Patent Publication Number: US-2023151821-A1

Title: Air-conditioning apparatus and refrigeration cycle apparatus [as amended]

Description:
TECHNICAL FIELD 
     The present disclosure relates to a centrifugal fan including a scroll casing, and an air-sending device, an air-conditioning apparatus, and a refrigeration cycle apparatus including the centrifugal fan. 
     BACKGROUND ART 
     Some centrifugal fans of the related art include a circumferential wall provided in a logarithmic spiral shape in which the distance between an axis of a fan and a circumferential wall of a scroll casing is sequentially extended from the downstream side to the upstream side of the air flow flowing in the scroll casing. In such a centrifugal fan, when the extension rate of the distance between the axis of the fan and the circumferential wall of the scroll casing is not sufficiently large in the direction of the air flow in the scroll casing, not only does the pressure recovery from the dynamic pressure to the static pressure is insufficient and the air-sending efficiency decreases, but the loss also increases and the noise also worsens. Thus, a centrifugal fan including an external form formed in a spiral shape and two substantially-parallel linear portions provided on the external form is proposed (for example, see Patent Literature 1). In the centrifugal fan, one linear portion out of the linear portions is connected to a discharge port in a scroll, and a rotational shaft of a motor is located near the linear portion close to a tongue portion of the scroll. Since a sirocco fan in Patent Literature 1 includes the above-mentioned configuration, a reverse flow phenomenon can be suppressed and the noise value can be reduced while maintaining a predetermined air volume. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent No. 4906555 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the centrifugal fan in Patent Literature 1, which can improve the noise problem, may suffer from a decrease in the air-sending efficiency because of insufficient pressure recovery from the dynamic pressure to the static pressure when the extension rate of the circumferential wall of the scroll casing to a predetermined direction cannot be sufficiently secured due to a restriction in the external dimensions depending on the place of installation. 
     An object of the present disclosure, which has been made to solve the above-mentioned problems, is to obtain a centrifugal fan, an air-sending device, an air-conditioning apparatus, and a refrigeration cycle apparatus configured to reduce noise and improve the air-sending efficiency. 
     Solution to Problem 
     According to an embodiment of the present disclosure, there is provided a centrifugal fan comprising: a fan including a main plate having a disk-shape, and a plurality of blades installed on a circumferential portion of the main plate; and a scroll casing configured to house the fan, the scroll casing including a discharge portion forming a discharge port from which an air flow generated by the fan is discharged, and a scroll portion including a side wall covering the fan in an axis direction of a rotational shaft of the fan, and formed with a suction port configured to suction air, a circumferential wall encircling the fan in a radial direction of the rotational shaft, and a tongue portion provided between the discharge portion and the circumferential wall, and configured to guide the air flow generated by the fan to the discharge port. In comparison with a centrifugal fan including a standard circumferential wall having a logarithmic spiral shape in cross-section perpendicular to the rotational shaft of the fan, in the circumferential wall, at a first end being a boundary between the circumferential wall and the tongue portion and at a second end being a boundary between the circumferential wall and the discharge portion, a distance L 1  between an axis of the rotational shaft and the circumferential wall is equal to a distance L 2  between the axis of the rotational shaft and the standard circumferential wall, the distance L 1  is greater than or equal to the distance L 2  between the first end and the second end of the circumferential wall, the circumferential wall includes a plurality of extended portions between the first end and the second end of the circumferential wall, and the plurality of extended portions include maximum points each have a length being a difference LH between the distance L 1  and the distance L 2 . 
     Advantageous Effects of Disclosure 
     In the centrifugal fan according to an embodiment of the present disclosure, in comparison with the centrifugal fan including the standard circumferential wall having a logarithmic spiral shape in cross-section perpendicular to the rotational shaft of the fan, in the circumferential wall, at the first end and at the second end, the distance L 1  is equal to the distance L 2 . In the circumferential wall, between the first end and the second end of the circumferential wall, the distance L 1  is greater than or equal to the distance L 2 . The circumferential wall includes the plurality of extended portions between the first end and the second end of the circumferential wall, and the plurality of extended portions include maximum points each having a length being a difference LH between the distance L 1  and the distance L 2 . Therefore, in the centrifugal fan, even when the extension rate of the circumferential wall of the scroll casing to a predetermined direction cannot be sufficiently secured due to the restriction in the external dimensions depending on the place of installation, the distance of an air passage in which the distance between the axis of the rotational shaft and the circumferential wall is extended can be increased because the circumferential wall includes the configuration above in the extendable direction. As a result, the centrifugal fan can convert the dynamic pressure to the static pressure by reducing the speed of the air flow flowing in the scroll casing while preventing the separation of the air flow, and hence can improve the air-sending efficiency while reducing the noise. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view of a centrifugal fan according to Embodiment 1 of the present disclosure. 
         FIG.  2    is a top view of the centrifugal fan according to Embodiment 1 of the present disclosure. 
         FIG.  3    is a cross-sectional view of the centrifugal fan in  FIG.  2    taken along line D-D. 
         FIG.  4    is a top view illustrating a comparison between a circumferential wall of the centrifugal fan according to Embodiment 1 of the present disclosure and a standard circumferential wall of a centrifugal fan of the related art having a logarithmic spiral shape. 
         FIG.  5    shows the relationship between an angle θ [degree] and a distance L [mm] from an axis to a circumferential wall surface in the centrifugal fan  1  or the centrifugal fan of the related art in  FIG.  4   . 
         FIG.  6    is a graph obtained by changing extension rates of extended portions in the circumferential wall of the centrifugal fan according to Embodiment 1 of the present disclosure. 
         FIG.  7    shows the differences between the extension rates of the extended portions in the circumferential wall of the centrifugal fan according to Embodiment 1 of the present disclosure. 
         FIG.  8    is a top view illustrating a comparison between a circumferential wall of the centrifugal fan according to Embodiment 1 of the present disclosure having other extension rates and the standard circumferential wall SW of the centrifugal fan of the related art having a logarithmic spiral shape. 
         FIG.  9    is a graph obtained by changing the other extension rates of the extended portions in the circumferential wall of the centrifugal fan in  FIG.  8   . 
         FIG.  10    is a top view illustrating a comparison between a circumferential wall of the centrifugal fan according to Embodiment 1 of the present disclosure having other extension rates, and the standard circumferential wall SW of the centrifugal fan of the related art having a logarithmic spiral shape. 
         FIG.  11    is a graph obtained by changing the other extension rates of the extended portions in the circumferential wall of the centrifugal fan in  FIG.  10   . 
         FIG.  12    shows the other extension rates in the circumferential wall of the centrifugal fan according to Embodiment 1 in  FIG.  5   . 
         FIG.  13    is a top view illustrating a comparison between the circumferential wall of the centrifugal fan according to Embodiment 1 of the present disclosure having other extension rates and the standard circumferential wall SW of the centrifugal fan of the related art having a logarithmic spiral shape. 
         FIG.  14    is a graph obtained by changing the other extension rates of the extended portions in the circumferential wall of the centrifugal fan in  FIG.  13   . 
         FIG.  15    is a cross-sectional view of a centrifugal fan according to Embodiment 2 of the present disclosure taken along the axis direction. 
         FIG.  16    is a cross-sectional view of a modified example of the centrifugal fan according to Embodiment 2 of the present disclosure taken along the axis direction. 
         FIG.  17    is a cross-sectional view of another modified example of the centrifugal fan according to Embodiment 2 of the present disclosure taken along the axis direction. 
         FIG.  18    illustrates a configuration of an air-sending device according to Embodiment 3 of the present disclosure. 
         FIG.  19    is a perspective view of an air-conditioning apparatus according to Embodiment 4 of the present disclosure. 
         FIG.  20    illustrates an inner configuration of the air-conditioning apparatus according to Embodiment 4 of the present disclosure. 
         FIG.  21    is a cross-sectional view of the air-conditioning apparatus according to Embodiment 4 of the present disclosure. 
         FIG.  22    illustrates a configuration of a refrigeration cycle apparatus according to Embodiment 5 of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A centrifugal fan  1 , an air-sending device  30 , an air-conditioning apparatus  40 , and a refrigeration cycle apparatus  50  according to embodiments of the present disclosure are described below with reference to the drawings, for example. Note that, in the drawings below including  FIG.  1   , the relationships between relative dimensions, shapes and other features of configuration parts may differ from actual ones. In the drawings below, parts denoted by the same reference characters are the same parts or parts equivalent thereto, and the above is common throughout the entire description. Terms (for example, “up”, “down”, “right”, “left”, “front”, and “rear”) indicating directions are used, as appropriate, for facilitating understanding, but those expressions are described as above for the sake of convenience, and the arrangement and the orientations of the devices or the parts are not limited thereby. 
     Embodiment 1 
     Centrifugal Fan  1   
       FIG.  1    is a perspective view of a centrifugal fan  1  according to Embodiment 1 of the present disclosure.  FIG.  2    is a top view of the centrifugal fan  1  according to Embodiment 1 of the present disclosure.  FIG.  3    is a cross-sectional view of the centrifugal fan  1  in  FIG.  2    taken along line D-D. A basic structure of the centrifugal fan  1  is described with reference to  FIG.  1    to  FIG.  3   . Note that the dotted line shown in  FIG.  3    is a standard circumferential wall SW in cross-section showing a circumferential wall of a centrifugal fan of the related art. The centrifugal fan  1  is a multi-wing centrifugal-type centrifugal fan, and includes a fan  2  configured to generate air flow, and a scroll casing  4  configured to house the fan  2 . 
