Patent Publication Number: US-9885364-B2

Title: Fan, molding die, and fluid feeder

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of co-pending U.S. application Ser. No. 13/634,480, filed on Sep. 12, 2012, which is a National Stage of PCT International Application No. PCT/JP2011/055225 filed on Mar. 7, 2011, which claims the benefit under 35 U.S.C. §119(a) to Japanese Patent Application No. 2010-057677, filed in Japan on Mar. 15, 2010, Japanese Patent Application No. 2010-057675, filed in Japan on Mar. 15, 2010, and Japanese Patent Application No. 2010-057669, filed in Japan on Mar. 15, 2010, all of which are hereby expressly incorporated by reference into the present application. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to a fan, a molding die, and a fluid feeder, and more particularly to a fan such as a centrifugal fan and a cross-flow fan, a molding die for use in production of the fan, and a fluid feeder provided with the centrifugal fan. 
     BACKGROUND ART 
     As for a conventional fan, for example, Japanese Patent Laying-Open No. 2008-241188 discloses a cross-flow blower aimed at reducing separation of the flow-in air while preventing a surging phenomenon or a reverse intake phenomenon by making the distribution of flow rate uniform in the unit even when resistance is adhered on the upstream side of the blower (PTL 1). The cross-flow blower disclosed in PTL 1 has a plurality of first blades each having an outer peripheral thickness greater than an inner peripheral thickness and a plurality of second blades each having an inner peripheral thickness greater than an outer peripheral thickness. The first blades and the second blades are disposed in order in the circumferential direction. When two first blades are in succession in the circumferential direction, the second blades are arranged on opposite sides of those first blades. When two second blades are in succession in the circumferential direction, the first blades are arranged on opposite sides of those second blades. 
     Japanese Patent Laying-Open No. 2006-170043 discloses a cross-flow fan aimed at reducing NZ noises while preventing reduction of air-blowing capacity and noise resulting from fluid oscillation (PTL 2). In the cross-flow fan disclosed in PTL 2, two or more kinds of blades having different shapes are arranged at random with a constant installation angle and installation pitch. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Laying-Open No. 2008-241188 
         PTL 2: Japanese Patent Laying-Open No. 2006-170043 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In recent years, for conservation of global environment, further energy savings in home electric equipment are desired. For example, it is known that the efficiency of electric equipment such as an air conditioner and an air purifier greatly depends on the efficiency of a blower included therein. It is also known that reducing the weight of a fan blade provided as a rotating body in a blower reduces power consumption of a motor for rotatably driving the fan blade and improves the efficiency of the blower or a fluid feeder. 
     However, an aerofoil employed as the shape in cross section of a fan blade is essentially assumed to be applied to the wing of an air plane and is mainly found in the field of aeronautical engineering. Therefore, an aerofoil fan blade is mainly optimized in a high Reynolds number region and is not always appropriate as the cross section of a fan blade used in a low Reynolds number region for an air conditioner, an air purifier, etc. for home use. 
     When an aerofoil or double arc is employed as the cross-sectional shape of a fan blade, a thick portion exists in a range of 30 to 50% from the front edge of the fan blade. This increases the weight of the fan blade, which becomes a cause of increased friction loss during rotation. However, simply reducing the weight of a fan blade may reduce the strength of the fan blade and result in fracture or other poor quality. 
     For the reasons above, in order to improve the blowing capacity of the fan and to save energy in electric equipment such as an air conditioner and an air purifier for home use, an appropriate blade cross-sectional shape has been sought for a fan blade to be used in the low Reynolds number region. A blade cross-sectional shape with a high lift-drag ratio, a small thickness and weight, and a high strength has also been sought. 
     On the other hand, in a case where fan blades whose blade cross sections are in a single shape are disposed at regular pitches (intervals), the blade ends of the fan blades pass through at a constant cycle when the fan is rotated. In this case, pressure variations occur in constant cycles at an approach place where the fan blades approach a casing covering them. This causes narrow-band noise called a blade-passing sound (nZ sound: a sound having a frequency determined by a value obtained by multiplying a natural number n by the number of fan blades Z). In the case where the fan blades whose blade cross sections are in a single shape are disposed at regular pitches, almost the same air flow is generated between adjacent fan blades. In this case, turbulent noise resulting from the air flow between adjacent fan blades becomes uniform among a plurality of fan blades, causing narrow-band noise. 
     In order to solve this problem, a random-pitch fan may be adopted, in which a plurality of fan blades are disposed at random. However, when a random-pitch fan is adopted, the intervals between adjacent fan blades have to be determined so as to intentionally include a large interval and a small interval departing from the optimum value based on the requested blowing performance. 
     In this case, at a place where the interval between adjacent fan blades is relatively large, the air flow against the normal air flow on the blade surface may be partially formed so that the air flow between adjacent fan blades becomes unstable. As a result, low-frequency noise (abnormal sound) like a bubbling sound is produced to give users unpleasant harsh sound. Such abnormal sound is not so loud at low rotation speeds of the fan, but becomes louder at higher rotation speeds of the fan, and finally becomes so loud as to vibrate the casing of the fan as a whole. 
     On the other hand, at a place where the interval between adjacent fan blades is relatively small, the flow resistance of the air flow passing through on the blade surface of the fan blade increases. As a result, the blowing capacity of the fan may be deteriorated. 
     Next, the blowing capacity of the blower has to be improved in order to promote energy savings in electric equipment because the efficiency of electric equipment greatly depends on the efficiency of the blower included therein. 
     Examples of the fan for use in a blower include a cross-flow fan which forms a flat outlet flow parallel to the rotation axis of the fan, and a centrifugal fan which blows air radially from the rotational center of the fan. In order to achieve a suitable blowing capacity in the blower using such a fan, a scroll shape (spiral shape) molded on the outlet side of the fan casing should be adapted to the direction of the airflow output from the fan. 
     For example, in a case where the scroll shape formed in the fan casing expands radially outward with respect to the direction of the airflow, the airflow may not conform to the scroll shape on the path in the fan casing and may be separated from the surface of the fan casing formed in a scroll shape. On the other hand, in a case where the scroll shape formed in the fan casing narrows radially inward with respect to the direction of the airflow, the direction of the airflow is abruptly deflected by the surface of the fan casing formed in a scroll shape. In these cases, the blowing efficiency is reduced, and the blowing capacity of the blower cannot be improved. 
     On the other hand, electric equipment such as an air conditioner and an air purifier requires quietness in operation, and it is therefore necessary to reduce noise resulting from rotation of the fan. 
     However, in the case where fan blades whose blade cross sections are in a single shape are disposed at regular pitches (intervals), the blade ends of the fan blades pass through in constant cycles as the fan is rotated. In this case, pressure variations occur at a constant cycle in the inside of the fan casing. This causes narrow-band noise called a blade-passing sound (nZ sound: a sound having a frequency determined by a value obtained by multiplying a natural number n by the number of fan blades Z). 
     In a cross-flow fan or a centrifugal fan, as the fan blades are rotated, the air flows in between adjacent fan blades and flows on the blade surface. Then, the air flowing on the blade surface flows out from between adjacent fan blades to be output from the fan. In order to achieve a suitable blowing capacity in the blower using such a fan, the air flow between adjacent fan blades has to be stabilized. 
     On the other hand, electric equipment such as an air conditioner and an air purifier requires quietness in operation, and it is therefore necessary to reduce noise resulting from rotation of the fan. 
     However, in the case where fan blades whose blade cross sections are in a single shape are disposed at regular pitches (intervals), the blade ends of the fan blades pass through at a constant cycle as the fan is rotated. In this case, pressure variations occur in constant cycles in the inside of the fan casing. This causes narrow-band noise called a blade-passing sound (nZ sound: a sound having a frequency determined by a value obtained by multiplying a natural number n by the number of fan blades Z). 
     An object of the present invention is therefore to solve the problem above and to provide a fan with excellent blowing capacity while preventing noise, a molding die for use in production of the fan, and a fluid feeder provided with the fan. 
     Solution to Problem 
     A fan according to an aspect of the present invention includes a plurality of blade portions arranged spaced apart from each other in a circumferential direction. Each blade portion has an inner edge portion disposed on an inner peripheral side thereof and an outer edge portion disposed on an outer peripheral side thereof. The blade portion extends between the inner edge portion and the outer edge portion. The blade surface includes a pressure surface disposed on a rotational direction side of the fan and a suction surface disposed on a back side of the pressure surface. As the fan is rotated, a fluid flow is produced on the blade surface to flow between the inner edge portion and the outer edge portion. When cut along a plane orthogonal to a rotation axis of the fan, the blade portion has a blade cross section having concave portions formed at the pressure surface and the suction surface. A plurality of blade portions include a first blade portion and a second blade portion having blade cross sections of different shapes. 
     According to such a configuration of the fan, during rotation of the fan, an air flow is produced to flow in from one of the inner edge portion and the outer edge portion, pass through on the blade surface, and flow out from the other of the inner edge portion and the outer edge portion. Here, a vortex of air flow (secondary flow) is generated in the concave portion, whereby the air flow (main flow) passing through on the blade surface flows along the outside of the vortex generated in the concave portion. Accordingly, the blade portion exhibits like a thick blade as if the thickness of the blade cross section is increased by the amount of formation of the vortex. As a result, the blowing capacity of the fan can be improved. 
     In the present invention, a plurality of blade portions include a first blade portion and a second blade portion having blade cross sections of different shapes. The static pressure distribution at the pressure surface and the suction surface of each blade portion is affected by the shape of the blade cross section. Therefore, in this configuration, the air flow between the adjacent blade portions and the air flow that flows in/out between the adjacent blade portions vary among the blade portions. Accordingly, noise can be reduced. 
     Preferably, the first blade portion and the second blade portion are different from each other in positions of the concave portions. According to such a configuration of the fan, the shape of the blade cross section can be varied by changing the positions of the concave portions. 
     Preferably, the first blade portion and the second blade portion are different from each other in number of the concave portions. According to such a configuration of the fan, the shape of the blade cross section can be varied by changing the number of the concave portions. 
     Preferably, the first blade portion and the second blade portion are different from each other in shape of the concave portions. According to such a configuration of the fan, the shape of the blade cross section can be varied by changing the shape of the concave portion. 
     Preferably, a plurality of blade portions are arranged such that an angle of a line connecting the rotation axis of the fan with the outer edge portion is equal between the adjacent blade portions. 
     According to such a configuration of the fan, although the outer edge portions of the blade portions pass through in constant cycles as the fan is rotated, the air flow that flows in/out between the adjacent blade portions is varied among blade portions, thereby preventing noise. In addition, because of reduction of noise, the interval between the adjacent blade portions can be set to an optimum value based on the blowing capacity required for the fan. Accordingly, the air flow between the blade portions can be stabilized, thereby preventing abnormal sound. An increase in ventilation resistance to the air flow between the blade portions can be prevented, thereby increasing the blowing capacity of the fan. 
     Preferably, a plurality of blade portions are arranged such that an angle of a line connecting the rotation axis of the fan with a centroid of the blade cross section of the blade portion is equal between the adjacent blade portions. 
     According to such a configuration of the fan, although turbulence noise caused by the air flow between the adjacent blade portions is uniform among a plurality of blade portions, the air flow between the adjacent blade portions is varied among the blade portions, thereby preventing noise. Because of reduction of noise, the interval between the adjacent blade portions can be set to an optimum value based on the blowing capacity required for the fan. Accordingly, the air flow between the blade portions can be stabilized, thereby preventing abnormal sound. An increase in ventilation resistance to the air flow between the blade portions can be prevented, thereby increasing the blowing capacity of the fan. 
     Preferably, plural kinds of the blade portions having blade cross sections of different shapes are arranged to be placed in an irregular order. According to such a configuration of the fan, the air flow between the adjacent blade portions and the air flow that flows in/out between the adjacent blade portions can be varied more effectively among a plurality of blade portions. 
     Preferably, the concave portion formed at the pressure surface forms a convex portion at the suction surface, and the concave portion formed at the suction surface forms a convex portion at the pressure surface. According to such a configuration of the fan, the shape of the blade cross section having the concave portions at the pressure surface and the suction surface can be obtained with a simple configuration. 
     Preferably, the blade portion has a blade cross section having a constant thickness between the inner edge portion and the outer edge portion. According to such a configuration of the fan, even when the blade portion having a blade cross section of a constant thickness is used, the blowing capacity of the fan can be improved. 
     Preferably, the blade portion has flection portions at which a center line of the blade cross section between the pressure surface and the suction surface is flexed at different points. The concave portions are formed of the flection portions. According to such a configuration of the fan, the strength of the blade portion can be increased by forming the flection portions. 
     An inside space is formed inside a plurality of blade portions arranged in the circumferential direction, and an outside space is formed outside thereof. Preferably, the fan described above is a centrifugal fan that outputs fluid from the inside space to the outside space. According to such a configuration of the fan, the blowing capacity of the centrifugal fan can be improved while noise can be prevented effectively. 
     An inside space is formed inside a plurality of blade portions arranged in the circumferential direction, and an outside space is formed outside thereof. Preferably, the fan described above is a cross-flow fan that takes in fluid to the inside space from the outside space on one side with respect to the rotation axis, as viewed from a direction of the rotation axis of the fan, and outputs the taken-in fluid to the outside space on the other side with respect to the rotation axis. According to such a configuration of the fan, the blowing capacity of the cross-flow fan can be improved while noise can be prevented effectively. 
     The fan described above is formed of resin. A molding die according to an aspect of the present invention is used to mold the fan. The molding die configured in this manner can produce a resin fan. 
     A fluid feeder according to an aspect of the present invention includes a blower configured with the fan described above and a driving motor coupled to the fan to rotate a plurality of blade portions. The fluid feeder configured in this manner can reduce power consumption of the driving motor while keeping the blowing capacity high. 
     A fan according to another aspect of the present invention includes a plurality of blade portions arranged spaced apart from each other in a circumferential direction. Each blade portion has a blade surface including a pressure surface disposed on a rotational direction side of the fan and a suction surface disposed on a back side of the pressure surface. When cut along a plane orthogonal to a rotation axis of the fan, the blade portion has an inner edge portion at which a center line between the pressure surface and the suction surface intersects an inner peripheral-side blade tip, and an outer edge portion at which the center line intersects an outer peripheral-side blade tip. As the fan is rotated, a fluid flow is produced on the blade surface to flow between the inner edge portion and the outer edge portion. 
     An angle between a straight line passing through a rotational center of the fan and the outer edge portion and a tangent of the center line at the outer edge portion is defined as an outer peripheral blade tip angle. An angle between a straight line passing through the rotational center of the fan and the inner edge portion and a tangent of the center line at the inner edge portion is defined as an inner peripheral blade tip angle. An angle between a chord line in contact with the inner peripheral-side and outer peripheral-side blade tips on the pressure surface side, and a straight line passing through the rotational center of the fan and a contact point of the chord line with the outer peripheral-side blade tip is defined as a discrepancy angle. In this case, a plurality of blade portions include a first blade portion and a second blade portion different from each other in at least one of the outer peripheral blade tip angle and the inner peripheral blade tip angle. A plurality of blade portions are provided such that the discrepancy angle of each blade portion is equal among a plurality of blade portions. 
     In such a configuration of the fan, the direction in which fluid passing through on the blade surface is output from the fan (hereinafter also referred to as a blowing direction of fluid) is mainly determined by the discrepancy angle of the blade portion. Therefore, a plurality of blade portions are provided such that the discrepancy angles of the blade portions are equal to each other, whereby the discrepancy angle can be set such that the blowing direction of fluid is optimized, and the blowing direction of fluid can be prevented from varying among a plurality of blade portions. Accordingly, the blowing capacity of the fan can be improved. 
     A plurality of blade portions include the first blade portion and the second blade portion different from each other in at least one of the outer peripheral blade tip angle and the inner peripheral blade tip angle. Accordingly, on at least one of the inner peripheral side and the outer peripheral side of the blade portion, the cycle of the blade tip passing through can be actively shifted between the first blade portion and the second blade portion. Thus, pressure variations caused by passage of the blade tips are brought into irregular cycles, thereby preventing noise resulting from pressure variations. 
     Preferably, the first blade portion and the second blade portion are equal in height of the blade portion with reference to the chord line. According to such a configuration of the fan, variations in interval between the adjacent blade portions due to a difference in height of the blade portions are not produced. Therefore, the interval between the adjacent fan blades can be optimized. Accordingly, the air flow between the blade portions can be stabilized thereby preventing abnormal sound. An increase in circulation resistance of fluid between the blade portions can be prevented thereby increasing the blowing capacity of the fan. 
     Preferably, the blade portion has flection portions at which the center line is flexed at different points between the inner edge portion and the outer edge portion. The first blade portion and the second blade portion are different from each other in flection angle at the flection portion. According to such a configuration of the fan, at least one of the outer peripheral blade tip angle and the inner peripheral blade tip angle is varied between the first blade portion and the second blade portion by changing the flection angle at the flection portion. 
     Preferably, plural kinds of the blade portions different from each other in at least one of the outer peripheral blade tip angle and the inner peripheral blade tip angle are arranged to be placed in an irregular order. According to such a configuration of the fan, the cycle of the blade tip passing through can be shifted among a plurality of blade portions more effectively. Accordingly, noise caused by rotation of the fan can be significantly reduced. 
     An inside space is formed inside a plurality of blade portions arranged in the circumferential direction, and an outside space is formed outside thereof. Preferably, the fan is a cross-flow fan that takes in fluid to the inside space from the outside space on one side with respect to the rotation axis, as viewed from a direction of the rotation axis of the fan, and outputs the taken-in fluid to the outside space on the other side with respect to the rotation axis. According to such a configuration of the fan, the blowing capacity of the cross-flow fan can be improved while noise can be prevented. 
     Preferably, a plurality of blade portions are arranged at irregular intervals. According to such a configuration of the fan, the cycle of the blade tip passing through can be shifted among a plurality of blade portions more effectively. Accordingly, noise caused by rotation of the fan can be significantly reduced. 
     An inside space is formed inside a plurality of blade portions arranged in the circumferential direction, and an outside space is formed outside thereof. Preferably, the fan described above is a centrifugal fan that outputs fluid from the inside space to the outside space. According to such a configuration of the fan, the blowing capacity of the centrifugal fan can be improved while noise can be prevented. 
     The fan described above is formed of resin. A molding die according to another aspect of the present invention is used to mold the fan. The molding die configured in this manner can produce a resin fan. 
     A fluid feeder according to another aspect of the present invention includes a blower configured with the fan described above and a driving motor coupled to the fan to rotate a plurality of blade portions. The fluid feeder configured in this manner can reduce power consumption of the driving motor while keeping the blowing capacity high. 
     A fan according to a further aspect of the present invention includes a plurality of blade portions arranged spaced apart from each other in a circumferential direction. Each blade portion has a blade surface including a pressure surface disposed on a rotational direction side of the fan and a suction surface disposed on a back side of the pressure surface. When cut along a plane orthogonal to a rotation axis of the fan, the blade portion has an inner edge portion at which a center line between the pressure surface and the suction surface intersects an inner peripheral-side blade tip, and an outer edge portion at which the center line intersects an outer peripheral-side blade tip. As the fan is rotated, a fluid flow is produced on the blade surface to flow between the inner edge portion and the outer edge portion. 
     An angle between a straight line passing through a rotational center of the fan and the outer edge portion and a tangent of the center line at the outer edge portion is defined as an outer peripheral blade tip angle. An angle between a straight line passing through the rotational center of the fan and the inner edge portion and a tangent of the center line at the inner edge portion is defined as an inner peripheral blade tip angle. In this case, a plurality of blade portions are provided such that the outer peripheral blade tip angle and the inner peripheral blade tip angle are each equal among a plurality of blade portions. A plurality of blade portions include a first blade portion and a second blade portion in which when they are rotated around the rotation axis of the fan and overlapped on one blade portion, one of the inner edge portion and the outer edge portion is disposed to be coincident with each other, and the other of the inner edge portion and the outer edge portion is disposed to be displaced from each other. 
