Patent Publication Number: US-10760799-B2

Title: Ultraviolet sterilizer and air conditioning apparatus using the same

Description:
TECHNICAL FIELD 
     The present invention relates to an ultraviolet sterilizer intended for airborne microbes, such as bacteria, fungi and viruses, in the air as treating objects and an air-conditioning apparatus on which the ultraviolet sterilizer is mounted. 
     BACKGROUND ART 
     It is known that ultraviolet ray having a wavelength of 200 nm to 360 nm not only takes a proliferating ability by acting on nucleic acid that is the protoplasm of bacteria to inhibit replication of DNA but also kills bacteria by destroying proteins, and other substances, that are formative substances of cytoplasm and cell membranes. An ultraviolet sterilizer that sterilizes air, or the like, by emit such ultraviolet ray is in actual use. The ultraviolet sterilizer is to sterilize microbes in the air by emit ultraviolet ray to influent air, and the like (see, for example, Patent Literature 1 and Patent Literature 2). 
     In the ultraviolet sterilizer of Patent Literature 1, in order for emit ultraviolet ray not to leak from a sterilizing chamber inside a casing that is a box, an upper portion of one of two facing sides in a sterilizing chamber is open as an air intake, a lower portion of the other one of the sides is open as an outlet opening, and air is caused to pass through the inside of the sterilizing chamber via these opening ports. 
     In the ultraviolet sterilizer of Patent Literature 2, to increase the irradiance of ultraviolet ray inside the sterilizer, reflectors are installed on wall surfaces inside a flow passage through which fluid flows, and ultraviolet ray is reflected multiple times by emitting ultraviolet ray obliquely to the reflectors. Thus, the ultraviolet sterilizer sterilizes fluid. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2014-100206 
     Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2013-240487 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the ultraviolet sterilizer of Patent Literature 1 requires a large number of ultraviolet ray emitting diodes and a relatively wide sterilizing chamber. The ultraviolet sterilizer of Patent Literature 2 has a wide ultraviolet ray irradiation range in a fluid traveling direction to increase the irradiance of ultraviolet ray by causing ultraviolet ray to be reflected multiple times. That is, the existing ultraviolet sterilizers have poor sterilizing efficiency per unit volume and need to be increased in size. 
     The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an ultraviolet sterilizer and an air-conditioning apparatus that efficiently sterilize fluid with a compact space. 
     Solution to Problem 
     An ultraviolet sterilizer of one embodiment of the present invention sterilizes air by using ultraviolet ray, and includes an ultraviolet sterilizer configured to emit ultraviolet ray to the air, the ultraviolet sterilizer including a sterilizing light screen forming unit configured to form a screen-shaped sterilizing light screen based on the emitted ultraviolet ray. 
     An air-conditioning apparatus of one embodiment of the present invention conditions introduced air. The air-conditioning apparatus includes an ultraviolet sterilizer that emits ultraviolet ray to the air. The ultraviolet sterilizer includes a sterilizing light screen forming unit that forms a screen-shaped sterilizing light screen based on the emitted ultraviolet ray. 
     Advantageous Effects of Invention 
     With the embodiments of the present invention, the sterilizing light screen forming unit forms a screen-shaped sterilizing light screen by emitting ultraviolet ray, so it is possible to efficiently sterilize fluid with a compact space. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram that shows the schematic configuration of an air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 2  is a diagram that shows the schematic configuration of an ultraviolet sterilizer of the air-conditioning apparatus shown in  FIG. 1 . 
         FIG. 3  is a schematic cross-sectional view of the ultraviolet sterilizer, taken along the line A-A in  FIG. 2 . 
         FIG. 4  is a diagram that illustrates the shape of each reflector of the ultraviolet sterilizer shown in  FIG. 3 . 
         FIG. 5  is a diagram regarding an incident angle of light and a reflection angle of the light. 
         FIG. 6  is a schematic diagram that shows an inclination angle of a reflecting surface relative to a flat surface in the case where ultraviolet ray vertically enters the reflector illustrated in  FIG. 4 . 
         FIG. 7  is a schematic diagram that shows an inclination angle of a reflecting surface relative to a flat surface in the case where ultraviolet ray is vertically reflected from the reflector illustrated in  FIG. 4 . 
         FIG. 8  is a schematic diagram that shows an inclination angle required to reflect ultraviolet ray that has vertically entered the reflector that constitutes one of sides of a polygonal shape that is the cross-sectional shape of a reflecting portion shown in  FIG. 3 , to the reflector that constitutes a specified one of the sides. 
         FIG. 9  is a schematic diagram for showing an inclination angle required to vertically reflect ultraviolet ray from the reflector that constitutes one of the sides of the polygonal shape that is the cross-sectional shape of the reflecting portion shown in  FIG. 3 , to the reflector that constitutes a specified one of the sides. 
         FIG. 10  is a graph that shows the relation between a distance from an emitting portion that is an ultraviolet ray source and an intensity of ultraviolet ray. 
         FIG. 11  is a table that shows an ultraviolet ray irradiance at the level of 1 mm above each reflector shown in  FIG. 3 . 
         FIG. 12  is a graph that shows the relation between an ultraviolet ray irradiance provided by the ultraviolet sterilizer shown in  FIG. 3  and a survival rate of airborne influenza virus. 
         FIG. 13  is a table that shows an energy (eV), a sterilizing effect and a sterilizing effect per 1 eV by wavelength where a plurality of wavelengths of ultraviolet ray is set in the range of 200 nm to 360 nm. 
         FIG. 14  is a graph that shows sterilizing effects as experimental results of an example according to Embodiment 1 of the present invention. 
         FIG. 15  is a graph that shows pressure losses as experimental results of the example according to Embodiment 1 of the present invention. 
         FIG. 16  is a schematic diagram that shows the schematic configuration of an air-conditioning apparatus according to an alternative embodiment to Embodiment 1 of the present invention. 
         FIG. 17  is a schematic cross-sectional view of the air-conditioning apparatus, taken along the line B-B in  FIG. 16 . 
         FIG. 18  is a schematic diagram that shows the schematic configuration of an air-conditioning apparatus according to Embodiment 2 of the present invention. 
         FIG. 19  is a diagram that shows the schematic cross sections of two ultraviolet sterilizers according to Embodiment 2 of the present invention in layers. 
         FIG. 20  is a schematic diagram that shows the schematic configuration of an air-conditioning apparatus according to Embodiment 3 of the present invention. 
         FIG. 21  is a diagram that shows a path along which ultraviolet ray travels in the schematic cross-sectional view of each ultraviolet sterilizer, taken along the line C-C in  FIG. 20 . 
         FIG. 22  is a diagram that shows the schematic cross sections of the two ultraviolet sterilizers according to Embodiment 3 of the present invention in layers. 
         FIG. 23  is a schematic diagram that shows a velocity distribution of air in an air course. 
         FIG. 24  is a schematic cross-sectional view that shows the configuration of an ultraviolet sterilizer according to Embodiment 4 of the present invention. 
         FIG. 25  is a diagram that shows a path along which ultraviolet ray travels in a reflecting portion shown in  FIG. 24 . 
         FIG. 26  is a table that shows an ultraviolet ray irradiance at the level of 1 mm above each reflector shown in  FIG. 24 . 
         FIG. 27  is a schematic cross-sectional view that shows the configuration of an ultraviolet sterilizer according to Embodiment 5 of the present invention. 
         FIG. 28  is a schematic cross-sectional view of an emitting portion of the ultraviolet sterilizer shown in  FIG. 27 . 
         FIG. 29  is a schematic diagram that illustrates the schematic configuration of an air-conditioning apparatus according to Embodiment 6 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
       FIG. 1  is a schematic diagram that shows the schematic configuration of an air-conditioning apparatus according to Embodiment 1.  FIG. 2  is a diagram that shows the schematic configuration of an ultraviolet sterilizer of the air-conditioning apparatus shown in  FIG. 1 .  FIG. 3  is a schematic cross-sectional view of the ultraviolet sterilizer, taken along the line A-A in  FIG. 2 .  FIG. 4  is a diagram that illustrates the shape of each reflector of the ultraviolet sterilizer shown in  FIG. 3 . The configuration of the ultraviolet sterilizer according to Embodiment 1 and the configuration of the air-conditioning apparatus using the ultraviolet sterilizer will be described with reference to  FIG. 1  to  FIG. 4 . 
     As shown in  FIG. 1 , the air-conditioning apparatus  11   a  includes a cylindrical casing  12 . The cylindrical casing  12  has an air intake  13  and an outlet opening  14 . The air intake  13  introduces air. Through the outlet opening  14  the air introduced from the air intake  13  flows out. The air-conditioning apparatus  11   a  includes the ultraviolet sterilizer  10   a  and an air-sending device  15 . The ultraviolet sterilizer  10   a  is disposed between the air intake  13  and the outlet opening  14 . The ultraviolet sterilizer  10   a  sterilizes air. The air-sending device  15  generates flow of air from the air intake  13  toward the outlet opening  14 . A direction from the air intake  13  toward the outlet opening  14  is defined as a flow direction. 
     The casing  12  has a circular shape in cross section taken along a plane perpendicular to the flow direction. In Embodiment 1, the diameter of the circular shape in the cross section of the casing  12  is 100 mm. The air-sending device  15  has the function of sending air at a velocity of 3 m/s. 
     As shown in  FIG. 2 , the ultraviolet sterilizer  10   a  includes a sterilizing light screen forming unit. The sterilizing light screen forming unit forms a screen-shaped sterilizing light screen based on emitted ultraviolet ray. Specifically, the ultraviolet sterilizer has a cylindrical casing  40   a . The cylindrical casing  40   a  has an inlet port  5  and an outlet port  6 . Air flows into the inlet port  5 . The air flowing from the inlet port  5  flows out through the outlet port  6 . That is, the cylindrical casing  40   a  has a shape such that both sides are open through the inlet port  5  and the outlet port  6 . As shown in  FIG. 2  and  FIG. 3 , the ultraviolet sterilizer  10   a  includes an emitting portion  20   a  and a reflecting portion  30   a . The emitting portion  20   a  is disposed at the outer peripheral portion of the cylindrical casing  40   a , and serves as an ultraviolet ray source. The reflecting portion  30   a  is disposed on the inner surface of the cylindrical casing  40   a , and reflects ultraviolet ray. A direction from the inlet port  5  toward the outlet port  6  is defined as an outflow direction. The ultraviolet sterilizer  10   a  is disposed inside the casing  12  such that the outflow direction agrees with the flow direction. That is, the outflow direction and the flow direction are the same direction as an air flow direction Da shown in  FIG. 2 . Hereinafter, the shape of a cross section taken along a plane perpendicular to the flow direction and the outflow direction is simply referred to as a cross-sectional shape. The cross-sectional shape corresponds to a front view when viewed from the inlet port  5  side in the axial longitudinal direction of the cylindrical casing  40   a . In Embodiment 1, it is assumed that the thickness d of the ultraviolet sterilizer  10   a  along the air flow direction Da is 1 cm or 10 cm. 
     The broken line arrows  7  in  FIG. 2  and  FIG. 3  indicate fluxes of ultraviolet ray that are emitted from the emitting portion  20   a  and that are reflected on reflectors  3  and also indicate the traveling directions of the fluxes of ultraviolet ray. The broken line arrows  7  in  FIG. 2  illustrate the optical axes of the fluxes of ultraviolet ray and the traveling directions of the fluxes of ultraviolet ray in a simplified manner. The broken line arrows  7  in  FIG. 3  illustrate the fluxes of ultraviolet ray and the traveling directions of the fluxes of ultraviolet ray. The emitting portion  20   a  is to emit a flux of ultraviolet ray, that is, a flux of rays; however, hereinafter, a flux of ultraviolet ray that the emitting portion  20   a  emits is also simply referred to as ultraviolet ray. 