     (Fan  2 ) 
     The fan  2  includes a main plate  2   a  having a disk-shape, and a plurality of blades  2   d  installed on a circumferential portion  2   a   1  of the main plate  2   a.  The fan  2  includes ring-shaped side plates  2   c  facing the main plate  2   a.  The ring-shaped side plates  2   c  are placed on ends of the fan  2  opposite to the main plate  2   a  of the plurality of blades  2   d.  Note that the fan  2  may have a structure not including the side plates  2   c.  When the fan  2  includes the side plates  2   c,  the plurality of blades  2   d  each have one end being connected to the main plate  2   a  and the other end being connected to each of the side plates  2   c,  and the plurality of blades  2   d  are disposed between the main plate  2   a  and the side plates  2   c.  A boss portion  2   b  is provided on the center portion of the main plate  2   a.  An output shaft  6   a  of a fan motor  6  is connected to the center of the boss portion  2   b,  and the fan  2  rotates by a driving force of the fan motor  6 . The fan  2  forms a rotational shaft X by the boss portion  2   b  and the output shaft  6   a.  The plurality of blades  2   d  encircle the rotational shaft X of the fan  2  between the main plate  2   a  and the side plates  2   c.  The fan  2  is formed in a cylindrical shape by the main plate  2   a  and the plurality of blades  2   d,  and suction ports  2   e  are formed on side plate  2   c  sides opposite to the main plate  2   a  in the axis direction of the rotational shaft X of the fan  2 . As shown in  FIG.  3   , the fan  2  has the plurality of blades  2   d  provided on both sides of the main plate  2   a  in the axis direction of the rotational shaft X. Note that the configuration of the fan  2  is not limited to a configuration in which the plurality of blades  2   d  are provided on both sides of the main plate  2   a  in the axis direction of the rotational shaft X, and the plurality of blades  2   d  may be provided on only one side of the main plate  2   a  in the axis direction of the rotational shaft X, for example. As shown in  FIG.  3   , in the fan  2 , the fan motor  6  is disposed on an inner peripheral side of the fan  2 , but the output shaft  6   a  only needs to be connected to the boss portion  2   b  in the fan  2 , and the fan motor  6  may be disposed outside of the centrifugal fan  1 . 
     (Scroll Casing  4 ) 
     The scroll casing  4  encircles the fan  2 , and rectifies the air blown out from the fan  2 . The scroll casing  4  includes a discharge portion  42  configured to form a discharge port  42   a  from which the air flow generated by the fan  2  is discharged, and a scroll portion  41  configured to form an air passage configured to convert the dynamic pressure of the air flow generated by the fan  2  to the static pressure. The discharge portion  42  forms the discharge port  42   a  from which the air flow passing through the scroll portion  41  is discharged. The scroll portion  41  includes side walls  4   a  covering the fan  2  in the axis direction of the rotational shaft X of the fan  2  and formed with suction ports  5  configured to suction air, and a circumferential wall  4   c  encircling the fan  2  in the radial direction of the rotational shaft X. The scroll portion  41  includes a tongue portion  4   b  provided between the discharge portion  42  and the circumferential wall  4   c  and configured to guide the air flow generated by the fan  2  to the discharge port  42   a  via the scroll portion  41 . Note that the radial direction of the rotational shaft X is a direction perpendicular to the rotational shaft X. An inner space in the scroll portion  41  made of the circumferential wall  4   c  and the side walls  4   a  is a space in which the air blown out from the fan  2  flows along the circumferential wall  4   c.    
     (Side Walls  4   a ) 
     The suction ports  5  are formed in the side walls  4   a  of the scroll casing  4 . On the side walls  4   a,  bell mouths  3  configured to guide the air flow suctioned into the scroll casing  4  through the suction ports  5 , are provided. The bell mouths  3  are formed in positions facing the suction ports  2   e  of the fan  2 . Each of the bell mouths  3  has a shape in which the air passage narrows from an upstream end  3   a  being an end on the upstream side of the air flow suctioned into the scroll casing  4  through the suction ports  5 , toward a downstream end  3   b  being an end on the downstream side. As shown in  FIG.  1    to  FIG.  3   , the centrifugal fan  1  includes a double-suction scroll casing  4  including the side walls  4   a  in which the suction ports  5  are formed on both sides of the main plate  2   a  in the axis direction of the rotational shaft X. Note that the centrifugal fan  1  is not limited to a configuration including the double-suction scroll casing  4 , and may include the single-suction scroll casing  4  including the side wall  4   a  in which the suction port  5  is formed on one side of the main plate  2   a  in the axis direction of the rotational shaft X. 
     (Circumferential Wall  4   c ) 
     The circumferential wall  4   c  encircles the fan  2  in the radial direction of the rotational shaft X, and forms an inner peripheral surface facing the plurality of blades  2   d  forming an outer peripheral surface of the fan  2  in the radial direction. The circumferential wall  4   c  has a width in the axis direction of the rotational shaft X, and is formed in a spiral shape in top view. As shown in  FIG.  2   , the circumferential wall  4   c  is provided in a portion from a first end  41   a  positioned in the boundary between the scroll portion  41  and the tongue portion  4   b  to a second end  41   b  positioned in the boundary between the discharge portion  42  and the scroll portion  41  on the side far from the tongue portion  4   b  along the direction of rotation of the fan  2 . The inner peripheral surface of the circumferential wall  4   c  forms a curved surface smoothly forming a curve from the first end  41   a  being the start of the winding of the spiral shape to the second end  41   b  being the end of the winding of the spiral shape along the circumferential direction of the fan  2 . The first end  41   a  is an edge portion on the upstream side of the air flow generated by the rotation of the fan  2 , and the second end  41   b  is an edge portion on the downstream side of the air flow generated by the rotation of the fan  2  in the circumferential wall  4   c  forming the curved surface. 
     An angle θ shown in  FIG.  2    is an angle shifted from a first reference line BL in the direction of rotation of the fan  2  between a first reference line BL 1  connecting an axis C 1  of the rotational shaft X and the first end  41   a  to each other and a second reference line BL 2  connecting the axis C 1  of the rotational shaft X and the second end  41   b  to each other in cross-section perpendicular to the rotational shaft X of the fan  2 . The angle θ of the first reference line BL 1  shown in  FIG.  2    is 0 degrees. Note that the angle of the second reference line BL 2  is an angle α, and does not indicate a predetermined value. This is because the angle α of the second reference line BL 2  differs depending on the spiral shape of the scroll casing  4 , and the spiral shape of the scroll casing  4  is defined by the opening port diameter of the discharge port  42   a , for example. The angle α of the second reference line BL 2  is specifically determined by the opening port diameter of the discharge port  42   a  needed depending on the purpose of the centrifugal fan  1 , for example. Therefore, in the centrifugal fan  1  of Embodiment 1, the angle α is described to be 270 degrees, but it may be 300 degrees or other angles depending on the opening port diameter of the discharge port  42   a,  for example. Similarly, the position of the standard circumferential wall SW having a logarithmic spiral shape is determined by the opening port diameter of the discharge port  42   a  of the discharge portion  42  in the direction perpendicular to the rotational shaft X. 
       FIG.  4    is a top view illustrating the comparison between the circumferential wall  4   c  of the centrifugal fan  1  according to Embodiment 1 of the present disclosure and the standard circumferential wall SW of the centrifugal fan of the related art having a logarithmic spiral shape.  FIG.  5    shows the relationship between the angle θ [degree] and the distance L [mm] from the axis to the circumferential wall surface in the centrifugal fan  1  or the centrifugal fan of the related art in  FIG.  4   . In  FIG.  5   , the solid line connecting the circles shows the circumferential wall  4   c,  and the broken line connecting the triangles shows the standard circumferential wall SW. The circumferential wall  4   c  is further described in detail by comparing the centrifugal fan  1  with the centrifugal fan including the standard circumferential wall SW having a logarithmic spiral shape in cross-section perpendicular to the rotational shaft X of the fan  2 . The standard circumferential wall SW of the centrifugal fan of the related art shown in  FIG.  4    and  FIG.  5    forms a curved surface having a spiral shape defined by a predetermined extension rate (predetermined extension rate). Examples of the standard circumferential wall SW having a spiral shape defined by the predetermined extension rate include a standard circumferential wall SW obtained by a logarithmic spiral, a standard circumferential wall SW obtained by an Archimedes&#39; screw, and a standard circumferential wall SW obtained by the involute curve. In a specific example of the centrifugal fan of the related art shown in  FIG.  4   , the standard circumferential wall SW is defined by a logarithmic spiral, but the standard circumferential wall SW obtained by an Archimedes&#39; screw or the standard circumferential wall SW obtained by an involute curve may be the standard circumferential wall SW of the centrifugal fan of the related art. As shown in  FIG.  5   , in the circumferential wall having a logarithmic spiral shape forming the centrifugal fan of the related art, an extension rate J defining the standard circumferential wall SW is an angle of the inclination of a graph in which the horizontal axis shows the angle θ being a winding angle, and the vertical axis shows the distance between the axis C 1  of the rotational shaft X and the standard circumferential wall SW. 