     According to such a configuration of the fan, the first blade portion and the second blade portion are provided in such a manner that when a plurality of blade portions are rotated around the rotation axis of the fan and overlapped on one blade portion, the inner edge portions or the outer edge portions are disposed to be displaced from each other. Accordingly, the cycle of the blade tip passing through at the inner peripheral side or the outer peripheral side of the blade portion can be actively shifted between the first blade portion and the second blade portion. Thus, pressure variations caused by passage of the blade tips are brought into irregular cycles, thereby preventing noise resulting from pressure variations. 
     Because of the configuration in which the inner peripheral blade tip angle and the outer peripheral blade tip angle of each blade portion are each equal among the blade portions, the direction in which fluid flows in on the blade surface and the direction in which fluid flows out on the blade surface between the adjacent blade portions can be made uniform among a plurality of blade portions. Accordingly, although the inner edge portion or the outer edge portion is displaced between the first blade portion and the second blade portion, a change in direction of fluid flow between the adjacent blade portions can be reduced, thereby stabilizing the fluid flow. Accordingly, the blowing capacity of the fan can be improved. 
     Preferably, the blade portion has flection portions at which the center line is flexed at different points between the inner edge portion and the outer edge portion. The first blade portion and the second blade portion are different from each other in flection angle at the flection portion. According to such a configuration of the fan, the inner edge portion or the outer edge position is displaced between the first blade portion and the second blade portion by changing the flection angle at the flection portion. 
     Preferably, plural kinds of the blade portions are arranged to be placed in an irregular order, in which when plural kinds of the blade portions are rotated around the rotation axis of the fan and overlapped on one blade portion, one of the inner edge portion and the outer edge portion is disposed to be coincident with each other, and the other of the inner edge portion and the outer edge portion is disposed to be displaced from each other. According to such a configuration of the fan, the cycle of the blade tip passing through can be shifted among a plurality of blade portions more effectively. Accordingly, noise caused by rotation of the fan can be significantly reduced. 
     An inside space is formed inside a plurality of blade portions arranged in the circumferential direction, and an outside space is formed outside thereof. Preferably, the fan described above is a cross-flow fan that takes in fluid to the inside space from the outside space on one side with respect to the rotation axis, as viewed from a direction of the rotation axis of the fan, and outputs the taken-in fluid to the outside space on the other side with respect to the rotation axis. According to such a configuration of the fan, the blowing capacity of the cross-flow fan can be improved while noise can be prevented. 
     Preferably, a plurality of blade portions are arranged at irregular intervals. According to such a configuration of the fan, the cycle of the blade tip passing through can be shifted among a plurality of blade portions more effectively. Accordingly, noise caused by rotation of the fan can be significantly reduced. 
     An inside space is formed inside a plurality of blade portions arranged in the circumferential direction, and an outside space is formed outside thereof. Preferably, the fan described above is a centrifugal fan that outputs fluid from the inside space to the outside space. According to such a configuration of the fan, the blowing capacity of the centrifugal fan can be improved while noise can be prevented. 
     The fan described above is formed of resin. A molding die according to a further aspect of the present invention is used to mold the fan. The molding die configured in this manner can produce a resin fan. 
     A fluid feeder according to a further aspect of the present invention includes a blower configured with the fan described above and a driving motor coupled to the fan to rotate a plurality of blade portions. The fluid feeder configured in this manner can reduce power consumption of the driving motor while keeping the blowing capacity high. 
     Advantageous Effects of Invention 
     As described above, the present invention provides a fan with excellent blowing capacity while preventing noise, a molding die for use in production of the fan, and a fluid feeder provided with the fan. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing a centrifugal fan according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the centrifugal fan taken along a line II-II in  FIG. 1 . 
         FIG. 3  is a diagram schematically showing a phenomenon that occurs on a blade surface of a fan blade in the centrifugal fan in  FIG. 1 . 
         FIG. 4  is a cross-sectional view of the fan blade for use in the centrifugal fan in  FIG. 1 . 
         FIG. 5  is a diagram schematically illustrating an arrangement of fan blades in the centrifugal fan in  FIG. 1 . 
         FIG. 6  is a diagram schematically illustrating a modification of the arrangement of fan blades shown in  FIG. 5 . 
         FIG. 7  is a cross-sectional view of a molding die for use in production of the centrifugal fan in  FIG. 1 . 
         FIG. 8  is a cross-sectional view of a blower using the centrifugal fan in  FIG. 1 . 
         FIG. 9  is a cross-sectional view of the blower taken along a line IX-IX in  FIG. 8 . 
         FIG. 10  is a cross-sectional view of an air purifier using the centrifugal fan in  FIG. 1 . 
         FIG. 11  is a cross-sectional view showing a first modification of plural kinds of fan blades in  FIG. 4 . 
         FIG. 12  is a cross-sectional view showing a second modification of plural kinds of fan blades in  FIG. 4 . 
         FIG. 13  is a side view of a cross-flow fan according to a third embodiment of the present invention. 
         FIG. 14  is a cross-sectional perspective view of the cross-flow fan taken along a line XIV-XIV in  FIG. 13 . 
         FIG. 15  is a cross-sectional view of an air conditioner using the cross-flow fan shown in  FIG. 13 . 
         FIG. 16  is an enlarged cross-sectional view showing the proximity of an outlet port of the air conditioner in  FIG. 15 . 
         FIG. 17  is a cross-sectional view of an air flow produced in the proximity of the outlet port of the air conditioner in  FIG. 15 . 
         FIG. 18  is a cross-sectional view illustrating a phenomenon that occurs on the blade surface of the fan blade in an upstream region shown in  FIG. 16 . 
         FIG. 19  is a cross-sectional view illustrating a phenomenon that occurs on the blade surface of the fan blade in a downstream region shown in  FIG. 16 . 
         FIG. 20  is a side view of a cross-flow fan according to a fourth embodiment of the present invention. 
         FIG. 21  is a cross-sectional perspective view of the cross-flow fan taken along a line XXI-XXI in  FIG. 20 . 
         FIG. 22  is a diagram showing a “discrepancy angle.” 
         FIG. 23  is a diagram showing an “outer peripheral blade tip angle” and an “inner peripheral blade tip angle.” 
         FIG. 24  is a cross-sectional view showing a shape and arrangement of fan blades in the cross-flow fan in  FIG. 20 . 
         FIG. 25  is an enlarged cross-sectional view showing a blade cross section of the fan blade. 
         FIG. 26  is a diagram showing that plural kinds of fan blades in  FIG. 24  are overlapped with each other. 
         FIG. 27  is a diagram schematically showing an arrangement of fan blades in the cross-flow fan in  FIG. 20 . 
         FIG. 28  is a cross-sectional view of an air conditioner using the cross-flow fan shown in  FIG. 20 . 
         FIG. 29  is an enlarged cross-sectional view showing the proximity of an outlet port of the air conditioner in  FIG. 28 . 
         FIG. 30  is a cross-sectional view of an air flow produced in the proximity of the outlet port of the air conditioner in  FIG. 28 . 
         FIG. 31  is a cross-sectional view of a molding die for use in production of the centrifugal fan in  FIG. 20 . 
         FIG. 32  is a diagram for explaining the operation and effects achieved by the cross-flow fan in  FIG. 20 . 
         FIG. 33  is another diagram for explaining the operation and effects achieved by the cross-flow fan in  FIG. 20 . 
         FIG. 34  is a cross-sectional view showing a first modification of plural kinds of fan blades in  FIG. 24 . 
         FIG. 35  is a diagram showing that plural kinds of fan blades in  FIG. 34  are overlapped with each other. 
         FIG. 36  is a cross-sectional view showing a second modification of plural kinds of fan blades in  FIG. 24 . 
         FIG. 37  is a perspective view of a centrifugal fan according to a sixth embodiment of the present invention. 
         FIG. 38  is a cross-sectional view of a blower using the centrifugal fan in  FIG. 37 . 
         FIG. 39  is a cross-sectional view of the blower taken along a line XXXIX-XXXIX in  FIG. 38 . 
         FIG. 40  is a cross-sectional view of an air purifier using the centrifugal fan in  FIG. 37 . 
         FIG. 41  is a side view of a cross-flow fan according to a seventh embodiment of the present invention. 
         FIG. 42  is a cross-sectional perspective view of the cross-flow fan taken along a line XLII-XLII in  FIG. 41 . 
         FIG. 43  is a diagram showing an “outer peripheral blade tip angle” and an “inner peripheral blade tip angle.” 
         FIG. 44  is a cross-sectional view showing a shape and arrangement of fan blades in the cross-flow fan in  FIG. 41 . 
         FIG. 45  is an enlarged cross-sectional view showing a blade cross section of the fan blade. 
         FIG. 46  is a diagram showing that plural kinds of fan blades in  FIG. 44  are overlapped with each other. 
         FIG. 47  is a diagram schematically showing an arrangement of fan blades in the cross-flow fan in  FIG. 41 . 
         FIG. 48  is a cross-sectional view of an air conditioner using the cross-flow fan shown in  FIG. 41 . 
         FIG. 49  is an enlarged cross-sectional view showing the proximity of an outlet port of the air conditioner in  FIG. 48 . 
         FIG. 50  is a cross-sectional view of an air flow produced in the proximity of the outlet port of the air conditioner in  FIG. 48 . 
         FIG. 51  is a cross-sectional view of a molding die for use in production of the cross-flow fan in  FIG. 41 . 
         FIG. 52  is a diagram for explaining the operation and effects achieved by the cross-flow fan in  FIG. 41 . 
         FIG. 53  is a cross-sectional view showing a first modification of plural kinds of fan blades in  FIG. 44 . 
         FIG. 54  is an enlarged cross-sectional view showing a blade cross section of the fan blade in  FIG. 53 . 
         FIG. 55  is a diagram showing that plural kinds of fan blades in  FIG. 53  are overlapped with each other. 
         FIG. 56  is a cross-sectional view showing a second modification of plural kinds of fan blades in  FIG. 44 . 
         FIG. 57  is a perspective view of a centrifugal fan according to a ninth embodiment of the present invention. 
         FIG. 58  is a cross-sectional view of a blower using the centrifugal fan in  FIG. 57 . 
         FIG. 59  is a cross-sectional view of the blower taken along a line LIX-LIX in  FIG. 58 . 
         FIG. 60  is a cross-sectional view of an air purifier using the centrifugal fan in  FIG. 57 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described with reference to the figures. In the following, the same or corresponding members in the figures are denoted with the same reference numerals. 
     First Embodiment 
     In the present embodiment, first of all, a structure of a centrifugal fan to which a fan according to the present invention is applied will be described. Next, a structure of a molding die for use in production of the centrifugal fan, and structures of a blower and an air purifier using the centrifugal fan will be described. 
     (Description of Structure of Centrifugal Fan) 
       FIG. 1  is a perspective view of a centrifugal fan in a first embodiment of the present invention.  FIG. 2  is a cross-sectional view of the centrifugal fan taken along a line II-II in  FIG. 1 . 
     Referring to  FIG. 1  and  FIG. 2 , a centrifugal fan  10  in the present embodiment has a plurality of fan blades  21 . Centrifugal fan  10  has an approximately cylindrical appearance as a whole. A plurality of fan blades  21  are disposed on a circumferential surface of the approximately cylindrical shape. Centrifugal fan  10  is integrally formed from resin. Centrifugal fan  10  rotates in the direction shown by arrow  103  around an imaginary center axis  101  shown in  FIG. 1 . 
     Centrifugal fan  10  is a fan using a plurality of rotating fan blades  21  to output air taken in from the radially inner side to the radially outer side. Centrifugal fan  10  is a fan using a centrifugal force to output the air from the rotational center side of the fan to the radial direction thereof. Centrifugal fan  10  is a sirocco fan. Centrifugal fan  10  is used with rotation speeds in a low Reynolds number region applied to fans for home electric equipment, etc. 
     Centrifugal fan  10  further has peripheral frames  13  serving as supports. Peripheral frames  13  are formed to annually extend around center axis  101 . Peripheral frames  13  are disposed spaced apart from each other in the axial direction of center axis  101 . A boss portion  16  for coupling centrifugal fan  10  to a driving motor is integrally formed with one of peripheral frames  13  with a disk portion  14  interposed therebetween. 
     A plurality of fan blades  21  are arranged spaced apart from each other in the circumferential direction around center axis  101 . A plurality of fan blades  21  are supported by peripheral frames  13  at opposite ends thereof in the axial direction of center axis  101 . Fan blade  21  is provided to stand on one peripheral frame  13  and formed to extend along the axial direction of center axis  101  toward the other peripheral frame  13 . 
     Fan blade  21  has an inner edge portion  26  and an outer edge portion  27 . Inner edge portion  26  is disposed at an end portion on the inner peripheral side of fan blade  21 . Outer edge portion  27  is disposed at an end portion on the outer peripheral side of fan blade  21 . Fan blade  21  is formed to be inclined in the circumferential direction around center axis  101  from inner edge portion  26  toward outer edge portion  27 . Fan blade  21  is formed to be inclined in the rotational direction of centrifugal fan  10  from inner edge portion  26  toward outer edge portion  27 . 
     Fan blade  21  has a blade surface  23  including a pressure surface  25  and a suction surface  24 . Pressure surface  25  is disposed on the rotational direction side of centrifugal fan  10 . Suction surface  24  is disposed on the back side of pressure surface  25 . During rotation of centrifugal fan  10 , as an air flow is produced on blade surface  23 , a pressure distribution is generated in such a manner that pressure is relatively large at pressure surface  25  and is relatively small at suction surface  24 . Fan blade  21  has a shape generally curved between inner edge portion  26  and outer edge portion  27  so as to be concave on the pressure surface  25  side and be convex on the suction surface  24  side. 
       FIG. 2  shows a blade cross section of fan blade  21  cut along a plane orthogonal to center axis  101  serving as the rotation axis of centrifugal fan  10 . 
     Fan blade  21  is formed to have a uniform blade cross section when cut anywhere in the axial direction of center axis  101 . Fan blade  21  is formed to have a thin blade cross section between inner edge portion  26  and outer edge portion  27 . Fan blade  21  is formed to have a generally constant thickness (the length between pressure surface  25  and suction surface  24 ) between inner edge portion  26  and outer edge portion  27 . 
     Fan blade  21  has such a blade cross section in that a concave portion  57  is formed at pressure surface  25  of blade surface  23  and a concave portion  56  is formed at suction surface  24  of blade surface  23 . A plurality of concave portions  56 ,  57  are formed at at least one of pressure surface  25  and suction surface  24 . 
     In the present embodiment, a plurality of concave portions  57  (concave portions  57   p ,  57   q ) are formed at pressure surface  25 . Convex portions  52  (convex portions  52   p ,  52   q ,  52   r ) are further formed at pressure surface  25 . Convex portion  52  is formed to protrude toward the rotational direction of centrifugal fan  10 . Concave portion  57  is formed by a valley portion between convex portions  52  disposed adjacent to each other. For example, concave portion  57   p  is formed by a valley portion between convex portion  52   p  and convex portion  52   q . Concave portions  57  and convex portions  52  are formed to be alternate in the direction in which inner edge portion  26  is connected with outer edge portion  27 . Concave portion  57  has an approximately U-shaped cross section. 
     A plurality of convex portions  51  (convex portions  51   p ,  51   q ) are further formed at suction surface  24 . Convex portion  51  is formed to protrude toward the direction opposite to the rotational direction of cross-flow fan  100 . Concave portion  56  is formed by a valley portion between convex portions  51  disposed adjacent to each other. For example, concave portion  56  is formed by a valley portion between convex portion  51   p  and convex portion  51   q . Concave portion  56  and convex portions  57  are formed to be alternately aligned in the direction in which inner edge portion  26  is connected with outer edge portion  27 . Concave portion  56  has an approximately U-shaped cross-sectional shape. 
     Concave portion  57  and convex portion  51  are formed at front and back corresponding positions of pressure surface  25  and suction surface  24 , respectively. Convex portion  52  and concave portion  56  are formed at front and back corresponding positions of pressure surface  25  and suction surface  24 , respectively. In the present embodiment, concave portion  57  formed at pressure surface  25  forms convex portion  51  at suction surface  24 , and concave portion  56  formed at suction surface  24  forms convex portion  52  at pressure surface  25 . The concave portion and the convex portion formed at the front and the back correspondingly at pressure surface  25  and suction surface  24  have a shape equal to each other. 
     Concave portions  57 ,  56  are shaped like a groove extending along the axial direction of center axis  101 . The groove portion formed of each concave portion  57 ,  56  is formed to continuously extend between one end and the other end of fan blade  21  in the axial direction of center axis  101 . The groove portion formed of each concave portion  57 ,  56  is formed to linearly extend between one end and the other end of fan blade  21  in the axial direction of center axis  101 . 
     In the present embodiment, the number of concave portions  57  formed at pressure surface  25  is greater than the number of concave portions  56  formed at suction surface  24 . 
       FIG. 2  shows a center line  106  in the thickness direction (the direction in which pressure surface  25  is connected with suction surface  24 ) of the blade cross section of fan blade  21 . Fan blade  21  has flection portions  41  at which center line  106  of the blade cross section of fan blade  21  is flexed at different points between inner edge portion  26  and outer edge portion  27 . Concave portions  56 ,  57  are formed by flection portions  41 . 
     In the present embodiment, fan blade  21  has flection portions  41  at three points between inner edge portion  26  and outer edge portion  27 . Fan blade  21  has flection portions  41 A arranged in the proximity of inner edge portion  26  and outer edge portion  27 , respectively, and a flection portion  41 B arranged at the blade midpoint between inner edge portion  26  and outer edge portion  27 . Flection portion  41 A forms concave portion  57  at pressure surface  25  and convex portion  51  at suction surface  24 . Flection portion  41 B forms convex portion  52  at pressure surface  25  and concave portion  56  at suction surface  24 . 
     In such a configuration, concave portions  57  are formed in the proximity of inner edge portion  26  and outer edge portion  27 , and concave portion  56  is formed at the blade midpoint between inner edge portion  26  and outer edge portion  27 . Fan blade  21  has an approximately W-shaped blade cross-sectional shape. 
     Flection portions  41  are flexed such that the depth T of concave portions  56 ,  57  is greater than the thickness t of fan blade  21  at at least one point. Flection portions  41  are formed such that the bending direction is alternately opposite in the direction in which inner edge portion  26  is connected with outer edge portion  27 . Flection portion  41  is formed to be bent so as to be rounded. Flection portion  41  may be formed to be bent to form a corner. 
       FIG. 3  is a diagram schematically showing a phenomenon that occurs on the blade surface in the centrifugal fan in  FIG. 1 . Referring to  FIG. 1  to  FIG. 3 , when centrifugal fan  10  is rotated, as shown by an arrow  102  in  FIG. 1 , an air flow is produced between adjacent fan blades  21  to flow in from inner edge portion  26 , pass through on blade surface  23 , and flow out from outer edge portion  27 . Here, vortexes  32  (secondary flow) of air flow are generated in concave portions  56 ,  57  formed at blade surface  23 , so that an air flow  31  (main flow) passing through on fan blade  23  flows along the outside of vortexes  32  produced in concave portions  56 ,  57 . 
     Accordingly, although having a thin blade cross section, fan blade  21  exhibits a behavior like a thick blade as if the blade cross section is increased in thickness by the depth of concave portions  56 ,  57  at which vortexes  32  are formed. As a result, the lift produced in the proximity of inner edge portion  26  having concave portions  56 ,  57  can be significantly increased. 