     The cross-sectional shape of the cylindrical casing  40   a  is a regular dodecagonal shape. The cross-sectional view is the front view when viewed from the inlet port  5  side in the axial longitudinal direction of the cylindrical casing  40   a . The emitting portion  20   a  is disposed at the outer peripheral portion of the cylindrical casing  40   a . More specifically, the emitting portion  20   a  is disposed at a location corresponding to one of the sides of the regular dodecagonal shape that is the cross-sectional shape of the cylindrical casing  40   a . The emitting portion  20   a  includes one or more ultraviolet ray emitting elements (not shown), and emits ultraviolet ray in a direction perpendicular to the outflow direction and toward the inner side of the cylindrical casing  40   a . The emitting portion  20   a  in Embodiment 1 is a UV-LED light source in which a collimate lens that is able to emit parallel rays having a wavelength of 254 nm at 0.1 W/cm 2  to 5.0 W/cm 2  is installed. The UV-LED light source that serves as the emitting portion  20   a  desirably emits parallel rays having a wavelength of 254 nm at 0.4 W/cm 2 . 
     The reflecting portion  30   a  is disposed on the inner surface of the cylindrical casing  40   a  of which the cross-sectional shape is a regular dodecagonal shape. The reflecting portion  30   a  is provided such that the cross-sectional shape is a regular dodecagonal annular shape. In the reflecting portion  30   a , at least part of the shape of a surface that is a surface that reflects ultraviolet ray is a prism shape. The reflecting portion  30   a  reflects ultraviolet ray, emitted from the emitting portion  20   a , multiple times on a plane perpendicular to the outflow direction, that is, along the radial direction of the cylindrical casing  40   a . The plane perpendicular to the outflow direction, on which ultraviolet ray is reflected, has a thickness corresponding to a flux of ultraviolet ray that is emitted in form of parallel rays. 
     The reflecting portion  30   a  includes the plurality of reflectors  3 A to  3 J that reflect ultraviolet ray. The reflectors  3 A to  3 K respectively constitute the sides of the regular dodecagonal shape that is the cross-sectional shape of the reflecting portion  30   a . That is, as shown in  FIG. 3 , the reflectors  3 A to  3 K are respectively disposed at the locations of the eleven sides of the regular dodecagonal shape that is the cross-sectional shape of the reflecting portion  30   a , and a line segment that connects an emitting portion  20   a -side end of the reflector  3 F to an emitting portion  20   a -side end of the reflector  3 G is a remaining one side. Hereinafter, the reflectors  3 A to  3 K are also simply collectively referred to as the reflectors  3  or any one of the reflectors  3 A to  3 K is also simply referred to as the reflector  3 . 
     As shown in  FIG. 4 , each reflector  3  includes a flat part  31  along the inner surface of the cylindrical casing  40   a  and a reflecting part  32  located on the inner surface side of the flat part  31 . That is, each reflector  3  is provided such that the thin-plate flat part  31  and the reflecting part  32  having a prism-shaped surface are integrally formed. 
     In the flat part  31 , a flat surface  31   a  that is a surface facing the inner surface of the cylindrical casing  40   a  is flat. The cross-sectional shape of the reflecting part  32  is a shape such that right-angled triangles each having a hypotenuse at an inclination angle of α relative to the flat surface  31   a  are arranged side by side, and a surface corresponding to each hypotenuse serves as a reflecting surface  32   a  that reflects ultraviolet ray. The inclination angle α of each of the reflectors  3 A to  3 J is set in advance such that ultraviolet ray travels widely over the entire area inside the cylindrical casing  40   a . In Embodiment 1, the surface shape of the reflecting part  32  having a cross-sectional shape such that right-angled triangles are arranged side by side is referred to as prism shape. 
     The inclination angle α and inclination direction of the reflecting surface  32   a  relative to the flat surface  31   a  of each reflector  3  will be specifically described. On the inner surface of the cylindrical casing  40   a , the reflector  3 A is provided at a location facing the emitting portion  20   a , and the reflectors  3 B to  3 K are provided clockwise from the location at which the reflector  3 A is provided. The emitting portion  20   a  is disposed such that ultraviolet ray to be emitted is vertically emit to the reflector  3 A. Since the cross-sectional shape of the ultraviolet sterilizer  10   a  is a regular dodecagonal shape, there are the facing reflectors  3  for the respective reflectors  3 . 
     As shown in  FIG. 3 , each of the reflector  3 A, the reflector  3 G, the reflector  3 I and the reflector  3 J has a prism shape such that the inclination angle α is 15° and upward sloping. Each of the reflector  3 B, the reflector  3 C, the reflector  3 E and the reflector  3 K has a prism shape such that the inclination angle α is 15° and downward sloping. The reflector  3 D has a prism shape such that the inclination angle α is 7.5° and upward sloping. The reflector  3 H has a prism shape such that the inclination angle α is 7.5° and downward sloping. The reflector  3 F has a flat surface. 
       FIG. 5  is a diagram regarding an incident angle of light and a reflection angle of the light.  FIG. 6  is a schematic diagram that shows an inclination angle of the reflecting surface  32   a  relative to the flat surface  31   a  in the case where ultraviolet ray vertically enters the reflector  3 .  FIG. 7  is a schematic diagram that shows an inclination angle of the reflecting surface  32   a  relative to the flat surface  31   a  in the case where ultraviolet ray is vertically reflected from the reflector  3 . 
     As shown in  FIG. 5 , when light passes through the air and is reflected by a metal plate, or the like, the law of reflection, that is, the incident angle of incident light  71  is equal to the reflection angle of reflected light  72 , holds. In  FIG. 5 , the incident angle and the reflection angle are denoted by β. Each of the incident angle and the reflection angle is defined as an angle between the traveling direction of corresponding light and a normal  73  that is the perpendicular to the reflecting surface  32   a.    
     As shown in  FIG. 6 , in the case where the inclination angle α is set, when ultraviolet ray vertically enters the flat surface  31   a  of the reflector  3 , the inclination angle α is equal to the incident angle and the reflection angle. For this reason, by providing the reflecting surface  32   a  having the inclination angle α that is the same as the reflection angle commensurate with a direction in which ultraviolet ray is intended to be reflected and causing the ultraviolet ray to vertically enter the flat surface  31   a , it is possible to control the traveling direction of the reflected light  72  relative to the incident light  71 . 
     As shown in  FIG. 7 , when ultraviolet ray is intended to be reflected vertically relative to the flat surface  31   a  of the reflector  3 , the reflecting surface  32   a  having the inclination angle α that is the same as the reflection angle commensurate with the reflected light  72  vertical to the flat surface  31   a  is provided. By causing ultraviolet ray to enter the reflecting surface  32   a  at the incident angle that is the same as the inclination angle α, it is possible to control the traveling direction of the reflected light  72  relative to the incident light  71 . 
       FIG. 8  is a schematic diagram for showing an inclination angle required to reflect ultraviolet ray that has vertically entered the reflector  3  that constitutes one of the sides of the polygonal shape that is the cross-sectional shape of the reflecting portion  30   a , to the reflector  3  that constitutes a specified one of the sides.  FIG. 8  illustrates a point at which ultraviolet ray is generated as a light flux generating point s, and illustrates a point on the reflector  3 A, at which the ultraviolet ray emitted from the light flux generating point s enters and is reflected by the reflector  3 A, as a light flux reflecting point a. In  FIG. 8 , among points that ultraviolet ray reflected at the light flux reflecting point a reaches and is reflected, the point on the reflector  3 E is illustrated as a light flux reflecting point e, and the point on the reflector  3 F is illustrated as a light flux reflecting point f. In addition, in  FIG. 8 , the center of the regular dodecagonal shape that is the cross-sectional shape of the reflecting portion  30   a  is shown as a center portion m. An inclination angle required to reflect ultraviolet ray that has vertically entered certain one of the reflectors  3 , to another one of the reflectors  3  will be described with reference to  FIG. 8 . 
     Initially, a situation in which ultraviolet ray vertically enters the reflector  3 A and is reflected to the reflector  3 F that is the fifth reflector in the clockwise direction will be described. As shown in  FIG. 8 , a triangle formed by connecting the light flux generating point s, the light flux reflecting point a and the center portion m is an isosceles triangle having an angle sma of 150° since a distance between m and s and a distance between m and a are the radius of a circle connecting the vertices of the regular dodecagonal shape. For this reason, the angle mas is 15°. 
     When ultraviolet ray that has vertically entered the reflector  3 A is reflected to the reflector  3 F, an angle obtained by adding the incidence angle and the reflection angle with each other needs to be the angle mas, so the incident angle and the reflection angle each are 7.5°. Thus, the ultraviolet sterilizer  10   a  includes the reflector  3 A having the upward-sloping reflecting surface  32   a  at an inclination angle of 7.5°, so it is possible to reflect ultraviolet ray that has vertically entered the reflector  3 A, to the reflector  3 F. 
     Next, the case where ultraviolet ray vertically enters the reflector  3 A and is reflected by the fourth reflector  3 E in the clockwise direction will be described. As shown in  FIG. 8 , a triangle that connects the center portion m, the light flux reflecting point a and the light flux reflecting point e is an isosceles triangle having an angle ema of 150° since a distance between m and a and a distance between m and e each are equal to the radius of the circle connecting the vertices of the regular dodecagonal shape. For this reason, the angle mae is calculated as 15°. 
     When ultraviolet ray that has vertically entered the reflector  3 A is reflected to the reflector  3 E, the incident angle that is the angle sam and the reflection angle that is the angle mae each are 15°. Thus, by providing the ultraviolet sterilizer  10   a  with the reflector  3 A having the upward-sloping reflecting surfaces  32   a  at an inclination angle of 15°, it is possible to reflect ultraviolet ray that has vertically entered the reflector  3 A, to the reflector  3 E. 
       FIG. 9  is a schematic diagram for showing an inclination angle required to vertically reflect ultraviolet ray from the reflector  3  that constitutes one of the sides of the polygonal shape that is the cross-sectional shape of the reflecting portion  30   a , to the reflector  3  that constitutes a specified one of the sides.  FIG. 9 , as well as  FIG. 8 , shows the light flux generating point s, the light flux reflecting point a, the light flux reflecting point e and the center portion m. In  FIG. 9 , a point on the reflector  3 J, at which ultraviolet ray that has been reflected at the light flux reflecting point e reaches and is reflected by the reflector  3 J, is illustrated as a light flux reflecting point j. 
     An inclination angle required to vertically reflect ultraviolet ray that has entered a certain one of the reflectors  3 , to another one of the reflectors  3  will be described with reference to  FIG. 9 . A central angle obtained by dividing 360° that is the angle of the center of the regular dodecagonal shape into twelve that is the number of angles of the polygonal shape is 30°. For this reason, in the regular dodecagonal shape, a certain one of the sides and the sixth side from that side in the clockwise direction are definitely parallel to each other and face each other. Thus, when ultraviolet ray is vertically reflected from a certain one of the sides, the reflected ultraviolet ray definitely vertically enters the flat surface  31   a  of the facing reflector  3  of the regular dodecagonal shape. Therefore, a situation in which ultraviolet ray from the reflector  3 A enters the reflector  3 E, the entered ultraviolet ray is reflected from the reflector  3 E to a direction perpendicular to the flat surface  31   a  and enters the reflector  3 J located at a facing surface in the regular dodecagonal shape will be described with reference to  FIG. 9 . 
     As shown in  FIG. 9 , a triangle obtained by connecting the center portion m, the light flux reflecting point a and the light flux reflecting point e is an isosceles triangle having an angle ema of 150° since a distance between m and a and a distance between m and e each are the radius of a circle obtained by connecting the vertices of the regular dodecagonal shape and are equal to each other. For this reason, the angle aem is calculated as 15°. A triangle obtained by connecting the center portion m, the light flux reflecting point e and the light flux reflecting point j is an isosceles triangle having an angle jme of 150° since a distance between m and e and a distance between m and j each are the radius of a circle having a regular dodecagonal shape as vertices and are equal to each other. For this reason, the angle mej is calculated as 15°. 
     When ultraviolet ray that has been reflected by the reflector  3 A and then vertically reflected by the reflector  3 E relative to the flat surface  31   a  is reflected to the reflector  3 J located at a facing surface in the regular dodecagonal shape, the incident angle that is the angle mea and the reflection angle that is the angle mej each are 15°. Thus, by providing the ultraviolet sterilizer  10   a  with the reflector  3 E having the downward-sloping reflecting surfaces  32   a  at an inclination angle of 15°, it is possible to reflect ultraviolet ray that has been vertically reflected relative to the flat surface  31   a  of the reflector  3 E, to the reflector  3 J located at the facing surface of the regular dodecagonal shape. 