     In  FIG.  5   , a point PS is the position of the first end  41   a  in the circumferential wall  4   c  and is a radius of the standard circumferential wall SW of the centrifugal fan of the related art. In  FIG.  5   , a point PL is the position of the second end  41   b  in the circumferential wall  4   c  and is the radius of the standard circumferential wall SW of the centrifugal fan of the related art. As shown in  FIG.  4    and  FIG.  5   , in the circumferential wall  4   c,  at the first end  41   a  being the boundary between the circumferential wall  4   c  and the tongue portion  4   b,  the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is equal to the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW. In the circumferential wall  4   c,  at the second end  41   b  being the boundary between the circumferential wall  4   c  and the discharge portion  42 , the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is equal to the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW. 
     As shown in  FIG.  4    and  FIG.  5   , in the circumferential wall  4   c,  between the first end  41   a  and the second end  41   b  of the circumferential wall  4   c,  the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is greater than or equal to the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW. The circumferential wall  4   c  includes three extended portions between the first end  41   a  and the second end  41   b  of the circumferential wall  4   c.  The three extended portions include maximum points each having a length being the difference LH between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW. 
     As shown in  FIG.  4   , the circumferential wall  4   c  includes a first extended portion  51  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 0 degrees or more and less than 90 degrees. As shown in  FIG.  5   , the first extended portion  51  includes a first maximum point P 1  in a section in which the angle θ is 0 degrees or more and less than 90 degrees. As shown in  FIG.  5   , the first maximum point P 1  is a position in the circumferential wall  4   c  at which the length of the difference LH 1  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 0 degrees or more and less than 90 degrees. As shown in  FIG.  4   , the circumferential wall  4   c  includes a second extended portion  52  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 90 degrees or more and less than 180 degrees. As shown in  FIG.  5   , the second extended portion  52  includes a second maximum point P 2  in a section in which the angle θ is 90 degrees or more and less than 180 degrees. As shown in  FIG.  5   , the second maximum point P 2  is a position in the circumferential wall  4   c  at which the length of a difference LH 2  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 90 degrees or more and less than 180 degrees. As shown in  FIG.  4   , the circumferential wall  4   c  includes a third extended portion  53  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 180 degrees or more and less than the angle α formed by the second reference line. As shown in  FIG.  5   , the third extended portion  53  includes a third maximum point P 3  in a section in which the angle θ is 180 degrees or more and less than the angle α formed by the second reference line. As shown in  FIG.  5   , the third maximum point P 3  is a position in the circumferential wall  4   c  at which the length of a difference LH 3  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 180 degrees or more and less than the angle α. 
       FIG.  6    is a graph obtained by changing the extension rates of the extended portions in the circumferential wall  4   c  of the centrifugal fan  1  according to Embodiment 1 of the present disclosure.  FIG.  7    shows the differences between the extension rates of the extended portions in the circumferential wall  4   c  of the centrifugal fan  1  according to Embodiment 1 of the present disclosure. As shown in 
       FIG.  6   , the point at which the difference LH is the smallest in a section in which the angle θ is 0 degrees or more and equal to or less than an angle at which the first maximum point P 1  is positioned is a first minimum point U 1 . The point at which the difference LH is the smallest in a section in which the angle θ is 90 degrees or more and equal to or less than an angle at which the second maximum point P 2  is positioned is a second minimum point U 2 . The point at which the difference LH is the smallest in a section in which the angle θ is 180 degrees or more and equal to or less than an angle at which the third maximum point P 3  is positioned is a third minimum point U 3 . In the cases mentioned above, as shown in  FIG.  7   , a difference L 11  between the distance L 1  at the first maximum point P 1  and the distance L 1  at the first minimum point U 1  relative to an increase θ 1  of the angle θ from the first minimum point U 1  to the first maximum point P 1  is an extension rate A. A difference L 22  between the distance L 1  at the second maximum point P 2  and the distance L 1  at the second minimum point U 2  relative to an increase θ 2  of the angle θ from the second minimum point U 2  to the second maximum point P 2  is an extension rate B. A difference L 33  between the distance L 1  at the third maximum point P 3  and the distance L 1  at the third minimum point U 3  relative to an increase θ 3  of the angle θ from the third minimum point U 3  to the third maximum point P 3  is an extension rate C. At this time, the circumferential wall  4   c  of the centrifugal fan  1  satisfies a relationship of the extension rate B&gt;the extension rate C, and the extension rate B≥the extension rate A&gt;the extension rate C, or a relationship of the extension rate B&gt;the extension rate C, and the extension rate B&gt;the extension rate C≥the extension rate A. 
       FIG.  8    is a top view illustrating a comparison between the circumferential wall  4   c  of the centrifugal fan  1  according to Embodiment 1 of the present disclosure having other extension rates, and the standard circumferential wall SW of the centrifugal fan of the related art having a logarithmic spiral shape.  FIG.  9    is a graph obtained by changing the other extension rates of the extended portions in the circumferential wall  4   c  of the centrifugal fan  1  in  FIG.  8   . As shown in  FIG.  9   , the point at which the difference LH is the smallest in a section in which the angle θ is 0 degrees or more and equal to or less than an angle at which the first maximum point P 1  is positioned is the first minimum point U 1 . The point at which the difference LH is the smallest in a section in which the angle θ is 90 degrees or more and equal to or less than an angle at which the second maximum point P 2  is positioned is the second minimum point U 2 . The point at which the difference LH is the smallest in a section in which the angle θ is 180 degrees or more and equal to or less than an angle at which the third maximum point P 3  is positioned is the third minimum point U 3 . In the cases above, as shown in  FIG.  9   , the difference L 11  between the distance L 1  at the first maximum point P 1  and the distance L 1  at the first minimum point U 1  relative to the increase θ 1  of the angle θ from the first minimum point U 1  to the first maximum point P 1  is the extension rate A. The difference L 22  between the distance L 1  at the second maximum point P 2  and the distance L 1  at the second minimum point U 2  relative to the increase θ 2  of the angle θ from the second minimum point U 2  to the second maximum point P 2  is the extension rate B. The difference L 33  between the distance L 1  at the third maximum point P 3  and the distance L 1  at the third minimum point U 3  relative to the increase θ 3  of the angle θ from the third minimum point U 3  to the third maximum point P 3  is the extension rate C. At this time, the circumferential wall  4   c  of the centrifugal fan  1  satisfies a relationship of the extension rate C&gt;the extension rate B≥the extension rate A. 
       FIG.  10    is a top view illustrating a comparison between the circumferential wall  4   c  of the centrifugal fan  1  according to Embodiment 1 of the present disclosure having other extension rates and the standard circumferential wall SW of the centrifugal fan of the related art having a logarithmic spiral shape.  FIG.  11    is a graph obtained by changing the other extension rates of the extended portions in the circumferential wall  4   c  of the centrifugal fan  1  in  FIG.  10   . Note that the one dot chain line shown in  FIG.  10    shows the position of a fourth extended portion  54 . The centrifugal fan  1  according to Embodiment 1 shown in  FIG.  10    includes the fourth extended portion  54  forming the fourth maximum point P 4  in a section of the circumferential wall  4   c  at which the angle θ is 90 degrees to 270 degrees (angle α) being a region opposite to the discharge port  72  of the scroll casing  4 . The centrifugal fan  1  according to Embodiment 1 shown in  FIG.  10    further includes the second extended portion  52  including the second maximum point P 2  and the third extended portion  53  including the third maximum point P 3  on the fourth extended portion  54  including the fourth maximum point P 4 . As shown in  FIG.  10   , the circumferential wall  4   c  includes the first extended portion  51  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 0 degrees or more and less than 90 degrees. As shown in  FIG.  11   , the first extended portion  51  includes the first maximum point P 1  in a section in which the angle θ is 0 degrees or more and less than 90 degrees. The first maximum point P 1  is a position in the circumferential wall  4   c  at which the length of the difference LH 1  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 0 degrees or more and less than 90 degrees. As shown in  FIG.  10   , the circumferential wall  4   c  includes the second extended portion  52  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 90 degrees or more and less than 180 degrees. As shown in  FIG.  11   , the second extended portion  52  includes the second maximum point P 2  in a section in which the angle θ is 90 degrees or more and less than 180 degrees. The second maximum point P 2  is a position in the circumferential wall  4   c  at which the length of the difference LH 2  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 90 degrees or more and less than 180 degrees. As shown in  FIG.  10   , the circumferential wall  4   c  includes the third extended portion  53  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 180 degrees or more and less than the angle α formed by the second reference line. As shown in  FIG.  11   , the third extended portion  53  includes the third maximum point P 3  in a section in which the angle θ is 180 degrees or more and less than the angle α formed by the second reference line. The third maximum point P 3  is a position in the circumferential wall  4   c  at which the length of the difference LH 3  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 180 degrees or more and less than the angle α. As shown in  FIG.  10   , the circumferential wall  4   c  includes the fourth extended portion  54  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 90 degrees or more and less than the angle α formed by the second reference line. As shown in  FIG.  11   , the fourth extended portion  54  includes the fourth maximum point P 4  in a section in which the angle θ is 90 degrees or more and less than the angle α formed by the second reference line. The fourth maximum point P 4  is a position in the circumferential wall  4   c  at which the length of the difference LH 4  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 90 degrees or more and less than the angle α. The centrifugal fan  1  further includes the second extended portion  52  including the second maximum point P 2  and the third extended portion  53  including the third maximum point P 3  on the fourth extended portion  54  including the fourth maximum point P 4 . Therefore, in the circumferential wall  4   c  forming a region from the second extended portion  52  to the third extended portion  53 , the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is greater than the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW. 