     Furthermore, the flection structure of flection portions  41  can improve the strength of fan blade  21 . As a result, the reliability in the strength of the fan can be improved although centrifugal fan  10  is a resin fan having a thin blade cross section. The improvement in strength can reduce the thickness of fan blade  21  accordingly. Therefore, the weight of centrifugal fan  10  can be reduced and the cost thereof can be reduced. 
     For the reasons above, centrifugal fan  10  having a blade cross section with a high lift-drag ratio, with a small thickness and weight, and with a high strength can be implemented. 
       FIG. 4  is a cross-sectional view of the fan blade for use in the centrifugal fan in  FIG. 1 . The figure shows the cross section of the fan blade shown in  FIG. 2 . Referring to  FIG. 3 , in centrifugal fan  10  in the present embodiment, a plurality of fan blades  21  are comprised of plural kinds of fan blades  21 A,  21 B,  21 C,  21 D, and  21 E. Fan blades  21 A to  21 E have blade cross sections having different shapes. A plurality of fan blades are provided for each of fan blades  21 A to  21 E. 
     The shapes of fan blades  21 A to  21 E will be described in more specific details. Fan blades  21 A to  21 E all have an approximately W-shape blade cross section but are different in positions where concave portions  56  and  57  are formed. Giving attention to the position where concave portion  56  is formed, concave portion  56  is formed at a position close to inner edge portion  26  in fan blade  21 A, and then, concave portion  56  is formed further away from inner edge portion  26  and closer to outer edge portion  27  in order of fan blades  21 B,  21 C, and  21 D. Then, in fan blade  21 E, concave portion  56  is formed at a position close to outer edge portion  27 . Concave portion  57   p  and concave portion  57   q  are also formed further away from inner edge portion  26  and closer to outer edge portion  27  in order from fan blade  21 A to fan blades  21 B,  21 C,  21 D, and  21 E. 
     As representatively illustrated in fan blade  21 A in  FIG. 4 , assuming that a suction surface  24 ′ extends smoothly from the top of convex portion  52  toward the top of convex portion  51  above concave portion  56 , preferably, fan blades  21 A to  21 E are formed such that the respective suction surfaces  24 ′ of the fan blades have different profiles between inner edge portion  26  and outer edge portion  27  in the cross sections shown in  FIG. 4 . 
       FIG. 5  is a diagram schematically illustrating an arrangement of fan blades in the centrifugal fan in  FIG. 1 . Referring to  FIG. 5 , fan blades  21 A,  21 B,  21 C,  21 D, and  21 E are arranged in an irregular (random) order in the circumferential direction around center axis  101 . To be more specific, fan blades  21 A to  21 E are arranged so as not be repeatedly placed in a regular order (for example, fan blades  21 A→ 21 B→ 21 C→ 21 D→ 21 E→ 21 A→ 21 B→ 21 C→ 21 D→ 21 E→ 21 A→ 21 B . . . ). 
     In the example shown in  FIG. 5 , fan blades  21 C,  21 E,  21 A,  21 D,  21 B,  21 A,  21 B,  21 C,  21 D,  21 E,  21 B,  21 D,  21 A,  21 C,  21 E are placed in order clockwise around center axis  101 . 
     In the example above, five kinds of fan blades  21 A to  21 E make one set, and different sets of fan blades  21 A to  21 E placed in different orders are disposed in order. However, the configuration is not limited thereto. For example, a plurality of fan blades may be prepared for each of fan blades  21 A to  21 E, and fan blades selected therefrom as appropriate may be placed in order. As long as fan blades  21 A to  21 E are arranged without a regularity as a whole, fan blades of a particular kind may be placed in succession. The number of each of fan blades  21 A to  21 E for use in centrifugal fan  10  may not be completely equal. All of fan blades  21  for use in centrifugal fan  10  may have blade cross-sectional shapes different from each other. Preferably, at least three kinds, more preferably, at least four kinds of fan blades  21  are used. 
     In centrifugal fan  10  in the present embodiment, a plurality of fan blades  21  are arranged such that an angle α of a line connecting center axis  101  with outer edge portion  27  of each fan blade  21  is equal between adjacent fan blades  21 . A plurality of fan blades  21  may be arranged such that the angle of a line connecting center axis  101  with inner edge portion  26  of each fan blade  21  is equal between adjacent fan blades  21 . 
       FIG. 6  is a diagram schematically illustrating a modification of the arrangement of the fan blades shown in  FIG. 5 . The arrangement in  FIG. 6  is the same as that in  FIG. 5  in that plural kinds of fan blades  21 A,  21 B,  21 C,  21 D, and  21 E having blade cross sections of different shapes are placed in an irregular order. In this modification, a plurality of fan blades  21  are arranged such that an angle β of a line connecting center axis  101  with the centroid of the blade cross section of each fan blade  21  is equal between adjacent fan blades  21 . The centroid of the blade cross section of fan blade  21  corresponds to the barycenter of the blade cross section and is obtained by dividing the first moment of area of the blade cross section by the sectional area of the entire blade cross section. 
     A plurality of fan blades  21  may be arranged so as to satisfy both the arrangement manner shown in  FIG. 5  and the arrangement manner shown in  FIG. 6 . 
     Referring to  FIG. 4  to  FIG. 6 , as described above, in centrifugal fan  10 , the blade cross sections differ among a plurality of fan blades  21  because fan blades  21 A,  21 B,  21 C,  21 D, and  21 E different in positions of concave portions  56  and  57  are used. Since the shape of blade cross section of fan blade  21  affects the static pressure distribution on pressure surface  25  and suction surface  24  during rotation of centrifugal fan  10 , the air flow between adjacent fan blades  21  and the air flow that flows in/out between adjacent fan blades  21  through outer edge portion  27  and inner edge portion  26  vary among fan blades  21 . 
     On the other hand, in the example shown in  FIG. 5 , a plurality of fan blades  21  are disposed such that the angle α of the line connecting center axis  101  with outer edge portion  27  of each fan blade  21  is equal between adjacent fan blades  21 . Even in this case, the air flow that flows in/out between adjacent fan blades  21  varies among fan blades  21  to cause a disturbance in the air flow in the approach place where outer edge portion  27  of fan blade  21  approaches the fan casing. Accordingly, the timing of pressure variation when outer edge portion  27  of fan blade  21  passes through the approach place can be brought out of constant cycles. As a result, the narrow-band noise resulting from the blade-passing sound (nZ sound) can be reduced to the permissible level. 
     In the example shown in  FIG. 6 , a plurality of fan blades  21  are disposed such that the angle β of the line connecting center axis  101  with the centroid of blade cross section of each fan blade  21  is equal between adjacent fan blades  21 . Even in this case, the air flow between adjacent fan blades  21  differs among fan blades  21  thereby reducing the narrow-band noise resulting from the air flow between fan blades  21  to the permissible level. 
     Because of the reduction of narrow-band noise as described above, in both examples shown in  FIG. 5  and  FIG. 6 , the interval between adjacent fan blades  21  can be set to an optimum value based on the blowing capacity required for centrifugal fan  10 . Accordingly, a phenomenon such as a backflow partially produced in the air flow between adjacent fan blades  21  can be prevented, thereby stabilizing the air flow between fan blades  21 . As a result, low-frequency noise (abnormal sound) can be prevented while the blowing capacity is increased. Furthermore, a phenomenon such as a significant increase of ventilation resistance to the air flow among fan blades  21  can be prevented, thereby increasing the blowing capacity. 
     Centrifugal fan  10  is applied to equipment having a large pressure loss of airflow exerted on the fan, when compared with a cross-flow fan described later. In this case, a backflow of airflow between adjacent fan blades  21  is more likely to be produced. Therefore, the structure of the present invention capable of preventing such a phenomenon is applied more effectively to centrifugal fan  10 . 
     The structure of centrifugal fan  10  according to the first embodiment of the present invention described above is summarized as follows. Centrifugal fan  10  in the present embodiment includes fan blades  21  serving as a plurality of blade portions arranged spaced apart from each other in the circumferential direction. Fan blade  21  has inner edge portion  26  disposed on the inner peripheral side and outer edge portion  27  disposed on the outer peripheral side. Fan blade  21  has blade surface  23  extending between inner edge portion  26  and outer edge portion  27 . Blade surface  23  includes pressure surface  25  disposed on the rotational direction side of the fan and suction surface  24  disposed on the back side of pressure surface  25 . As the fan is rotated, an airflow is produced on blade surface  23  as a fluid flow flowing between inner edge portion  26  and outer edge portion  27 . When cut along the plane orthogonal to center axis  101  serving as the rotation axis of the fan, fan blade  21  has a blade cross section having concave portions  56  and  57  formed at pressure surface  25  and suction surface  24 . A plurality of fan blades  21  include fan blades  21 A to  21 E having blade cross sections of different shapes. 
     (Description of Structures of Molding Die, Blower, and Air Purifier) 
       FIG. 7  is a cross-sectional view of a molding die for use in production of the centrifugal fan in  FIG. 1 . Referring to  FIG. 7 , a molding die  110  has a stationary die  114  and a movable die  112 . Stationary die  114  and movable die  112  define a cavity  116  which has approximately the same shape as centrifugal fan  10  and into which flowable resin is injected. 
     Molding die  110  may be provided with a not-shown heater for increasing the flowability of resin injected into cavity  116 . The installation of such a heater is particularly effective, for example, when synthetic resin with an increased strength, such as glass-fiber-filled AS resin (acrylonitrile-styrene copolymer), is used. 
     Cross-flow fan  100  in a third embodiment described later is also produced with a molding die having a similar structure as molding die  110  in  FIG. 7 . 
       FIG. 8  is a cross-sectional view of a blower using the centrifugal fan in  FIG. 1 .  FIG. 9  is a cross-sectional view of the blower taken along a line IX-IX in  FIG. 8 . Referring to  FIG. 8  and  FIG. 9 , a blower  120  has a driving motor  128 , centrifugal fan  10 , and a casing  129  inside an outer casing  126 . 
     The output shaft of driving motor  128  is coupled to boss portion  16  molded integrally with centrifugal fan  10 . Casing  129  has a guide wall  129   a . Guide wall  129   a  is formed by an approximately ¾ arc disposed on the periphery of centrifugal fan  10 . Guide wall  129   a  guides an airflow generated by rotation of fan blades  21  to the rotational direction of fan blades  21  while increasing the speed of the airflow. 
     Casing  129  has an intake portion  130  and an outlet portion  127 . Intake portion  130  is formed to be positioned on an extension of center axis  101 . Outlet portion  127  is formed to be open to one side of the tangent direction of guide wall  129   a  from part of guide wall  129   a . Outlet portion  127  is shaped like a prismatic cylinder protruding from part of guide wall  129   a  to one side of the tangent direction of guide wall  129   a.    
     Driven by driving motor  128 , centrifugal fan  10  rotates in the direction shown by arrow  103 . Here, air is taken in from intake portion  130  to the inside of casing  129  and is output from a radially inside space  131  to a radially outside space  132  of centrifugal fan  10 . The air output to radially outside space  132  circumferentially flows in the direction shown by arrow  104  and is blown to the outside through outlet portion  127 . 
       FIG. 10  is a cross-sectional view of an air purifier using the centrifugal fan in  FIG. 1 . Referring to  FIG. 10 , an air purifier  140  has a housing  144 , a blower  150 , a duct  145 , and an HEPA (High Efficiency Particulate Air Filter) filter  141 . 
     Housing  144  has a rear wall  144   a  and a top wall  144   b . Housing  144  has an intake port  142  for sucking the air in the room in which air purifier  140  is installed. Intake port  142  is formed at rear wall  144   a . Housing  144  further has an outlet port  143  discharging the purified air to the inside of the room. Outlet port  143  is formed at top wall  144   b . Air purifier  140  is generally installed against a wall such that rear wall  144   a  is opposed to a wall in the room. 
     Filter  141  is disposed to face intake port  142  in the inside of housing  144 . The air introduced to the inside of housing  144  through intake port  142  passes through filter  141 . The foreign matters in the air are thus removed. 
     Blower  150  is provided to suck the room air to the inside of housing  144  and to output the air purified by filter  141  to the room through outlet port  143 . Blower  150  has centrifugal fan  10 , a casing  152 , and a driving motor  151 . Casing  152  has a guide wall  152   a . Casing  152  has an intake portion  153  and an outlet portion  154 . 
     Duct  145  is provided above blower  150  and is provided as an air channel for guiding the purified air from casing  152  to outlet port  143 . Duct  145  has a prismatic cylindrical shape with its lower end connecting to outlet portion  154  and with its upper end open. Duct  145  is formed to guide the purified air blown from outlet portion  154  to a laminar flow toward outlet port  143 . 
     In air purifier  140  having such a configuration, blower  150  is driven to rotate fan blades  21  to cause the room air to be taken in from intake port  142  to the inside of housing  144 . Here, an airflow is generated between intake port  142  and outlet port  143 , and foreign matters such as dust included in the intake air are removed by filter  141 . 
     The purified air obtained by passage through filter  141  is taken in to the inside of casing  152 . Here, the purified air taken in to the inside of casing  152  forms a laminar flow through guide wall  152   a  around fan blades  21 . The air in the form of a laminar flow is guided to outlet portion  154  along guide wall  152   a  and blown from outlet portion  154  to the inside of duct  145 . The air is discharged from outlet port  143  toward the external space. 
     Although an air purifier has been described by way of example in this embodiment, the centrifugal fan in the present invention is also applicable to a fluid feeding device such as, for example, an air conditioner, a humidifier, a cooling device, and a ventilating device. 
     In centrifugal fan  10  according to the first embodiment of the present invention as described above, because of concave portions  56  and  57  formed in fan blades  21 , the lift caused by rotation of fan blades  21  can be greatly increased in the low Reynolds number region applied to fans in home electric equipment. The use of fan blades  21 A to  21 E having blade cross sections of different shapes can reduce the narrow-band noise produced by rotation of the fan. Therefore, the blowing capacity of centrifugal fan  10  can be increased while noise is prevented. 
     In air purifier  140  according to the present embodiment, the use of centrifugal fan  10  having an excellent blowing capacity reduces power consumption of driving motor  151  and provides air purifier  140  that can contribute to energy savings. The use of centrifugal fan  10  with reduced noise also provides a quiet air purifier  140 . 
     Second Embodiment 
     In the present embodiment, variations of plural kinds of fan blades shown in  FIG. 4  will be described. 
       FIG. 11  is a cross-sectional view showing a first modification of plural kinds of fan blades in  FIG. 4 . Referring to  FIG. 11 , in this modification, a plurality of fan blades  21  are comprised of plural kinds of fan blades  21 A,  21 B,  21 C, and  21 D having blade cross sections of different shapes. 
     The shapes of fan blades  21 A to  21 D will be described in more specific details. Fan blades  21 A to  21 D are different from each other in number of concave portions  56 ,  57 . Fan blade  21 A has one concave portion  56  and two concave portions  57 . Fan blade  21 B has two concave portions  56  and three concave portions  57 . Fan blade  21 C has three concave portions  56  and four concave portions  57 . Fan blade  21 D has four concave portions  56  and five concave portions  57 . 
       FIG. 12  is a cross-sectional view showing a second modification of plural kinds of fan blades in  FIG. 4 . Referring to  FIG. 12 , in this modification, a plurality of fan blades  21  are comprised of plural kinds of fan blades  21 A,  21 B,  21 C, and  21 D having blade cross sections of different shapes. Each fan blade of fan blades  21 A to  21 D is formed to be bent to form a corner at different points between inner edge portion  26  and outer edge portion  27 . The corner portion may be slightly rounded in consideration of a process of removing fan blade  21  from a die for resin molding. 
     The shapes of fan blades  21 A to  21 D will be described in more specific details. Fan blades  21 A to  21 D are different from each other in position and number of concave portions  56  and  57  and in shape of concave portions  56  and  57 . Fan blade  21 A has three concave portions  56  and four concave portions  57 . Fan blades  21 B to  21 D each have two concave portions  56  and three concave portions  57 . Basically, concave portions  56  and  57  formed in fan blades  21 A to  21 D each have a triangular shape, two sides of which define a concave shape. However, one concave portion  56  formed in fan blade  21 B and one concave portion  57  formed in fan blade  21 C each have a rectangular shape, three sides of which define a concave shape. 
     As shown in  FIG. 11  and  FIG. 12 , the position, number, and shape of concave portions  56  and  57  are varied to readily provide plural kinds of fan blades  21  having different shapes. 
     The centrifugal fan in the second embodiment of the present invention configured in this manner achieves the effects as described in the first embodiment similarly. 
     Third Embodiment 
     In the present embodiment, a structure of a cross-flow fan to which a fan in the present invention is applied will be described. Next, a structure of an air conditioner using the cross-flow fan will be described. The cross-flow fan in the present embodiment partially has a structure similar to that of centrifugal fan  10  in the first embodiment. In the following, a description of the overlapping structure will not be repeated. 
     (Description of Structure of Cross-Flow Fan) 
       FIG. 13  is a side view of a cross-flow fan in a third embodiment of the present invention.  FIG. 14  is a cross-sectional perspective view of the cross-flow fan taken along a line XIV-XIV in  FIG. 13 . 
     Referring to  FIG. 13  and  FIG. 14 , a cross-flow fan  100  in the present embodiment has a plurality of fan blades  21 . Cross-flow fan  100  has an approximately cylindrical appearance as a whole. A plurality of fan blades  21  are disposed on a circumferential surface of the approximately cylindrical shape. Cross-flow fan  100  is integrally formed from resin. Cross-flow fan  100  rotates in the direction shown by arrow  103  around an imaginary center axis  101  shown in the figures. 
     Cross-flow fan  100  is a fan using a plurality of rotating fan blades  21  to output air in a direction orthogonal to center axis  101  serving as the rotation axis. As viewed from the axial direction of center axis  101 , cross-flow fan  100  takes in air from an outside space on one side with respect to center axis  101  to an inside space of the fan and outputs the intake air to the outside space on the other side with respect to center axis  101 . Cross-flow fan  100  forms an air flow that flows in the direction crossing center axis  101  in a flat plane orthogonal to center axis  101 . Cross-flow fan  100  forms an outlet flow in the form of a flat plane parallel to center axis  101 . 
     Cross-flow fan  100  is used with rotation speeds in the low Reynolds number region applied to fans for home electric equipment, etc. 
     Cross-flow fan  100  is configured such that a plurality of impellers  12  aligned in the axial direction of center axis  101  are combined. In each impeller  12 , a plurality of fan blades  21  are provided to be circumferentially spaced apart from each other around center axis  101 . 
     Cross-flow fan  100  further has a peripheral frame  13  serving as a support. Peripheral frame  13  has a ring shape annularly extending around center axis  101 . Peripheral frame  13  has an end surface  13   a  and an end surface  13   b . End surface  13   a  is formed to face one direction along the axial direction of center axis  101 . End surface  13   b  is disposed on the back side of end surface  13   a  and is formed to face the other direction along the axial direction of center axis  101 . 
     Peripheral frame  13  is provided to be interposed between impellers  12  adjacent to each other in the axial direction of center axis  101 . 
     Giving attention to impeller  12 A and impeller  12 B in  FIG. 13  disposed adjacent to each other, a plurality of fan blades  21  provided in impeller  12 A are provided to stand on end surface  13   a  and are formed to extend like plates along the axial direction of center axis  101 . A plurality of fan blades  21  provided in impeller  12 B are provided to stand on end surface  13   b  and are formed to extend like plates along the axial direction of center axis  101 . 
     A plurality of fan blades  21  have a structure similar to that of fan blades  21  described in the first embodiment (concave portions  56  and  57  are formed; plural kinds of fan blades  21 A to  21 E have blade cross sections of different shapes; and fan blades  21 A to  21 E are arranged in an irregular order). 