     Based on the above-described method of calculating the angle of each reflecting surface  32   a  of the reflector  3  relative to the incident angle and the reflection angle, the shape each the reflecting surface  32   a  of each reflector  3  as described above is prepared as follows in Embodiment 1. 
     Each of the reflector  3 A, the reflector  3 G, the reflector  3 I and the reflector  3 J has a prism shape such that the inclination angle α is 15° and upward sloping. 
     Each of the reflector  3 B, the reflector  3 C, the reflector  3 E and the reflector  3 K has a prism shape such that the inclination angle α is 15° and downward sloping. 
     The reflector  3 D has a prism shape such that the inclination angle α is 7.5° and upward sloping. 
     The reflector  3 H has a prism shape such that the inclination angle α is 7.5° and downward sloping. 
     The reflector  3 F has a flat shape. 
     With the reflecting portion  30   a  prepared as described above, starting from a situation in which ultraviolet ray is caused to vertically enter the reflector  3 A, the ultraviolet ray is reflected by all the reflectors  3  along the radial direction in order of the reflector  3 A, the reflector  3 E, the reflector  3 J, the reflector  3 C, the reflector  3 H, the reflector  3 D, the reflector  3 I, the reflector  3 B, the reflector  3 G, the reflector  3 K and the reflector  3 F. Since the surface shape of the reflector  3 F is a flat shape, ultraviolet ray that vertically enters from the reflector  3 K is totally reflected by the reflector  3 F, and is vertically reflected to the reflector  3 K. After that, based on the relation between the incident angle and the reflection angle, the ultraviolet ray is reflected in the reverse order, that is, in order of the reflector  3 K, the reflector  3 G, the reflector  3 B, the reflector  3 I, the reflector  3 D, the reflector  3 H, the reflector  3 C, the reflector  3 J, the reflector  3 E and the reflector  3 A, and further continues to be reflected along the radial direction. 
     That is, in the ultraviolet sterilizer  10   a , ultraviolet ray that has vertically entered the reflector  3 A alternately repeats reflection in the traveling direction indicated by the broken line arrows  7  in  FIG. 3  and reflection in the traveling direction reverse to the broken line arrows  7 . As a result, as shown in  FIG. 3 , ultraviolet ray emitted from the emitting portion  20   a  of the ultraviolet sterilizer  10   a  is reflected all over the area through which air passes in the ultraviolet sterilizer  10   a . In this way, the ultraviolet sterilizer  10   a  forms a screen-shaped sterilizing light screen based on ultraviolet ray. That is, the ultraviolet sterilizer  10   a  forms the screen-shaped sterilizing light screen based on ultraviolet ray inside the cylindrical casing  40   a , so it is possible to sterilize air all over the area perpendicular to the outflow direction. That is, with the ultraviolet sterilizer  10   a , the irradiance of ultraviolet ray inside the cylindrical casing  40   a  increases as compared to the case where ultraviolet ray is not reflected, so it is possible to obtain high sterilizing effect. 
     Incidentally, microbes in the air are suspended while being adherent to cough, sputum, dust, or the like; however, inside the ultraviolet sterilizer  10   a , ultraviolet ray is reflected at multiple angles, so the shade of a deposit reduces. For this reason, with the ultraviolet sterilizer  10   a , ultraviolet ray is emit to further more microbes, and it is possible to efficiently sterilize air. 
       FIG. 10  is a graph that shows the relation between a distance from the emitting portion  20   a  that is the ultraviolet ray source and an intensity of ultraviolet ray. The intensity of light attenuates in accordance with the inverse-square law when light is divergently emitted from a point light source. On the other hand, parallel rays having strong directivity do not diverge and travel with an equal irradiation area, so the intensity is difficult to attenuate. 
     In this respect, with the ultraviolet sterilizer  10   a , since the emitting portion  20   a  emits ultraviolet ray as parallel rays having strong directivity via the collimate lens, it is possible to reduce attenuation of the intensity of ultraviolet ray as shown by the graph L indicated by the continuous line in  FIG. 10 . That is, ultraviolet ray that is reflected on the reflectors  3  of the ultraviolet sterilizer  10   a  just decreases in irradiation intensity due to reflection and travels with almost no attenuation even passing through the air. Thus, ultraviolet ray is emit to the entire inner surface of the reflecting portion  30   a  of the ultraviolet sterilizer  10   a , and the intensity of the ultraviolet ray increases as compared to the intensity at the time of emission in accordance with the number of reflections. As a result, in all the inside of the cylindrical casing  40   a  of the ultraviolet sterilizer  10   a , the intensity of ultraviolet ray increases in accordance with the number of reflections, so it is possible to increase the efficiency of sterilizing microbes contained in the air. If the emitting portion  20   a  is not equipped with the collimate lens, or the like, the intensity of ultraviolet ray attenuates in accordance with the inverse-square law as shown by the graph N indicated by the broken line in  FIG. 10 . 
       FIG. 11  is a table that shows an ultraviolet ray irradiance at the level of 1 mm above each reflector  3  shown in  FIG. 3 . An increase in ultraviolet ray irradiance due to reflection at each reflector  3  will be specifically described with reference to  FIG. 11 . 
     In Embodiment 1, an ultraviolet ray irradiance provided by the ultraviolet sterilizer  10   a  is defined as the following mathematical expression 1. Here, an ultraviolet ray intensity is a quantity obtained by accumulating the intensity of ultraviolet ray that enters each reflector  3  and the intensity of ultraviolet ray that has been reflected on each of the reflectors  3  in the case where the total radiant flux of ultraviolet ray emitted from the emitting portion  20   a  has been reflected until the total radiant flux attenuates to 1%. The reflectance of ultraviolet ray is 95%. For example, when the emitting portion  20   a  emits parallel rays at 0.4 W/cm 2  and the area of the emitting portion  20   a  is 3 cm 2  (1 cm×3 cm), the total radiant flux of ultraviolet ray is 1.2 W. When the thickness of the ultraviolet sterilizer  10   a  in an air course direction is 1 cm, an air velocity caused by the air-sending device  15  is 3 m/s, so an irradiation time is 0.0033 s.
 
[Math. 1]
 
(Ultraviolet Light Irradiance)=(Ultraviolet Light Intensity)×(Irradiation Time)   (1)
 
     Ultraviolet light emitted from the emitting portion  20   a  continue to be reflected on the reflectors  3  until the total radiant flux attenuates to 1% or below, and ultraviolet ray is emit all over the cross section of the ultraviolet sterilizer  10   a . For this reason, an ultraviolet ray irradiance on each reflector  3  is higher than or equal to 4.5 mW·s/cm 2  at each of the reflector  3 A, the reflector  3 E, the reflector  3 J, the reflector  3 C, the reflector  3 H, the reflector  3 D, the reflector  3 I, the reflector  3 B, the reflector  3 G and the reflector  3 K, and is higher than or equal to 2.2 mW·s/cm 2  at each of the emitting portion  20   a  and the reflector  3 F. Since the emitting portion  20   a  and the reflector  3 F each are a surface on which reflection turns back, the number of reflections is smaller than that of the other reflectors, so an ultraviolet ray irradiance is about half. 
     Since an accumulated value of irradiances of overlapping rays of ultraviolet ray is an ultraviolet ray irradiance at a portion at which rays of ultraviolet ray from the reflectors  3  to the corresponding reflectors  3  overlap, including the center portion of the ultraviolet sterilizer  10   a , an ultraviolet ray irradiance further increases. 
     As described above, the ultraviolet sterilizer  10   a  is able to keep the ultraviolet ray irradiance at 2.2 mW·s/cm 2  or above over the entire ultraviolet sterilizer  10   a  with ultraviolet ray emitted from all surfaces corresponding to a regular dodecagonal shape in cross section. 
       FIG. 12  is a graph that shows the relation between an ultraviolet ray irradiance provided by the ultraviolet sterilizer  10   a  shown in  FIG. 3  and a survival rate (PFU/m 3 ) of airborne influenza virus. In  FIG. 12 , the ordinate axis represents the survival rate of airborne influenza virus, that is, an infectious influenza virus rate to an initial airborne influenza virus 2.5×10 5  PFU/m 3 . The abscissa axis represents the irradiance of UV-LED light having a wavelength of 254 nm. PFU is an abbreviation of plaque forming unit. 
     As shown in  FIG. 12 , airborne influenza virus exponentially decreases in survival rate with an increase in ultraviolet ray irradiance. For example, the survival rate of airborne influenza virus is 0.01 at an ultraviolet ray irradiance of 2 mW·s/cm 2 . That is, when ultraviolet ray having a wavelength of 254 nm is emit to airborne influenza virus at 2 mW·s/cm 2 , it is possible to deactivate 99% of the airborne influenza virus. 
     In this respect, the ultraviolet sterilizer  10   a  is able to keep the ultraviolet ray irradiance at 2 mW·s/cm 2  or above in all the area in the cross section inside the ultraviolet sterilizer  10   a  with only the total radiant flux 1.2 W of ultraviolet ray emitted from the emitting portion  20   a . It is possible to deactivate 99% of airborne influenza virus at 2 mW·s/cm 2  or above. That is, with the ultraviolet sterilizer  10   a , it is possible to increase the irradiance of ultraviolet ray inside the cylindrical casing  40   a  as compared to when ultraviolet ray is not reflected, so a high sterilizing effect is obtained. 
     That is, different from the ultraviolet sterilizer  10   a , in the case of the existing ultraviolet sterilizer that does not reflect ultraviolet ray, ultraviolet ray emitted from the emitting portion is not reflected, so the ultraviolet ray is emit to only the center portion (about 13% of the cross section) of the ultraviolet sterilizer. That is, with the ultraviolet sterilizer  10   a , in comparison with the case where ultraviolet ray is not reflected, it is possible to increase the irradiance of ultraviolet ray in all the space inside the cylindrical casing  40   a , so a high sterilizing effect is obtained. 
     As described above, the ultraviolet sterilizer  10   a  according to Embodiment 1 reflects ultraviolet ray in all over the area in the cross section of the ultraviolet sterilizer  10   a , so it is possible to increase the irradiance of ultraviolet ray. For this reason, by causing airborne microbes in the air to pass through the ultraviolet sterilizer  10   a , it is possible to efficiently sterilize the air. 
     Since the existing ultraviolet sterilizer is configured such that only parts of the sides are open, there is a problem that installation of the ultraviolet sterilizer in a duct or an air-conditioning apparatus causes a high pressure loss due to the ultraviolet sterilizer and, as a result, the ultraviolet sterilizer is not applicable to the air-conditioning apparatus. In this respect, since the ultraviolet sterilizer  10   a  is configured such that the sides of the cylindrical casing  40   a  are open through the inlet port  5  and the outlet port  6 , installation of the ultraviolet sterilizer  10   a  in various devices does not increase a pressure loss. 
     That is, since the ultraviolet sterilizer  10   a  is configured such that the entire areas of the sides of the cylindrical casing  40   a  are open and an opening area relative to the air flow direction Da is large, it is possible to prevent an increase in pressure loss resulting from installation of the ultraviolet sterilizer in various devices. Thus, the ultraviolet sterilizer  10   a  is allowed to be suitably mounted in a duct or an air-conditioning apparatus. 
     In addition, since the emitting portion  20   a  and reflectors  3  of the ultraviolet sterilizer  10   a  are disposed such that ultraviolet ray is emitted or reflected vertically relative to the air flow direction Da, the optical axis of the ultraviolet ray is emitted or reflected vertically relative to the air flow direction Da, as shown in  FIG. 2 . Therefore, even with a casing of which the sides are open, like the cylindrical casing  40   a , ultraviolet ray emitted from the emitting portion  20   a  is not reflected to the outside of the ultraviolet sterilizer  10   a  relative to the air flow direction Da, and it is not necessary to consider the degradation of members or the influence on a human body due to leakage of ultraviolet ray. 