       FIG.  12    is a graph showing other extension rates in the circumferential wall  4   c  of the centrifugal fan  1  according to Embodiment 1 in  FIG.  5   .  FIG.  12    shows a more-desirable shape of the circumferential wall  4   c  with reference to  FIG.  5   . A difference L 44  (not shown) between the distance L 1  at the second minimum point U 2  and the distance L 1  at the first maximum point P 1  relative to an increase θ 11  of the angle θ from the first maximum point P 1  to the second minimum point U 2  is an extension rate D. A difference L 55  (not shown) between the distance L 1  at the third minimum point U 3  and the distance L 1  at the second maximum point P 2  relative to an increase θ 22  of the angle θ from the second maximum point P 2  to the third minimum point U 3  is an extension rate E. A difference L 66  (not shown) between the distance L 1  at the angle α and the distance L 1  at the third maximum point P 3  relative to an increase θ 33  of the angle θ from the third maximum point P 3  to the angle α is an extension rate F. The distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW relative to the increase of the angle θ is an extension rate J. In the cases above, in the circumferential wall  4   c  of the centrifugal fan  1 , the extension rate J&gt;the extension rate D≥0, the extension rate J&gt;the extension rate E≥0, and the extension rate J&gt;the extension rate F≥0 are desired to be satisfied. Note that, although the circumferential wall  4   c  is desired to have a shape having the extension rates described with reference to  FIG.  12   , the circumferential wall  4   c  does not necessarily need to have a shape having the extension rates described with reference to  FIG.  12   . The circumferential wall  4   c  having a structure with the extension rates shown in  FIG.  12    may be combined with the circumferential wall  4   c  having a structure with the extension rates shown in  FIG.  6   , the circumferential wall  4   c  having a structure with the extension rates shown in  FIG.  9   , and the circumferential wall  4   c  having a structure with the extension rates shown in  FIG.  11   . 
       FIG.  13    is a top view illustrating a comparison between the circumferential wall  4   c  of the centrifugal fan  1  according to Embodiment 1 of the present disclosure having other extension rates and the standard circumferential wall SW of the centrifugal fan of the related art having a logarithmic spiral shape.  FIG.  14    is a graph obtained by changing the other extension rates of the extended portions in the circumferential wall  4   c  of the centrifugal fan  1  in  FIG.  13   . Note that the one dot chain line shown in  FIG.  13    shows the position of the fourth extended portion  54 . The centrifugal fan  1  according to Embodiment 1 shown in  FIG.  13    includes the fourth extended portion  54  forming the fourth maximum point P 4  in a section of the circumferential wall  4   c  at which the angle θ is 90 degrees to 270 degrees (angle α) being a region opposite to the discharge port  72  of the scroll casing  4 . The centrifugal fan  1  according to Embodiment 1 shown in  FIG.  13    further includes the second extended portion  52  including the second maximum point P 2  and the third extended portion  53  including the third maximum point P 3  on the fourth extended portion  54  including the fourth maximum point P 4 . As shown in  FIG.  13   , the circumferential wall  4   c  has a circumferential wall along the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 0 degrees or more and less than 90 degrees. In other words, in the circumferential wall  4   c,  the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is equal to the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW in a section in which the angle θ is 0 degrees or more and less than 90 degrees. As shown in  FIG.  13   , the circumferential wall  4   c  includes the second extended portion  52  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 90 degrees or more and less than 180 degrees. As shown in  FIG.  14   , the second extended portion  52  includes the second maximum point P 2  in a section in which the angle θ is 90 degrees or more and less than 180 degrees. The second maximum point P 2  is a position in the circumferential wall  4   c  at which the length of the difference LH 2  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 90 degrees or more and less than 180 degrees. As shown in  FIG.  13   , the circumferential wall  4   c  includes the third extended portion  53  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 180 degrees or more and less than the angle α formed by the second reference line. As shown in  FIG.  14   , the third extended portion  53  includes the third maximum point P 3  in a section in which the angle θ is 180 degrees or more and less than the angle α formed by the second reference line. The third maximum point P 3  is a position in the circumferential wall  4   c  at which the length of the difference LH 3  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 180 degrees or more and less than the angle α. As shown in  FIG.  13   , the circumferential wall  4   c  includes the fourth extended portion  54  bulging out to the radially outer side of the standard circumferential wall SW having a logarithmic spiral shape in a section in which the angle θ is 90 degrees or more and less than the angle α formed by the second reference line. As shown in  FIG.  14   , the fourth extended portion  54  includes the fourth maximum point P 4  in a section in which the angle θ is 90 degrees or more and less than the angle α formed by the second reference line. 
     The fourth maximum point P 4  is a position in the circumferential wall  4   c  at which the length of the difference LH 4  between the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW is the greatest in a section in which the angle θ is 90 degrees or more and less than the angle α. The centrifugal fan  1  further includes the second extended portion  52  including the second maximum point P 2  and the third extended portion  53  including the third maximum point P 3  on the fourth extended portion  54  including the fourth maximum point P 4 . Therefore, in the circumferential wall  4   c  forming the region from the second extended portion  52  to the third extended portion  53 , the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is greater than the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW. 
     (Tongue Portion  4   b ) 
     The tongue portion  4   b  guides the air flow generated by the fan  2  to the discharge port  42   a  via the scroll portion  41 . The tongue portion  4   b  is a protruding portion provided in a boundary portion between the scroll portion  41  and the discharge portion  42 . The tongue portion  4   b  extends in a direction parallel to the rotational shaft X in the scroll casing  4 . 
     Operation of Centrifugal Fan  1   
     When the fan  2  rotates, the air outside the scroll casing  4  is suctioned into the scroll casing  4  through the suction ports  5 . The air suctioned into the scroll casing  4  is suctioned by the fan  2  by being guided by the bell mouths  3 . In the process in which the air suctioned by the fan  2  passes through the plurality of blades  2   d,  the air suctioned by the fan  2  is turned to be an air flow to which the dynamic pressure and the static pressure are applied and is blown out toward the radially outer side of the fan  2 . In the air flow blown out from the fan  2 , the dynamic pressure is converted to the static pressure while the air flow is guided between the inner side of the circumferential wall  4   c  and the blades  2   d  in the scroll portion  41 . The air flow passes through the scroll portion  41 , and then is blown out to the outside of the scroll casing  4  from the discharge port  42   a  formed at the discharge portion  42 . 
     As described above, in the centrifugal fan  1  according to Embodiment 1, the distance L 1  is equal to the distance L 2  at the first end  41   a  and the second end  41   b  in the circumferential wall  4   c  in comparison with the centrifugal fan including the standard circumferential wall SW having a logarithmic spiral shape in cross-section perpendicular to the rotational shaft X of the fan  2 . In the circumferential wall  4   c , between the first end  41   a  and the second end  41   b  of the circumferential wall  4   c,  the distance L 1  is greater than or equal to the distance L 2 . The circumferential wall  4   c  includes the plurality of extended portions between the first end  41   a  and the second end  41   b  of the circumferential wall  4   c.  The plurality of extended portions include maximum points each having a length being the difference LH between the distance L 1  and the distance L 2 . In the centrifugal fan  1 , the dynamic pressure is increased when the distance between the fan  2  and the wall surface of the circumferential wall  4   c  is the smallest near the tongue portion  4   b.  To recover the pressure from the dynamic pressure to the static pressure, the dynamic pressure is converted to the static pressure by reducing the speed by gradually extending the distance between the fan  2  and the wall surface of the circumferential wall  4   c  in the flow direction of the air flow. At this time, ideally, the amount of pressure recovery can be increased and the air-sending efficiency can be increased as the distance for which the air flow flows along the circumferential wall  4   c  increases. In other words, a configuration in which the maximum pressure recovery can be obtained is obtained when the configuration includes the circumferential wall  4   c  having extension rates greater than or equal to the extension rates of a normal logarithmic spiral shape (involute curve), and when the circumferential wall  4   c  of the scroll portion  41  is configured to have extension rates set within the range in which the separation of the air flow due to sudden extension such as an extension causing the air flow to be bent at almost a right angle does not occur, for example. The centrifugal fan  1  according to Embodiment 1 further includes a plurality of extended portions from a uniform logarithmic spiral shape (involute curve), and can extend the distance of the air passage in the scroll portion  41 . As a result, the centrifugal fan  1  can convert the dynamic pressure to the static pressure by reducing the speed of the air flow flowing in the scroll casing  4  while preventing the separation of the air flow, and hence can improve the air-sending efficiency while reducing the noise. The centrifugal fan  1  can increase the distance of the air passage in which the distance between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is extended by including the abovementioned configuration in the direction in which the circumferential wall  4   c  can be extended even when the extension rate of the circumferential wall  4   c  of the scroll casing to a predetermined direction cannot be sufficiently secured due to a restriction in the external dimensions depending on the place of installation. As a result, the centrifugal fan  1  can improve the air-sending efficiency while reducing the noise because the centrifugal fan  1  can convert the dynamic pressure to the static pressure by reducing the speed of the air flow flowing in the scroll casing  4  while preventing the separation of the air flow even when the extension rate of the circumferential wall  4   c  of the scroll casing to a predetermined direction cannot be sufficiently secured. 
