at a first edge line according to Embodiment. 
         FIG.  4    is a schematic diagram illustrating the relationship between the first curvature radius and a second curvature radius at a first tapered portion according to Embodiment. 
         FIG.  5    is an enlarged schematic view of a first section and a second section of the bellmouth in  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiment 
     The structure of an outdoor unit  100  for an air-conditioning apparatus according to Embodiment will be described.  FIG.  1    is a schematic top view of an example of the internal structure of the outdoor unit  100  for an air-conditioning apparatus according to Embodiment. In  FIG.  1   , the direction of a main flow of air when the outdoor unit  100  is driven is represented by white block arrows, and directions of air flow different from the direction of the main flow of air are represented by dot-patterned block arrows. 
     In the following drawings including  FIG.  1   , the size relationships or the shapes of the components of the outdoor unit  100  may differ from those of actual ones. In addition, basically, the positional relationships between the components of the outdoor unit  100  in, for example, an up-down direction, a left-right direction, or a front-rear direction are those when the outdoor unit  100  is set in a usable state. In the following drawings including  FIG.  1   , the same or similar components or parts have the same reference signs or have no reference signs. 
     The outdoor unit  100  includes a casing  10 , which accommodates a heat exchanger  1 , an axial flow fan  3 , and a compressor  5 . The casing  10  is formed by combining a plurality of sheet metal panels, for example. The casing  10  has an opening  10   a  in communication with the inside of the casing  10 . As illustrated in  FIG.  1   , for example, the opening  10   a  is disposed at the front of the casing  10 . In addition, a grille  10   b , which covers the opening  10   a , is disposed at the casing  10 . 
     The heat exchanger  1  exchanges heat between airflow passing through the heat exchanger  1  and refrigerant flowing in the heat exchanger  1 . For example, an air-cooled heat exchanger  1  such as a finned tube heat exchanger that includes a plurality of plate-like fins disposed side by side and a plurality of heat transfer tubes passing through the plate-like fins is used as the heat exchanger  1 . In  FIG.  1   , the heat exchanger  1  is formed as a heat exchanger  1  having an L shape in top view and including a first portion  1   a , which is disposed at the rear of the casing  10 , and a second portion  1   b , which is disposed at the left of the casing  10 . The heat exchanger  1  having an L shape is merely an example of the heat exchanger  1 . The heat exchanger  1  can have a different shape. 
     The axial flow fan  3  is disposed between the heat exchanger  1  and the opening  10   a  provided in the casing  10 . For example, a propeller fan is used as the axial flow fan  3 . The axial flow fan  3  includes a plurality of blades  3   a , which are configured to rotate to generate flow of air, a hub  3   b , which is configured to support and rotate the blades  3   a , a shaft  3   c , which has one tip end connected to the hub  3   b , and a motor  3   d , which is connected to the other tip end of the shaft  3   c  and is configured to rotate the shaft  3   c . The one tip end of the shaft  3   c  of the axial flow fan  3  is disposed to face the opening  10   a . For example, a three-phase induction motor or a brushless DC motor capable of controlling the rotation speed of the shaft  3   c  on the basis of voltage is used as the motor  3   d.    
     The compressor  5  compresses suctioned low-pressure refrigerant into high-pressure refrigerant and discharges the high-pressure refrigerant. For example, a rotary compressor or a scroll compressor is used as the compressor  5 . Although not illustrated, the compressor  5  is connected to the heat exchanger  1  by a refrigerant pipe. 
     In addition, a partition plate  15  is set in the casing  10 . The inside of the casing  10  is partitioned into a fan chamber  15   a  and a machine chamber  15   b  with the partition plate  15 . The heat exchanger  1  and the axial flow fan  3  are disposed in the fan chamber  15   a . The compressor  5  is disposed in the machine chamber  15   b . In  FIG.  1   , the partition plate  15  is formed as a plate-like component having a section shaped by a single straight line but can be a plate-like component having a section having a different shape. For example, the partition plate  15  may be a plate-like component having a section shaped by one or more curved surfaces, a plate-like component having a section shaped by a plurality of straight lines, or a plate-like component having both a section shaped by a straight line and a section shaped by a curved line. The partition plate  15  can be omitted according to the use of the outdoor unit  100 , for example. 
     In addition, the outdoor unit  100  includes a bellmouth  20 , which is accommodated in the casing  10 . The bellmouth  20  is an annular component having an air passage along which airflow generated by rotation of the axial flow fan  3  is guided into the opening  10   a . The bellmouth  20  connects to the casing  10  at the front of the casing  10 , for example, around the periphery of the opening  10   a  provided in a front panel thereof. For example, the bellmouth  20  is integrally formed with the front panel of the casing  10  by subjecting sheet metal to plastic deformation by press working or other methods.  FIG.  1    illustrates an inlet  20   a , into which air generated by rotation of the axial flow fan  3  flows, of the bellmouth  20 . In addition,  FIG.  1    illustrates a first section  20   b , which is located between the axial flow fan  3  and the second portion  1   b  of the heat exchanger  1 , and a second section  20   c , which is located between the axial flow fan  3  and the partition plate  15 , of the bellmouth  20 . 