     In addition, since the thickness d of the ultraviolet sterilizer  10   a  in the air flow direction Da is reduced, an ultraviolet ray irradiation distance in the air flow direction Da is not extended unlike the ultraviolet sterilizer of Patent Literature 2, so it is possible to prevent an increase in the size of a device, and the ultraviolet sterilizer  10   a  is suitably applicable to an air-conditioning apparatus, and other devices. In this way, with the ultraviolet sterilizer  10   a  that allows compact design, it is possible to efficiently perform sterilization with a short distance and to reduce the size of a device to be mounted. 
     [Installation Method] 
     A method of installing the ultraviolet sterilizer  10   a  inside the casing  12  of the air-conditioning apparatus  11   a  will be described. As shown in  FIG. 3  and  FIG. 4 , since the reflectors  3  of the ultraviolet sterilizer  10   a  have a prism shape, dust, or other substances, suspended in the air can collide with and adhere to the prism-shaped cross section end of the reflecting portion  30   a  at the inlet port  5  side. For this reason, the prism-shaped cross section end of the reflecting portion  30   a  at the inlet port  5  side is desirably treated with soil-resistant coating. For example, a coating using a paint containing modified polyvinyl alcohol and a crosslinking agent, a coating using a paint containing carboxymethyl-cellulose, polyethylene glycol and a crosslinking agent, or other coatings, may be employed as the soil-resistant coating. 
     [Ultraviolet Light Source] 
       FIG. 13  is a table that shows an energy (eV), a sterilizing effect and a sterilizing effect per 1 eV by wavelength where a plurality of wavelengths of ultraviolet ray is set in the range of 200 nm to 360 nm. The emitting portion  20   a  that is the ultraviolet ray source will be described with reference to  FIG. 13 . 
     Initially, the wavelength range of ultraviolet ray will be described. Light is a kind of electromagnetic wave, and has an energy. The energy is calculated from the following mathematical expression 1. 
     
       
         
           
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                     hv 
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                       h 
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                         c 
                         λ 
                       
                     
                   
                 
               
               
                 
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     In the mathematical expression 1, E is the energy of ultraviolet ray, h is a Planck constant (6.63×10−34 J·s=4.1×10−15 eV·s), ν is the frequency of the ultraviolet ray, c is the velocity of light (3.0×108 m/s), and λ is the wavelength of the ultraviolet ray.  FIG. 13  shows an energy E by wavelength in the range of 200 nm to 360 nm. As the wavelength λ increases, an energy per one electron reduces. 
     Incidentally, ultraviolet ray having a wavelength of 200 nm to 360 nm takes a proliferating ability by acting on nucleic acid that is the protoplasm of bacteria to inhibit replication of DNA, thus sterilizing microbes. Ultraviolet light having a wavelength of 200 nm to 360 nm kills bacteria by destroying proteins, and other substances, that are formative substances of cytoplasm and cell membranes, thus sterilizing microbes. According to  FIG. 13  that shows a sterilizing effect by wavelength in the range of 200 nm to 360 nm, a range near a wavelength of 260 nm has the highest sterilizing effect. 
     When the sterilizing effect per 1 eV of each wavelength increases, it is recognized that sterilization is efficiently performed. That is, although the wavelength range of ultraviolet ray having the effect of sterilizing microbes is 200 nm to 360 nm, ultraviolet ray having a wavelength of 200 nm to 360 nm may be used as the ultraviolet ray that the emitting portion  20   a  emits. Desirably, the emitting portion  20   a  should be configured to emit ultraviolet ray that has a wavelength of 200 nm to 300 nm and that provides a relatively high sterilizing effect. More desirably, the emitting portion  20   a  should be configured to emit ultraviolet ray that has a wavelength of 240 nm to 290 nm and that is able to efficiently perform sterilization while reducing a consumption energy. 
     [Ultraviolet Light Emitting Element] 
     Next, the ultraviolet ray emitting element of the emitting portion  20   a  will be described. An ultraviolet ray emitting diode (ultraviolet LED) configured to emit ultraviolet ray that has a wavelength of 200 nm to 360 nm and that provides the effect of sterilizing microbes may be used as the ultraviolet ray emitting element. More desirably, the wavelength of ultraviolet ray that the ultraviolet ray emitting element emits should be 240 nm to 290 nm. 
     The emitting portion  20   a  that is the ultraviolet ray source has a structure configured to emit parallel rays having strong directivity in addition to the ultraviolet ray emitting element as an ultraviolet ray emitter. In Embodiment 1, the structure that the collimate lens is disposed inside the ultraviolet ray emitting element is employed as the structure configured to emit parallel rays having strong directivity; however, the structure configured to emit parallel rays having strong directivity is not limited to this structure. Instead of the collimate lens, for example, a Fresnel lens may be provided. The emitting portion  20   a  may have a structure such that a reflector is provided behind a light source. 
     The ultraviolet ray emitting element, the collimate lens, and other components, may be packaged or modularized as the ultraviolet ray source. By packaging or modularizing the ultraviolet ray emitting element, the collimate lens, and other components, simple installation of the emitting portion  20   a  is possible. 
     One or more ultraviolet ray emitting elements are disposed so as to be able to emit parallel rays of ultraviolet ray from the entire surface defined by the sides along the air flow direction Da and one of the sides of the regular dodecagonal shape that is the cross-sectional shape, in the reflecting portion  30   a  at which the emitting portion  20   a  is installed. 
     [Method of Preparing Reflectors] 
     Next, a method of preparing the reflectors  3  of which the surface has a prism shape will be described. 
     Initially, the prism shape of each reflector  3  will be described. An average pitch Ap that is the length of the flat surface of each right-angled triangle in the prism shape shown in  FIG. 4  just needs to be 0.01 mm to 10 mm, and desirably 0.1 mm to 10 mm. 
     Subsequently, the base material of each reflector  3  will be described. An ultraviolet ray reflecting material means, for example, a material having a reflectance of 40% or above, desirably, 60% or above and, more desirably, 70% or above on, for example, ultraviolet ray having a wavelength of 250 nm to 270 nm, particularly, ultraviolet ray of 265 nm. Examples of the ultraviolet ray reflecting material that may be suitably used in the invention include chromium (ultraviolet ray reflectance: about 50%), platinum (ultraviolet ray reflectance: about 50%), rhodium (ultraviolet ray reflectance: about 65%), magnesium carbonate (ultraviolet ray reflectance: about 75%), calcium carbonate (ultraviolet ray reflectance: about 75%), magnesia oxide (ultraviolet ray reflectance: about 90%) and aluminum (ultraviolet ray reflectance: about 90%). Additionally, when a surface treatment, such as an electroplating method and a vapor deposition method, is applied to these ultraviolet ray reflecting materials, the surface has a high reflectance. 
     Since aluminum is excellent in workability, aluminum may be suitably used as the ultraviolet ray reflecting material. By further coating aluminum with magnesium fluoride MgF 2  as a surface treatment for aluminum, it is possible to protect the surface of the aluminum material and increase the reflectance in the ultraviolet range. 
     Subsequently, a method of molding each reflector  3  of which the surface has a prism shape will be described. Initially, a die having the shape of the reflector  3  is prepared. A material plate for the reflector  3 , cut into a length approximately equal to the thickness d of the cylindrical casing  40   a  in the air flow direction Da is put on the prepared die, the put material plate is worked by mechanical bending, such as hand bending, pressing, roll bender and roll forming. The worked material plate is bent into a polyhedral shape. Thus, the reflecting portion  30   a  is formed. Each reflector  3  may be formed by cutting and working a metal plate having a thickness larger than an average depth. 
     Furthermore, each reflector  3  may be prepared as follows. A base having the same shape as the reflector  3  is molded by using a material other than the above-described metals, and then metal powder paste is evaporated onto the surface of the base. In this case, a die having the shape of the reflector  3  is prepared, and a member that corresponds to the base may be formed by using a resin material by press working, injection molding, compression molding, or the like. After that, metal powder paste that becomes a reflecting material is evaporated onto the surface layer of the base, thus forming the reflector  3 . In this way, when the reflector  3  is formed by using a combination of a resin material and evaporation of metal powder paste, it is advantageous in that material cost is reduced as compared to when a metal plate is used and this combination is easier to be molded than the metal material. 
     A thermoplastic resin, such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET) and ABS resin, may be used as a resin material for molding a base. The base of each reflector  3  may be molded by using a thermosetting resin, such as phenolic resin, amino resin, epoxy resin and urethane resin, synthetic rubber, such as polyisoprene and butadiene, and synthetic fiber, such as nylon, vinylon, acrylic fiber and rayon, that are plastic materials other than the above. 
     In Embodiment 1, the case where the cross-sectional shape of the ultraviolet sterilizer  10   a , that is, the front view when viewed from the inlet port  5  side in the axial longitudinal direction of the cylindrical casing  40   a , is a regular dodecagonal shape is described; however, the cross-sectional shape of the ultraviolet sterilizer  10   a  is not limited to this. As long as the reflectors  3  are disposed and the reflecting surfaces  32   a  are worked such that ultraviolet ray is reflected all over the area in the cross section of the ultraviolet sterilizer  10   a , that is, ultraviolet ray is reflected along the radial direction of the cylindrical casing  40   a , the cross-sectional shape of the ultraviolet sterilizer  10   a  may be a regular polygonal shape having the different number of vertices, a polygonal shape with sides having different lengths or a polygonal shape in which interior angles are freely set. 
     The shape in which right-angled triangles having a hypotenuse inclined at the inclination angle α relative to the flat part  31  are arranged side by side is illustrated as the prism shape of the surface of each reflector  3 ; however, the prism shape is not limited to this shape. As long as a shape allows ultraviolet ray to be reflected to the intended reflector  3 , another shape may be employed. In addition, in Embodiment 1, the case where the reflecting part  32  of each reflector  3  is the prism shape is illustrated; however, the reflecting part  32  is not limited to this shape. The reflecting surfaces  32   a  of each reflecting part  32  each may be formed so as to be inclined at a set angle relative to the flat surface  31   a  of the flat part  31 . That is, the cross-sectional shape of the reflecting part  32  may be a single right-angled triangular shape having a hypotenuse inclined at the inclination angle α relative to the flat part  31 . 
     In Embodiment 1, the ultraviolet sterilizer  10   a  in which the single emitting portion  20   a  is installed at the outer peripheral portion is illustrated; however, the ultraviolet sterilizer  10   a  is not limited to this. The ultraviolet sterilizer  10   a  may be configured such that a plurality of emitting portions  20   a  is installed. In this case, the emitting portions  20   a  just need to be installed at certain intervals. In this way, when the plurality of emitting portions  20   a  is installed in the ultraviolet sterilizer  10   a , the outgoing strength increases, so it is possible to increase the sterilizing effect. In Embodiment 1, the structure that the emitting portion  20   a  vertically emits ultraviolet ray to the facing reflector  3  is described. As long as the prism shape of each reflector  3  is able to be designed such that ultraviolet ray is repeatedly reflected inside the cylindrical casing  40   a , the emitting portion  20   a  may be configured to emit ultraviolet ray to the reflector  3  other than the reflector  3 A. In addition, the air-sending device  15  may be arranged inside the casing  12 . 
     Example 
       FIG. 14  is a graph that shows sterilizing effects as the experimental results of an example according to Embodiment 1.  FIG. 15  is a graph that shows pressure losses as experimental results of the example according to Embodiment 1. In the present example, to examine the sterilizing effect for microbes,  staphylococcus  epidermidis was suspended in the air of the inlet port  5  by spraying  staphylococcus  epidermidis into the air, and then a temporal change in the survival rate of  staphylococcus  epidermidis in each of Experiment 1, Experiment 2, Comparative Experiment 1 and Comparative Experiment 2 with different experimental conditions was investigated. 