     In the centrifugal fan  1 , the three extended portions includes the first maximum point P 1  in a section in which the angle θ is 0 degrees or more and less than 90 degrees, the second maximum point P 2  in a section in which the angle θ is 90 degrees or more and less than 180 degrees, and the third maximum point P 3  in a section in which the angle θ is 180 degrees or more and less than the angle α formed by the second reference line. The present disclosure further includes extended portions having three maximum points in addition to a uniform logarithmic spiral shape (involute curve), and hence can extend the distance of the air passage in the scroll portion  41 . When the extension rates of the logarithmic spiral shape (involute curve) of the related art are set as the standard, a case of the extended portions including three maximum points always has the highest extension rates as compared to a case of the extended portions including two maximum points because the configuration thereof is included in the extended portions including three maximum points. Therefore, as compared to the centrifugal fan including the standard circumferential wall SW having a logarithmic spiral shape of the related art, the centrifugal fan  1  satisfying the relationship can extend the distance between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and extend the distance of the air passage while preventing the separation of the air flow. For example, when a device (for example, an air-conditioning apparatus) in which the centrifugal fan  1  is installed has a restriction in external dimensions due to its low profile or the like, there may be a case where the distance between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  of the centrifugal fan  1  cannot be extended in the direction in which the angle θ is 270 degrees or the direction in which the angle θ is 90 degrees. The centrifugal fan  1  includes three maximum points in a section in which the angle θ is within the abovementioned range, and hence can increase the distance of the air passage in which the distance between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is extended even when the device in which the centrifugal fan  1  is installed has a restriction in external dimensions due to its low profile or the like. As a result, the centrifugal fan  1  can convert the dynamic pressure to the static pressure by reducing the speed of the air flow flowing in the scroll casing  4  while preventing the separation of the air flow, and hence can improve the air-sending efficiency while reducing the noise. 
     In the centrifugal fan  1 , the extension rates of the three extended portions of the circumferential wall  4   c  satisfy a relationship of the extension rate B&gt;the extension rate C, and the extension rate B≥the extension rate A&gt;the extension rate C, or a relationship of the extension rate B&gt;the extension rate C, and the extension rate B&gt;the extension rate C≥the extension rate A. The scroll portion  41  also has a function of raising the dynamic pressure in a region in which the angle θ is 0 degrees to 90 degrees, and hence the static pressure conversion can be increased more when the extension rates of a region in which the angle θ is 90 degrees to 180 degrees are increased as compared to increasing the extension rates of the region above. Therefore, as compared to the centrifugal fan including the standard circumferential wall SW having a logarithmic spiral shape of the related art, the centrifugal fan  1  satisfying the relationship can extend the distance between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  and extend the distance of the air passage while preventing the separation of the air flow in a region with excellent static pressure conversion efficiency. As a result, the centrifugal fan  1  can convert the dynamic pressure to the static pressure by reducing the speed of the air flow flowing in the scroll casing  4  while preventing the separation of the air flow, and hence can improve the air-sending efficiency while reducing the noise. When a device (for example, an air-conditioning apparatus) in which the centrifugal fan  1  is installed has a restriction in external dimensions due to its low profile or the like, there may be a case where the distance between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  of the centrifugal fan  1  cannot be extended in the direction in which the angle θ is 270 degrees or the direction in which the angle θ is 90 degrees. The centrifugal fan  1  includes the abovementioned extension rates, and hence can increase the distance of the air passage in which the distance between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is extended even when the device in which the centrifugal fan  1  is installed has a restriction in external dimensions due to its low profile or the like. As a result, the centrifugal fan  1  can convert the dynamic pressure to the static pressure by reducing the speed of the air flow flowing in the scroll casing  4  while preventing the separation of the air flow, and hence can improve the air-sending efficiency while reducing the noise. 
     In the centrifugal fan  1 , the extension rates of the three extended portions of the circumferential wall  4   c  satisfy a relationship of the extension rate C&gt;the extension rate B≥the extension rate A. The scroll portion  41  also has a function of raising the dynamic pressure in a region in which the angle θ is 0 degrees to 90 degrees, and hence the static pressure conversion can be increased when the extension rates of a region in which the angle θ is 90 degrees to 180 degrees are increased as compared to raising the extension rates of the region above. However, a part of the function of the scroll portion  41  for raising the dynamic pressure also remains in the region in which the angle θ is 90 degrees to 180 degrees. Therefore, the air-sending efficiency further increases when the extension rate is increased in a region in which the angle θ is 180 degrees to 270 degrees as compared to when the extension rate is increased in the region in which the angle θ is 90 degrees to 180 degrees. In the region (the angle θ is 180 degrees to 270 degrees) in which the distance between the fan  2  and the circumferential wall  4   c  is the farthest, the function of the scroll portion  41  for raising the dynamic pressure is almost lost. Therefore, the air-sending efficiency can be maximized by maximizing the extension rate of the scroll portion  41  in that region. As a result, the centrifugal fan  1  can improve the air-sending efficiency while reducing the noise. 
     In the centrifugal fan  1 , the plurality of extended portions include the first extended portion  51  including the first maximum point P 1  in a section in which the angle θ is 0 degrees or more and less than 90 degrees, the second extended portion  52  including the second maximum point P 2  in a section in which the angle θ is 90 degrees or more and less than 180 degrees, and the third extended portion  53  including the third maximum point P 3  in a section in which the angle θ is 180 degrees or more and less than the angle α formed by the second reference line. In the circumferential wall  4   c  forming the region from the second extended portion  52  to the third extended portion  53 , the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is greater than the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW. The centrifugal fan  1  has a configuration in which the scroll bulges out to the opposite side of the discharge port  72 , and hence can extend the distance of the wall surface of the scroll along the flow of the air flow by the effect of the three extended portions and the bulged-out scroll. As a result, the centrifugal fan  1  can convert the dynamic pressure to the static pressure by reducing the speed of the air flow flowing in the scroll casing  4  while preventing the separation of the air flow, and hence can improve the air-sending efficiency while reducing the noise. 
     In the centrifugal fan  1 , the plurality of extended portions include the second extended portion  52  including the second maximum point P 2  in a section in which the angle θ is 90 degrees or more and less than 180 degrees, and the third extended portion  53  including the third maximum point P 3  in a section in which the angle θ is 180 degrees or more and less than the angle α formed by the second reference line. In the circumferential wall  4   c  forming the region from the second extended portion  52  to the third extended portion  53 , the distance L 1  between the axis C 1  of the rotational shaft X and the circumferential wall  4   c  is greater than the distance L 2  between the axis C 1  of the rotational shaft X and the standard circumferential wall SW. The centrifugal fan  1  has a configuration in which the scroll bulges out to the side opposite to the discharge port  72 , and hence can extend the distance of the wall surface of the scroll along the flow of the air flow by the effect of the two extended portions and the bulged-out scroll. As a result, the centrifugal fan  1  can convert the dynamic pressure to the static pressure by reducing the speed of the air flow flowing in the scroll casing  4  while preventing the separation of the air flow, and hence can improve the air-sending efficiency while reducing the noise. 
     In the centrifugal fan  1 , the circumferential wall  4   c  of the centrifugal fan  1  is desired to satisfy the extension rate J&gt;the extension rate D≥0, the extension rate J&gt;the extension rate E≥0, and the extension rate J&gt;the extension rate F≥0. Because the circumferential wall  4   c  of the centrifugal fan  1  has the abovementioned extension rates, the air passage between the rotational shaft X and the circumferential wall  4   c  does not narrow, a pressure loss of the air flow generated by the fan  2  is not generated. As a result, the centrifugal fan  1  can reduce the speed and convert the dynamic pressure to the static pressure, and can improve the air-sending efficiency while reducing the noise. 