     The bellmouth  20  is formed to guide air suctioned into the casing  10  to the axial flow fan  3  and to optimize the angle at which air flows to the blades  3   a . The axial flow fan  3  is surrounded by the bellmouth  20  and accommodated in the casing  10 . A part of the axial flow fan  3  is accommodated in the bellmouth  20  by surrounding the axial flow fan  3  by the bellmouth  20 . Thus, it is possible to reduce the width of the outdoor unit  100  in the front-rear direction. Other parts of the structure of the bellmouth  20  will be described later. 
     When the outdoor unit  100  is driven, air outside the outdoor unit  100  is guided into the casing  10 , for example, into the fan chamber  15   a , by rotation of the axial flow fan  3  and is subjected to heat exchange in the heat exchanger  1 . In addition, the air that is in the outdoor unit  100  and that has been subjected to heat exchange in the heat exchanger  1  is discharged to the outside of the outdoor unit  100  via the bellmouth  20 , the opening  10   a  of the casing  10 , and the grille  10   b  by rotation of the axial flow fan  3 . 
     Next, the structure of the bellmouth  20  will be described.  FIG.  2    is an enlarged schematic view of a part of a section of the bellmouth  20  in  FIG.  1   . The section in  FIG.  2    is a section taken along an axis AX of a straight pipe portion  21 , which will be described later. In  FIG.  2   , the direction along the shaft  3   c  of the axial flow fan  3  in  FIG.  1    is represented by a black block arrow. Similarly to  FIG.  1   , in  FIG.  2   , the direction of the main flow of air is represented by a white block arrow. 
     The bellmouth  20  has the straight pipe portion  21  and a first tapered portion  23 , which connects to the straight pipe portion  21  at a position upstream in the direction of the main flow of air. 
     The straight pipe portion  21  has an end portion  21   a , which is closer to the heat exchanger  1 , and an end portion  21   b , which is closer to the opening  10   a  of the casing  10 . As illustrated in  FIG.  2   , an inner surface of the straight pipe portion  21  is straight. The inner diameter of the straight pipe portion  21 , in which the axis AX represented by a chain dashed line is centered, is the same at any position in the direction from the end portion  21   a  to the end portion  21   b . As illustrated in  FIG.  2   , the direction in which the axis AX of the straight pipe portion  21  extends is substantially parallel to the direction of the main flow of air. As illustrated in  FIG.  2   , the direction along the shaft  3   c  of the axial flow fan  3  can be set to be substantially parallel to the direction of the main flow of air and the direction in which the axis AX of the straight pipe portion  21  extends. Although not illustrated in  FIG.  2   , the straight pipe portion  21  is disposed closer to the peripheries of the blades  3   a  of the axial flow fan  3 . 
     The first tapered portion  23  is a contraction pipe portion whose inner diameter is reduced from the upstream side toward the downstream side in the direction of the main flow of air. The first tapered portion  23  is disposed at a position that is upstream of the straight pipe portion  21  and that is downstream of the heat exchanger  1  in the direction of the main flow of air. That is, the first tapered portion  23  connects to the end portion  21   a , which is closer to the heat exchanger  1 , of the straight pipe portion  21 . The specific structure of the first tapered portion  23  will be described later. 
     In the following description, flow of air along an inner surface of the first tapered portion  23  in the bellmouth  20  is referred to as a branch flow of air. 
     In addition, the bellmouth  20  can include a second tapered portion  25 , which connects to the straight pipe portion  21  and the opening  10   a  of the casing  10  to be located therebetween and whose inner diameter is increased in a direction from the straight pipe portion  21  toward the opening  10   a.    
     The second tapered portion  25  has an end portion  25   b , which is closer to the heat exchanger  1 , and an end portion  25   a , which is closer to the opening  10   a  of the casing  10 . The second tapered portion  25  is an expanding pipe portion whose inner diameter is increased in the direction from the end portion  25   b  disposed upstream in the direction of the main flow of air toward the end portion  25   a  disposed downstream in the direction of the main flow of air. The second tapered portion  25  is disposed at a position that is downstream of the straight pipe portion  21  and that is upstream of the opening  10   a  of the casing  10 . That is, the end portion  25   b  of the second tapered portion  25  connects to the end portion  21   b  of the straight pipe portion  21 . In addition, the end portion  25   a  of the second tapered portion  25  connects to the casing  10 , for example, an edge of the opening  10   a  in the front panel of the casing  10 . 
     For example, a second opening length D2 of the end portion  25   a , which is located downstream of the second tapered portion  25 , can be set to be larger than a first opening length D1 of an end portion  23   a   1 , which is located upstream of the first tapered portion  23 . The first opening length D1 is a distance between the axis AX and the end portion  23   a   1  of the first tapered portion  23  and is half the inner diameter of the first tapered portion  23  at the end portion  23   a   1 . The second opening length D2 is a distance between the axis AX and the end portion  25   a  of the second tapered portion  25  and is half the inner diameter of the second tapered portion  25  at the end portion  25   a.    