     Cross-flow fan  100  in the present embodiment, however, differs from centrifugal fan  10  in the first embodiment in that a plurality of fan blades  21  are arranged at random pitches. The random pitches are realized by disposing a plurality of fan blades  21  at irregular intervals according to random-number normal distribution. A plurality of impellers  12  are configured such that the arrangement of fan blades  21  is the same. In other words, the intervals at which a plurality of fan blades  21  are arranged and the order in which fan blades  21  are arranged at such intervals in each impeller  12  are equal among impellers  12 . 
     A plurality of impellers  12  are stacked such that a displacement angle θ is formed between adjacent impellers  12  as viewed from the axial direction of center axis  101 . For example, attention is given to impeller  12 A, impeller  12 B, and impeller  12 C in  FIG. 13  disposed adjacent to each other in the order of appearance. Impeller  12 B is stacked on impeller  12 A so as to be displaced about center axis  101  by displacement angle θ from the position where all of fan blades  21  in impellers  12 A and  12 B overlap in the axial direction of center axis  101 . Impeller  12 C is stacked on impeller  12 B so as to be displaced about center axis  101  by displacement angle θ ( 2 θ when viewed from impeller  12 A) from the position where all of fan blades  21  in impellers  12 B and  12 C overlap in the axial direction of center axis  101 . 
     The reason for providing displacement angle θ is as follows. The positions of fan blades  21  in different impellers  12  are intentionally displaced in the axial direction of center axis  101 , so that the blade passing sounds (nZ sounds) generated in impellers  12  can counteract each other to be weakened. 
     (Description of Structure of Air Conditioner) 
       FIG. 15  is a cross-sectional view of an air conditioner using the cross-flow fan shown in  FIG. 13 . Referring to  FIG. 15 , an air conditioner  210  is configured with an indoor unit  220  installed in a room and provided with an indoor heat exchanger  229  and a not-shown outdoor unit installed in the outside of the room and provided with an outdoor heat exchanger and a compressor. Indoor unit  220  and the outdoor unit are connected by piping for circulating refrigerant gas between indoor heat exchanger  229  and the outdoor heat exchanger. 
     Indoor unit  220  has a blower  215 . Blower  215  is configured to include cross-flow fan  100 , a not-shown driving motor for rotating cross-flow fan  100 , and a casing  222  for producing a prescribed airflow with rotation of cross-flow fan  100 . 
     Casing  222  has a cabinet  222 A and a front panel  222 B. Cabinet  222 A is supported on a wall surface in the room. Front panel  222 B is removably attached to cabinet  222 A. An outlet port  225  is formed in a gap between a lower end portion of front panel  222 B and a lower end portion of cabinet  222 A. Outlet port  225  is formed in an approximately rectangular shape extending in the width direction of indoor unit  220  and is provided to be directed forward and downward. On the top surface of front panel  222 B, a grid-like intake port  224  is formed. 
     At a position opposing front panel  222 B, an air filter  228  is provided for collecting and removing dust included in the intake air from intake port  224 . A not-shown air filter cleaner is provided in a space formed between front panel  222 B and air filter  228 . The air filter cleaner automatically removes dust accumulated in air filter  228 . 
     In the inside of casing  222 , an air flow channel  226  is formed, through which air is circulated from intake port  224  toward outlet port  225 . Outlet port  225  is provided with a vertical louver  232  that can change the blowing angle in the left and right directions and a plurality of horizontal louvers  231  that can change the blowing angle in the up and down directions to a forward-upward direction, a horizontal direction, a forward-downward direction, and an immediately downward direction. 
     Indoor heat exchanger  229  is arranged between cross-flow fan  100  and air filter  228  on a path of air flow channel  226 . Indoor heat exchanger  229  has not-shown serpentine refrigerant pipes arranged side by side in a plurality of layers in the up and down directions and in a plurality of columns in the front and back directions. Indoor heat exchanger  229  is connected to the compressor of the outdoor unit installed in the outdoor, and the compressor is driven to operate a refrigeration cycle. Through the operation of the refrigeration cycle, indoor heat exchanger  229  is cooled to a temperature lower than the ambient temperature during cooling operation, and indoor heat exchanger  229  is heated to a temperature higher than the ambient temperature during heating operation. 
       FIG. 16  is an enlarged cross-sectional view showing the proximity of the outlet port of the air conditioner in  FIG. 15 . Referring to  FIG. 15  and  FIG. 16 , casing  222  has a front wall portion  251  and a rear wall portion  252 . Front wall portion  251  and rear wall portion  252  are disposed to face each other at a distance from each other. 
     On a path of air flow channel  226 , cross-flow fan  100  is disposed to be positioned between front wall portion  251  and rear wall portion  252 . A protrusion portion  253  is formed at front wall portion  251  to protrude toward the radially outer surface of cross-flow fan  100  so as to decrease the gap between cross-flow fan  100  and front wall portion  251 . A protrusion portion  254  is formed at rear wall portion  252  to protrude toward the radially outer surface of cross-flow fan  100  so as to decrease the gap between cross-flow fan  100  and rear wall portion  252 . 
     Casing  222  has an upper guide portion  256  and a lower guide portion  257 . Air flow channel  226  is defined by upper guide portion  256  and lower guide portion  257  on the downstream side of air flow from cross-flow fan  100 . 
     Upper guide portion  256  and lower guide portion  257  are continuous from front wall portion  251  and rear wall portion  252 , respectively, and extend toward outlet port  225 . Upper guide portion  256  and lower guide portion  257  are formed to curve the air output by cross-flow fan  100  with upper guide portion  256  on the inner peripheral side and with lower guide portion  257  on the outer peripheral side, and to guide the air forward and downward. Upper guide portion  256  and lower guide portion  257  are formed such that the cross section of air flow channel  226  increases from cross-flow fan  100  toward outlet port  225 . 
     In the present embodiment, front wall portion  251  and upper guide portion  256  are integrally formed with front panel  222 B. Rear wall portion  252  and lower guide portion  257  are integrally formed with cabinet  222 A. 
     In the first embodiment, a phenomenon caused by a disturbance in the airflow in the place where outer edge portion  27  of fan blade  21  approaches the fan casing has been described. In air conditioner  210 , the approach place corresponds to a space where front wall portion  251  of casing  222  faces fan blade  21 . 
       FIG. 17  is a cross-sectional view of an air flow produced in the proximity of the outlet port of the air conditioner in  FIG. 15 . Referring to  FIG. 15  to  FIG. 17 , on the path on air flow channel  226 , an upstream outside space  246  is formed to be positioned upstream of air flow from cross-flow fan  100 , an inside space  247  is formed to be positioned in the inside of cross-flow fan  100  (the inner peripheral side of a plurality of fan blades  21  circumferentially arranged), and a downstream outside space  248  is formed to be positioned downstream of air flow from cross-flow fan  100 . 
     During rotation of cross-flow fan  100 , at an upstream region  241  of air flow channel  226  with respect to protrusion portions  253 ,  254  as a boundary, an air flow  261  is formed to pass through on blade surface  23  of fan blade  21  from upstream outside space  246  toward inside space  247 . At a downstream region  242  of air flow channel  226  with respect to protrusion portions  253 ,  254  as a boundary, air flow  261  is formed to pass through on blade surface  23  of fan blade  21  from inside space  247  toward downstream outside space  248 . Here, at a position adjacent to front wall portion  251 , a forced vortex  262  of air flow is formed. 
       FIG. 18  is a cross-sectional view illustrating a phenomenon that occurs on the blade surface of the fan blade in the upstream region shown in  FIG. 16 . 
     Referring to  FIG. 18 , when an air flow directed from upstream outside space  246  toward inside space  247  is formed at upstream region  241  in  FIG. 16 , an air flow is produced on blade surface  23  of fan blade  21  to flow in from outer edge portion  27 , pass through on blade surface  23 , and flow out from inner edge portion  26 . Here, a clockwise vortex  63  of air flow (secondary flow) is formed in concave portion  57  formed at pressure surface  25 , and a counterclockwise vortex  62  of air flow is generated in concave portion  56  formed at suction surface  24 . Accordingly, an air flow  61  (main flow) passing through on blade surface  23  flows along the outside of vortexes  63 ,  62  produced in concave portions  57 ,  56 . 
       FIG. 19  is a cross-sectional view illustrating a phenomenon that occurs on the blade surface of the fan blade in the downstream region shown in  FIG. 16 . 
     Referring to  FIG. 19 , when an air flow directed from inside space  247  toward downstream outside space  248  is formed in downstream region  242  in  FIG. 16 , an air flow is produced on blade surface  23  of fan blade  21  to flow in from inner edge portion  26 , pass through on blade surface  23 , and flow out from outer edge portion  27 . Here, a counterclockwise vortex  68  of air flow (secondary flow) is formed in concave portion  57  formed at pressure surface  25 , and a clockwise vortex  67  of air flow is generated in concave portion  56  formed at suction surface  24 . Accordingly, an air flow  66  (main flow) passing through on blade surface  23  flows along the outside of vortexes  68 ,  67  produced in concave portions  57 ,  56 . 
     In other words, in cross-flow fan  100 , when fan blade  21  moves from upstream region  241  to downstream region  242 , the direction of air flow on blade surface  23  is reversed, and the rotational directions of the vortexes produced in concave portions  57 ,  56  are also reversed accordingly. 
     In cross-flow fan  100  in the present embodiment, fan blade  21  exhibits a behavior like a thick blade as if the blade cross section is increased in thickness because of vortexes (secondary flows) formed in concave portions  57 ,  56 . As a result, the lift produced at fan blade  21  can be significantly increased. 
     In cross-flow fan  100 , fan blades  21 A,  21 B,  21 C,  21 D, and  21 E in  FIG. 4  different in position of concave portions  56  and  57  are used. Because of this configuration, the narrow-band noise resulting from blade passing sound (nZ sound) and the narrow-band noise resulting from the air flow between fan blades  21  can be reduced. Because of the reduction of narrow-band noise in this manner, the interval between adjacent fan blades  21  can be set to an optimum value based on the blowing capacity required for cross-flow fan  100 . In other words, when a plurality of fan blades  21  are arranged at random pitches, variations of the random pitches can minimized. 
     As shown in  FIG. 13 , cross-flow fan  100  is configured to include a plurality of impellers  12  aligned in the axial direction of center axis  101 . Therefore, when compared with the centrifugal fan previously described, in cross-flow fan  100 , a pressure loss of an air flow applied to the fan of each impeller  12  is reduced, so that a back flow of air flow is hardly produced between adjacent fan blades  21 . Therefore, in the present embodiment, noise (abnormal sound) at low frequencies resulting from a back flow of air flow can be prevented even in a configuration in which a plurality of fan blades  21  are arranged at random pitches. 
     Cross-flow fan  100  may also be configured such that a plurality of fan blades  21  are arranged at regular pitches as shown in  FIG. 5  and  FIG. 6 . Although an air conditioner has been described by way of example in this embodiment, the cross-flow fan in the present invention is also applicable to a fluid feeding device such as, for example, an air purifier, a humidifier, a cooling device, and a ventilating device. 
     Cross-flow fan  100  and air conditioner  210  in the third embodiment of the present invention configured in this manner can achieve the effects described in the first embodiment similarly. 
     The structures of the fans described in the first to third embodiments as described above may be combined as appropriate to configure a new fan. For example, cross-flow fan  100  in the third embodiment may be configured using the fan blades described in the second embodiment. 
     Fourth Embodiment 
     In the present embodiment, first of all, a structure of a cross-flow fan to which a fan in the present invention is applied will be described. Next, structures of an air conditioner using the cross-flow fan and a molding die for use in production of the cross-flow fan will be described. 
     (Description of Structure of Cross-Flow Fan) 
       FIG. 20  is a side view of a cross-flow fan in a fourth embodiment of the present invention.  FIG. 21  is a cross-sectional perspective view of the cross-flow fan taken along a line XXI-XXI in  FIG. 20 . 
     Referring to  FIG. 20  and  FIG. 21 , a cross-flow fan  500  in the present embodiment has a plurality of fan blades  421 . Cross-flow fan  500  has an approximately cylindrical appearance as a whole. A plurality of fan blades  421  are disposed on a circumferential surface of the approximately cylindrical shape. Cross-flow fan  500  is integrally formed from resin. Cross-flow fan  500  rotates in the direction shown by arrow  103  around an imaginary center axis  501  shown in the figures. 
     Cross-flow fan  500  is a fan using a plurality of rotating fan blades  421  to flow air in a direction orthogonal to center axis  501  serving as the rotation axis. As viewed from the axial direction of center axis  501 , cross-flow fan  500  takes in air from an outside space on one side with respect to center axis  501  to an inside space of the fan and outputs the intake air to the outside space on the other side with respect to center axis  501 . Cross-flow fan  500  forms an air flow that flows in the direction crossing center axis  501  in a flat plane orthogonal to center axis  501 . Cross-flow fan  500  forms an outlet flow in the form of a flat plane parallel to center axis  501 . 
     Cross-flow fan  500  is used with rotation speeds in the low Reynolds number region applied to fans for home electric equipment, etc. 
     Cross-flow fan  500  is configured such that a plurality of impellers  412  aligned in the axial direction of center axis  501  are combined. In each impeller  412 , a plurality of fan blades  421  are provided to be circumferentially spaced apart from each other around center axis  501 . 
     Cross-flow fan  500  further has a peripheral frame  413  serving as a support. Peripheral frame  413  has a ring shape annularly extending around center axis  501 . Peripheral frame  413  has an end surface  413   a  and an end surface  413   b . End surface  413   a  is formed to face one direction along the axial direction of center axis  501 . End surface  413   b  is disposed on the back side of end surface  413   a  and is formed to face the other direction along the axial direction of center axis  501 . 
     Peripheral frame  413  is provided to be interposed between impellers  412  adjacent to each other in the axial direction of center axis  501 . 
     Giving attention to impeller  412 A and impeller  412 B in  FIG. 20  disposed adjacent to each other, a plurality of fan blades  421  provided in impeller  412 A are provided to stand on end surface  413   a  and are formed to extend like plates along the axial direction of center axis  501 . A plurality of fan blades  421  provided in impeller  412 B are provided to stand on end surface  413   b  and are formed to extend like plates along the axial direction of center axis  501 . 
       FIG. 21  shows a blade cross section of fan blade  421  cut along a plane orthogonal to center axis  501  serving as a rotation axis of cross-flow fan  500 . 
     Fan blade  421  has an inner peripheral blade tip portion  428  and an outer peripheral blade tip portion  429 . Inner peripheral blade tip portion  428  is disposed at an end portion on the inner peripheral side of fan blade  421 . Outer peripheral blade tip portion  429  is disposed at an end portion on the outer peripheral side of fan blade  421 . Fan blade  421  is formed to be inclined in the circumferential direction around center axis  501  from inner peripheral blade tip portion  428  toward outer peripheral blade tip portion  429 . Fan blade  421  is formed to be inclined in the rotational direction of cross-flow fan  500  from inner peripheral blade tip portion  428  toward outer peripheral blade tip portion  429 . 
     Fan blade  421  has a blade surface  423  including a pressure surface  425  and a suction surface  424 . Pressure surface  425  is disposed on the rotational direction side of cross-flow fan  500 , and suction surface  424  is disposed on the back side of pressure surface  425 . During rotation of cross-flow fan  500 , as an air flow is produced on the blade surface  423 , a pressure distribution is generated in such a manner that pressure is relatively large at pressure surface  425  and is relatively small at suction surface  424 . Fan blade  421  has a bent shape as a whole between inner peripheral blade tip portion  428  and outer peripheral blade tip portion  429  so that fan blade  421  is concave on the pressure surface  425  side and convex on the suction surface  424  side. 
     Fan blade  421  is formed to have a uniform blade cross section when cut anywhere in the axial direction of center axis  501 . Fan blade  421  is formed to have a thin blade cross section between inner peripheral blade tip portion  428  and outer peripheral blade tip portion  429 . Fan blade  421  is formed to have an almost constant thickness (the length between pressure surface  425  and suction surface  424 ) between inner peripheral blade tip portion  428  and outer peripheral blade tip portion  429 . 
     In cross-flow fan  500  in the present embodiment, the shape and arrangement of each fan blade  421  is determined so that an “outer peripheral blade tip angle,” an “inner peripheral blade tip angle” and a “discrepancy angle” satisfy a predetermined relationship among a plurality of fan blades  421 . First, the meaning of the terms “outer peripheral blade tip angle,” “inner peripheral blade tip angle” and “discrepancy angle” used to describe the structure of cross-flow fan  500  will be described. 
       FIG. 22  is a diagram showing the “discrepancy angle.”  FIG. 22  illustrates a chord line  633  in contact with inner peripheral blade tip portion  428  and outer peripheral blade tip portion  429 . Chord line  633  is in contact with blade surface  423  from the pressure surface  425  side at inner peripheral blade tip portion  428  and at outer peripheral blade tip portion  429 . Chord line  633  is a straight line. The point at which chord line  633  and outer peripheral blade tip portion  429  intersect is shown as a contact point  631 . The figure also shows a straight line  632  passing through center axis  501  serving as the rotational center of cross-flow fan  500  and contact point  631 . 
     In this case, the angle α between chord line  633  and straight line  632  is the discrepancy angle. The discrepancy angle is an angle of inclination of chord line  633  with reference to straight line  632  passing through center axis  501  and contact point  631 . The discrepancy angle α in the figure is smaller than 90°. 
       FIG. 23  is a diagram showing the “outer peripheral blade tip angle” and the “inner peripheral blade tip angle.”  FIG. 23  illustrates a center line  506  in the thickness direction (the direction connecting pressure surface  425  and suction surface  424 ) of the blade cross section of fan blade  421 . Center line  506  extends in the blade cross section so as to divide the blade cross section of fan blade  421  into the pressure surface  425  side and the suction surface  424  side. Fan blade  421  has an outer edge portion  427  at a position where center line  506  intersects outer peripheral blade tip portion  429 , and an inner edge portion  426  at a position where center line  506  intersects inner peripheral blade tip portion  428 . Center line  506  continuously extends between outer edge portion  427  and inner edge portion  426 . 
     The figure also shows a tangent  637  on outer edge portion  427  with respect to center line  506 , and a tangent  639  on inner edge portion  426  with respect to center line  506 . In the example in the figure, center line  506  is curved at outer edge portion  427  and inner edge portion  426 . However, in the case where it extends in a straight line, tangent  637  and tangent  639  overlap with center line  506  at outer edge portion  427  and inner edge portion  426 , respectively. 
     The figure also shows a straight line  636  passing through center axis  501  serving as the rotational center of cross-flow fan  500  and outer edge portion  427 , and a straight line  638  passing through center axis  501  serving as the rotational center of cross-flow fan  500  and inner edge portion  426 . 
     In this case, the angle between straight line  636  and tangent  637  is the outer peripheral blade tip angle, and the angle γ between straight line  638  and tangent  639  is the inner peripheral blade tip angle. The outer peripheral blade tip angle means the angle of outer peripheral blade tip portion  429  at outer edge portion  427  with reference to straight line  636  passing through center axis  501  and outer edge portion  427 . The inner peripheral blade tip angle means the angle of inner peripheral blade tip portion  428  at inner edge portion  426  with reference to straight line  638  passing through center axis  501  and inner edge portion  426 . The outer peripheral blade tip angle β and the inner peripheral blade tip angle γ shown in the figure are smaller than 90°. 