     In each experiment, the diameter of the casing  12  was set to 100 mm, and the velocity of flow of air was set to 3 m/s. An ultraviolet diode that is able to emit ultraviolet ray having a wavelength of 254 nm in parallel rays at an irradiation intensity of 0.01 W/cm 2  to 5.0 W/cm 2  was used as the emitting portion  20   a  that is the ultraviolet ray source. The ultraviolet diode that serves as the emitting portion  20   a  desirably emits ultraviolet ray at an irradiation intensity of 0.04 W/cm 2 . In addition, a regular dodecagonal aluminum plate having an average pitch Ap of 1 mm was used as each reflector  3 . The ultraviolet sterilizer  10   a  having a thickness d of 1 cm in the air flow direction Da was used.  Staphylococcus epidermidis  was sprayed by nebulizer into the air, and the number of bacteria in the air at the inlet port  5  was adjusted to 10 5  CFU (Colony Forming Unit)/cm 3 . 
     Experiment 1 was carried out under the experimental condition that the ultraviolet sterilizer  10   a  is installed in the casing  12  and is operated. Experiment 2 was carried out under the experimental condition that the ultraviolet sterilizer  10   a  is installed in the casing  12  and is stopped. Comparative Experiment 1 was carried out under the experimental condition that the ultraviolet sterilizer  10   a  in which no reflector  3  is installed is installed in the casing  12  and is operated. Comparative Experiment 2 was carried out under the experimental condition that the ultraviolet sterilizer  10   a  in which the opening area of the inlet port  5  and the opening area of the outlet port  6  are narrowed to 10% is installed in the casing  12  and is operated. 
     The ordinate axis of  FIG. 14  represents a one-pass removal rate that is the removal rate of bacteria in the air at the time when air has passed through the ultraviolet sterilizer  10   a  once. That is, the one-pass removal rate is a value obtained by dividing a value obtained by subtracting the number of bacteria in the effluent air from the number of bacteria in the influent air, by the number of bacteria in the influent air. The ordinate axis of  FIG. 15  represents a comparative result of pressure loss at the time when air passes through the ultraviolet sterilizer  10   a . That is, in  FIG. 15 , the proportions (%) of pressure losses in the other Experiments with reference to the pressure loss in Experiment 1 are shown. 
     In Experiment 1, the pressure loss did not increase, and the number of bacteria was able to be reduced by 99%. However, in Experiment 2, the pressure loss did not increase, but the number of bacteria was just reduced by 1%. In Comparative Experiment 1, the pressure loss did not increase, but the number of bacteria was just reduced by 50%. In Comparative Experiment 2, the number of bacteria was able to be reduced by 99%, but the pressure loss was high. 
     From the above, it is understood that, only in the case of Experiment 1, there was no pressure loss and sterilization was efficiently performed. In Experiment 2 and Comparative Experiment 1, although the pressure losses did not increase, but the rates of sterilization were lower than that in the case of Experiment 1. In Comparative Experiment 2, the rate of sterilization was high, but the pressure loss was high and the air-sending device  15  stopped along the way. 
     From these results, with the experimental condition of Experiment 1 in which sterilization is performed by the ultraviolet sterilizer  10   a , it is possible to efficiently perform sterilization at the one-pass removal rate of 99% without increasing the pressure loss. That is, even when the ultraviolet sterilizer  10   a  in Embodiment 1 is mounted on the air-conditioning apparatus  11   a , the ultraviolet sterilizer  10   a  is able to perform efficient sterilization without increasing the pressure loss. 
     &lt;Alternative Embodiment&gt; 
       FIG. 16  is a schematic diagram that shows the schematic configuration of an air-conditioning apparatus according to an alternative embodiment to Embodiment 1 of the present invention.  FIG. 17  is a schematic cross-sectional view of the air-conditioning apparatus, taken along the line B-B in  FIG. 16 . The ultraviolet sterilizer  10   a  is configured such that the entire areas of the sides of the cylindrical casing  40   a  are open as described above. In the alternative embodiment, as shown in  FIG. 16  and  FIG. 17 , the inside diameter of the inlet port  5  is larger than or equal to the inside diameter of the air intake  13 , and the inside diameter of the outlet port  6  is larger than or equal to the inside diameter of the outlet opening  14 . Thus, the ultraviolet sterilizer  10   a  of the alternative embodiment is further suitably mounted in a duct or the air-conditioning apparatus. 
     The air-conditioning apparatus  110   a  of the alternative embodiment is configured such that the inside diameter of the reflecting portion  30   a  of the ultraviolet sterilizer  10   a  is larger than or equal to the outside diameter of the casing  12 . That is, since the air-conditioning apparatus  110   a  is configured such that the protrusions of the prism shape of each reflector  3  do not project into the air course of the casing  12 , there is a low possibility that dust, or other substances, suspended in the air collide with and adhere to the prism-shaped cross section end of the reflecting portion  30   a  at the inlet port  5  side. For this reason, with the air-conditioning apparatus  110   a , it is possible to reduce adhesion of dust, or other substances, to the prism-shaped cross section end of the reflecting portion  30   a  at the inlet port  5  side without applying soil-resistant coating to the cross section end. In addition, with the air-conditioning apparatus  110   a , since air does not collide with the prism-shaped cross section end of the reflecting portion  30   a  at the inlet port  5  side, it is possible to reduce the pressure loss. The air-conditioning apparatus  110   a  may also be configured such that at least part of the protrusions of the prism shape of each reflector  3  do not project into the air course of the casing  12 . 
     Embodiment 2 
       FIG. 18  is a schematic diagram that shows the schematic configuration of an air-conditioning apparatus according to Embodiment 2.  FIG. 19  is a diagram that shows the schematic cross sections of two ultraviolet sterilizers according to Embodiment 2 in layers. As shown in  FIG. 18 , the air-conditioning apparatus  11   b  according to Embodiment 2 includes the two ultraviolet sterilizers  10   a  disposed in parallel between the air intake  13  and the outlet opening  14  as an ultraviolet sterilizer  10   b . That is, the air-conditioning apparatus  11   b  has similar components to the components in the above-described Embodiment 1 except that the two ultraviolet sterilizers  10   a  are installed in the air flow direction Da. Thus, like reference numerals denote equivalent constituent members to those of the ultraviolet sterilizer  10   a  and the air-conditioning apparatus  11   a  in Embodiment 1, and the description is omitted. 
     The centers of the two ultraviolet sterilizers  10   a  in the outflow direction agree with each other, and the positions of the emitting portions  20   a  of the two ultraviolet sterilizers  10   a  are different in the outflow direction. More specifically, as shown in  FIG. 19 , in the ultraviolet sterilizer  10   b , the positions of the emitting portions  20   a  of the two ultraviolet sterilizers  10   a  are shifted by 15° about the center of the regular dodecagonal shape that is the cross-sectional shape of each reflecting portion  30   a . That is, one of the ultraviolet sterilizers  10   a  is disposed in a state rotated by 15° about the center relative to the other one of the ultraviolet sterilizers  10   a . As a result, as shown in  FIG. 19 , the optical axis of ultraviolet ray that is generated in each ultraviolet sterilizer  10   a  is not parallel to each other and does not overlap each other. That is, in the air-conditioning apparatus  11   b , the direction of ultraviolet ray that is emit to microbes suspended in the air is twice as many as that of the air-conditioning apparatus  11   a  in Embodiment 1, so the possibility that airborne microbes are hidden by deposits further decreases. For this reason, with the air-conditioning apparatus  11   b , it is possible to further improve sterilizing efficiency. 
     In Embodiment 2, the case where the two ultraviolet sterilizers  10   a  are installed in parallel is described; however, the configuration is not limited to this. The air-conditioning apparatus  11   b  may include three or more ultraviolet sterilizers  10   a  as the ultraviolet sterilizer  10   b . The ultraviolet sterilizers  10   a  just need to be disposed such that the positions of the emitting portions  20   a  in the outflow direction are shifted from one another. With this configuration, the direction of ultraviolet ray that is emit to airborne microbes further increases, and the possibility that airborne microbes are hidden by deposits further decreases, so it is possible to further improve sterilizing efficiency. 
     Embodiment 3 
       FIG. 20  is a schematic diagram that shows the schematic configuration of an air-conditioning apparatus according to Embodiment 3.  FIG. 21  is a diagram that shows a path along which ultraviolet ray travels in the schematic cross-sectional view of each ultraviolet sterilizer, taken along the line C-C in  FIG. 20 .  FIG. 22  is a diagram that shows the schematic cross sections of the two ultraviolet sterilizers according to Embodiment 3 in layers.  FIG. 23  is a schematic view that shows a velocity distribution of air in an air course. 
     As shown in  FIG. 21  and  FIG. 22 , each ultraviolet sterilizer  10   c  includes a reflecting portion  30   c  of which the cross-sectional shape that is a front view when viewed from the inlet port  5  side in the axial longitudinal direction of a cylindrical casing  40   c  is a regular hexadecagonal shape. The reflecting portion  30   c  includes the reflectors  3  that constitute the sides of the regular hexadecagonal shape. Excepting the above point, each ultraviolet sterilizer  10   c  is similar to the ultraviolet sterilizer  10   a  of the above-described Embodiment 1 and Embodiment 2. In the air-conditioning apparatus  11   c , the two ultraviolet sterilizers  10   c  are disposed in parallel in the casing  12 , and an emitting portion  20   c  that is the ultraviolet ray source of one of the ultraviolet sterilizers  10   c  is disposed in a state inclined by 45° relative to an emitting portion  20   c  of the other one of the ultraviolet sterilizers  10   c . Excepting the above point, the air-conditioning apparatus  11   c  is similar to the air-conditioning apparatus  11   b  according to the above-described Embodiment 2. Thus, like reference numerals denote equivalent constituent members to those of Embodiment 1 and Embodiment 2, and the description is omitted. 
     As shown in  FIG. 20 , the air-conditioning apparatus  11   c  according to Embodiment 3 includes the two ultraviolet sterilizers  10   c  disposed in parallel between the air intake  13  and the outlet opening  14  as an ultraviolet sterilizer  100   c.    
     As shown in  FIG. 21 , each ultraviolet sterilizer  10   c  includes the cylindrical casing  40   c , the emitting portion  20   c  and the reflecting portion  30   c . The cylindrical casing  40   c  has a regular hexadecagonal shape as the cross-sectional shape that is the front view when viewed from the inlet port  5  side in the axial longitudinal direction of the cylindrical casing  40   c . The emitting portion  20   c  is disposed at the outer peripheral portion of the cylindrical casing  40   c . The reflecting portion  30   c  is disposed on the inner surface of the cylindrical casing  40   c . The cross-sectional shape of the reflecting portion  30   c  is a regular hexadecagonal annular shape. The emitting portion  20   c  is provided at one of the sides of the regular hexadecagonal shape that is the cross-sectional shape of the reflecting portion  30   c . The emitting portion  20   c  is an ultraviolet ray emitter including an ultraviolet ray emitting element and a collimate lens. 
     The reflecting portion  30   d  includes a plurality of reflectors  3 Ac to  3 Oc that reflect ultraviolet ray. The reflectors  3 Ac to  3 Oc respectively constitute the sides of the regular hexadecagonal shape that is the cross-sectional shape of the reflecting portion  30   c . Hereinafter, the reflectors  3 Ac to  3 Oc are also simply collectively referred to as the reflectors  3  or any one of the reflectors  3 Ac to  3 Oc is also simply referred to as the reflector  3 . 
     The reflector  3 Ac is provided on the right side next to the reflector  3 Bc facing the emitting portion  20   c . The reflectors  3 Bc to  3 Oc are provided in the clockwise direction from the reflector  3 Ac. The emitting portion  20   c  emits ultraviolet ray toward the reflector  3 Ac. 
     The traveling direction of ultraviolet ray emitted from the emitting portion  20   c  in the cross section direction of the cylindrical casing  40   c  will be described with reference to  FIG. 21 .  FIG. 21  shows one of the two ultraviolet sterilizers  10   c  that constitute the ultraviolet sterilizer  100   c.    
     The surface shape of each of the reflectors  3  that constitute the regular hexadecagonal shape that is the cross-sectional shape, that is, the front view when viewed from the inlet port  5  side in the axial longitudinal direction of the cylindrical casing  40   c , is prepared as follows based on the principles of the incident angle and reflection angle of light in consideration of the inclinations of the incident light  71  and reflected light  72  relative to the flat part  31  and the reflecting part  32 , as in the case of Embodiment 1. 