     As described above, the bellmouth  20  may be integrally formed with the front panel of the casing  10  by subjecting sheet metal to plastic deformation by, for example, press working in which a metal mold is used. In such press working with a metal mold, the front panel of the casing  10  is held by a lower die of the metal mold, and the sheet metal is bent in a direction toward the lower die of the metal mold by, for example, bending work to form the bellmouth  20 . The second tapered portion  25  is formed at a position closer to the front panel. The first tapered portion  23  is formed at a position apart from the front panel. When the second opening length D2 of the end portion  25   a  located downstream of the second tapered portion  25  is set to be larger than the first opening length D1 of the end portion  23   a   1  located upstream of the first tapered portion  23 , it is possible to inhibit the end portion  23   a   1  located upstream of the first tapered portion  23  from interfering with the lower die of the metal mold during release of the front panel of the casing  10  from the lower die of the metal mold. Thus, when the second opening length D2 of the end portion  25   a  located downstream of the second tapered portion  25  is set to be larger than the first opening length D1 of the end portion  23   a   1  located upstream of the first tapered portion  23 , it is possible to improve the manufacturing efficiency of the bellmouth  20 . 
     In  FIG.  2   , an inner surface of the second tapered portion  25  has a shape that bulges toward the inside of the bellmouth  20 . However, the shape of the inner surface of the second tapered portion  25  is not limited to this shape and may be, for example, straight. In addition, the inner surface of the second tapered portion  25  may be shaped by combining a straight inner surface and an inner surface having a shape that bulges toward the inside of the bellmouth  20 . 
     The second tapered portion  25  can be omitted according to, for example, the shape or the size of the outdoor unit  100 . That is, the end portion  21   b  of the straight pipe portion  21  may directly connect to the opening  10   a  of the casing  10 . 
     Next, the structure and the shape of the first tapered portion  23  will be described. 
     As described above, the first tapered portion  23  is a contraction portion whose inner diameter is reduced from the upstream side toward the downstream side in the direction of the main flow of air. The first tapered portion  23  is formed such that a length H1 of at least a part of the first tapered portion  23  along the direction along the axis AX is larger than a length H2 of the straight pipe portion  21  along the direction along the axis AX. The first tapered portion  23  may be formed such that the length H1 of the first tapered portion  23  is larger than the length H2 of the straight pipe portion  21  along the direction along the axis AX throughout in the circumferential direction of the first tapered portion  23 . 
     The expression “the length H1 of at least a part of the first tapered portion  23  is larger than the length H2 of the straight pipe portion  21 ” means that the length of a passage in the first tapered portion  23  in the direction of the main flow of air is larger than the length of a passage in the straight pipe portion  21  in the direction of the main flow of air. Accordingly, the configuration in which the length H1 of the first tapered portion  23  is larger than the length H2 of the straight pipe portion  21  enables flow of air in the first tapered portion  23 , which is a contraction portion, to be smoothly contracted. Thus, it is possible to inhibit vortices from being generated at the straight pipe portion  21  due to contracted flow. 
     When the length of the passage in the straight pipe portion  21  is long, the degree of air flow separation at the inner surface of the straight pipe portion  21  is increased toward the downstream side in the direction of the main flow of air. Thus, when the length of the passage in the straight pipe portion  21  is long, a vortex generated upstream of the straight pipe portion  21  may be enlarged. Generation of a vortex at the straight pipe portion  21  substantially narrows the air passage in the straight pipe portion  21 . 
     However, in the above configuration, the length H2 of the straight pipe portion  21  is shorter than the length H1 of the first tapered portion  23 . Thus, it is possible to inhibit a vortex generated at the straight pipe portion  21  from being enlarged. As a result, the above configuration enables provision of the outdoor unit  100  for an air-conditioning apparatus capable of inhibiting pressure loss from occurring in the bellmouth  20 . 
     Air flow separation occurs at the straight pipe portion  21  due to a branch flow of air into the end portion  21   a  of the straight pipe portion  21 . As a result, a vortex is generated upstream of the straight pipe portion  21 . In addition, it becomes difficult to direct a branch flow of air in the direction of the main flow of air with increasing the angle between the direction of the branch flow of air and the direction of the main flow of air. As a result, a vortex generated at the straight pipe portion  21  is enlarged. 
     However, the configuration in which the length H1 of at least a part of the first tapered portion  23  is larger than the length H2 of the straight pipe portion  21  enables the first tapered portion  23  to have a sufficient air passage length for directing a branch flow of air in the direction of the main flow of air. Thus, it is possible to inhibit vortices from being generated due to air flow separation at the end portion  21   a  of the straight pipe portion  21 . In addition, the ratio of the length H2 of the straight pipe portion  21  to the length H1 of the first tapered portion  23  is low, and it is thus possible to inhibit vortices generated at the straight pipe portion  21  from being enlarged. Accordingly, the configuration in which the length H1 of the first tapered portion  23  is larger than the length H2 of the straight pipe portion  21  enables inhibition of generation of vortices due to air flow separation at the straight pipe portion  21 . As a result, this configuration enables provision of the outdoor unit  100  for an air-conditioning apparatus capable of inhibiting pressure loss from occurring in the bellmouth  20 . 