       FIG. 24  is a cross-sectional view showing a shape and arrangement of fan blades in the cross-flow fan in  FIG. 20 . Referring to  FIG. 24 , in cross-flow fan  500  in the present embodiment, a plurality of fan blades  421  are comprised of plural kinds of fan blades  421 A,  421 B,  421 C,  421 D,  421 E,  421 F, and  421 G. Fan blades  421 A to  421 G have blade cross sections of different shapes. A plurality of fan blades are provided for each of fan blades  421 A to  421 G. 
       FIG. 25  is an enlarged cross-sectional view showing a blade cross section of the fan blade. In the figure, a blade cross section of fan blade  421 D in  FIG. 24  is representatively illustrated.  FIG. 26  is a diagram showing that plural kinds of fan blades in  FIG. 24  are overlapped with each other. 
     Referring to  FIG. 24  to  FIG. 26 , a plurality of fan blades  421  are provided such that the discrepancy angle α of each fan blade  421  is equal among fan blades  421 . In other words, the angle at which fan blade  421  extending from inner peripheral blade tip portion  428  to outer peripheral blade tip portion  429  is inclined in the circumferential direction around center axis  501  is equal among fan blades  421 . 
     As far as the range shown in  FIG. 24  is concerned, the discrepancy angles α of fan blades  421 A to  421 G are equal to each other. Therefore, as shown in  FIG. 26 , when fan blades  421 A to  421 G are rotated in the circumferential direction around center axis  501  and overlapped on any one of the fan blades, chord lines  633  of fan blades  421 A to  421 G overlie one another. 
     A plurality of fan blades  421  include fan blades  421 A to  421 G in which at least one of the outer peripheral blade tip angle and the inner peripheral blade tip angle of each fan blade  421  is different from each other. In the present embodiment, fan blades  421 A to  421 G are provided such that the outer peripheral blade tip angle β of each fan blade is different among fan blades  421 A to  421 G. Therefore, as shown in  FIG. 26 , when fan blades  421 A to  421 G are rotated in the circumferential direction around center axis  501  and overlapped on any one of the fan blades, outer peripheral blade tip portions  429  of fan blades  421 A to  421 G do not overlie one another. 
     Fan blade  421  has flection portions  441  at which center line  506  of the blade cross section of fan blade  421  is flexed at different points between inner edge portion  426  and outer edge portion  427 . In the present embodiment, fan blade  421  has flection portions  441  at two points between inner edge portion  426  and outer edge portion  427 . Fan blade  421  has a flection portion  441   q  at a position adjacent to outer edge portion  427  and a flection portion  441   p  at the blade midpoint between inner edge portion  426  and outer edge portion  427 . At flection portion  441   q , center line  506  is bent by a flection angle θq. At flection portion  441   p , center line  506  is bent by a flection angle θp. 
     Fan blades  421 A to  421 G are formed such that the flection angle θq is different among the fan blades. More specifically, in fan blade  421 A, flection portion  441   q  is convex on the suction surface  424  side and is concave on the pressure surface  425  side (θq&lt;180°). The flection angle θq gradually increases in fan blades  421 B,  421 C,  421 D,  421 E,  421 F, and  421 G in this order. In fan blade  421 G, flection portion  441   q  is convex on the pressure surface  425  side and is concave on the suction surface  424  side (θq&gt;180°). The inclination of outer peripheral blade tip portion  429  changes with changing flection angle θq at flection portion  441   q , so that the outer peripheral blade tip angle differs among fan blades  421 A to  421 G. 
     The flection angle θp also changes with changing flection angle θq. As shown in  FIG. 26 , the flection angle θp changes such that the blade cross sections of fan blades  421 A to  421 G are kept overlapped on the side of inner peripheral blade tip portion  428 . 
     The flection structure of flection portions  441  can improve the strength of fan blade  421 . As a result, the reliability of the strength of the fan can be improved although cross-flow fan  500  is a resin fan having a thin blade cross section. The improvement in strength can reduce the thickness of fan blade  421  accordingly. Therefore, the weight of cross-flow fan  500  can be reduced and the cost thereof also can be reduced. 
     In the present embodiment, flection portion  441  is formed to be bent to form a corner. However, flection portion  441  may be formed to be bent so as to be rounded. 
       FIG. 27  is a diagram schematically showing an arrangement of fan blades in the cross-flow fan in  FIG. 20 . Referring to  FIG. 27 , fan blades  421 A,  421 B,  421 C,  421 D,  421 E,  421 F, and  421 G are arranged so as to be placed in an irregular (random) order in the circumferential direction around center axis  501 . More specifically, fan blades  421 A to  421 E are arranged so as not be repeatedly placed in a regular order (for example, fan blades  421 A→ 421 B→ 421 C→ 421 D→ 421 E→ 421 F→ 421 G→ 421 A→ 421 B→ 421 C→ 421 D→ 421 E→ 421 F→ 421 G  421 A→ 421 B . . . ). 
     In the example shown in  FIG. 27 , fan blades  421 C,  421 G,  421 E,  421 A,  421 D,  421 F,  421 B,  421 A,  421 B,  421 C,  421 D,  421 E,  421 F,  421 G,  421 B,  421 D,  421 G,  421 F,  421 A,  421 C,  421 E are placed in order clockwise around center axis  501 . 
     In the example above, seven kinds of fan blades  421 A to  421 G make one set, and plural sets of fan blades  421 A to  421 G placed in different orders are disposed in order. However, the configuration is not limited thereto. For example, a plurality of fan blades may be prepared for each of fan blade  421 A to  421 G, and fan blades selected therefrom as appropriate may be placed in order. As long as fan blades  421 A to  421 G are arranged without a regularity as a whole, fan blades of a particular kind may be placed in succession. The number of each of fan blades  421 A to  421 G for use in cross-flow fan  500  may not be completely equal. All of fan blades  421  for use in cross-flow fan  500  may have blade cross-sectional shapes different from each other. Preferably, at least three kinds, more preferably, at least four kinds of fan blades  421  are used. 
     Referring to  FIG. 20  and  FIG. 27 , a plurality of fan blades  421  are arranged such that the pitch between adjacent fan blades  421  (in  FIG. 27 , the angle η of a straight line passing through center axis  501  and contact point  631  between adjacent fan blades  421 ) is random. The random pitches are realized by disposing a plurality of fan blades  421  at irregular intervals according to random-number normal distribution. 
     A plurality of impellers  412  are configured such that the arrangement of fan blades  421  is the same. In other words, the intervals at which a plurality of fan blades  421  are arranged and the order in which fan blades  421  are arranged at such intervals in each impeller  412  are the same among impellers  412 . 
     A plurality of fan blades  421  may be arranged at regular pitches rather than at random pitches. 
     A plurality of impellers  412  are stacked such that a displacement angle T is formed between adjacent impellers  412  as viewed from the axial direction of center axis  501 . For example, attention is given to impeller  412 A, impeller  412 B, and impeller  412 C in  FIG. 20  disposed adjacent to each other in the order of appearance. Impeller  412 B is stacked on impeller  412 A so as to be displaced about center axis  501  by displacement angle T from the position where all of fan blades  421  in impellers  412 A and  412 B overlap in the axial direction of center axis  501 . Impeller  412 C is stacked on impeller  412 B so as to be displaced about center axis  501  by displacement angle T (2T when viewed from impeller  412 A) from the position where all of fan blades  421  in impellers  412 B and  412 C overlap in the axial direction of center axis  501 . 
     The structure of cross-flow fan  500  as a fan in the fourth embodiment of the present invention as described above is summarized as follows. Cross-flow fan  500  in the present embodiment has fan blades  421  as a plurality of blade portions arranged spaced apart from each other in the circumferential direction. Fan blade  421  has blade surface  423  including pressure surface  425  disposed on the rotational direction side of the fan and suction surface  424  disposed on the back side of pressure surface  425 . When cut along the plane orthogonal to center axis  501  serving as the rotation axis of the fan, fan blade  421  has inner edge portion  426  at which center line  506  between pressure surface  425  and suction surface  424  intersects inner peripheral blade tip portion  428  that is a blade tip on the inner peripheral side, and outer edge portion  427  at which center line  506  intersects outer peripheral blade tip portion  429  that is a blade tip on the outer peripheral side. As the fan is rotated, an air flow as a fluid flow flowing between inner edge portion  426  and outer edge portion  427  is generated on blade surface  423 . 
     The outer peripheral blade tip angle is defined as the angle between straight line  636  passing through center axis  501  as the rotational center of the fan and outer edge portion  427 , and tangent  637  of center line  506  at outer edge portion  427 . The inner peripheral blade tip angle is defined as the angle between straight line  638  passing through center axis  501  as the rotational center of the fan and inner edge portion  426 , and tangent  639  of center line  506  at inner edge portion  426 . The discrepancy angle is defined as the angle formed between chord line  633  in contact with inner peripheral blade tip portion  428  and outer peripheral blade tip portion  429  on the pressure surface  425  side, and straight line  632  passing through center axis  501  as the rotational center of the fan and contact point  631  of chord line  633  with outer peripheral blade tip portion  429 . 
     In this case, a plurality of fan blades  421  include fan blades  421 A to  421 G as a first blade portion and a second blade portion whose outer peripheral blade tip angles, as at least one of the outer peripheral blade tip angle and the inner peripheral blade tip angle, are different from each other. A plurality of fan blades  421  are provided such that the discrepancy angles of fan blades  421  are equal to each other. 
     In the present embodiment, a plurality of fan blades  421  comprised of fan blades  421 A to  421 G whose outer peripheral blade tip angles are different from each other have been described. However, a plurality of fan blades  421  may be comprised of plural kinds of fan blades whose inner peripheral blade tip angles are different from each other, or may be comprised of plural kinds of fan blades whose outer peripheral blade tip angles and inner peripheral blade tip angles are both different from each other. 
     (Description of Structures of Air Conditioner and Molding Die) 
       FIG. 28  is a cross-sectional view of an air conditioner using the cross-flow fan in  FIG. 20 . Referring to  FIG. 28 , an air conditioner  210  is configured with an indoor unit  220  installed in a room and provided with an indoor heat exchanger  229  and a not-shown outdoor unit installed in the outside of the room and provided with an outdoor heat exchanger and a compressor. Indoor unit  220  and the outdoor unit are connected by piping for circulating refrigerant gas between indoor heat exchanger  229  and the outdoor heat exchanger. 
     Indoor unit  220  has a blower  215 . Blower  215  is configured to include cross-flow fan  500 , a not-shown driving motor for rotating cross-flow fan  500 , and a casing  222  for producing a prescribed airflow with rotation of cross-flow fan  500 . 
     Casing  222  has a cabinet  222 A and a front panel  222 B. Cabinet  222 A is supported on a wall surface in the room. Front panel  222 B is removably attached to cabinet  222 A. An outlet port  225  is formed in a gap between a lower end portion of front panel  222 B and a lower end portion of cabinet  222 A. Outlet port  225  is formed in an approximately rectangular shape extending in the width direction of indoor unit  220  and is provided to be directed forward and downward. On the top surface of front panel  222 B, a grid-like intake port  224  is formed. 
     At a position opposing front panel  222 B, an air filter  228  is provided for collecting and removing dust included in the air taken in from intake port  224 . A not-shown air filter cleaner is provided in a space formed between front panel  222 B and air filter  228 . The air filter cleaner automatically removes dust accumulated in air filter  228 . 
     In the inside of casing  222 , an air flow channel  226  is formed, through which air is circulated from intake port  224  toward outlet port  225 . Outlet port  225  is provided with a vertical louver  232  that can change the blowing angle in the left and right directions and a plurality of horizontal louvers  231  that can change the blowing angle in the up and down directions to a forward-upward direction, a horizontal direction, a forward-downward direction, and an immediately downward direction. 
     Indoor heat exchanger  229  is disposed between cross-flow fan  500  and air filter  228  on a path of air flow channel  226 . Indoor heat exchanger  229  has not-shown serpentine refrigerant pipes arranged side by side in a plurality of layers in the up and down directions and in a plurality of columns in the front and back directions. Indoor heat exchanger  229  is connected to the compressor of the outdoor unit installed in the outdoor, and the compressor is driven to operate a refrigeration cycle. Through the operation of the refrigeration cycle, indoor heat exchanger  229  is cooled to a temperature lower than the ambient temperature during cooling operation, and indoor heat exchanger  229  is heated to a temperature higher than the ambient temperature during heating operation. 
       FIG. 29  is an enlarged cross-sectional view showing the proximity of the outlet port of the air conditioner in  FIG. 28 . Referring to  FIG. 28  and  FIG. 29 , casing  222  has a front wall portion  251  and a rear wall portion  252 . Front wall portion  251  and rear wall portion  252  are disposed to face each other at a distance from each other. 
     On a path of air flow channel  226 , cross-flow fan  500  is disposed to be positioned between front wall portion  251  and rear wall portion  252 . A protrusion portion  253  is formed at front wall portion  251  to protrude toward the radially outer surface of cross-flow fan  500  so as to decrease the gap between cross-flow fan  500  and front wall portion  251 . A protrusion portion  254  is formed at rear wall portion  252  to protrude toward the radially outer surface of cross-flow fan  500  so as to decrease the gap between cross-flow fan  500  and rear wall portion  252 . 
     Casing  222  has an upper guide portion  256  and a lower guide portion  257 . Air flow channel  226  is defined by upper guide portion  256  and lower guide portion  257  on the downstream side of air flow from cross-flow fan  500 . 
     Upper guide portion  256  and lower guide portion  257  are continuous from front wall portion  251  and rear wall portion  252 , respectively, and extend toward outlet port  225 . Upper guide portion  256  and lower guide portion  257  are formed to curve the air output by cross-flow fan  500  with upper guide portion  256  on the inner peripheral side and with lower guide portion  257  on the outer circumferential side, and to guide the air forward and downward. Upper guide portion  256  and lower guide portion  257  are formed such that the cross section of air flow channel  226  increases from cross-flow fan  500  toward outlet port  225 . 
     In the present embodiment, front wall portion  251  and upper guide portion  256  are integrally formed with front panel  222 B. Rear wall portion  252  and lower guide portion  257  are integrally formed with cabinet  222 A. 
       FIG. 30  is a cross-sectional view of an air flow produced in the proximity of the outlet port of the air conditioner in  FIG. 28 . Referring to  FIG. 28  to  FIG. 30 , on the path on air flow channel  226 , an upstream outside space  246  is formed to be positioned upstream of air flow from cross-flow fan  500 , an inside space  247  is formed to be positioned in the inside of cross-flow fan  500  (the inner peripheral side of a plurality of fan blades  421  circumferentially arranged), and a downstream outside space  248  is formed to be positioned downstream of air flow from cross-flow fan  500 . 
     During rotation of cross-flow fan  500 , at an upstream region  241  of air flow channel  226  with respect to protrusion portions  253 ,  254  as a boundary, an air flow  261  is formed to pass through on blade surface  423  of fan blade  421  from upstream outside space  246  toward inside space  247 . At a downstream region  242  of air flow channel  226  with respect to protrusion portions  253 ,  254  as a boundary, air flow  261  is formed to pass through on blade surface  423  of fan blade  421  from inside space  247  toward downstream outside space  248 . Here, at a position adjacent to front wall portion  251 , a forced vortex  262  of air flow is formed. 
     Although an air conditioner has been described in the present embodiment by way of example, the cross-flow fan in the present invention is also applicable to a fluid feeding device such as, for example, an air purifier, a humidifier, a cooling device, and a ventilating device. 
       FIG. 31  is a cross-sectional view of a molding die for use in production of the cross-flow fan in  FIG. 20 . Referring to  FIG. 31 , a molding die  110  has a stationary die  114  and a movable die  112 . Stationary die  114  and movable die  112  define a cavity  116  which has approximately the same shape as cross-flow fan  500  and into which flowable resin is injected. 
     Molding die  110  may be provided with a not-shown heater for increasing the flowability of resin injected into cavity  116 . The installation of such a heater is particularly effective, for example, when synthetic resin with an increased strength, such as glass-fiber-filled AS (acrylonitrile-styrene copolymer) resin, is used. 
     A centrifugal fan  410  in a sixth embodiment described later is also produced with a molding die having a similar structure as molding die  110  in  FIG. 31 . 
     (Detailed Description of Effects and Operation) 
     The operation and effects achieved by cross-flow fan  500  in the present embodiment will now be described assuming that cross flow-fan  500  is applied to an air conditioner. 
       FIG. 32  is a diagram for explaining the operation and effects achieved by the cross-flow fan in  FIG. 20 .  FIG. 32  and  FIG. 33 , which will be described later, illustrate a cross section of an air conditioner corresponding to  FIG. 28 . 
     Referring to  FIG. 32 , in order to obtain a suitable blowing capacity in air conditioner  210 , a scroll shape  601  (spiral shape) formed the outlet side of casing  222  should be adapted to the blowing direction of airflow output from cross-flow fan  500  as shown by arrow  310 . 
     More specifically, in a case, as in a scroll shape  602  shown in the figure, where the scroll shape formed in casing  222  expands radially outward with respect to the blowing direction of airflow from cross-flow fan  500 , the airflow may not conform to the scroll shape on the path toward outlet port  225  and may separate from the surface of casing  222  formed in a scroll shape. On the other hand, in a case, as in a scroll shape  603  shown in the figure, where the scroll shape formed in casing  222  narrows radially inward with respect to the blowing direction of airflow, the direction of airflow toward outlet port  225  is abruptly deflected by the surface of casing  222  formed in a scroll shape. In these cases, the blowing efficiency is reduced on air flow channel  226  in casing  222 . 
     On the other hand, the parameter for mainly determining the direction in which the air flowing on blade surface  423  is output from the fan is the discrepancy angle of fan blade  421 . In cross-flow fan  500  in the present embodiment, a plurality of fan blades  421  are provided such that the discrepancy angle of each fan blade  421  is equal among fan blades  421 . Therefore, the discrepancy angles of all the fan blades  421  can be set to a value adapted to scroll shape  601  of casing  222 . Accordingly, the air flow on air flow channel  226  becomes smooth, thereby improving the blowing capacity of blower  215  built in air conditioner  210 . 
       FIG. 33  is another diagram for explaining the operation and effects achieved by the cross-flow fan in  FIG. 20 . 
     Referring to  FIG. 33 , first, a phenomenon that occurs on the side of outer peripheral blade tip portion  429  of fan blade  421  will be described. As cross-flow fan  500  is rotated, outer peripheral blade tip portions  429  of fan blades  421  pass through one by one to cause periodic pressure variations at an approach place  606  where fan blade  421  approaches casing  222  (a space where fan blade  421  faces front wall portion  251  of casing  222 ). The periodic pressure variations are a cause for narrow-band noise called a blade passing sound. 
     By contrast, in cross-flow fan  500  in the present embodiment, a plurality of fan blades  421  are comprised of plural kinds of fan blades  421 A to  421 G whose outer peripheral blade tip angles are different from each other. Accordingly, the inclination of outer peripheral blade tip portion  429  varies among fan blades  421 , so that the direction of air flow flowing out through outer peripheral blade tip portion  429  from on blade surface  423  of fan blade  421  minutely varies among fan blades  421 . Accordingly, at approach place  606  downstream from outer peripheral blade tip portion  429 , the timing of pressure variation is changed. As a result, the cycles of pressure variations become less uniform, and the narrow-band noise can be reduced accordingly. 
     Next, a phenomenon that occurs on the side of inner peripheral blade tip portion  428  of fan blade  421  will be described. As described with reference to  FIG. 30 , on the side of inner peripheral blade tip portion  428 , forced vortex  262  is produced with rotation of fan blade  421 . At a center portion  607  of a region in which forced vortex  262  is produced, when inner peripheral blade tip portions  428  of fan blades  421  pass through one by one, periodic pressure variations are caused by interference of forced vortex  262  with inner peripheral blade tip portions  428 . Accordingly, narrow-band noise is generated as is the case with the outer peripheral blade tip portions  429 . 