     The surface shape of each of the reflector  3 Ac, the reflector  3 Ec, the reflector  3 Lc and the reflector  3 Ic is a prism shape such that the inclination angle α is 11.25° and upward sloping. 
     The surface shape of each of the reflector  3 Bc, the reflector  3 Fc and the reflector  3 Mc is a prism shape such that the inclination angle α is 11.25° and downward sloping. 
     The surface shape of the light source-side reflector of the emitting portion  20   c , as well as the surface shape of each of the reflector  3 Bc, the reflector  3 Fc and the reflector  3 Mc, is a prism shape such that the inclination angle α is 11.25° and downward sloping. 
     Each ultraviolet sterilizer  10   c  includes the reflecting portion  30   c  having the above-described reflectors  3 , and causes ultraviolet ray to enter the seventh reflector  3 Ac in the clockwise direction from the emitting portion  20   c  at 22.5°. The ultraviolet ray emitted from the emitting portion  20   c  and reflected on the reflector  3 Ac is reflected on the reflectors  3  in order of the reflector  3 Fc, the reflector  3 Lc, the reflector  3 Bc, the reflector  3 Ic, the reflector  3 Mc and the reflector  3 Ec, and enters the side at which the emitting portion  20   c  is provided, as shown in  FIG. 21 . The ultraviolet ray that has entered the emitting portion  20   c  is reflected on the light source-side reflector and further emitted toward the reflector  3 Ac. 
     That is, reflection of ultraviolet ray emitted from the emitting portion  20   c  continues repeatedly in order of the reflector  3 Ac, the reflector  3 Fc, the reflector  3 Lc, the reflector  3 Bc, the reflector  3 Ic, the reflector  3 Mc, the reflector  3 Ec and the light source-side reflector, as shown in  FIG. 21 . As a result, in the cross-sectional direction of the one ultraviolet sterilizer  10   c , ultraviolet ray emitted from the emitting portion  20   c  passes mainly through a center portion Ce inside the cylindrical casing  40   c , and there are portions to which ultraviolet ray is not emit at a peripheral portion Pe. In  FIG. 21 , a passage region Fi 1  that is a region through which ultraviolet ray emitted from the emitting portion  20   c  passes is indicated by a gray area. The passage region Fi 1  corresponds to a screen-shaped sterilizing light screen based on ultraviolet ray. 
     As shown in  FIG. 22 , the centers of the two ultraviolet sterilizers  10   c  in the outflow direction agree with each other, and the positions of the emitting portions  20   c  of the two ultraviolet sterilizers  10   c  are different in the outflow direction. More specifically, in the ultraviolet sterilizer  100   c , the emitting portion  20   c  of one of the ultraviolet sterilizers  10   c  is disposed in a state inclined by 45° relative to the emitting portion  20   c  of the other one of the ultraviolet sterilizers  10   c . For this reason, ultraviolet ray is identified in all over the area in the ultraviolet sterilizer  100   c . That is, ultraviolet ray is identified in any of the center portion Ce and the peripheral portion Pe. 
     Since ultraviolet ray of the two ultraviolet sterilizers  10   c  intensively passes through the center portion Ce inside the cylindrical casing  40   c , the irradiance is higher than that of the peripheral portion Pe inside the cylindrical casing  40   c . That is, in the air-conditioning apparatus  11   c , the irradiance of ultraviolet ray in an overlap passage region Fi 2  becomes relatively high. The overlap passage region Fi 2  is a region in which the passage region Fi 1  in one of the ultraviolet sterilizers  10   c  and the passage region Fit in the other one of the ultraviolet sterilizers  10   c  overlap. In  FIG. 22 , a difference in the irradiance of ultraviolet ray is expressed by thickening the gray color of the overlap passage region Fi 2  that is the region in which the passage regions Fi 1  overlap, as compared to the region in which the passage regions Fi 1  do not overlap. 
     As described above, with the ultraviolet sterilizer  100   c  according to Embodiment 3, it is possible to emit ultraviolet ray all over the area in the cross section of the cylindrical casing  40   c . The ultraviolet sterilizer  100   c  is able to provide a state where the irradiance of ultraviolet ray at the center portion inside the cylindrical casing  40   c  is large. 
     Incidentally, as shown in  FIG. 23 , the velocity of flow of air flowing through the casing  12  that is a cylindrical member, such as a duct having a radius of 100 mm, increases at the center portion of the casing  12  because of friction between air and the air course. 
     In this respect, with the ultraviolet sterilizer  100   c  according to Embodiment 3, even when the ultraviolet sterilizer  100   c  is mounted in the casing  12  in which the velocity of flow at the center portion increases, such as the inside of the duct, it is possible to gather ultraviolet ray at the center portion inside the cylindrical casing  40   c . Therefore, as compared to the ultraviolet sterilizer  10   a  of Embodiment 1, it is possible to improve a sterilizing effect for microbes in the air. 
     In Embodiment 3, the ultraviolet sterilizer  100   c  in which the two ultraviolet sterilizers  10   c  each including the reflecting portion  30   c  of which the cross-sectional shape that is the front view when viewed from the inlet port  5  side in the axial longitudinal direction of the cylindrical casing  40   c  is a regular hexadecagonal cross-sectional shape are disposed is described; however, the ultraviolet sterilizer  100   c  is not limited to this. That is, as long as a structure reflects ultraviolet ray on reflectors such that ultraviolet ray gathers and crosses at the center portion inside the cylindrical casing  40   c , the number of the ultraviolet sterilizers  10   c , the number of the reflectors and the prism shape of the surface of each reflector may be selectively changed. At this time, to make the optical axes of rays of ultraviolet ray not parallel to each other, the positions of the emitting portions  20   c  in the outflow direction should be shifted. The air-conditioning apparatus  11   c  may be configured such that only one ultraviolet sterilizer  10   c  is mounted. 
     Embodiment 4 
       FIG. 24  is a schematic cross-sectional view that shows the configuration of an ultraviolet sterilizer according to Embodiment 4 of the present invention. As shown in  FIG. 24 , in the ultraviolet sterilizer  10   d  according to Embodiment 4, the cross-sectional shape that is a front view from the inlet port  5  side in the axial longitudinal direction of a cylindrical casing  40   d  is a regular pentagonal shape, and all the surface shapes of the reflectors  3  are worked into a flat shape. The ultraviolet sterilizer  10   d  has a Fresnel lens  9  at a side at which an emitting portion  20   d  is disposed among the sides of the regular pentagonal shape that is the cross-sectional shape. Excepting the above point, the ultraviolet sterilizer  10   d  is configured as in the case of the ultraviolet sterilizer  10   a  of the above-described Embodiment 1. The emitting portion  20   d  is configured as in the case of the emitting portion  20   a  of Embodiment 1. Thus, like reference numerals denote equivalent constituent members to those of the above-described Embodiment 1, and the description is omitted. 
     As shown in  FIG. 24 , the cross-sectional shape of the ultraviolet sterilizer  10   d , that is, the front view when viewed from the inlet port  5  side in the axial longitudinal direction of the cylindrical casing  40   d , is a regular pentagonal shape. That is, the ultraviolet sterilizer  10   d  includes the cylindrical casing  40   d , the emitting portion  20   d  and the reflecting portion  30   d . The cross-sectional shape of the cylindrical casing  40   d  is a regular pentagonal shape. The emitting portion  20   d  is disposed at the outer peripheral portion of the cylindrical casing  40   d . The reflecting portion  30   d  is arranged on the inner surface of the cylindrical casing  40   d , and the cross-sectional shape of the reflecting portion  30   d  is a regular pentagonal annular shape. In the ultraviolet sterilizer  10   d , the Fresnel lens  9  is disposed in front of an ultraviolet ray emitting element. 
     The reflecting portion  30   d  includes a plurality of reflectors  3 Ad to  3 Ed that reflect ultraviolet ray. The reflectors  3 Ad to  3 Ed respectively constitute the sides of the regular pentagonal shape that is the cross-sectional shape of the reflecting portion  30   d . Hereinafter, the reflectors  3 Ad to  3 Ed are also simply collectively referred to as the reflectors  3  or any one of the reflectors  3 Ad to  3 Ed is also simply referred to as the reflector  3 . 
       FIG. 25  is a diagram that shows a path through which ultraviolet ray travels in the reflecting portion  30   d  shown in  FIG. 24 . The traveling direction of ultraviolet ray emitted from the emitting portion  20   d  in the cross section direction of the cylindrical casing  40   d  will be described with reference to  FIG. 25 . The ultraviolet sterilizer  10   d  is configured such that ultraviolet ray that is emitted from the emitting portion  20   d  enters the facing reflector  3 Ad at an angle of 72°. 
     As shown in  FIG. 25 , the five vertices of the regular polygonal shape that is the cross-sectional shape of the ultraviolet sterilizer  10   d  are respectively a vertex d 1 , a vertex d 2 , a vertex d 3 , a vertex d 4  and a vertex d 5 , and the reflectors  3  are the reflector  3 Ad, the reflector  3 Bd, the reflector  3 Cd, the reflector  3 Dd and the reflector  3 Ed in the clockwise direction in order from the reflector  3  located at the side on the right side of the vertex d 1 . 
     In the regular pentagonal shape that is the cross-sectional shape of the ultraviolet sterilizer  10   d , all the central angles are 72°, so a triangle connecting the intersection of extension lines of the sides across one side to the intersection-side vertices of those sides is an isosceles triangle having an apex angle of 36°. That is, for example, when it is assumed that the sides across one side are the side at which the reflector  3 Bd is located and the side at which the reflector  3 Ed is located, and the intersection of the extension lines of these sides is an intersection d 6  as shown in  FIG. 25 , a triangle that connects the vertex d 1 , the intersection d 6  and the vertex d 5  is an isosceles triangle having two angles of 72°. For this reason, when ultraviolet ray is caused to enter the reflector  3 Ad at an angle of 72°, the ultraviolet ray is reflected at a reflection angle of 18°, and the reflected ultraviolet ray enters the reflector  3 Cd at an incident angle of 72°. As shown in  FIG. 25 , the ultraviolet ray reflected on the reflector  3 Cd is reflected on the reflectors  3  along the radial direction of the cylindrical casing  40   d  in order of the reflector  3 Ed, the reflector  3 Bd, the reflector  3 Dd, the reflector  3 Ad and the reflector  3 Cd. That is, ultraviolet ray emitted from the emitting portion  20   d  is sequentially repeatedly reflected along the radial direction of the cylindrical casing  40   d  on the five reflectors  3 , so the ultraviolet ray is reflected all over the area in the cross section of the cylindrical casing  40   d , as shown in  FIG. 25 . 
     As described above, with the ultraviolet sterilizer  10   d , even when the surface of each reflector  3  is not worked into a prism shape, it is possible to emit ultraviolet ray all over the area in the cross section of the cylindrical casing  40   d  by utilizing the plurality of reflectors  3  of which the surface is a flat shape. That is, in Embodiment 4, since no special working needs to be applied to each reflector  3 , it is possible to easily prepare the ultraviolet sterilizer  10   d.    
       FIG. 26  is a table that shows an ultraviolet ray irradiance at the level of 1 mm above each reflector  3  shown in  FIG. 24 . An increase in ultraviolet ray irradiance due to reflection at each reflector  3  will be specifically described with reference to  FIG. 26 . 
     In Embodiment 4 as well, an ultraviolet ray irradiance provided by the ultraviolet sterilizer  10   d  is defined as expressed by the mathematical expression 1. An ultraviolet intensity is a quantity obtained by accumulating the intensity of ultraviolet ray that enters each reflector  3  and the intensity of ultraviolet ray that has been reflected on each of the reflectors  3  in the case where ultraviolet ray emitted from the emitting portion  20   d  has been reflected until the total radiant flux of ultraviolet ray attenuates to 1%. For example, when the emitting portion  20   d  emits parallel rays at 0.01 W/cm 2  and the area of the emitting portion  20   d  is 75 cm 2  (10 cm×7.5 cm), the total radiant flux of ultraviolet ray is 0.75 W. When the thickness of the ultraviolet sterilizer  10   d  in an air course direction is 1 cm, an air velocity caused by the air-sending device  15  is 3 m/s, so an irradiation time is 0.0033 s. 