     Furthermore, the configuration in which the length H1 of at least a part of the first tapered portion  23  is larger than the length H2 of the straight pipe portion  21  enables a branch flow of air to be directed, in the first tapered portion  23 , in the direction of the main flow of air. Thus, it is possible to reduce the load on each leading edge of the blades  3   a  of the axial flow fan  3 . As a result, it is possible to design the axial flow fan  3  to use low power input and to thus achieve power saving of the outdoor unit  100  for an air-conditioning apparatus. 
     The first tapered portion  23  can be formed to include a first bend portion  23   a , which forms the inlet  20   a  for air of the bellmouth  20 , and a second bend portion  23   b , which connects to the straight pipe portion  21  and has an inner diameter smaller than that of the first bend portion  23   a . The first bend portion  23   a  and the second bend portion  23   b  are located at respective ends of the first tapered portion  23  in the direction along the axis AX. The first bend portion  23   a  is located upstream of the second bend portion  23   b  in the direction of the main flow of air. As illustrated in  FIG.  2   , the end portion  23   a   1  of the first bend portion  23   a , which is located upstream in the direction of the main flow of air, forms the inlet  20   a  for air. In addition, an end portion  23   b   1  of the second bend portion  23   b , which is located downstream in the direction of the main flow of air, connects to the end portion  21   a  of the straight pipe portion  21 . 
     When the first tapered portion  23  includes the first bend portion  23   a  and the second bend portion  23   b , the shape or the size of the bellmouth  20  can be optimally set by separately adjusting the shapes or the sizes of the first bend portion  23   a  and the second bend portion  23   b . For example, the first bend portion  23   a  enables a branch flow of air to enter the first tapered portion  23  along an inner surface of the first bend portion  23   a , and the second bend portion  23   b  enables a branch flow of air to be directed in the direction of the main flow of air. 
     In addition, the first tapered portion  23  can be formed to include a connection portion  23   c , which connects to the first bend portion  23   a  and the second bend portion  23   b . The connection portion  23   c  has an end portion  23   c   1 , which is located upstream in the direction of the main flow of air, and an end portion  23   c   2 , which is located downstream in the direction of the main flow of air. The end portion  23   c   1  of the connection portion  23   c  connects to an end portion  23   a   2 , which is located downstream of the first bend portion  23   a  in the direction of the main flow of air. The end portion  23   c   2  of the connection portion  23   c  connects to an end portion  23   b   2 , which is located upstream of the second bend portion  23   b  in the direction of the main flow of air. The inner diameter of the connection portion  23   c  is reduced from the end portion  23   c   1  toward the end portion  23   c   2 . 
     When the first tapered portion  23  includes the connection portion  23   c , a branch flow of air that has entered the first tapered portion  23  along the inner surface of the first bend portion  23   a  can enter the second bend portion  23   b  along the inner surface of the connection portion  23   c . Thus, when the first tapered portion  23  includes the connection portion  23   c , it is possible to inhibit air flow separation from occurring at the first tapered portion  23 . 
     The connection portion  23   c  can be omitted according to, for example, the shape or the size of the outdoor unit  100 . That is, the first tapered portion  23  can be formed such that the end portion  23   a   2 , which is located downstream of the first bend portion  23   a , directly connects to the end portion  23   b   2  of the second bend portion  23   b.    
     For example, as illustrated in  FIG.  2   , the inner surface of the first bend portion  23   a  extending from the upstream side from which air flows in toward the downstream side can have a shape that bulges toward the inside of the bellmouth  20 , that is, a shape that is bent to be a curved shape toward the inside of the bellmouth  20  in a radial direction of the bellmouth  20 . In addition, an inner surface of the second bend portion  23   b  in the direction along the axis AX has a shape that bulges toward the inside of the bellmouth  20 , that is, a shape that is bent to be a curved shape toward the inside of the bellmouth  20  in the radial direction. Furthermore, the shape of the inner surface of the connection portion  23   c  is, for example, straight as illustrated in  FIG.  2   . 
     For example, according to the internal structure of the outdoor unit  100 , a part or the whole of the first bend portion  23   a  can have a shape that bulges toward the outside of the bellmouth  20 , that is, a shape that is bent to be a curved shape toward the outside of the bellmouth  20  in the radial direction. When the first bend portion  23   a  is bent toward the outside of the bellmouth  20  in the radial direction, it is easy to inhibit an increase in the opening length of the inlet  20   a  of the bellmouth  20  compared with a case in which the first bend portion  23   a  is bent toward the inside of the bellmouth  20  in the radial direction. Accordingly, it is possible to reduce the size of the bellmouth  20 . 
     For example, in the second section  20   c  in  FIG.  1   , the first bend portion  23   a  can have a shape that is bent to be a curved shape toward the outside of the bellmouth  20  in the radial direction. In the second section  20   c , when the first bend portion  23   a  is bent toward the outside of the bellmouth  20  in the radial direction, it is possible to extend, along a surface of the partition plate  15  in  FIG.  1   , part of an inner surface of the bellmouth  20  closer to the inlet. This enables air flowing along the partition plate  15  to smoothly flow into the bellmouth  20 . 