     By contrast, in the case where a plurality of fan blades  421  are comprised of plural kinds of fan blades whose inner peripheral blade tip angles are different from each other, the inclination of inner peripheral blade tip portion  428  varies among fan blades  421 , so that the direction of air flow flowing onto blade surface  423  through inner peripheral blade tip portion  428  of each fan blade  421  minutely varies among fan blades  421 . Accordingly, at center portion  607  upstream from inner peripheral blade tip portion  29 , the timing of pressure variation is changed. Thus, the narrow-band noise can be reduced as in the foregoing description. 
     On both the side of outer peripheral blade tip portion  429  and the side of inner peripheral blade tip portion  428 , the noise generation mechanism is the same in that noise results from pressure variations caused by passage of blade tips. However, the center of forced vortex  262  is moved flexibly to some extent between forced vortex  262  and inner peripheral blade tip portion  428 . Therefore, the pressure variations at center portion  607  become small and less affect narrow-band noise. By contrast, at approach place  606  between casing  222  and fan blade  421 , the relative position therebetween does not change. Therefore, the pressure variations at approach place  606  become large and more affect narrow-band noise. 
     In cross-flow fan  500  in the fourth embodiment of the present invention configured in this manner, the blowing capacity of blower  215  using cross-flow fan  500  can be improved, while narrow-band noise caused by the rotation of fan blades  421  can be reduced. The use of cross-flow fan  500  in this manner reduces power consumption of the driving motor and provides air conditioner  210  that can contribute to energy savings. Furthermore, quiet air conditioner  210  is provided. 
     Fifth Embodiment 
     In the present embodiment, variations of plural kinds of fan blades  421  shown in  FIG. 24  will be described. 
       FIG. 34  is a cross-sectional view showing a first modification of plural kinds of fan blades in  FIG. 24 .  FIG. 35  is a diagram showing that plural kinds of fan blades in  FIG. 34  are overlapped with each other. 
     Referring to  FIG. 34  and  FIG. 35 , a plurality of fan blades  421  are comprised of plural kinds of fan blades  421 A,  421 B,  421 C,  421 D,  421 E,  421 F, and  421 G. The configuration of this modification is similar to that of the fourth embodiment in that the discrepancy angle of each fan blade is equal among fan blades  421  and in that the outer peripheral blade tip angle of each fan blade  421  is different among fan blades  421 A to  421 G. However, the modification differs from the fourth embodiment in the structure of flection portion  441  that makes the outer peripheral blade tip angle different among fan blades  421 A to  421 G. 
     More specifically, fan blade  421  has flection portions  441  at three points between inner edge portion  426  and outer edge portion  427 . Fan blade  421  has a flection portion  441   q  at a position adjacent to outer edge portion  427 , a flection portion  441   p  at the blade midpoint between inner edge portion  426  and outer edge portion  427 , and a flection portion  441   r  at a position adjacent to inner edge portion  426 . 
     In a similar manner as in the fourth embodiment, fan blades  421 A to  421 G are formed such that the flection angle θq (see  FIG. 25 ) of flection portion  441   q  differs among those fan blades, whereby the inclination of outer peripheral blade tip portion  429  varies. Here, the flection angle θq is smaller than 180° in all of fan blades  421 A to  421 G. 
     The flection angle θp (see  FIG. 25 ) of flection portion  441   p  also changes with changing flection angle θq. The flection angle θp is greater than 180° in all of fan blades  421 A to  421 G. On the other hand, when the flection angle θr of flection portion  441   r  is defined in the same way as in θp and θq, the flection angle θr is the same among fan blades  421 A to  421 G. The flection angle θr is smaller than 180°. 
     In such a configuration, in this modification, fan blades  421 A to  421 G each have an approximately W-shaped blade cross-sectional shape. Fan blades  421 A to  421 G each have such a blade cross section in that a concave portion  457  is formed at pressure surface  425  of blade surface  423  and a concave portion  456  is formed at suction surface  424  of blade surface  423 . 
     During rotation of cross-flow fan  500 , the air flow passing through on blade surface  423  is produced between adjacent fan blades  421 . Here, vortexes of air flow (secondary flows) are generated in concave portions  456  and  457  formed on blade surface  423 , whereby the air flow (main flow) passing through on blade surface  423  flows along the outside of the vortexes produced in concave portions  456  and  457 . Accordingly, although having a thin blade cross section, fan blade  421  exhibits a behavior like a thick blade as if the blade cross section is increased by the depth of concave portions  456  and  457  in which vortexes are formed. As a result, the lift produced in proximity to concave portions  456  and  457  can be significantly increased. 
       FIG. 36  is a cross-sectional view showing a second modification of plural kinds of fan blades in  FIG. 24 . Referring to  FIG. 36 , a plurality of fan blades  421  are comprised of plural kinds of fan blades  421 A,  421 B, and  421 C. The figure illustrates a state in which fan blades  421 A,  421 B, and  421 C are overlapped. The configuration of this modification is similar to that of the fourth embodiment in that the discrepancy angle of each fan blade  421  is equal among fan blades  421  and in that the outer peripheral blade tip angle of each fan blade is different among fan blades  421 A to  421 C. 
     In the present modification, plural kinds of fan blades  421 A,  421 B, and  421 C are provided such that a height H of fan blade  421  with reference to chord line  633  is equal. The height H is the length between chord line  633  and the position of suction surface  424  most distant from chord line  633 . 
     In such a configuration, variations in interval between adjacent fan blades  421  due to differences in height among fan blades  421 A to  421 C are not produced. Therefore, the interval between adjacent fan blades  421  can be optimized in accordance with the blowing performance required for the cross-flow fan. Accordingly, the air flow between fan blades  421  can be stabilized, thereby preventing abnormal sound. An increase in ventilation resistance to the air flow between fan blades  421  is prevented, thereby increasing the blowing capacity of the fan. 
     The cross-flow fan in the fifth embodiment of the present invention configured in this manner can achieve the effects described in the fourth embodiment similarly. 
     Sixth Embodiment 
     In the present embodiment, first of all, a structure of a centrifugal fan to which a fan according to the present invention is applied will be described. Next, structures of a blower and an air purifier using the centrifugal fan will be described. The centrifugal fan in the present embodiment partially has the same structure as cross-flow fan  500  in the fourth embodiment. In the following, a description of the overlapping structure will not be repeated. 
     (Description of Structure of Centrifugal Fan) 
       FIG. 37  is a perspective view of a centrifugal fan in a sixth embodiment of the present invention. Referring to  FIG. 37 , a centrifugal fan  410  in the present embodiment has a plurality of fan blades  421 . Centrifugal fan  410  has an approximately cylindrical appearance as a whole. A plurality of fan blades  421  are disposed on a circumferential surface of the approximately cylindrical shape. Centrifugal fan  410  is integrally formed from resin. Centrifugal fan  410  rotates in the direction shown by arrow  103  around an imaginary center axis  501  shown in  FIG. 37 . 
     Centrifugal fan  410  is a fan using a plurality of rotating fan blades  421  to output air taken in from the radially inner side to the radially outer side. Centrifugal fan  410  is a fan using a centrifugal force to output the air from the rotational center side of the fan to the radial direction thereof. Centrifugal fan  410  is a sirocco fan. Centrifugal fan  410  is used with rotation speeds in a low Reynolds number region applied to fans for home electric equipment, etc. 
     Centrifugal fan  410  further has a peripheral frames  413  serving as supports. Peripheral frames  413  are formed to annually extend around center axis  501 . Peripheral frames  413  are disposed spaced apart from each other in the axial direction of center axis  501 . A boss portion  416  for coupling centrifugal fan  410  to a driving motor is integrally formed with one of peripheral frames  413  with a disk portion  414  interposed therebetween. 
     A plurality of fan blades  421  are arranged spaced apart from each other in the circumferential direction around center axis  501 . A plurality of fan blades  421  are supported by peripheral frames  413  at opposite ends thereof in the axial direction of center axis  501 . Fan blade  421  is provided to stand on one peripheral frame  413  and formed to extend along the axial direction of center axis  501  toward the other peripheral frame  413 . 
     A plurality of fan blades  421  are comprised of plural kinds of fan blades  421 A to  421 G shown in  FIG. 24  and have a similar structure as that of fan blades  421  described in the fourth embodiment (a plurality of fan blades  421  are provided such that the discrepancy angles of fan blades  421  are equal to each other; a plurality of fan blades  421  are comprised of plural kinds of fan blades  421 A to  421 G whose outer peripheral blade tip angles are different from each other; and fan blades  421 A to  421 G are arranged in an irregular order). 
     However, centrifugal fan  410  in the present embodiment differs from cross-flow fan  500  in the fourth embodiment in that a plurality of fan blades  421  are arranged at regular intervals. 
     (Description of Structures of Blower and Air Purifier) 
       FIG. 38  is a cross-sectional view of a blower using the centrifugal fan in  FIG. 37 .  FIG. 39  is a cross-sectional view of the blower taken along a line XXXIX-XXXIX in  FIG. 38 . Referring to  FIG. 38  and  FIG. 39 , a blower  120  has a driving motor  128 , centrifugal fan  410 , and a casing  129  inside an outer casing  126 . 
     The output shaft of driving motor  128  is coupled to boss portion  416  molded integrally with centrifugal fan  410 . Casing  129  has a guide wall  129   a . Guide wall  129   a  is formed by an approximately ¾ arc disposed on the periphery of centrifugal fan  410 . Guide wall  129   a  is formed to guide an airflow generated by rotation of fan blade  421  to the rotational direction of fan blade  421  while increasing the speed of the airflow. 
     Casing  129  has an intake portion  130  and an outlet portion  127 . Intake portion  130  is formed to be positioned on an extension of center axis  501 . Outlet portion  127  is formed to be open to one side of the tangent direction of guide wall  129   a  from part of guide wall  129   a . Outlet portion  127  is shaped like a prismatic cylinder protruding from part of guide wall  129   a  to one side of the tangent direction of guide wall  129   a.    
     Driven by driving motor  128 , centrifugal fan  410  rotates in the direction shown by arrow  103 . Here, air is taken in from intake portion  130  to the inside of casing  129  and is output from a radially inside space  131  to a radially outside space  132  of centrifugal fan  410 . The air output to radially outside space  132  circumferentially flows in the direction shown by arrow  104  and is blown to the outside through outlet portion  127 . 
       FIG. 40  is a cross-sectional view of an air purifier using the centrifugal fan in  FIG. 37 . Referring to  FIG. 40 , an air purifier  140  has a housing  144 , a blower  150 , a duct  145 , and an HEPA (High Efficiency Particulate Air Filter) filter  141 . 
     Housing  144  has a rear wall  144   a  and a top wall  144   b . Housing  144  has an intake port  142  for sucking the air in the room in which air purifier  140  is installed. Intake port  142  is formed at rear wall  144   a . Housing  144  further has an outlet port  143  discharging the purified air to the inside of the room. Outlet port  143  is formed at top wall  144   b . Air purifier  140  is generally installed against a wall such that rear wall  144   a  is opposed to a wall in the room. 
     Filter  141  is disposed to face intake port  142  in the inside of housing  144 . The air introduced to the inside of housing  144  through intake port  142  passes through filter  141 . The foreign matters in the air are thus removed. 
     Blower  150  is provided to suck the room air to the inside of housing  144  and to output the air purified by filter  141  to the room through outlet port  143 . Blower  150  has centrifugal fan  410 , a casing  152 , and a driving motor  151 . Casing  152  has a guide wall  152   a . Casing  152  has an intake portion  153  and an outlet portion  154 . 
     Duct  145  is provided above blower  150  and is provided as an air channel for guiding the purified air from casing  152  to outlet port  143 . Duct  145  has a prismatic cylindrical shape with its lower end connecting to outlet portion  154  and with its upper end open. Duct  145  is configured to guide the purified air blown from outlet portion  154  to a laminar flow toward outlet port  143 . 
     In air purifier  140  having such a configuration, blower  150  is driven to rotate fan blades  421  to cause the room air to be taken in from intake port  142  to the inside of housing  144 . Here, an airflow is generated between intake port  142  and outlet port  143 , and foreign matters such as dust included in the intake air are removed by filter  141 . 
     The purified air obtained by passage through filter  141  is taken in to the inside of casing  152 . Here, the purified air taken in to the inside of casing  152  forms a laminar flow through guide wall  152   a  around fan blades  421 . The air in the form of a laminar flow is guided to outlet portion  154  along guide wall  152   a  and blown from outlet portion  154  to the inside of duct  145 . The air is discharged from outlet port  143  toward the external space. 
     Although an air purifier has been described by way of example in this embodiment, the centrifugal fan in the present invention is also applicable to a fluid feeding device such as, for example, an air conditioner, a humidifier, a cooling device, and a ventilating device. 
     Centrifugal fan  410  and air purifier  140  in the sixth embodiment of the present invention configured in this manner can achieve the effects described in the fourth embodiment similarly. 
     The structures of the fans described in the foregoing fourth to sixth embodiments may be combined as appropriate to configure a new fan. For example, centrifugal fan  410  in the sixth embodiment may be configured using the fan blades described in the fifth embodiment. 
     Seventh Embodiment 
     In the present embodiment, first of all, a structure of a cross-flow fan to which a fan in the present invention is applied will be described. Next, structures of an air conditioner using the cross-flow fan and a molding die for use in production of the cross-flow fan will be described. 
     (Description of Structure of Cross-Flow Fan) 
       FIG. 41  is a side view of a cross-flow fan in a seventh embodiment of the present invention.  FIG. 42  is a cross-sectional perspective view of the cross-flow fan taken along a line XLII-XLII in  FIG. 41 . 
     Referring to  FIG. 41  and  FIG. 42 , a cross-flow fan  800  in the present embodiment has a plurality of fan blades  721 . Cross-flow fan  800  has an approximately cylindrical appearance as a whole. A plurality of fan blades  721  are disposed on a circumferential surface of the approximately cylindrical shape. Cross-flow fan  800  is integrally formed from resin. Cross-flow fan  800  rotates in the direction shown by arrow  103  around an imaginary center axis  801  shown in the figures. 
     Cross-flow fan  800  is a fan using a plurality of rotating fan blades  721  to flow air in a direction orthogonal to center axis  801  serving as the rotation axis. As viewed from the axial direction of center axis  801 , cross-flow fan  800  takes in air from an outside space on one side with respect to center axis  801  to an inside space of the fan and outputs the intake air to the outside space on the other side with respect to center axis  801 . Cross-flow fan  800  forms an air flow that flows in the direction crossing center axis  801  in a flat plane orthogonal to center axis  801 . Cross-flow fan  800  forms an outlet flow in the form of a flat plane parallel to center axis  801 . 
     Cross-flow fan  800  is used with rotation speeds in the low Reynolds number region applied to fans for home electric equipment, etc. 
     Cross-flow fan  800  is configured such that a plurality of impellers  712  aligned in the axial direction of center axis  801  are combined. In each impeller  712 , a plurality of fan blades  721  are provided to be circumferentially spaced apart from each other around center axis  801 . 
     Cross-flow fan  800  further has a peripheral frame  713  serving as a support. Peripheral frame  713  has a ring shape annularly extending around center axis  801 . Peripheral frame  713  has an end surface  713   a  and an end surface  713   b . End surface  713   a  is formed to face one direction along the axial direction of center axis  801 . End surface  713   b  is disposed on the back side of end surface  713   a  and is formed to face the other direction along the axial direction of center axis  801 . 
     Peripheral frame  713  is provided to be interposed between impellers  712  adjacent to each other in the axial direction of center axis  801 . 
     Giving attention to impeller  712 A and impeller  712 B in  FIG. 41  disposed adjacent to each other, a plurality of fan blades  721  provided in impeller  712 A are provided to stand on end surface  713   a  and are formed to extend like plates along the axial direction of center axis  801 . A plurality of fan blades  721  provided in impeller  712 B are provided to stand on end surface  713   b  and are formed to extend like plates along the axial direction of center axis  801 . 
       FIG. 42  shows a blade cross section of fan blade  721  when cut along a plane orthogonal to center axis  801  serving as a rotation axis of cross-flow fan  800 . 
     Fan blade  721  has an inner peripheral blade tip portion  728  and an outer peripheral blade tip portion  729 . Inner peripheral blade tip portion  728  is disposed at an end of fan blade  721  on the inner peripheral side. Outer peripheral blade tip portion  729  is disposed at an end of fan blade  721  on the outer peripheral side. Fan blade  721  is formed to be inclined in the circumferential direction around center axis  801  from inner peripheral blade tip portion  728  toward outer peripheral blade tip portion  729 . Fan blade  721  is formed to be inclined in the rotational direction of cross-flow fan  800  from inner peripheral blade tip portion  728  toward outer peripheral blade tip portion  729 . 
     Fan blade  721  has a blade surface  723  including a pressure surface  725  and a suction surface  724 . Pressure surface  725  is disposed on the rotational direction side of cross-flow fan  800 . Suction surface  724  is disposed on the back side of pressure surface  725 . During rotation of cross-flow fan  800 , as an air flow is produced on blade surface  723 , a pressure distribution is generated in such a manner that pressure is relatively large at pressure surface  725  and is relatively small at suction surface  724 . Fan blade  721  has a bent shape as a whole between inner peripheral blade tip portion  728  and outer peripheral blade tip portion  729  so that fan blade  721  is concave on the pressure surface  725  side and convex on the suction surface  724  side. 
     Fan blade  721  is formed to have a uniform blade cross section when cut anywhere in the axial direction of center axis  801 . Fan blade  721  is formed to have a thin blade cross section between inner peripheral blade tip portion  728  and outer peripheral blade tip portion  729 . Fan blade  721  is formed to have an almost constant thickness (the length between pressure surface  725  and suction surface  724 ) between inner peripheral blade tip portion  728  and outer peripheral blade tip portion  729 . 
     In cross-flow fan  800  in the present embodiment, the shape and arrangement of fan blades  721  is determined so that an “outer peripheral blade tip angle” and an “inner peripheral blade tip angle” satisfy a predetermined relationship among a plurality of fan blades  721 . First, the meaning of the terms “outer peripheral blade tip angle” and “inner peripheral blade tip angle” used to describe the structure of cross-flow fan  800  will be described. 
       FIG. 43  is a diagram showing the “outer peripheral blade tip angle” and the “inner peripheral blade tip angle.”  FIG. 43  illustrates a center line  806  in the thickness direction (the direction connecting pressure surface  725  and suction surface  724 ) of the blade cross section of fan blade  721 . Center line  806  extends in the blade cross section so as to divide the blade cross section of fan blade  721  into the pressure surface  725  side and the suction surface  724  side. Fan blade  721  has an outer edge portion  727  at a position where center line  806  intersects outer peripheral blade tip portion  729 , and an inner edge portion  726  at a position where center line  806  intersects inner peripheral blade tip portion  728 . Center line  806  continuously extends between outer edge portion  727  and inner edge portion  726 . 
     The figure also shows a tangent  937  on outer edge portion  727  with respect to center line  806 , and a tangent  939  on inner edge portion  726  with respect to center line  806 . In the example in the figure, center line  806  is curved at outer edge portion  727  and inner edge portion  726 . However, in the case where it extends in a straight line, tangent  937  and tangent  939  overlap with center line  806  at outer edge portion  727  and inner edge portion  726 , respectively. 
     The figure also shows a straight line  936  passing through center axis  801  serving as the rotational center of cross-flow fan  800  and outer edge portion  727 , and a straight line  938  passing through center axis  801  serving as the rotational center of cross-flow fan  800  and inner edge portion  726 . 