     Since ultraviolet ray emitted from the emitting portion  20   d  continues to be reflected on the reflectors  3  until the total radiant flux attenuates to 1% or below, the ultraviolet ray irradiance on each reflector  3  becomes about 2.65 mW·s/cm 2 . At the portion at which ultraviolet ray from each reflector  3  to a corresponding one of the reflectors  3  overlaps each other, including the center portion of the ultraviolet sterilizer  10   d , an accumulated value of the irradiances of the overlapping rays of ultraviolet ray is an ultraviolet ray irradiance, so the ultraviolet ray irradiance further increases. 
     As described above, the ultraviolet sterilizer  10   d  is able to increase the ultraviolet ray irradiance to 2.0 mW·s/cm 2  or above all over the cross section. 
     As described above, when ultraviolet ray having a wavelength of 254 nm is emit to airborne influenza virus at 2 mW·s/cm 2 , it is possible to deactivate the airborne influenza virus by 99%. In this respect, the ultraviolet sterilizer  10   d  is able to increase the ultraviolet ray irradiance to 2 mW·s/cm 2  or above, at which airborne influenza virus is able to be deactivated by 99%, over all the area in the cross section within the ultraviolet sterilizer  10   a  with the use of ultraviolet ray emitted from the emitting portion  20   d.    
     In the ultraviolet sterilizer  10   d , variations in ultraviolet ray irradiance on the reflectors  3  are reduced to 15.5% relative to the average value of the ultraviolet ray irradiances. This will be described below. In the case of Embodiment 4, different from Embodiment 1, as shown in  FIG. 26 , ultraviolet ray emitted from the emitting portion  20   d  is reflected in order of the reflector  3 Ad, the reflector  3 Cd, the reflector  3 Ed, the reflector  3 Bd and the reflector  3 Dd, and is further reflected on the reflectors  3  along the radial direction of the cylindrical casing  40   d  in order of the reflector  3 Ad, the reflector  3 Cd, the reflector  3 Ed, the reflector  3 Bd and the reflector  3 Dd. That is, ultraviolet ray emitted from the emitting portion  20   d  are sequentially repeatedly reflected on the five reflectors  3  along the radial direction of the cylindrical casing  40   d . As a result, in the ultraviolet sterilizer  10   d , the numbers of reflections of ultraviolet ray on the reflectors  3  are equivalent to one another, so it is possible to reduce variations in ultraviolet ray irradiance on the reflectors  3 . That is, the ultraviolet sterilizer  10   d  is able to suppress variations in ultraviolet ray irradiance on the reflectors  3  to about 15% relative to the average value, so it is possible to increase the uniformity of the ultraviolet ray irradiance. 
     [Ultraviolet Light Source] 
     The emitting portion  20   d  that is the ultraviolet ray source will be described. 
     The emitting portion  20   d  is configured to cause ultraviolet ray to enter the facing reflector  3  at an angle of 72°. In Embodiment 4, the emitting portion  20   d  has a structure such that the Fresnel lens  9  is disposed in front of the ultraviolet ray emitting element. The Fresnel lens  9  is a lens such that a normal lens is divided into concentric regions and the thickness of each divided region is reduced. The Fresnel lens  9  has a sawtooth cross section. The Fresnel lens  9  has the function of emitting ultraviolet ray that has entered from the ultraviolet ray emitting element, in a certain specific direction in form of parallel rays. 
     As long as ultraviolet ray that has entered from the ultraviolet ray emitting element is able to be emitted in a certain specific direction in form of parallel rays, the emitting portion  20   d  may include another lens, or the like, other than the Fresnel lens  9 . The emitting portion  20   d  may be formed of a light emitter that also has a similar function to the function of the Fresnel lens  9 . In addition, the emitting portion  20   d  may be configured such that the ultraviolet ray emitter including the ultraviolet ray emitting element and the collimate lens is disposed vertically relative to a direction in which ultraviolet ray is intended to be emitted, and parallel rays of ultraviolet ray may be caused to enter the facing reflector  3  at an angle of 72°. A reflector may be provided behind the ultraviolet ray emitter, and parallel rays of ultraviolet ray may be caused to enter the facing reflector  3  at an angle of 72°. 
     [Method of Preparing Reflectors] 
     A method of preparing the reflectors  3  will be described. 
     An ultraviolet ray reflecting material as in the case of the above-described Embodiment 1 may be used as the material of each reflector  3 . When a surface treatment, such as an electroplating method and a vapor deposition method, is applied to the ultraviolet ray reflecting material, the surface has a high reflectance. In addition, because of the reason why workability is excellent, using aluminum as the ultraviolet ray reflecting material is particularly desirable. 
     Next, a method of molding each reflector  3  will be described. 
     Initially, a metal flat plate is cut into a length approximately equal to the thickness d of the cylindrical casing  40   d  in the air flow direction Da. After that, the cut metal flat pate is bent into a regular pentagonal shape by mechanical bending, such as hand bending, pressing, roll bender and roll forming. 
     Each reflector  3  may be prepared as follows as in the case of Embodiment 1. A base having the same shape as the reflector  3  is molded by using a material other than a metal, such as a resin material, and then metal powder paste is evaporated onto the surface of the material. With this configuration, it is possible to reduce cost and to increase the easiness of molding. 
     In Embodiment 4, the ultraviolet sterilizer  10   d  of which the cross-sectional shape that is the front view when viewed from the inlet port  5  side in the axial longitudinal direction of the cylindrical casing  40   d  is a regular pentagonal shape is illustrated and described; however, the ultraviolet sterilizer  10   d  is not limited to this. That is, the ultraviolet sterilizer  10   d  may, for example, have a cross-sectional shape that is a regular polyhedral shape having odd vertices, such as a regular heptagonal shape and a regular nonagonal shape. With the thus configured ultraviolet sterilizer  10   d , even when the surface of each reflector  3  is not worked into a prism shape, it is possible to emit ultraviolet ray all over the area in the cross section of the cylindrical casing  40   d  by utilizing the plurality of reflectors  3  of which the surface has a flat shape. 
     In Embodiment 4, the case where the single ultraviolet sterilizer  10   d  is installed in the air-conditioning apparatus  11   a  is described; however, the configuration is not limited to this. Two or more ultraviolet sterilizers  10   d  may be mounted on the air-conditioning apparatus  11   a . With this configuration, it is possible to increase the ultraviolet ray irradiance and the irradiation direction of ultraviolet ray in the cross section perpendicular to the air flow direction Da, so it is possible to further increase a sterilizing effect. 
     Embodiment 5 
       FIG. 27  is a schematic cross-sectional view that shows the configuration of an ultraviolet sterilizer according to Embodiment 5 of the present invention.  FIG. 28  is a schematic cross-sectional view of an emitting portion of the ultraviolet sterilizer shown in  FIG. 27 . The ultraviolet sterilizer  10   e  according to Embodiment 5 includes the emitting portion  20   e  that serves as an ultraviolet ray source, as shown in  FIG. 27 , and the emitting portion  20   e  includes a plurality of light emitting elements  80 . In the emitting portion  20   e , as shown in  FIG. 28 , a plurality of ultraviolet ray emitting elements  81  and at least one visible light emitting element  82  are disposed as the plurality of light emitting elements  80 . The ultraviolet ray emitting elements  81  each are formed of, for example, a UV-LED and emit ultraviolet ray. The at least one visible light emitting element  82  is formed of, for example, a visible light-LED and emits visible light. That is, the broken line arrows  7   e  in  FIG. 27  illustrate the fluxes of ultraviolet ray and visible light that are emitted from the emitting portion  20   e  and reflected on the reflectors  3  and also illustrate the traveling directions of the fluxes of ultraviolet ray and visible light. Excepting the above point, the ultraviolet sterilizer  10   e  is configured similarly to the ultraviolet sterilizer  10   a  of the above-described Embodiment 1. Thus, like reference numerals denote equivalent constituent members to those of the ultraviolet sterilizer  10   a  in Embodiment 1, and the description is omitted. 
     [Visible Light Source] 
     Visible light that the visible light emitting element  82  emits may be any visually recognizable light. That is, light having a wavelength of 360 nm to 830 nm may be used as visible light that the emitting portion  20   e  emits. Desirably, the emitting portion  20   e  should be configured to emit visible light having a wavelength of 400 nm to 760 nm, which is visually recognizable by almost all the humans. 
     [Visible Light Emitting Element] 
     Subsequently, the visible light emitting element  82  of the emitting portion  20   e  will be described. 
     To make it possible to keep track of ultraviolet ray that is emitted from the ultraviolet ray emitting elements  81  visually, the visible light emitting element  82  is disposed such that visible light that is emitted from the visible light emitting element  82  passes through a similar path to the path through which ultraviolet ray that is emitted from the ultraviolet ray emitting elements  81  passes. 
     The ultraviolet ray source of the emitting portion  20   e  has a structure configured to emit parallel rays having strong directivity in addition to the ultraviolet ray emitting elements  81 . For this reason, a visible light source that is disposed in the emitting portion  20   e  also has a similar structure configured to emit parallel rays having strong directivity to the ultraviolet ray source of the emitting portion  20   e.    
     In Embodiment 5, the structure that the collimate lens is disposed inside the visible light emitting element  82  is employed; however, the structure is not limited to this. Instead of the collimate lens, for example, a Fresnel lens may be provided. A reflector may be provided behind the light source. 
     The visible light emitting element  82 , the collimate lens, and other components, may be packaged or modularized as a visible light source. By packaging or modularizing the visible light emitting element  82 , the collimate lens, and other components, simple installation of the emitting portion  20   e  is possible. 
     The emitting portion  20   e  emits parallel rays of ultraviolet ray from the entire surface defined by the sides along the air flow direction Da and one of the sides of the regular dodecagonal shape that is the cross-sectional shape, in the reflecting portion  30   e  at which the emitting portion  20   e  is installed. For this reason, one or two of the visible light emitting elements  82  are disposed at the center of the emitting portion  20   e  such that visible light travels at the center portion of an ultraviolet ray plane that is emitted from the emitting portion  20   e .  FIG. 28  illustrates the case where the emitting portion  20   e  has the two visible light emitting elements  82 ; however, the configuration is not limited to this. The emitting portion  20   e  may have the single visible light emitting element  82  at the center.  FIG. 28  illustrates the case where the ultraviolet ray emitting elements  81  are disposed between one of the visible light emitting elements  82  and the other one of the visible light emitting elements  82 ; however, the configuration is not limited to this. The two visible light emitting elements  82  may be arranged next to each other. 
     [Method of Preparing Reflectors] 
     Next, a method of preparing the reflectors  3  of which the surface has a prism shape will be described. 
     Since the shape of each of the reflectors  3  that constitute the reflecting portion  30   e  is similar to that in the case of the above-described Embodiment 1, the prism shape of each reflector  3  will be initially described with reference to  FIG. 4 . The average pitch Ap that is the length of the flat surface of each right-angled triangle in the prism shape shown in  FIG. 4  should be 0.01 mm to 10 mm, and desirably should be 0.1 mm to 10 mm. 
     Subsequently, the base material of each reflector  3  will be described. 
     The usable reflecting material is desirably a material that is able to reflect ultraviolet ray and visible light at a reflectance of 40% or above, desirably 60% or above and more desirably 70% or above. Examples of the usable reflecting material include magnesium carbonate (visible light reflectance: about 90% or above, ultraviolet ray reflectance: about 75%) and calcium carbonate (visible light reflectance: about 90% or above, ultraviolet ray reflectance: about 75%). In addition, the desirable reflecting material to be used is a material that is able to reflect visible light at the same level as an ultraviolet ray reflectance. Examples of the ultraviolet ray reflecting material that is suitably usable in the ultraviolet sterilizer  10   e  include platinum (ultraviolet ray reflectance and visible light reflectance: about 50%), aluminum (ultraviolet ray reflectance and visible light reflectance: about 90%) and magnesium oxide (ultraviolet ray reflectance and visible light reflectance: about 90% to 99%). Additionally, when a surface treatment, such as an electroplating method and a vapor deposition method, is applied to these ultraviolet ray reflecting materials, the surface has a high reflectance. 