     In the following description, a line forming the inner surface of the first bend portion  23   a  is referred to as a first edge line  23   a   3 . The first edge line  23   a   3  extends from the upstream side of the first bend portion  23   a  from which air flows in toward the downstream side of the first bend portion  23   a . In addition, a line forming an inner surface of the second bend portion  23   b  is referred to as a second edge line  23   b   3 . The second edge line  23   b   3  is disposed on an extension of the first edge line  23   a   3 . Furthermore, a line that forms the inner surface of the connection portion  23   c  and that connects to the first edge line  23   a   3  and the second edge line  23   b   3  to be located therebetween is referred to as a third edge line  23   c   3 . 
       FIG.  3    is a schematic diagram illustrating the relationship between a first curvature radius R1 and a first central angle θ1 at the first edge line  23   a   3  according to Embodiment. In  FIG.  3   , the curvature center of the first edge line  23   a   3  is represented by a point O, the end portion  23   a   1 , which is located at one end of the first bend portion  23   a , is represented by a point P 1 , and the end portion  23   a   2 , which is located at the other end of the first bend portion  23   a , is represented by a point P 2 . A line segment OP 1  and a line segment OP 2  are equal in length and can be determined as the first curvature radius R1 of the first edge line  23   a   3 . The first central angle θ1 can be determined as the angle between the line segment OP 1  and the line segment OP 2  whose vertex is the point O. 
     The shape and the size of the first tapered portion  23  can be determined on the basis of the first curvature radius R1 and the first central angle θ1 of the first edge line  23   a   3  and a second curvature radius R2 and a second central angle θ2 of the second edge line  23   b   3 . 
     For example, the bent shape of the first edge line  23   a   3  becomes straighter with increasing the first curvature radius R1 when the first central angle θ1 is fixed. Accordingly, the bent shape of the first edge line  23   a   3  becomes gentler. The length of the first edge line  23   a   3  is reduced with reducing the first central angle θ1 when the first curvature radius R1 is fixed. Accordingly, it is possible to reduce the size of the first bend portion  23   a.    
     As illustrated in  FIG.  4   , the relationship between the second curvature radius R2 and the second central angle θ2 at the second edge line  23   b   3  is similar to the relationship in  FIG.  3    described above with reference to  FIG.  3   .  FIG.  4    is a schematic diagram illustrating the relationship between the first curvature radius R1 and the second curvature radius R2 at the first tapered portion  23  according to Embodiment. In  FIG.  4   , each length of the first curvature radius R1 of the first edge line  23   a   3  and the second curvature radius R2 of the second edge line  23   b   3  is represented by an arrow. 
     That is, the bent shape of the second edge line  23   b   3  becomes straighter with increasing the second curvature radius R2 when the second central angle θ2 is fixed. Accordingly, the bent shape of the second edge line  23   b   3  becomes gentler. The length of the second edge line  23   b   3  is reduced with reducing the second central angle θ2 when the second curvature radius R2 is fixed. Accordingly, it is possible to reduce the size of the second bend portion  23   b.    
     In addition, when the inner surface of the connection portion  23   c  is straight, the shape and the size of the first tapered portion  23  can be determined on the basis of a length L of the third edge line  23   c   3 . The width of the connection portion  23   c  in the direction along the shaft  3   c  of the axial flow fan  3  is reduced with reducing the length L. Accordingly, it is possible to reduce the size of the connection portion  23   c.    
     As illustrated in  FIG.  4   , the first tapered portion  23  can be formed such that the first curvature radius R1 of the first edge line  23   a   3  is larger than the second curvature radius R2 of the second edge line  23   b   3 . That is, in the first tapered portion  23 , the curvature of the first bend portion  23   a  formed by the first edge line  23   a   3  can be smaller than the curvature of the second bend portion  23   b  formed by the second edge line  23   b   3 . A curvature is the reciprocal of a curvature radius. 
     This configuration enables air to flow along the first edge line  23   a   3  even when a branch flow of air that has entered the first tapered portion  23  has to be greatly deflected due to the first central angle θ1 of the first edge line  23   a   3  being large. In addition, air that has passed through the first tapered portion  23  can flow along the second edge line  23   b   3  of the second bend portion  23   b  and then flow into the axial flow fan  3  in the direction along the shaft  3   c  of the axial flow fan  3 . That is, the bellmouth  20  includes the first tapered portion  23  and thus enables a branch flow of air to be guided to the axial flow fan  3  without separation of the branch flow of air and to enter the straight pipe portion  21  in the same direction as the direction of the main flow of air. 
     The outdoor unit  100  normally includes the axial flow fan  3 , which is configured to generate flow of air. In the outdoor unit  100 , when the blades  3   a  of the axial flow fan  3  are disposed in the straight pipe portion  21 , it is possible to reduce the size of the outdoor unit  100 . However, when pressure loss of flow of air occurs in the straight pipe portion  21 , the blowing performance of the axial flow fan  3  is impaired. Thus, power consumption of the axial flow fan  3  has to be increased to compensate the impairment of the blowing performance. 
     However, with this configuration, it is possible to inhibit vortices from being generated due to air flow separation at the first tapered portion  23  and to inhibit pressure loss of flow of air from occurring in the straight pipe portion  21 . In addition, it is possible to uniform the distribution of flow of air in the straight pipe portion  21  and to thus inhibit impairment of the blowing performance of the axial flow fan  3 . 