     Embodiment 2 
       FIG.  15    is a cross-sectional view of a centrifugal fan  1  according to Embodiment 2 of the present disclosure  1  taken along the axis direction. The dotted line shown in  FIG.  15    shows the position of the standard circumferential wall SW of the centrifugal fan having a logarithmic spiral shape being a related-art example. Note that sections having the same configurations as the centrifugal fan  1  in  FIG.  1    to  FIG.  14    are denoted by the same reference characters, and descriptions thereof are omitted. The centrifugal fan  1  of Embodiment 2 is the centrifugal fan  1  including the double-suction scroll casing  4  having the side walls  4   a  in which the suction ports  5  are formed on both sides of the main plate  2   a  in the axis direction of the rotational shaft X. As shown in  FIG.  15   , in the centrifugal fan  1  of Embodiment 2, the circumferential wall  4   c  extends more to the radial direction of the rotational shaft X as the circumferential wall  4   c  is farther away from the suction ports  5  in the axis direction of the rotational shaft X. In other words, in the centrifugal fan  1  of Embodiment 2, in the axis direction of the rotational shaft X, the distance between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  increases as the circumferential wall  4   c  is farther away from the suction ports  5 . In the circumferential wall  4   c  of the centrifugal fan  1 , the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at a position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a  in the direction parallel to the axis direction of the rotational shaft X. A distance LM 1  shown in  FIG.  15    shows a portion at which the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest in the direction parallel to the axis direction of the rotational shaft X at the position  4   c   1  in the circumferential wall  4   c  facing the circumferential portion  2   a   1  of the main plate  2   a.  In the circumferential wall  4   c  of the centrifugal fan  1 , the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the smallest at positions  4   c   2  being boundaries with the side walls  4   a  in the direction parallel to the axis direction of the rotational shaft X. Each of distances LS 1  shown in  FIG.  15    shows a portion at which the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the smallest in the direction parallel to the axis direction of the rotational shaft X at the position  4   c   2  being the boundary between the circumferential wall  4   c  and the side wall  4   a.  The circumferential wall  4   c  bulges out at the position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a  in the direction parallel to the rotational shaft X, and the distance L 1  is the greatest at the position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a  in the direction parallel to the rotational shaft X. In other words, in the centrifugal fan  1  of Embodiment 2, the circumferential wall  4   c  is formed in an arc shape, so that the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at a position facing the circumferential portion  2   a   1  of the main plate  2   a  in a cross-sectional view parallel to the rotational shaft X. Note that, in the circumferential wall  4   c  in cross-section, the circumferential wall  4   c  only needs to be formed in a convex shape, so that the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at the position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a,  and may include a linear portion in a part or the entirety thereof in cross-section. 
       FIG.  16    is a cross-sectional view of a modified example of the centrifugal fan  1  according to Embodiment 2 of the present disclosure taken along the axis direction. The dotted line shown in  FIG.  16    shows the position of the standard circumferential wall SW of the centrifugal fan of the related-art example having a logarithmic spiral shape. Note that sections having the same configurations as the centrifugal fan  1  in  FIG.  1    to  FIG.  14    are denoted by the same reference characters, and descriptions thereof are omitted. The modified example of the centrifugal fan  1  of Embodiment 2 is the centrifugal fan  1  including the single-suction scroll casing  4  having the side wall  4   a  in which the suction port  5  is formed on one side of the main plate  2   a  in the axis direction of the rotational shaft X. As shown in  FIG.  16   , in the modified example of the centrifugal fan  1  of Embodiment 2, the circumferential wall  4   c  extends more to the radial direction of the rotational shaft X as the circumferential wall  4   c  is farther away from the suction port  5  in the axis direction of the rotational shaft X. In other words, in the centrifugal fan  1  of Embodiment 2, the distance between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  increases as the circumferential wall  4   c  is farther away from the suction ports  5  in the axis direction of the rotational shaft X. In the circumferential wall  4   c  of the centrifugal fan  1 , the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at the position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a  in the direction parallel to the axis direction of the rotational shaft X. The distance LM 1  shown in  FIG.  16    shows a portion at which the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest in the direction parallel to the axis direction of the rotational shaft X at the position  4   c   1  in the circumferential wall  4   c  facing the circumferential portion  2   a   1  of the main plate  2   a.  In the circumferential wall  4   c  of the centrifugal fan  1 , the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the smallest at the position  4   c   2  being a boundary with the side wall  4   a  in the direction parallel to the axis direction of the rotational shaft X. The distance LS 1  shown in  FIG.  16    shows a portion at which the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the smallest in the direction parallel to the axis direction of the rotational shaft X at the position  4   c   2  being the boundary between the circumferential wall  4   c  and the side wall  4   a.  The circumferential wall  4   c  bulges out at the position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a  in the direction parallel to the rotational shaft X, and the distance L 1  is the greatest at the position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a  in the direction parallel to the rotational shaft X. In other words, in the centrifugal fan  1  of Embodiment 2, the circumferential wall  4   c  is formed in a curved shape, so that the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at a position facing the circumferential portion  2   a   1  of the main plate  2   a  in a cross-sectional view parallel to the rotational shaft X. Note that the circumferential wall  4   c  in cross-section only needs to be formed in a convex shape in which the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at the position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a,  and may include a linear portion in a part or the entirety thereof in cross-section. 
       FIG.  17    is a cross-sectional view of another modified example of the centrifugal fan  1  according to Embodiment 2 of the present disclosure taken along the axis direction. The dotted line shown in  FIG.  17    shows the position of the standard circumferential wall SW of the centrifugal fan of the related-art example having a logarithmic spiral shape. Note that sections having the same configurations as the centrifugal fan  1  in  FIG.  1    to  FIG.  14    are denoted by the same reference characters, and descriptions thereof are omitted. The other modified example of the centrifugal fan  1  of Embodiment 2 is the centrifugal fan  1  including the double-suction scroll casing  4  having the side walls  4   a  in which the suction ports  5  are formed on both sides of the main plate  2   a  in the axis direction of the rotational shaft X. As shown in  FIG.  17   , the circumferential wall  4   c  of the centrifugal fan  1  of Embodiment 2 has a protruding portion  4   d  at which a part of the circumferential wall  4   c  protrudes in the radial direction of the rotational shaft X at the position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a  in the axis direction of the rotational shaft X. The protruding portion  4   d  is a portion in a part of the circumferential wall  4   c  at which the distance between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  increases in the axis direction of the rotational shaft X. The protruding portion  4   d  is formed on a portion of the circumferential wall  4   c  between the first end  41   a  and the second end  41   b  in a longitudinal direction thereof. Note that, on a portion of the circumferential wall  4   c  between the first end  41   a  and the second end  41   b,  the protruding portion  4   d  may be formed in the entire range from the first end  41   a  to the second end  41   b  or in only a part of the range. The circumferential wall  4   c  has the protruding portion  4   d  protruding to the radial direction of the rotational shaft X in the circumferential direction of the rotational shaft X. In the circumferential wall  4   c  of the centrifugal fan  1 , the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at the position  4   c   1  facing the circumferential portion  2   a   1  of the main plate  2   a  in the direction parallel to the axis direction of the rotational shaft X. In other words, in the circumferential wall  4   c  of the centrifugal fan  1 , the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at the protruding portion  4   d  in the direction parallel to the axis direction of the rotational shaft X. The distance LM 1  shown in  FIG.  17    shows a portion at which the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest in the direction parallel to the axis direction of the rotational shaft X at the position  4   c   1  in the circumferential wall  4   c  facing the circumferential portion  2   a   1  of the main plate  2   a.  In the circumferential wall  4   c  of the centrifugal fan  1 , the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the smallest at the positions  4   c   2  being boundaries with the side walls  4   a  in the direction parallel to the axis direction of the rotational shaft X. Each of the distances LS 1  shown in  FIG.  17    shows a portion at which the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the smallest in the direction parallel to the axis direction of the rotational shaft X at the position  4   c   2  being the boundary between the circumferential wall  4   c  and the side wall  4   a.  As shown in  FIG.  17   , in the circumferential wall  4   c,  the distance LS 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is fixed in the axis direction of the rotational shaft X. Note that the protruding portion  4   d  is formed in a rectangular shape made of linear portions in cross-section, but may be formed in an arc shape made of curved portions, for example, or may be other shapes having a linear portion and a curved portion. The circumferential wall  4   c  is not limited to have a configuration in which the distance LS 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is fixed in the axis direction of the rotational shaft X. In the circumferential wall  4   c,  the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  may be extended from the side walls  4   a  to the protruding portion  4   d,  for example. 
     The centrifugal fan including the standard circumferential wall SW having a logarithmic spiral shape being the related-art example, has the following features regarding the air flow flowing in the air passage in the portion at a position  4   c   1  or the position  4   c   2  in the circumferential wall  4   c  in the direction parallel to the axis direction of the rotational shaft X. In the centrifugal fan of the related art, the speed of the air flow is fast and the dynamic pressure is high in the air passage between the circumferential wall  4   c  at the position  4   c   1  and the rotational shaft X. In the centrifugal fan of the related art, the speed of the air flow is slow and the dynamic pressure is low in the air passage between the circumferential wall  4   c  at the position  4   c   2  and the rotational shaft X. Therefore, in the centrifugal fan of the related art, a case where the air flow does not flow along the inner peripheral surface of the circumferential wall  4   c  may tend to occur as the air flow flows from the center portion of the circumferential wall  4   c  to the suction end in the direction parallel to the axis direction of the rotational shaft X. Meanwhile, in the centrifugal fan  1  of Embodiment 2 and the centrifugal fans  1  of the modified examples, the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at the position  4   c   1  in the circumferential wall  4   c  facing the circumferential portion  2   a   1  of the main plate  2   a  when seen from the direction parallel to the rotational shaft X. Therefore, the air flow tends to be collected in the air passage at a portion of the circumferential wall  4   c  at the position  4   c   1  at which the speed of the air flow is fast and the dynamic pressure is high along the circumferential wall  4   c  in cross-section, and a portion at which the speed of the air flow is slow and the dynamic pressure is low can be reduced in the air passage. As a result, in the centrifugal fans  1  of Embodiment 2 and the modified examples, the air flow can be efficiently caused to flow along the inner peripheral surface of the circumferential wall  4   c.    