     Since aluminum is excellent in workability, aluminum may be suitably used as the ultraviolet ray reflecting material and the visible light reflecting material. By further coating aluminum with magnesium fluoride MgF 2  as a surface treatment for aluminum, it is possible to protect the surface of the aluminum material and increase the reflectance in the ultraviolet range. 
     Subsequently, a method of molding the single reflector  3  of which the surface has a prism shape will be described. 
     Initially, a method of preparing the single reflector  3  shown in  FIG. 4  will be described. First, a die for the single reflector  3  is prepared. A material plate for the reflector  3 , cut into a length approximately equal to the thickness d of the cylindrical casing  40   a  in the air flow direction Da is put on the prepared die, and the put material plate is worked by mechanical bending, such as hand bending, pressing, roll bender and roll forming. 
     The reflector  3  may be formed by cutting and working a metal plate having a thickness larger than an average depth. Alternatively, the single reflector  3  may be prepared as follows. A base having the same shape as the single reflector  3  is molded by using a material other than the above-described metal, and then metal powder paste is evaporated onto the surface of the base. In this case, a die having the shape of the single reflector  3  is prepared, and a member that corresponds to the base may be formed by using a resin material by press working, injection molding, compression molding, or the like. After that, metal powder paste that becomes a reflecting material is evaporated onto the surface layer of the base, thus forming the reflector  3 . In this way, when the reflector  3  is formed by using a combination of a resin material and evaporation of metal powder paste, it is advantageous in that material cost is reduced as compared to when a metal plate is used and this combination is easier to be molded than the metal material. 
     A thermoplastic resin, such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET) and ABS resin, may be used as a resin material for molding a base. The base of each reflector  3  may be molded by using a thermosetting resin, such as phenolic resin, amino resin, epoxy resin and urethane resin, synthetic rubber, such as polyisoprene and butadiene, and synthetic fiber, such as nylon, vinylon, acrylic fiber and rayon, that are plastic materials other than the above. 
     Next, a method of assembling the reflecting portion  30   e  by mating the single reflectors  3  will be described. Initially, an assembly jig that is utilized at the time of assembling the reflecting portion  30   e  by mating the single reflectors  3  is prepared. The assembly jig is an apparatus for directing or guiding working positions of parts and tools. Subsequently, the reflectors  3  and the emitting portion  20   e  are set in the assembly jig. After that, visible light is emitted from the emitting portion  20   e . Each reflecting surface is minutely adjusted while the visible light is kept track of. The surfaces of the reflecting portion  30   e  are adjusted and assembled such that visible light is reflected on all the reflecting surfaces. The reflecting portion  30   e  is provided inside the cylindrical casing  40   e.    
     As described above, the ultraviolet sterilizer  10   e  allows the optical path of UV light to be visually recognized with visible light at the time of manufacturing the reflecting portion  30   e , so it is possible to easily assemble and prepare the ultraviolet sterilizer  10   e . The ultraviolet sterilizer  10   e  also allows the optical path of UV light to be visually recognized with visible light at the time of ultraviolet sterilization, so a user, or the like, is allowed to visually recognize whether sterilization is being properly performed by UV light. In addition, when at least one of the ultraviolet ray emitting elements  81  is short circuited at the time of ultraviolet sterilization, the ultraviolet sterilizer  10   e  is configured such that the visible light emitting element  82  does not turn on. For this reason, with the ultraviolet sterilizer  10   e , it is possible to find a short circuit in the ultraviolet ray emitting elements  81  by making sure that visible light is not turned on, so it is possible to visually check the service life of the ultraviolet ray emitting elements  81 . 
     Embodiment 6 
       FIG. 29  is a schematic diagram that illustrates the schematic configuration of an air-conditioning apparatus according to Embodiment 6. The air-conditioning apparatus  11   f  on which the ultraviolet sterilizer  10   a  described in Embodiment 1 is mounted inside will be described with reference to  FIG. 29 . Like reference numerals denote equivalent constituent members to those of the above-described Embodiment 1, and the description is omitted. 
     As shown in  FIG. 29 , the air-conditioning apparatus  11   f  in Embodiment 6 includes a casing  12   f . The casing  12   f  includes an air intake  13   f  and an outlet opening  14   f . The air intake  13   f  introduces air. Through the outlet opening  14   f  air introduced from the air intake  13   f  flows out. The air-conditioning apparatus  11   f  further includes a prefilter  51 , an air-sending device  15   f  and a heat exchanger  52 . The prefilter  51  removes dust and trash contained in air introduced from the air intake  13   f  into the casing  12   f . The air-sending device  15   f  generates flow of air from the air intake  13  toward the outlet opening  14 . The heat exchanger  52  is formed of, for example, a fin and tube heat exchanger. The air-conditioning apparatus  11   f  includes the ultraviolet sterilizer  10   a  installed at the air inlet side of the air-sending device  15   f . That is, in the air-conditioning apparatus  11   f , air introduced from the air intake  13   f  flows out from the outlet opening  14   f  through the prefilter  51 , the ultraviolet sterilizer  10   a , the air-sending device  15   f  and the heat exchanger  52 . 
     Inside the air-conditioning apparatus  11   f , air pumped by the air-sending device  15   f  and introduced from the air intake  13   f  definitely passes through the blade portion of the air-sending device  15   f . For this reason, in the air-conditioning apparatus  11   f , the ultraviolet sterilizer  10   a  is disposed such that the ultraviolet sterilizer  10   a  covers the blade portion of the air-sending device  15   f . As the air-conditioning apparatus  11   f  starts operating, the air-sending device  15   f  works, and air flows from an interior, or other space, into the casing  12   f . The ultraviolet sterilizer  10   a  sterilizes microbes in the air flowing into the casing  12   f.    
     In this way, the air-conditioning apparatus  11   f  in which the ultraviolet sterilizer  10   a  is installed is able to sterilize microbes, such as fungi, bacteria and viruses, in the air introduced into the casing  12   f . For this reason, with the air-conditioning apparatus  11   f , it is possible to inhibit adhesion of microbes to the inside of the air-conditioning apparatus  11   f  and proliferation of the microbes, so it is possible to reduce the number of microbes in the air in an interior, or other space. By inhibiting adhesion of microbes to the inside of the air-conditioning apparatus  11   f  and proliferation of microbes inside the air-conditioning apparatus  11   f , it is possible to reduce odor that is generated from the air-conditioning apparatus  11   f.    
     In Embodiment 6, a structure that the air-conditioning apparatus  11   f  takes air in from the air intake  13   f  and air from the outlet opening  14   f  flows out through the prefilter  51 , the air-conditioning apparatus  11   f , the air-sending device  15   f  and the heat exchanger  52  is described; however, the structure is not limited to this. That is, even when the air-conditioning apparatus  11   f  has another configuration that the air-sending device  15   f  is disposed, for example, downstream of the heat exchanger  52 , similar advantageous effects are expected when the ultraviolet sterilizer  10   a  is disposed at a location through which air taken into the casing  12   f  passes. From the viewpoint of inhibiting adhesion of microbes to the constituent members inside the air-conditioning apparatus  11   f , the configuration that the ultraviolet sterilizer  10   a  is disposed upstream of the air-sending device  15   f  and the heat exchanger  52  is desirable. 
     Embodiment 7 
     In Embodiment 7, mounting the ultraviolet sterilizer  10   a  on an air cleaner will be described. The air cleaner in Embodiment 7 has the same components as the air-conditioning apparatus  11   f  of Embodiment 6, so like reference numerals are used, and the description is omitted. As the air cleaner starts operating, an air-sending device works, and air flows from an interior, or other space, into the casing  12   f . The ultraviolet sterilizer  10   a  sterilizes microbes in the air flowing into the casing  12   f.    
     In this way, the air cleaner in which the ultraviolet sterilizer  10   a  is installed is able to sterilize microbes, such as fungi, bacteria and viruses, in the air taken into the casing  12   f . For this reason, with the air cleaner, it is possible to inhibit adhesion of microbes to the inside of the air cleaner and proliferation of the microbes, so it is possible to reduce the number of microbes in the air in an interior, or other space. By inhibiting adhesion of microbes to the inside of the air cleaner and proliferation of microbes inside the air cleaner, it is possible to reduce odor that is generated from the air cleaner. 
     The above-described Embodiments are suitable specific examples of the ultraviolet sterilizer and the air-conditioning apparatus, including the air cleaner, and the technical scope of the invention is not limited to these modes. For example, in the above-described Embodiments, description is made on the assumption that the thickness d of each of the ultraviolet sterilizers  10   a ,  10   c ,  10   d ,  10   e  in the air flow direction Da, that is, the thickness of the screen-shaped sterilizing light screen based on ultraviolet ray that is generated by each of the ultraviolet sterilizers  10   a ,  10   c ,  10   d ,  10   e  is 1 cm or 10 cm; however, the configuration is not limited to this. For example, when the thickness d is increased, an ultraviolet ray irradiation time extends, so a sterilizing effect increases. On the other hand, when the thickness d is reduced, a compact design is possible, so it is advantageous in that it is allowed to be mounted inside a relatively small-sized device. 
     The cross-sectional shape of the ultraviolet sterilizer of the invention, that is, the front view when viewed from the inlet port  5  side in the axial longitudinal direction of the cylindrical casing  40   a , is not limited to a regular pentagonal shape, a regular dodecagonal shape or a regular hexadecagonal shape, and may be various polygonal shapes. That is, the cross-sectional shape of the reflecting portion is formed into a selected polygonal annular shape. The inclination angle α of each of the reflectors should be adjusted based on the principles of the incident angle and reflection angle of light, or the like. When the number of the sides of a polygonal shape increases, the shape of a reflecting portion approaches to a circular shape. Therefore, when the ultraviolet sterilizer is disposed at a circular portion, such as a duct, of the air-conditioning apparatus, it is possible to further reduce an increase in pressure loss. 
     In addition, two or more of the ultraviolet sterilizers  10   a ,  10   c ,  10   d ,  10   e  described in the above Embodiments may be mounted on a device, such as the air-conditioning apparatus, in combination. At this time, the positions of the emitting portions of the ultraviolet sterilizers should be shifted such that the optical axes of rays of ultraviolet ray in the ultraviolet sterilizers are not parallel to each other. 
     Furthermore, in the above-described Embodiments, description is made on the assumption that the ultraviolet sterilizer is mounted on the air-conditioning apparatus; however, the configuration is not limited to this. The ultraviolet sterilizer of the present invention is also allowed to be mounted on a device other than the air-conditioning apparatus. That is, the ultraviolet sterilizer may be configured to set not only air but also various fluids including liquid as a sterilizing target. 
     In the above-described Embodiments, the case where the diameter of the circular shape of the casing  12  is 100 mm is illustrated; however, the case is not limited to this. The diameter of the circular shape of the casing  12  should be changed as needed in response to, for example, application of a device on which the casing  12  is mounted. 
     REFERENCE SIGNS LIST 
       3 ,  3 A to  3 K,  3 Ac to  3 Oc,  3 Ad to  3 Ed reflector  5  inlet port  6  outlet port  7 ,  7   e  broken line arrow  9  Fresnel lens  10   a  to  10   e ,  100   c  ultraviolet sterilizer  11   a  to  11   c ,  11   e ,  110   a  air-conditioning apparatus  12 ,  12   f  casing  13 ,  13   f  air intake  14 ,  14   f  outlet opening  15 ,  15   f  air-sending device  20   a ,  20   c ,  20   d ,  20   e  emitting portion  30   a ,  30   c ,  30   d ,  30   e  reflecting portion  31  flat part  31   a  flat surface  32  reflecting part  32   a  reflecting surface  40   a ,  40   c ,  40   d ,  40   e  cylindrical casing  51  prefilter  52  heat exchanger  71  incident light  72  reflected light  73  normal  80  light emitting element  81  ultraviolet ray emitting element  82  visible light emitting element d thickness α inclination angle