     Furthermore, even when the blades  3   a  of the axial flow fan  3  are disposed in the straight pipe portion  21  to reduce the size of the outdoor unit  100 , power consumption of the axial flow fan  3  does not have to be increased to maintain the blowing performance of the axial flow fan  3 . Thus, this configuration enables provision of the outdoor unit  100  whose size and power consumption can be reduced. 
     In addition, the first tapered portion  23  can be formed to include the connection portion  23   c , which connects to the first bend portion  23   a  and the second bend portion  23   b . When the first tapered portion  23  includes the connection portion  23   c , it is possible to inhibit separation of flow of air that has entered along the first edge line  23   a   3  of the first bend portion  23   a  from occurring at the boundary between the first bend portion  23   a  and the second bend portion  23   b . In particular, when the connection portion  23   c  is formed to include the third edge line  23   c   3 , which extends straight between the first bend portion  23   a  and the second bend portion  23   b , it is possible to smoothly guide the flow of air described above along the third edge line  23   c   3 . Thus, it is possible to further inhibit air flow separation at the first tapered portion  23 . 
     Furthermore, when the shape of the first tapered portion  23  varies in a circumferential direction around the shaft  3   c  of the axial flow fan  3 , it is possible to further uniform the distribution of flow of air entering the straight pipe portion  21  and to more flexibly reduce the size of the bellmouth  20 . 
     For example, as described above, the shape and the size of the first tapered portion  23  can be determined on the basis of the length L of the third edge line  23   c   3 . Thus, when the length L of the third edge line  23   c   3  varies in the circumferential direction of the first tapered portion  23 , it is possible to flexibly set the shape and the size of the first tapered portion  23 . For example, when the length L of the third edge line  23   c   3  is reduced with the shapes and the sizes of the first bend portion  23   a  and the second bend portion  23   b  maintained in the circumferential direction, it is possible to reduce the width of the first tapered portion  23  in the radial direction with air flow separation inhibited from occurring at the first tapered portion  23 . 
     The bellmouth  20  provided around the axial flow fan  3  such as a propeller fan used in the outdoor unit  100  for an air-conditioning apparatus may be set in a small space due to the influence of a size reduction of the outdoor unit  100 . However, when the length L of the third edge line  23   c   3  is reduced with the shapes and the sizes of the first bend portion  23   a  and the second bend portion  23   b  maintained in the circumferential direction, it is possible to inhibit impairment of the blowing performance and to reduce the size of the bellmouth  20  even in such a small space. 
     In addition, the shape and the size of the first tapered portion  23  can be determined on the basis of the length H1 of the first tapered portion  23  along the direction along the axis AX. When the length H1 varies in the circumferential direction of the first tapered portion  23 , it is possible to flexibly set the shape and the size of the first tapered portion  23 . 
     Furthermore, the shape and the size of the first tapered portion  23  can be determined on the basis of at least one of the first curvature radius R1 of the first edge line  23   a   3 , the first central angle θ1 of the first edge line  23   a   3 , the second curvature radius R2 of the second edge line  23   b   3 , and the second central angle θ2 of the second edge line  23   b   3 . When at least one of the first curvature radius R1, the first central angle θ1, the second curvature radius R2, and the second central angle θ2 varies in the circumferential direction of the first tapered portion  23 , it is possible to flexibly set the shape and the size of the first tapered portion  23 . 
     Embodiment, in which the shape of the first tapered portion  23  varies in the circumferential direction around the axis AX, will be described by taking, as an example, the outdoor unit  100  including the heat exchanger  1  having an L shape in top view as illustrated in  FIG.  1   . The following description of Embodiment is merely an example, and Embodiment is not intended to limit the content of the present disclosure. 
     As described above, the heat exchanger  1  includes the first portion  1   a , which is disposed at the rear of the casing  10 , and the second portion  1   b , which is disposed at the left of the casing  10 . At the rear of the casing  10 , the first portion  1   a  extends in a direction crossing the direction along the shaft  3   c  of the axial flow fan  3 . The second portion  1   b  extends in a direction crossing the first portion  1   a  and is disposed with a space between the second portion  1   b  and the first tapered portion  23 . The partition plate  15  is set in the casing  10 . 
     In such an outdoor unit  100 , components disposed in the circumferential direction of the bellmouth  20  differ from each other. Thus, rotation of the axial flow fan  3  generates a branch flow of air in a direction different from the direction of the main flow of air. When a branch flow of air enters the axial flow fan  3 , blowing performance such as fan efficiency may be impaired compared with a case in which air flows in a single direction. 
       FIG.  1    illustrates the first section  20   b , which is located between the second portion  1   b  and the axial flow fan  3 , and the second section  20   c , which is located between the axial flow fan  3  and the partition plate  15 , of the bellmouth  20 .  FIG.  5    is an enlarged schematic view of the first section  20   b  and the second section  20   c  of the bellmouth  20  in  FIG.  1   . In the first section  20   b , the second portion  1   b  is disposed on an extension of the first edge line  23   a   3  forming the inner surface of the first bend portion  23   a . In the second section  20   c , the second portion  1   b  is not disposed on an extension of the first edge line  23   a   3  forming the inner surface of the first bend portion  23   a.    