     As described above, in the centrifugal fan  1  according to Embodiment 2 and the modified examples, the distance L 1  between the axis C 1  of the rotational shaft X and the inner wall surface of the circumferential wall  4   c  is the greatest at the position  4   c   1  in the circumferential wall  4   c  facing the circumferential portion  2   a   1  of the main plate  2   a  when seen from the direction parallel to the rotational shaft X. Therefore, in the circumferential wall  4   c  in cross-section parallel to the rotational shaft X, the air flow tends to be collected in the air passage in the portion of the circumferential wall  4   c  at the position  4   c   1  at which the speed of the air flow is fast and the dynamic pressure is high. Meanwhile, in the circumferential wall  4   c  in cross-section parallel to the rotational shaft X, the air volume of the air flow flowing through the portion at the position  4   c   2  in the circumferential wall  4   c  at which the speed of the air flow is slow and the dynamic pressure is low in the air passage is reduced. As a result, in the centrifugal fans  1  of Embodiment 2 and the modified examples, the air flow can be efficiently caused to flow along the inner peripheral surface of the circumferential wall  4   c.  As compared to the centrifugal fan including the standard circumferential wall SW having a logarithmic spiral shape of the related art, the centrifugal fan  1  can increase the distance between the axis C 1  of the rotational shaft X and the circumferential wall  4   c,  and can increase the distance of the air passage while preventing the separation of the air flow. As a result, the centrifugal fan  1  can reduce the speed and convert the dynamic pressure to the static pressure, and can improve the air-sending efficiency while reducing the noise. 
     Embodiment 3 
     Air-Sending Device  30   
       FIG.  18    illustrates a configuration of the air-sending device  30  according to Embodiment 3 of the present disclosure. Sections having the same configurations as the centrifugal fan  1  in  FIG.  1    to  FIG.  14    are denoted by the same reference characters, and descriptions thereof are omitted. The air-sending device  30  according to Embodiment 3 is a ventilating fan or a desk fan, for example, and includes the centrifugal fan  1  according to Embodiment 1 or 2, and a case  7  accommodating the centrifugal fan  1 . In the case  7 , two opening ports, specifically, a suction port  71  and a discharge port  72  are formed. As shown in  FIG.  18   , the suction port  71  and the discharge port  72  are formed in opposite positions in the air-sending device  30 . Note that the suction port  71  and the discharge port  72  do not necessarily need to be formed in opposite positions in the air-sending device  30 . For example, either one of the suction port  71  and the discharge port  72  may be formed on the top or the bottom of the centrifugal fan  1 . In the case  7 , a space S 1  including the portion in which the suction port  71  is formed and a space S 2  including the portion in which the discharge port  72  is formed are partitioned by a partition plate  73 . The centrifugal fan  1  is installed in a state in which the suction ports  5  are positioned in the space S 1  in which the suction port  71  is formed and the discharge port  42   a  is positioned in the space S 2  in which the discharge port  72  is formed. 
     When the fan  2  rotates, air is suctioned into the case  7  through the suction port  71 . The air suctioned into the case  7  is guided by the bell mouths  3 , and is suctioned by the fan  2 . The air suctioned by the fan  2  is blown out to the radially outer side of the fan  2 . The air blown out from the fan  2  is blown out from the discharge port  42   a  of the scroll casing  4  after passing through the inside of the scroll casing  4 , and is blown out from the discharge port  72 . 
     The air-sending device  30  according to Embodiment 3 includes the centrifugal fan  1  according to Embodiment 1 or 2, and hence can efficiently recover the pressure, and can improve the air-sending efficiency and reduce the noise. 
     Embodiment 4 
     Air-Conditioning Apparatus  40   
       FIG.  19    is a perspective view of the air-conditioning apparatus  40  according to Embodiment 4 of the present disclosure.  FIG.  20    illustrates an inner configuration of the air-conditioning apparatus  40  according to Embodiment 4 of the present disclosure.  FIG.  21    is a cross-sectional view of the air-conditioning apparatus  40  according to Embodiment  4  of the present disclosure. Note that, in a centrifugal fan  11  used in the air-conditioning apparatus  40  according to Embodiment 4, sections having the same configurations as the centrifugal fan  1  in  FIG.  1    to  FIG.  14    are denoted by the same reference characters, and descriptions thereof are omitted. In  FIG.  20   , an upper surface portion  16   a  is omitted to illustrate the inner configuration of the air-conditioning apparatus  40 . The air-conditioning apparatus  40  according to Embodiment 4 includes the centrifugal fan  1  of Embodiment 1 or 2, and a heat exchanger  10  disposed in a position facing the discharge port  42   a  of the centrifugal fan  1 . The air-conditioning apparatus  40  according to Embodiment 4 includes a case  16  installed above a ceiling of an air-conditioned room. As shown in  FIG.  19   , the case  16  is formed in a cuboid shape including the upper surface portion  16   a,  a lower surface portion  16   b,  and side surface portions  16   c.  Note that the shape of the case  16  is not limited to a cuboid shape, and may be other shapes such as a cylindrical shape, a prismatic shape, a conical shape, a shape having a plurality of corners, and a shape having a plurality of curved portions. 
     (Case  16 ) 
     The case  16  includes the side surface portion  16   c  at which a case discharge port  17  is formed as one of the side surface portions  16   c.  The shape of the case discharge port  17  is formed in a rectangular shape as shown in  FIG.  19   . Note that the shape of the case discharge port  17  is not limited to a rectangular shape, and may be a circular shape or an oval shape, for example, or may be other shapes. The case  16  includes the side surface portion  16   c  at which the case suction port  18  is formed on a surface opposite to the surface at which the case discharge port  17  is formed out of the side surface portions  16   c.  The shape of the case suction port  18  is formed in a rectangular shape as shown in  FIG.  20   . Note that the shape of the case suction port  18  is not limited to a rectangular shape, and may be a circular shape or an oval shape, for example, or may be other shapes. A filter configured to remove dust in the air, may be disposed on the case suction port  18 . 
     In the case  16 , two centrifugal fans  11 , a fan motor  9 , and the heat exchanger  10  are accommodated. Each of the centrifugal fans  11  includes the fan  2 , and the scroll casing  4  in which the bell mouth  3  is formed. The shape of the bell mouth  3  of the centrifugal fan  11  is a shape similar to the shape of the bell mouth  3  of the centrifugal fan  1  of Embodiment 1. Each of the centrifugal fans  11  includes the fan  2  and the scroll casing  4  similar to the fan  2  and the scroll casing  4  of the centrifugal fan  1  according to Embodiment 1, but is different in that the fan motor  6  is not disposed in the scroll casing  4 . The fan motor  9  is supported by a motor support  9   a  fixed to the upper surface portion  16   a  of the case  16 . The fan motor  9  includes the output shaft  6   a.  The output shaft  6   a  is disposed to extend in a direction parallel to the surface at which the case suction port  18  is formed and the surface at which the case discharge port  17  is formed out of the side surface portions  16   c.  As shown in  FIG.  20   , in the air-conditioning apparatus  40 , two fans  2  are mounted on the output shaft  6   a.  The fans  2  form the flow of the air suctioned into the case  16  from the case suction port  18  and blown out to the air-conditioned space from the case discharge port  17 . Note that the number of the fans  2  disposed in the case  16  is not limited to two and may be one or three or more. 
     As shown in  FIG.  20   , the centrifugal fans  11  are installed in the partition plate  19 , and the inner space of the case  16  is partitioned into a space S 11  on the suction side of the scroll casing  4  and a space S 12  on the blow out side of the scroll casing  4  by the partition plate  19 . 
     As shown in  FIG.  21   , the heat exchanger  10  is disposed in a position facing the discharge ports  42   a  of the centrifugal fan  11 , and is disposed on the air passage of the air discharged from the centrifugal fan  11  in the case  16 . The heat exchanger  10  adjusts the temperature of the air suctioned into the case  16  from the case suction port  18  and blown out to the air-conditioned space from the case discharge port  17 . Note that a well-known structure can be applied to the heat exchanger  10 . 
     When the fans  2  rotate, the air in the air-conditioned space is suctioned into the case  16  through the case suction port  18 . The air suctioned into the case  16  is the guided by bell mouths  3  and is suctioned by the fans  2 . The air suctioned by the fans  2  is blown out toward the radially outer side of the fans  2 . The air blown out from the fans  2  passes through the inside of the scroll casings  4 . Then, the air is blown out from the discharge ports  42   a  of the scroll casings  4  and is supplied to the heat exchanger  10 . When the air supplied to the heat exchanger  10  passes through the heat exchanger  10 , the heat thereof is exchanged and the humidity thereof is adjusted. The air passing through the heat exchanger  10  is blown out to the air-conditioned space from the case discharge port  17 . 
     The air-conditioning apparatus  40  according to Embodiment 4 includes the centrifugal fan  1  according to Embodiment 1 or 2, and hence can efficiently recover the pressure, and can improve the air-sending efficiency and reduce the noise. 