     In this case, the angle β between straight line  936  and tangent  937  is the outer peripheral blade tip angle, and the angle γ between straight line  938  and tangent  939  is the inner peripheral blade tip angle. The outer peripheral blade tip angle means the angle of outer peripheral blade tip portion  729  at outer edge portion  727  with reference to straight line  936  passing through center axis  801  and outer edge portion  727 . The inner peripheral blade tip angle means the angle of inner peripheral blade tip portion  728  at inner edge portion  726  with reference to straight line  938  passing through center axis  801  and inner edge portion  726 . The outer peripheral blade tip angle β and the inner peripheral blade tip angle γ shown in the figure are smaller than 90°. 
       FIG. 44  is a cross-sectional view showing a shape and arrangement of fan blades in the cross-flow fan in  FIG. 41 . Referring to  FIG. 44 , in cross-flow fan  800  in the present embodiment, a plurality of fan blades  721  are comprised of plural kinds of fan blades  721 A,  721 B,  721 C,  721 D,  721 E,  721 F, and  721 G. Fan blades  721 A to  721 G have blade cross sections of different shapes. A plurality of fan blades are provided for each of fan blades  721 A to  721 G. 
       FIG. 45  is an enlarged cross-sectional view showing a blade cross section of the fan blade. In the figure, a blade cross section of fan blade  721 D in  FIG. 44  is representatively illustrated.  FIG. 46  is a diagram showing that plural kinds of fan blades in  FIG. 44  are overlapped with each other. 
     Referring to  FIG. 44  to  FIG. 46 , a plurality of fan blades  721  are provided such that the outer peripheral blade tip angle β of each fan blade  721  is equal among fan blades  721  and that the inner peripheral blade tip angle γ of each fan blade  721  is equal among fan blades  721 . As far as the range shown in  FIG. 44  is concerned, the outer peripheral blade tip angles β of fan blades  721 A to  721 G are equal to each other, and the inner peripheral blade tip angles γ of fan blades  721 A to  721 G are equal to each other. 
     A plurality of fan blades  721  include fan blades  721 A to  721 G in which when they are rotated around center axis  801  as the rotation axis of the fan and overlapped on any one of the fan blades  721 , one of inner edge portion  726  and outer edge portion  727  is disposed to be coincident with each other, and the other of inner edge portion  726  and outer edge portions  727  is disposed to be displaced from each other. 
     In the present embodiment, as shown in  FIG. 46 , when fan blades  721 A to  721 G are rotated around center axis  801 , inner edge portions  726  of fan blades  721 A to  721 G are coincident with each other, and outer edge portions  727  of fan blades  721 A to  721 G are displaced from each other. In  FIG. 46 , the blade cross sections of fan blades  721  are disposed to be displaced from each other on the side of outer peripheral blade tip portions  729 , and the blade cross sections of fan blades  721  are disposed to be overlapped with each other on the side of inner peripheral blade tip portions  728 . 
     Fan blade  721  has flection portions  741  at which center line  806  of the blade cross section of fan blade  721  is bent at different points between inner edge portion  726  and outer edge portion  727 . In the present embodiment, fan blade  721  has flection portions  741  at two points between inner edge portion  726  and outer edge portion  727 . Fan blade  721  has a flection portion  741   q  at a position adjacent to outer edge portion  727  and has a flection portion  741   p  at the blade midpoint between inner edge portion  726  and outer edge portion  727 . At flection portion  741   q , center line  806  is bent by a flection angle θq. At flection portion  741   p , center line  806  is bent by a flection angle θp. 
     Fan blades  721 A to  721 G are formed such that the flection angle θq and the flection angle θp are different among fan blades. 
     More specifically, in fan blade  721 A, flection portion  741   q  is formed so as to be convex on the suction surface  724  side and concave on the pressure surface  725  side (θq&lt;) 180°. The flection angle θq gradually increases in fan blades  721 B,  721 C,  721 D,  721 E,  721 F, and  721 G in this order, and in fan blade  721 G, flection portion  741   q  is formed to be convex on the pressure surface  725  side and concave on the suction surface  724  side (θq&gt;180°). As the flection angle θq increases in order from fan blade  721 A to fan blades  721 B,  721 C,  721 D,  721 E,  721 F, and  721 G, the flection angle θp at flection portion  741   p  gradually decreases. Here, flection portion  741   p  has the flection angle θp changed so that the blade cross sections of fan blades  721 A to  721 G are kept overlapped on the side of inner peripheral blade tip portions  728 . 
     Accordingly, the shape of fan blade  721  is varied such that the blade cross section on the side of outer peripheral blade tip portion  729  is displaced in the thickness direction with the position of flection portion  741   p  being fixed. As a result, the outer peripheral blade tip angle β and the inner peripheral blade tip angle γ are each equal among fan blades  721 A to  721 G, while outer edge portions  727  are displaced from each other. 
     The flection structure of flection portions  741  can improve the strength of fan blade  721 . As a result, the reliability of the strength of the fan can be improved although cross-flow fan  800  is a resin fan having a thin blade cross section. The improvement in strength can reduce the thickness of fan blade  721  accordingly. Therefore, the weight of cross-flow fan  800  can be reduced and the cost thereof also can be reduced. 
     In the present embodiment, flection portion  741  is formed to be bent to form a corner. However, flection portion  741  may be formed to be bent so as to be rounded. In this case, the blade cross section of fan blade  721  extends in the shape of an S at flection portion  741 . Even when flection portion  741  is shaped like a corner, flection portion  741  may be slightly rounded in consideration of a process of removing fan blade  721  from a die for resin molding. 
       FIG. 47  is a diagram schematically showing an arrangement of fan blades in the cross-flow fan in  FIG. 41 . Referring to  FIG. 47 , fan blades  721 A,  721 B,  721 C,  721 D,  721 E,  721 F, and  721 G are arranged to be placed in an irregular (random) order in the circumferential direction around center axis  801 . More specifically, fan blades  721 A to  721 E are arranged so as not be repeatedly placed in a regular order (for example, an order of fan blades  721 A→ 721 B→ 721 C→ 721 D→ 721 E→ 721 F→ 721 G→ 721 A→ 721 B→ 721 C→ 721 D→ 721 E→ 721 F→ 721 G→ 721 A→ 721 B . . . ). 
     In the example shown in  FIG. 47 , fan blades  721 C,  721 G,  721 E,  721 A,  721 D,  721 F,  721 B,  721 A,  721 B,  721 C,  721 D,  721 E,  721 F,  721 G,  721 B,  721 D,  721 G,  721 F,  721 A,  721 C,  721 E are placed in order clockwise around center axis  801 . 
     In the example above, seven kinds of fan blades  721 A to  721 G make one set, and plural sets of fan blades  721 A to  721 G placed in different orders are disposed in order. However, the configuration is not limited thereto. For example, a plurality of fan blades may be prepared for each of fan blades  721 A to  721 G, and fan blades selected therefrom as appropriate may be placed in order. As long as fan blades  721 A to  721 G are arranged without a regularity as a whole, fan blades of a particular kind may be placed in succession. The number of each of fan blades  721 A to  721 G for use in cross-flow fan  800  may not be completely equal. All of fan blades  721  for use in cross-flow fan  800  may have blade cross-sectional shapes different from each other. Preferably, at least three kinds, more preferably, at least four kinds of fan blades  721  are used. 
     Referring to  FIG. 41  and  FIG. 47 , a plurality of fan blades  721  are arranged such that the pitch between adjacent fan blades  721  (in  FIG. 47 , the angle η of a straight line passing through center axis  801  and inner edge portion  726  between adjacent fan blades  721 ) is random. The random pitches are realized by disposing a plurality of fan blades  721  at irregular intervals according to random-number normal distribution. 
     A plurality of impellers  712  are configured such that the arrangement of fan blades  721  is the same. In other words, the intervals at which a plurality of fan blades  721  are arranged and the order in which fan blades  721  are arranged at such intervals in each impeller  712  are the same among impellers  712 . 
     A plurality of fan blades  721  may be arranged at regular pitches rather than at random pitches. 
     A plurality of impellers  712  are stacked such that a displacement angle T is formed between adjacent impellers  712  as viewed from the axial direction of center axis  801 . For example, attention is given to impeller  712 A, impeller  712 B, and impeller  712 C in  FIG. 41  disposed adjacent to each other in the order of appearance. Impeller  712 B is stacked on impeller  712 A so as to be displaced about center axis  801  by displacement angle T from the position where all of fan blades  721  in impellers  712 A and  712 B overlap in the axial direction of center axis  801 . Impeller  712 C is stacked on impeller  712 B so as to be displaced about center axis  801  by displacement angle T (2T when viewed from impeller  712 A) from the position where all of fan blades  721  in impellers  712 B and  712 C overlap in the axial direction of center axis  801 . 
     The structure of cross-flow fan  800  in the seventh embodiment of the present invention as described above is summarized as follows. Cross-flow fan  800  as a fan in the present embodiment includes fan blades  721  as a plurality of blade portions arranged spaced apart from each other in the circumferential direction. Fan blade  721  has blade surface  723  including pressure surface  725  disposed on the rotational direction side of the fan and suction surface  724  disposed on the back side of pressure surface  725 . When cut along the plane orthogonal to center axis  801  serving as the rotation axis of the fan, fan blade  721  has inner edge portion  726  at which center line  806  between pressure surface  725  and suction surface  724  intersects inner peripheral blade tip portion  728  that is a blade tip on the inner peripheral side, and outer edge portion  727  at which center line  806  intersects outer peripheral blade tip portion  729  that is a blade tip on the outer peripheral side. As the fan is rotated, an air flow as a fluid flow flowing between inner edge portion  726  and outer edge portion  727  is generated on blade surface  723 . 
     The outer peripheral blade tip angle β is defined as the angle between straight line  936  passing through center axis  801  as the rotational center of the fan and outer edge portion  727 , and tangent  937  of center line  806  at outer edge portion  727 . The inner peripheral blade tip angle γ is defined as the angle between straight line  938  passing through center axis  801  as the rotational center of the fan and inner edge portion  726 , and tangent  939  of center line  806  at inner edge portion  726 . In this case, a plurality of fan blades  721  are provided such that the outer peripheral blade tip angle β and the inner peripheral blade tip angle γ are each equal among fan blades  721 . A plurality of fan blades  721  include fan blades  721 A to  721 G as a first blade portion and a second blade portion in which when they are rotated around center axis  801  as the rotation axis of the fan and overlapped on one fan blade  721 , inner edge portions  726 , as one of inner edge portion  726  and outer edge portion  727 , are disposed to be coincident with each other, and outer edge portions  727 , as the other of inner edge portion  726  and outer edge portion  727 , are disposed to be displaced from each other. 
     (Description of Structures of Air Conditioner and Molding Die) 
       FIG. 48  is a cross-sectional view of an air conditioner using the cross-flow fan in  FIG. 41 . Referring to  FIG. 48 , an air conditioner  210  is configured with an indoor unit  220  installed in a room and provided with an indoor heat exchanger  229  and a not-shown outdoor unit installed in the outside of the room and provided with an outdoor heat exchanger and a compressor. Indoor unit  220  and the outdoor unit are connected by piping for circulating refrigerant gas between indoor heat exchanger  229  and the outdoor heat exchanger. 
     Indoor unit  220  has a blower  215 . Blower  215  is configured to include cross-flow fan  800 , a not-shown driving motor for rotating cross-flow fan  800 , and a casing  222  for producing a prescribed airflow with rotation of cross-flow fan  800 . 
     Casing  222  has a cabinet  222 A and a front panel  222 B. Cabinet  222 A is supported on a wall surface in the room. Front panel  222 B is removably attached to cabinet  222 A. An outlet port  225  is formed in a gap between a lower end portion of front panel  222 B and a lower end portion of cabinet  222 A. Outlet port  225  is formed in an approximately rectangular shape extending in the width direction of indoor unit  220  and is provided to be directed forward and downward. On the top surface of front panel  222 B, a grid-like intake port  224  is formed. 
     At a position opposing front panel  222 B, an air filter  228  is provided for collecting and removing dust included in the air taken in from intake port  224 . A not-shown air filter cleaner is provided in a space formed between front panel  222 B and air filter  228 . The air filter cleaner automatically removes dust accumulated in air filter  228 . 
     In the inside of casing  222 , an air flow channel  226  is formed, through which air is circulated from intake port  224  toward outlet port  225 . Outlet port  225  is provided with a vertical louver  232  that can change the blowing angle in the left and right directions and a plurality of horizontal louvers  231  that can change the blowing angle in the up and down directions to a forward-upward direction, a horizontal direction, a forward-downward direction, and an immediately downward direction. 
     Indoor heat exchanger  229  is arranged between cross-flow fan  800  and air filter  228  on a path of air flow channel  226 . Indoor heat exchanger  229  has not-shown serpentine refrigerant pipes arranged side by side in a plurality of layers in the up and down directions and in a plurality of columns in the front and back directions. Indoor heat exchanger  229  is connected to the compressor of the outdoor unit installed in the outdoor, and the compressor is driven to operate a refrigeration cycle. Through the operation of the refrigeration cycle, indoor heat exchanger  229  is cooled to a temperature lower than the ambient temperature during cooling operation, and indoor heat exchanger  229  is heated to a temperature higher than the ambient temperature during heating operation. 
       FIG. 49  is an enlarged cross-sectional view showing the proximity of the outlet port of the air conditioner in  FIG. 48 . Referring to  FIG. 48  and  FIG. 49 , casing  222  has a front wall portion  251  and a rear wall portion  252 . Front wall portion  251  and rear wall portion  252  are disposed to face each other at a distance from each other. 
     On a path of air flow channel  226 , cross-flow fan  800  is disposed to be positioned between front wall portion  251  and rear wall portion  252 . A protrusion portion  253  is formed at front wall portion  251  to protrude toward the radially outer surface of cross-flow fan  800  so as to decrease the gap between cross-flow fan  800  and front wall portion  251 . A protrusion portion  254  is formed at rear wall portion  252  to protrude toward the radially outer surface of cross-flow fan  800  so as to decrease the gap between cross-flow fan  800  and rear wall portion  252 . 
     Casing  222  has an upper guide portion  256  and a lower guide portion  257 . Air flow channel  226  is defined by upper guide portion  256  and lower guide portion  257  on the downstream side of air flow from cross-flow fan  800 . 
     Upper guide portion  256  and lower guide portion  257  are continuous from front wall portion  251  and rear wall portion  252 , respectively, and extend toward outlet port  225 . Upper guide portion  256  and lower guide portion  257  are formed to curve the air output by cross-flow fan  800  with upper guide portion  256  on the inner circumferential side and with lower guide portion  257  on the outer circumferential side, and to guide the air forward and downward. Upper guide portion  256  and lower guide portion  257  are formed such that the cross section of air flow channel  226  increases from cross-flow fan  800  toward outlet port  225 . 
     In the present embodiment, front wall portion  251  and upper guide portion  256  are integrally formed with front panel  222 B. Rear wall portion  252  and lower guide portion  257  are integrally formed with cabinet  222 A. 
       FIG. 50  is a cross-sectional view of an air flow produced in the proximity of the outlet port of the air conditioner in  FIG. 48 . Referring to  FIG. 48  to  FIG. 50 , on the path on air flow channel  226 , an upstream outside space  246  is formed to be positioned upstream of air flow from cross-flow fan  800 , an inside space  247  is formed to be positioned in the inside of cross-flow fan  800  (the inner peripheral side of a plurality of fan blades  721  circumferentially arranged), and a downstream outside space  248  is formed to be positioned downstream of air flow from cross-flow fan  800 . 
     During rotation of cross-flow fan  800 , at an upstream region  241  of air flow channel  226  with respect to protrusion portions  253 ,  254  as a boundary, an air flow  261  is formed to pass through on blade surface  723  of fan blade  721  from upstream outside space  246  toward inside space  247 . At a downstream region  242  of air flow channel  226  with respect to protrusion portions  253 ,  254  as a boundary, air flow  261  is formed to pass through on blade surface  723  of fan blade  721  from inside space  247  toward downstream outside space  248 . Here, at a position adjacent to front wall portion  251 , a forced vortex  262  of air flow is formed. 
     Although an air conditioner has been described in the present embodiment by way of example, the cross-flow fan in the present invention is also applicable to a fluid feeding device such as, for example, an air purifier, a humidifier, a cooling device, and a ventilating device. 
       FIG. 51  is a cross-sectional view of a molding die for use in production of the cross-flow fan in  FIG. 41 . Referring to  FIG. 51 , a molding die  110  has a stationary die  114  and a movable die  112 . Stationary die  114  and movable die  112  define a cavity  116  which has approximately the same shape as cross-flow fan  800  and into which flowable resin is injected. 
     Molding die  110  may be provided with a not-shown heater for increasing the flowability of resin injected into cavity  116 . The installation of such a heater is particularly effective, for example, when synthetic resin with an increased strength, such as glass-fiber-filled AS (acrylonitrile-styrene copolymer) resin, is used. 
     A centrifugal fan  710  in a ninth embodiment described later is also produced with a molding die having a similar structure as molding die  110  in  FIG. 51 . 
     (Detailed Description of Operation and Effects) 
     The operation and effects achieved by cross-flow fan  800  in the present embodiment will now be described assuming that cross flow-fan  800  is applied to an air conditioner. 
       FIG. 52  is a diagram for explaining the operation and effects achieved by the cross-flow fan in  FIG. 41 . In the figure, a cross section of an air conditioner corresponding to  FIG. 48  is shown. 
     Referring to  FIG. 52 , a phenomenon that occurs on the side of outer peripheral blade tip portion  729  of fan blade  721  will be described. As cross-flow fan  800  is rotated, outer peripheral blade tip portions  729  of fan blades  721  pass through one by one to cause periodic pressure variations at an approach place  906  where fan blade  721  approaches casing  222  (a space where fan blade  721  faces front wall portion  251  of casing  222 ). The periodic pressure variations are a cause for narrow-band noise called a blade passing sound. 
     By contrast, in cross-flow fan  800  in the present embodiment, a plurality of fan blades  721  are comprised of fan blades  721 A to  721 G in which when a plurality of fan blades  721  are rotated around center axis  801  and overlapped, outer edge portions  727  are disposed to be displaced from each other. Accordingly, the cycle of outer peripheral blade tip end portion  729  of fan blade  721  passing through can be shifted more actively among fan blades  721 A to  721 G. As a result, the cycles of pressure variations become less uniform, thereby reducing narrow-band noise. 
     On the other hand, when fan blades  721 A to  721 G different in position of outer peripheral blade tip portion  729  are used, the air flow between adjacent fan blades  721  varies among a plurality of fan blades  721 . In this case, it is difficult to set an optimum air flow channel between all the fan blades  721 , and separation or constriction of air flow may occur between part of fan blades  721 . 
     By contrast, in cross-flow fan  800  in the present embodiment, a plurality of fan blades  721  are provided such that the outer peripheral blade tip angle β and the inner peripheral blade tip angle γ are each equal among fan blades  721 . With such a configuration, the direction in which the air flows in on blade surface  723  and the direction in which the air flows out on blade surface  723  between adjacent fan blades  723  can be made uniform among fan blades  721 . This can prevent the direction of the air flow between adjacent fan blades  721  from being significantly changed between inner edge portion  726  and outer edge portion  727 , thereby effectively preventing separation and constriction of air flow as described above. In the present embodiment, the blade cross section on the side of outer peripheral blade tip portion  729  is disposed to be actively displaced among fan blades  721 , while the blade cross section on the side of inner peripheral blade tip portion  728  is disposed at a fixed position. Therefore, for example, the angle η in  FIG. 47  can be set small between adjacent fan blades  721 . Accordingly, the blade interval on the inner edge portion  726  side can be brought closer to the optimum interval, so that separation or constriction of air flow that may occur between part of fan blades  721  can be effectively prevented. In particular, when the angle  11  in  FIG. 47  is equal among all the fan blades  721  (in other words, inner edge portions  726  are positioned at regular pitches), the blade interval on the inner edge portion  726  side can be set to an optimum interval. Accordingly, separation or constriction of air flow between fan blades  721  on the inner edge portion  726  side can be prevented suitably. As a result, the blowing capacity of cross-flow fan  800  can be improved. 