     In Embodiment, the inner surface of the first bend portion  23   a  is formed by a first upstream region  33   a   1  and a second upstream region  33   a   2 . The first upstream region  33   a   1  and the second upstream region  33   a   2  are formed by respective first edge lines  23   a   3 . The second portion  1   b  is disposed on an extension of the first edge line  23   a   3  forming the first upstream region  33   a   1 . That is, the part of the inner surface of the first bend portion  23   a  in the first section  20   b  in  FIG.  5    is an example of the first upstream region  33   a   1 . The second portion  1   b  is not disposed on an extension of the first edge line  23   a   3  forming the second upstream region  33   a   2 . That is, the part of the inner surface of the first bend portion  23   a  in the second section  20   c  in  FIG.  5    is an example of the second upstream region  33   a   2 . In Embodiment, the shape of the first edge line  23   a   3  forming the first upstream region  33   a   1  is a shape that bulges toward the inside of the bellmouth  20 . In  FIG.  5   , the shape of the first edge line  23   a   3  forming the second upstream region  33   a   2  bulges toward the inside of the bellmouth but is not limited to this shape. For example, the first edge line  23   a   3  forming the second upstream region  33   a   2  may have a shape that bulges toward the outside of the bellmouth  20 . 
     The inner surface of the second bend portion  23   b  is formed by a first downstream region  33   b   1  and a second downstream region  33   b   2 . The first downstream region  33   b   1  and the second downstream region  33   b   2  are formed by respective second edge lines  23   b   3 . The second edge line  23   b   3  forming the first downstream region  33   b   1  is disposed on an extension of the first edge line  23   a   3  of the first upstream region  33   a   1 . That is, the part of the inner surface of the second bend portion  23   b  in the first section  20   b  in  FIG.  5    is an example of the first downstream region  33   b   1 . The second edge line  23   b   3  forming the second downstream region  33   b   2  is disposed on an extension of the first edge line  23   a   3  of the second upstream region  33   a   2 . That is, the part of the inner surface of the second bend portion  23   b  in the second section  20   c  in  FIG.  5    is an example of the second downstream region  33   b   2 . The first downstream region  33   b   1  and the second downstream region  33   b   2  have respective shapes that bulge toward the inside of the bellmouth  20 . 
     The inner surface of the connection portion  23   c  is formed by a first intermediate region  33   c   1  and a second intermediate region  33   c   2 . The first intermediate region  33   c   1  and the second intermediate region  33   c   2  are formed by respective third edge lines  23   c   3 . The third edge line  23   c   3  forming the first intermediate region  33   c   1  connects to the first edge line  23   a   3  forming the first upstream region  33   a   1  and the second edge line  23   b   3  forming the first downstream region  33   b   1  to be located therebetween. That is, the part of the inner surface of the connection portion  23   c  in the first section  20   b  in  FIG.  5    is an example of the first intermediate region  33   c   1 . The third edge line  23   c   3  forming the second intermediate region  33   c   2  connects to the first edge line  23   a   3  forming the second upstream region  33   a   2  and the second edge line  23   b   3  forming the second downstream region  33   b   2  to be located therebetween. That is, the part of the inner surface of the connection portion  23   c  in the second section  20   c  in  FIG.  5    is an example of the second intermediate region  33   c   2 . For example, the third edge lines  23   c   3  have a straight shape. 
     In Embodiment, a first central angle θ1a of the first edge line  23   a   3  forming the first upstream region  33   a   1  can differ from a first central angle θ1b of the first edge line  23   a   3  forming the second upstream region  33   a   2 . For example, the first central angle θ1a of the first edge line  23   a   3  forming the first upstream region  33   a   1  can be formed to be smaller than the first central angle θ1b of the first edge line  23   a   3  forming the second upstream region  33   a   2 . A branch flow of air enters the second portion  1   b  in a direction different from the direction of the main flow of air by rotation of the axial flow fan  3 . When the first central angle θ1a of the first edge line  23   a   3  forming the first upstream region  33   a   1  is reduced, the first edge line  23   a   3  forming the first upstream region  33   a   1  is shortened. However, when the first curvature radius R1 of the first edge line  23   a   3  is maintained to be fixed, a branch flow of air can be carried along the first edge line  23   a   3  forming the first upstream region  33   a   1 . Thus, it is possible to reduce air separation occurring at the first tapered portion  23 . In addition, when the first central angle θ1a of the first edge line  23   a   3  forming the first upstream region  33   a   1  is smaller than the first central angle θ1b of the first edge line  23   a   3  of the second upstream region  33   a   2 , it is possible to reduce the width of the first tapered portion  23  in the radial direction. Thus, even when the space between the bellmouth  20  and the heat exchanger  1  is narrow, this configuration enables impairment of blowing performance to be inhibited and enables the size of the bellmouth  20  to be reduced. 
     The first central angle θ1a of the first edge line  23   a   3  forming the first upstream region  33   a   1  may be changed in the circumferential direction of the first tapered portion  23  as long as the above relationship is satisfied. For example, the first bend portion  23   a  can be formed such that the first central angle θ1a of the first edge line  23   a   3  is minimum in the first section  20   b , in which the distance between the second portion  1   b  and the first bend portion  23   a  is minimum. In addition, the first central angle θ1b of the first edge line  23   a   3  forming the second upstream region  33   a   2  may be changed in the circumferential direction of the first tapered portion  23  as long as the above relationship is satisfied. Furthermore, the first curvature radius R1 of the first edge line  23   a   3  can be changed in the circumferential direction of the first tapered portion  23 . 