     Embodiment 5 
     Refrigeration Cycle Apparatus  50   
       FIG.  22    illustrates the configuration of the refrigeration cycle apparatus  50  according to Embodiment 5 of the present disclosure. Note that, in the centrifugal fan  1  used in the refrigeration cycle apparatus  50  according to Embodiment 5, sections having the same configurations as those of the centrifugal fan  1  or the centrifugal fan  11  in  FIG.  1    to  FIG.  14    are denoted by the same reference characters, and descriptions thereof are omitted. The refrigeration cycle apparatus  50  according to Embodiment 5 conditions air by heating or cooling the inside of a room by moving the heat between the outside air and the indoor air via refrigerant. The refrigeration cycle apparatus  50  according to Embodiment 5 includes an outdoor unit  100  and an indoor unit  200 . In the refrigeration cycle apparatus  50 , a refrigerant circuit in which the refrigerant circulates is formed by connecting the outdoor unit  100  and the indoor unit  200  to each other by pipes, specifically, a refrigerant pipe  300  and a refrigerant pipe  400 . The refrigerant pipe  300  is a gas pipe through which refrigerant in a gas phase flows, and the refrigerant pipe  400  is a liquid pipe through which refrigerant in a liquid phase flows. Note that two-phase gas-liquid refrigerant may flow through the refrigerant pipe  400 . In the refrigerant circuit of the refrigeration cycle apparatus  50 , a compressor  101 , a flow switching device  102 , an outdoor heat exchanger  103 , an expansion valve  105 , and an indoor heat exchanger  201  are sequentially connected to each other via the refrigerant pipes. 
     (Outdoor Unit  100 ) 
     The outdoor unit  100  includes the compressor  101 , the flow switching device  102 , the outdoor heat exchanger  103 , and the expansion valve  105 . The compressor  101  compresses and discharges the suctioned refrigerant. The compressor  101  may include an inverter device, and may be formed to be able to change the capacity of the compressor  101  by changing the operating frequency by the inverter device. Note that the capacity of the compressor  101  is the amount of the refrigerant sent out per unit time. The flow switching device  22  is a four-way valve, for example, and is a device in which the direction of the refrigerant flow passage is switched. The refrigeration cycle apparatus  50  can realize the heating operation or the cooling operation by switching the flow of the refrigerant with use of the flow switching device  102  on the basis of the instruction from a controller (not shown). 
     The outdoor heat exchanger  103  exchanges the heat between the refrigerant and the outdoor air. The outdoor heat exchanger  103  functions as an evaporator at the time of the heating operation, and exchanges the heat between low-pressure refrigerant flowing into the outdoor heat exchanger  103  from the refrigerant pipe  400  and the outdoor air, to thereby evaporate and gasify the refrigerant. The outdoor heat exchanger  103  functions as a condenser at the time of the cooling operation, and exchanges the heat between the refrigerant compressed in the compressor  101  flowing into the outdoor heat exchanger  103  from the flow switching device  102  side and the outdoor air, to thereby condense and liquefy the refrigerant. In the outdoor heat exchanger  103 , an outdoor fan  104  is provided to increase the efficiency of the heat exchange between the refrigerant and the outdoor air. Regarding the outdoor fan  104 , an inverter device may be mounted, and the rotation speed of the fan may be changed by changing the operating frequency of a fan motor. The expansion valve  105  is an expansion device (flow rate control unit), and functions as an expansion valve by adjusting the flow rate of the refrigerant flowing through the expansion valve  105 . The expansion valve  105  adjusts the pressure of the refrigerant by changing the opening degree. For example, the expansion valve  105  adjusts the opening degree on the basis of the instruction from the controller (not shown) and other units when the expansion valve  105  is made of an electronic expansion valve or other valves. 
     (Indoor Unit  200 ) 
     The indoor unit  200  includes the indoor heat exchanger  201  configured to exchange the heat between the refrigerant and the indoor air, and an indoor fan  202  configured to adjust the flow of the air with which the indoor heat exchanger  201  performs heat exchange. The indoor heat exchanger  201  functions as a condenser at the time of the heating operation. The indoor heat exchanger  201  performs heat exchange between the refrigerant flowing into the indoor heat exchanger  201  from the refrigerant pipe  300  and the indoor air, condenses and liquefies the refrigerant, and causes the refrigerant to flow out to the refrigerant pipe  400  side. The indoor heat exchanger  201  functions as an evaporator at the time of the cooling operation. The indoor heat exchanger  201  performs heat exchange between the refrigerant placed in the low-pressure state by the expansion valve  105  and the indoor air, and causes the refrigerant to draw the heat from the air, so that the refrigerant is evaporated and vaporized. Then, the indoor heat exchanger  201  causes the refrigerant to flow out to the pipe  300  side. The indoor fan  202  is provided to face the indoor heat exchanger  201 . The centrifugal fan  1  according to Embodiment 1 or 2 and the centrifugal fan  11  according to Embodiment 5 are applied to the indoor fan  202 . The operation speed of the indoor fan  202  is determined by the setting by a user. An inverter device may be mounted on the indoor fan  202 , and the rotation speed of the fan  2  may be changed by changing the operating frequency of the fan motor  6 . 
     Operation Example of Refrigeration Cycle Apparatus  50   
     Next, an operation of the cooling operation is described as an operation example of the refrigeration cycle apparatus  50 . High-temperature high-pressure gas refrigerant compressed by and discharged from the compressor  101  flows into the outdoor heat exchanger  103  via the flow switching device  102 . The gas refrigerant flowing into the outdoor heat exchanger  103  is condensed by heat exchange with the outside air blown by the outdoor fan  104 , is turned to be low-temperature refrigerant, and flows out from the outdoor heat exchanger  103 . The expansion valve  105  expands the refrigerant flowing out of the outdoor heat exchanger  103  and reduces the pressure thereof. As a result, the refrigerant is turned to be low-temperature low-pressure two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant flows into the indoor heat exchanger  201  of the indoor unit  200 , and is evaporated by the heat exchange with the indoor air blown by the indoor fan  202 . As a result, the two-phase gas-liquid refrigerant is turned to be low-temperature low-pressure gas refrigerant and flows out from the indoor heat exchanger  201 . At this time, the heat of the indoor air is absorbed by the refrigerant and the indoor air cooled. As a result, the indoor air is turned to be conditioned air (blown air), and is blown out into the room (air-conditioned space) from the air outlet of the indoor unit  200 . The gas refrigerant flowing out from the indoor heat exchanger  201  is suctioned by the compressor  101  via the flow switching device  102  and is compressed again. The operation above is repeated. 
     Next, an operation of the heating operation is described as an operation example of the refrigeration cycle apparatus  50 . The high-temperature high-pressure gas refrigerant compressed by and discharged from the compressor  101  flows into the indoor heat exchanger  201  of the indoor unit  200  via the flow switching device  102 . The gas refrigerant flowing into the indoor heat exchanger  201  is condensed by the heat exchange with the indoor air blown by the indoor fan  202 , is turned to be low-temperature refrigerant, and flows out from the indoor heat exchanger  201 . At this time, the indoor air heated by receiving heat from the gas refrigerant is turned to be conditioned air (blown air), and is blown out into the room (air-conditioned space) from the air outlet of the indoor unit  200 . The expansion valve  105  expands the refrigerant flowing out from the indoor heat exchanger  201  and reduces the pressure of the refrigerant. As a result, the refrigerant is turned to be low-temperature low-pressure two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant flows into the outdoor heat exchanger  103  of the outdoor unit  100 , and is evaporated by the heat exchange with the outside air blown by the outdoor fan  104 . As a result, the two-phase gas-liquid refrigerant is turned to be low-temperature low-pressure gas refrigerant and flows out from the outdoor heat exchanger  103 . The gas refrigerant flowing out from the outdoor heat exchanger  103  is suctioned by the compressor  101  via the flow switching device  102 , and is compressed again. The operation above is repeated. 
     The refrigeration cycle apparatus  50  according to Embodiment 5 includes the centrifugal fan  1  according to Embodiment 1 or 2, and hence can efficiently recover the pressure, and can improve the air-sending efficiency and reduce the noise. 
     The configurations described in the embodiments given above describe one example of the content of the present disclosure, and can be combined with other well-known technologies. Further, a part of the configuration can be omitted or changed without departing from the gist of the present disclosure. 
     REFERENCE SIGNS LIST 
       1  centrifugal fan  2  fan  2   a  main plate  2   a   1  circumferential portion  2   b  boss portion  2   c  side plate  2   d  blade  2   e  suction port  3  bell mouth  3   a  upstream end  3   b  downstream end  4  scroll casing  4   a  side wall  4   b  tongue portion  4   c  circumferential wall  4   d  protruding portion  5  suction port  6  fan motor  6   a  output shaft  7  case  9  fan motor  9   a  motor support  10  heat exchanger  11  centrifugal fan  16  case  16   a  upper surface portion  16  fan surface portion  16   c  side surface portion  17  case discharge port  18  case suction port  19  partition plate  22  flow switching device  30  air-sending device  40  air-conditioning apparatus  41  scroll portion  41   a  first end  41   b  second end  42  discharge portion  42   a  discharge port  50  refrigeration cycle apparatus  51  first extended portion  52  second extended portion  53  third extended portion  54  fourth extended portion  71  suction port  72  discharge port  73  partition plate  100  outdoor unit  101  compressor  102  flow switching device  103  outdoor heat exchanger  104  outdoor fan  105  expansion valve  200  indoor unit  201  indoor heat exchanger  202  indoor fan  300  refrigerant pipe  400  refrigerant pipe