     In cross-flow fan  800  in the seventh embodiment of the present invention configured in this manner, the blowing capacity of cross-flow fan  800  can be improved, while narrow-band noise caused by rotation of fan blades  721  can be reduced. The use of cross-flow fan  800  in this manner reduces power consumption of the driving motor and provides air conditioner  210  that can contribute to energy savings. Furthermore, quiet air conditioner  210  is provided. 
     Eighth Embodiment 
     In the present embodiment, variations of plural kinds of fan blades  721  shown in  FIG. 44  will be described. 
       FIG. 53  is a cross-sectional view showing a first modification of plural kinds of fan blades in  FIG. 44 . Referring to  FIG. 53 , a plurality of fan blades  721  are comprised of plural kinds of fan blades  721 A,  721 B,  721 C,  721 D,  721 E,  721 F, and  721 G. 
       FIG. 54  is an enlarged cross-sectional view showing a blade cross section of the fan blade in  FIG. 53 . In the figure, a blade cross section of fan blade  721 D in  FIG. 53  is representatively illustrated.  FIG. 55  is a diagram showing that plural kinds of fan blades in  FIG. 53  are overlapped with each other. 
     Referring to  FIG. 53  to  FIG. 55 , also in this modification, a plurality of fan blades  721  are provided such that the outer peripheral blade tip angle β of each fan blade  721  is equal among fan blades  721  and that the inner peripheral blade tip angle γ of each fan blade  721  are equal among fan blades  721 . As far as the range shown in  FIG. 53  is concerned, the outer peripheral blade tip angles β of fan blades  721 A to  721 G are equal to each other, and the inner peripheral blade tip angles γ of fan blades  721 A to  721 G are equal to each other. 
     Furthermore, as shown in  FIG. 55 , when fan blades  721 A to  721 G are rotated around center axis  801 , outer edge portions  727  of fan blades  721 A to  721 G are coincident with each other, and inner edge portions  726  of fan blades  721 A to  721 G are displaced from each other. In  FIG. 55 , the blade cross sections of fan blades  721  on the side of inner peripheral blade tip portions  728  are disposed to be displaced from each other, whereas the blade cross sections of fan blades  721  on the side of outer peripheral blade tip portions  729  are disposed to be overlapped with each other. 
     Fan blade  721  has flection portions  741  at two points between inner edge portion  726  and outer edge portion  727 . In the present modification, fan blade  721  has a flection portion  741   r  at a position adjacent to inner edge portion  726  and a flection portion  741   p  at the blade midpoint between inner edge portion  726  and outer edge portion  727 . At flection portion  741   r , center line  806  is bent by a flection angle θr. At flection portion  741   p , center line  806  is bent by a flection angle θp. 
     Fan blades  721 A to  721 G are formed such that the flection angle θr and the flection angle θp differ among the fan blades. 
     More specifically, in fan blade  721 A, flection portion  741   r  is convex on the suction surface  724  side and is concave on the pressure surface  725  side (θr&lt;180°). The flection angle θr gradually increases in order of fan blades  721 B,  721 C,  721 D,  721 E,  721 F, and  721 G. In fan blade  721 G, flection portion  741   r  is convex on the pressure surface  725  side and is concave on the suction surface  724  side (θr&gt;180°). As the flection angle θr increases in order from fan blade  721 A to fan blades  721 B,  721 C,  721 D,  721 E,  721 F, and  721 G, the flection angle θp at flection portion  741   p  gradually decreases. Here, flection portion  741   p  has the flection angle θp changed so that the blade cross sections of fan blades  721 A to  721 G are kept overlapped on the side of outer peripheral blade tip portions  729 . 
     Accordingly, the shape of fan blade  721  is varied such that the blade cross section on the side of inner peripheral blade tip portion  728  is displaced in the thickness direction with the position of flection portion  741   p  being fixed. As a result, the outer peripheral blade tip angle β and the inner peripheral blade tip angle γ are each equal among fan blades  721 A to  721 G, while inner edge portions  726  are displaced from each other. 
     Also in this modification, as described with reference to  FIG. 47 , fan blades  721 A,  721 B,  721 C,  721 D,  721 E,  721 F, and  721 G are arranged to be placed in an irregular (random) order in the circumferential direction around center axis  801 . A plurality of fan blades  721  are arranged such that the pitch between adjacent fan blades  721  is random. Here, the pitch between adjacent fan blades  721  is represented by the angle of the straight line passing through center axis  801  and outer edge portion  727  between adjacent fan blades  721 . 
     Referring to  FIG. 52 , a phenomenon that occurs on the side of inner peripheral blade tip portion  728  of fan blade  721  will be described. As described with reference to  FIG. 50 , forced vortex  262  is produced by rotation of fan blade  721  on the side of inner peripheral blade tip portion  728 . When inner peripheral blade tip portions  728  of fan blades  721  pass through one by one at a center portion  907  in the region in which forced vortex  262  is formed, periodic pressure variations are caused by interference of forced vortex  262  with inner peripheral blade tip portions  728 . Accordingly, narrow-band noise is produced as is the case with the side of outer peripheral blade tip portions  729 . 
     By contrast, in the cross-flow fan in the present modification, a plurality of fan blades  721  are comprised of fan blades  721 A to  721 G in which when a plurality of fan blades  721  are rotated around center axis  801  and overlapped, inner edge portions  726  are displaced from each other. Accordingly, the cycle of inner peripheral blade tip portion  728  of fan blade  721  passing through can be shifted among fan blades  721 A to  721 G more actively. As a result, the cycles of pressure variations become less uniform, thereby reducing narrow-band noise. 
     On both the side of outer peripheral blade tip portion  729  and the side of inner peripheral blade tip portion  728 , the noise generation mechanism is the same in that noise results from pressure variations caused by passage of blade tips. However, the center of forced vortex  262  is moved flexibly to some extent between forced vortex  262  and inner peripheral blade tip portion  728 . Therefore, the pressure variations at center portion  907  become small and less affect narrow-band noise. By contrast, at approach place  906  between casing  222  and fan blade  721 , the relative position therebetween does not change. Therefore, the pressure variations at approach place  906  become large and more affect narrow-band noise. 
       FIG. 56  is a cross-sectional view showing a second modification of plural kinds of fan blades in  FIG. 44 .  FIG. 56  corresponds to  FIG. 46  in the seventh embodiment. 
     Referring to  FIG. 56 , in this modification, fan blade  721  has flection portions  741  at three points between inner edge portion  726  and outer edge portion  727 . Fan blade  721  has a flection portion  741   q  at a position adjacent to outer edge portion  727 , a flection portion  741   p  at the blade midpoint between inner edge portion  726  and outer edge portion  727 , and a flection portion  741   r  at a position adjacent to inner edge portion  726 . 
     In a similar manner as in the seventh embodiment, fan blades  721 A to  721 G are formed such that the flection angle θq and the flection angle θp (see  FIG. 45 ) differ among the fan blades, whereby the outer peripheral blade tip angle β and the inner peripheral blade tip angle γ are each equal among fan blades  721 A to  721 G, and outer edge portions  727  are displaced from each other. 
     It is noted that the flection angle θq is smaller than 180° in all the fan blades  721 A to  721 G, whereas the flection angle θp is greater than 180° in all the fan blades  721 A to  721 G. On the other hand, when the flection angle θr of flection portion  741   r  is defined in a similar manner as in θp and θq, the flection angle θr is equal among fan blades  721 A to  721 G. The flection angle θr is smaller than 180°. 
     In such a configuration, in this modification, fan blades  721 A to  721 G each have an approximately W-shaped blade cross-sectional shape. Fan blades  721 A to  721 G each have such a blade cross section in that concave portion  757  is formed at pressure surface  725  of blade surface  723  and concave portion  756  is formed at suction surface  724  of blade surface  723 . 
     During rotation of cross-flow fan  800 , the air flow passing through on blade surface  723  is produced between adjacent fan blades  721 . Here, vortexes of air flow (secondary flows) are generated in concave portions  756  and  757  formed on blade surface  723 , whereby the air flow (main flow) passing through on blade surface  723  flows along the outside of the vortexes produced in concave portions  756  and  757 . Accordingly, although having a thin blade cross section, fan blade  721  exhibits a behavior like a thick blade as if the blade cross section is increased by the depth of concave portions  756  and  757  in which vortexes are formed. As a result, the lift produced in proximity to concave portions  756  and  757  can be significantly increased. 
     The cross-flow fan in the eighth embodiment of the present invention configured in this manner can achieve the effects as described in the seventh embodiment similarly. 
     Ninth Embodiment 
     In the present embodiment, first of all, a structure of a centrifugal fan to which a fan according to the present invention is applied will be described. Next, structures of a blower and an air purifier using the centrifugal fan will be described. The centrifugal fan in the present embodiment partially has the same structure as cross-flow fan  800  in the seventh embodiment. In the following, a description of the overlapping structure will not be repeated. 
     (Description of Structure of Centrifugal Fan) 
       FIG. 57  is a perspective view of a centrifugal fan in a ninth embodiment of the present invention. Referring to  FIG. 57 , a centrifugal fan  710  in the present embodiment has a plurality of fan blades  721 . Centrifugal fan  710  has an approximately cylindrical appearance as a whole. A plurality of fan blades  721  are disposed on a circumferential surface of the approximately cylindrical shape. Centrifugal fan  710  is integrally formed from resin. Centrifugal fan  710  rotates in the direction shown by arrow  103  around an imaginary center axis  801  shown in  FIG. 57 . 
     Centrifugal fan  710  is a fan using a plurality of rotating fan blades  721  to output air taken in from the radially inner side to the radially outer side. Centrifugal fan  710  is a fan using a centrifugal force to output the air from the rotational center side of the fan to the radial direction thereof. Centrifugal fan  710  is a sirocco fan. Centrifugal fan  710  is used with rotation speeds in a low Reynolds number region applied to fans for home electric equipment, etc. 
     Centrifugal fan  710  further has peripheral frames  713  serving as supports. Peripheral frames  713  are formed to annually extend around center axis  801 . Peripheral frames  713  are disposed spaced apart from each other in the axial direction of center axis  801 . A boss portion  716  for coupling centrifugal fan  710  to a driving motor is integrally formed with one of the peripheral frames  713  with a disk portion  714  interposed therebetween. 
     A plurality of fan blades  721  are arranged spaced apart from each other in the circumferential direction around center axis  801 . A plurality of fan blades  721  are supported by peripheral frames  713  at opposite ends thereof in the axial direction of center axis  801 . Fan blade  721  is provided to stand on one peripheral frame  713  and formed to extend along the axial direction of center axis  801  toward the other peripheral frame  713 . 
     A plurality of fan blades  721  are comprised of plural kinds of fan blades  721 A to  721 G shown in  FIG. 44  and have a similar structure as that of fan blades  721  described in the seventh embodiment (the outer peripheral blade tip angle β of each fan blade  721  is equal among fan blades  721  and the inner peripheral blade tip angle γ of each fan blade  721  is equal among fan blades  721 ; when fan blades  721 A to  721 G are rotated around center axis  801 , inner edge portions  726  of fan blades  721 A to  721 G are coincident with each other and outer edge portions  727  of fan blades  721 A to  721 G are displaced from each other; and fan blades  721 A to  721 G are arranged in an irregular order). 
     However, centrifugal fan  710  in the present embodiment differs from cross-flow fan  800  in the seventh embodiment in that a plurality of fan blades  721  are arranged at regular intervals. 
     (Description of Structures of Blower and Air Purifier) 
       FIG. 58  is a cross-sectional view of a blower using the centrifugal fan in  FIG. 57 .  FIG. 59  is a cross-sectional view of the blower taken along a line LIX-LIX in  FIG. 58 . Referring to  FIG. 58  and  FIG. 59 , a blower  120  has a driving motor  128 , centrifugal fan  710 , and a casing  129  inside an outer casing  126 . 
     The output shaft of driving motor  128  is coupled to boss portion  716  of centrifugal fan  710 . Casing  129  has a guide wall  129   a . Guide wall  129   a  is formed by an approximately ¾ arc disposed on the periphery of centrifugal fan  710 . Guide wall  129   a  is formed to guide an airflow generated by rotation of fan blade  721  to the rotational direction of fan blade  721  while increasing the speed of the airflow. 
     Casing  129  has an intake portion  130  and an outlet portion  127 . Intake portion  130  is formed to be positioned on an extension of center axis  801 . Outlet portion  127  is formed to be open to one side of the tangent direction of guide wall  129   a  from part of guide wall  129   a . Outlet portion  127  is shaped like a prismatic cylinder protruding from part of guide wall  129   a  to one side of the tangent direction of guide wall  129   a.    
     Driven by driving motor  128 , centrifugal fan  710  rotates in the direction shown by arrow  103 . Here, air is taken in from intake portion  130  to the inside of casing  129  and is output from a radially inside space  131  to a radially outside space  132  of centrifugal fan  710 . The air output to radially outside space  132  circumferentially flows in the direction shown by an arrow  104  and is blown to the outside through outlet portion  127 . 
       FIG. 60  is a cross-sectional view of an air purifier using the centrifugal fan in  FIG. 57 . Referring to  FIG. 60 , an air purifier  140  has a housing  144 , a blower  150 , a duct  145 , and an HEPA (High Efficiency Particulate Air Filter) filter  141 . 
     Housing  144  has a rear wall  144   a  and a top wall  144   b . Housing  144  has an intake port  142  for sucking the air in the room in which air purifier  140  is installed. Intake port  142  is formed at rear wall  144   a . Housing  144  further has an outlet port  143  discharging the purified air to the inside of the room. Outlet port  143  is formed at top wall  144   b . Air purifier  140  is generally installed against a wall such that rear wall  144   a  is opposed to a wall in the room. 
     Filter  141  is disposed to face intake port  142  in the inside of housing  144 . The air introduced to the inside of housing  144  through intake port  142  passes through filter  141 . The foreign matters in the air are thus removed. 
     Blower  150  is provided to suck the room air to the inside of housing  144  and to output the air purified by filter  141  to the room through outlet port  143 . Blower  150  has centrifugal fan  710 , a casing  152 , and a driving motor  151 . Casing  152  has a guide wall  152   a . Casing  152  has an intake portion  153  and an outlet portion  154 . 
     Duct  145  is provided above blower  150  and is provided as an air channel for guiding the purified air from casing  152  to outlet port  143 . Duct  145  has a prismatic cylindrical shape with its lower end connecting to outlet portion  154  and with its upper end open. Duct  145  is configured to guide the purified air blown from outlet portion  154  to a laminar flow toward outlet port  143 . 
     In air purifier  140  having such a configuration, blower  150  is driven to rotate fan blades  721  to cause the room air to be taken in from intake port  142  to the inside of housing  144 . Here, an airflow is generated between intake port  142  and outlet port  143 , and foreign matters such as dust included in the intake air are removed by filter  141 . 
     The purified air obtained by passage through filter  141  is taken in to the inside of casing  152 . Here, the purified air taken in to the inside of casing  152  forms a laminar flow through guide wall  152   a  around fan blades  721 . The air in the form of a laminar flow is guided to outlet portion  154  along guide wall  152   a  and blown from outlet portion  154  to the inside of duct  145 . The air is discharged from outlet port  143  toward the external space. 
     Although an air purifier has been described by way of example in this embodiment, the centrifugal fan in the present invention is also applicable to a fluid feeding device such as, for example, an air conditioner, a humidifier, a cooling device, and a ventilating device. 
     Centrifugal fan  710  and air purifier  140  in the ninth embodiment of the present invention configured in this manner can achieve the effects described in the seventh embodiment similarly. 
     The structures of the fans described in the foregoing seventh to ninth embodiments may be combined as appropriate to configure a new fan. For example, centrifugal fan  710  in the ninth embodiment may be configured using the fan blades described in the eighth embodiment. 
     The embodiment disclosed here should be understood as being illustrative rather than being limitative in all respects. The scope of the present invention is shown not in the foregoing description but in the claims, and it is intended that all modifications that come within the meaning and range of equivalence to the claims are embraced here. 
     INDUSTRIAL APPLICABILITY 
     The present invention is mainly applied to home electric equipment having an air blowing function, such as an air purifier and an air conditioner. 
     DESCRIPTION OF THE REFERENCE SIGNS 
     
         
         
           
               10  centrifugal fan,  12 ,  12 A,  12 B,  12 C impeller,  13  peripheral frame,  13   a ,  13   b  end surface,  14  disk portion,  16  boss portion,  21 ,  21 A,  21 B,  21 C,  21 D,  21 E fan blade,  23  blade surface,  24  suction surface,  25  pressure surface,  26  inner edge portion,  27  outer edge portion,  31 ,  61  air flow,  32 ,  62 ,  63 ,  67 ,  68  vortex,  41 ,  41 A,  41 B flection portion,  51 ,  51   p ,  51   q ,  52 ,  52   p ,  52   q  convex portion,  56 ,  57 ,  57   p ,  57   q  concave portion,  100  cross-flow fan,  101  center axis,  106  center axis,  110  molding die,  112  movable die,  114  stationary die,  116  cavity,  120 ,  150 ,  215  blower,  126  outer casing,  127 ,  154  outlet portion,  128 ,  151  driving motor,  129 ,  152 ,  222  casing,  129   a ,  152   a  guide wall,  130 ,  153  intake portion,  131  radially inside space,  132  radially outside space,  140  air purifier,  141  filter,  142 ,  224  intake port,  143 ,  225  outlet port,  144  housing,  144   a  rear wall,  144   b  top wall,  145  duct,  210  air conditioner,  220  indoor unit,  222 A,  222 B cabinet,  226  air flow channel,  228  air filter,  229  indoor heat exchanger,  231  horizontal louver,  232  vertical louver,  241  upstream region,  242  downstream region,  246  upstream outside space,  247  inside space,  248  downstream outside space,  251  front wall portion,  252  rear wall portion,  253 ,  254  protrusion portion,  256  upper guide portion,  257  lower guide portion,  262  forced vortex,  410  centrifugal fan,  412 ,  412 A,  412 B,  412 C impeller,  413  peripheral frame,  413   a ,  413   b  end surface,  414  disk portion,  416  boss portion,  421 ,  421 A to  421 G fan blade,  423  blade surface,  424  suction surface,  425  pressure surface,  426  inner edge portion,  427  outer edge portion,  428  inner peripheral blade tip portion,  429  outer peripheral blade tip portion,  441 ,  441   p ,  441   q ,  441   r  flection portion,  456 ,  457  concave portion,  500  cross-flow fan,  501  center axis,  506  center line,  601 ,  602 ,  603  scroll shape,  606  approach place,  607  midpoint,  631  contact point,  632 ,  636 ,  638  straight line,  633  chord line,  637 ,  639  tangent,  710  centrifugal fan,  712 ,  712 A,  712 B,  712 C impeller,  713  peripheral frame,  713   a ,  713   b  end surface,  714  disk portion,  716  boss portion,  721 ,  721 A to  721 G fan blade,  723  blade surface,  724  suction surface,  725  pressure surface,  726  inner edge portion,  727  outer edge portion,  728  inner peripheral blade tip portion,  729  outer peripheral blade tip portion,  741 ,  741   p ,  741   q ,  741   r  flection portion,  756 ,  757  concave portion,  800  cross-flow fan,  801  center axis,  806  center line,  906  approach place,  907  midpoint,  936 ,  938  straight line,  937 ,  939  tangent.