     Furthermore, in Embodiment, a second central angle θ2a of the second edge line  23   b   3  forming the first downstream region  33   b   1  can differ from a second central angle θ2b of the second edge line  23   b   3  forming the second downstream region  33   b   2 . For example, the second central angle θ2a of the second edge line  23   b   3  forming the first downstream region  33   b   1  can be formed to be larger than the second central angle θ2b of the second edge line  23   b   3  forming the second downstream region  33   b   2 . Air flowing in a direction different from the direction of the main flow of air, the air passing through the second portion  1   b  and flowing in along the first edge line  23   a   3  of the first upstream region  33   a   1 , flows into the straight pipe portion  21  along the second edge line  23   b   3  forming the first downstream region  33   b   1 . In this case, when the second central angle θ2a of the second edge line  23   b   3  forming the first downstream region  33   b   1  is increased, the second edge line  23   b   3  forming the first downstream region  33   b   1  can be lengthened. When the second edge line  23   b   3  forming the first downstream region  33   b   1  is lengthened, air flowing along the second edge line  23   b   3  of the first downstream region  33   b   1  can more reliably flow in a direction similar to the direction along the shaft  3   c  of the axial flow fan  3 . Thus, when the second central angle θ2a of the second edge line  23   b   3  forming the first downstream region  33   b   1  is increased, it is possible to further uniform the distribution of flow of air in the straight pipe portion  21 . Accordingly, it is possible to inhibit impairment of the blowing performance of the axial flow fan  3 . In addition, when the second central angle θ2b of the second edge line  23   b   3  forming the second downstream region  33   b   2  is reduced, it is possible to reduce the size of the first tapered portion  23 . Thus, it is possible to reduce the size of the outdoor unit  100 . 
     The second central angle θ2a of the second edge line  23   b   3  forming the first downstream region  33   b   1  may be changed in the circumferential direction of the first tapered portion  23  as long as the above relationship is satisfied. For example, the second bend portion  23   b  can be formed such that the second central angle θ2a of the second edge line  23   b   3  is maximum in the first section  20   b , in which the distance between the second portion  1   b  and the second bend portion  23   b  is minimum. In addition, the second central angle θ2b of the second edge line  23   b   3  forming the second downstream region  33   b   2  may be changed in the circumferential direction of the first tapered portion  23  as long as the above relationship is satisfied. Furthermore, the second curvature radius R2 of the second edge line  23   b   3  can be changed in the circumferential direction of the first tapered portion  23 . 
     Furthermore, in Embodiment, a length L1 of the third edge line  23   c   3  forming the first intermediate region  33   c   1  can differ from a length L2 of the third edge line  23   c   3  of the second intermediate region  33   c   2 . For example, the length L1 of the third edge line  23   c   3  forming the first intermediate region  33   c   1  can be set to be shorter than the length L2 of the third edge line  23   c   3  forming the second intermediate region  33   c   2 . When the length L1 of the third edge line  23   c   3  forming the first intermediate region  33   c   1  is shorter than the length L2 of the third edge line  23   c   3  of the second intermediate region  33   c   2 , it is possible to reduce the size of the first tapered portion  23 . Thus, it is possible to reduce the size of the outdoor unit  100 . In particular, in Embodiment, when the length L1 of the third edge line  23   c   3  of the first intermediate region  33   c   1  is reduced, it is possible to narrow the space between the axial flow fan  3  and the second portion  1   b  of the heat exchanger  1 . 
     Furthermore, when the length L1 of the third edge line  23   c   3  of the first intermediate region  33   c   1  is reduced with the shapes and the sizes of the first upstream region  33   a   1  and the first downstream region  33   b   1  maintained, it is possible to reduce the width of the first tapered portion  23  in the radial direction. Thus, even when the space between the heat exchanger  1  and the bellmouth  20  is narrow, it is possible to inhibit impairment of blowing performance and to reduce the size of the bellmouth  20 . 
     Furthermore, in Embodiment, the connection portion  23   c  can be omitted to reduce the size of the outdoor unit  100 . 
     Furthermore, a length H1a, along the direction along the axis AX, of the part of the first tapered portion  23  where the first upstream region  33   a   1  is located can differ from a length H1b, along the direction along the axis AX, of the part of the first tapered portion  23  where the second upstream region  33   a   2  is located. The length H1a and the length H1b different from each other enable a size reduction of the bellmouth  20  even when the space between the heat exchanger  1  and the bellmouth  20  is narrow. This is because the size of the bellmouth  20  in the direction of the main flow of air can be set flexibly. 
     Embodiment described above can be variously modified without departing from the gist of the present disclosure. For example, even when the outdoor unit  100  is a chiller unit, Embodiment described above can be applied thereto in a similar manner. Even when the air-conditioning apparatus is formed by integrating the outdoor unit  100  and an indoor unit, Embodiment described above can be applied thereto in a similar manner.