Patent Publication Number: US-2011067571-A1

Title: Air purification apparatus

Description:
TECHNICAL FIELD 
     The present invention is directed to air purification apparatuses, and more particularly to an air purification apparatus including an electrostatically atomizing device. 
     BACKGROUND ART 
     As disclosed in Japanese patent laid-open publication No. 2004-85185 (hereinafter referred to as “document 1”), and Japanese patent laid-open publication No. 2005-180865 (hereinafter referred to as “document 2”), there has been proposed an air purification apparatus provided with an electrostatically atomizing device. 
     In the air purification apparatuses respectively disclosed in the documents 1 and 2, a filter is placed inside of an air duct. 
     Notably, concerning the air purification apparatus disclosed in the document 1, the electrostatically atomizing device is placed downstream of the filter. Therefore, a mist of charged minute water particles generated by the electrostatically atomizing device is discharged into an external space not through the filter. The air purification apparatus disclosed in the document 1 discharges a mist of charged minute water particles into the external space in order to purify air in the external space by use of a mist of charged minute water particles. 
     In the air purification apparatus disclosed in the document 2, the electrostatically atomizing device is placed upstream of the filter. Therefore, a mist of charged minute water particles generated by the electrostatically atomizing device comes into contact with the filter. The air purification apparatus disclosed in the document 2 makes a mist of charged minute water particles into contact with the filter in order to regenerate the filter by use of a mist of charged minute water particles. 
     As apparent from the above configurations, the air purification apparatus of the document 1 does not utilize the electrostatically atomizing device to regenerate the filter, and the air purification apparatus of the document 2 does not utilize the electrostatically atomizing device to purify air in the external space. 
     In order to make both air purification and filter regeneration, the electrostatically atomizing devices can be placed both downstream and upstream of the filter. 
     However, with this situation, at least two electrostatically atomizing devices are required. As a result, the air purification apparatus is likely to be upsized and its cost is likely to become high. 
     DISCLOSURE OF INVENTION 
     In view of the above insufficiency, the present invention has been aimed to propose an air purification apparatus capable of making both air purification and filter regeneration by use of a single electrostatically atomizing device. 
     The air purification apparatus in accordance with the present invention includes a duct, a filter designed to purify air, an electrostatically atomizing device, a fan, and a switching means. The duct has an inlet and an outlet. The filter is placed inside of the duct. The electrostatically atomizing device is configured to generate a mist of charged minute water particles by means of electrostatically atomizing phenomenon and discharge the same into the duct. The fan is configured to send air from the inlet to the outlet. The switching means is configured to switch one of a first mode and a second mode. The air purification apparatus is configured to send a mist of charged minute water particles from the electrostatically atomizing device to the outlet without passing through the filter in the first mode. The air purification apparatus is configured to send a mist of charged minute water particles from the electrostatically atomizing device to the filter in the second mode. 
     According to the air purification apparatus in accordance with the present invention, it is possible to purify air in the first mode, and to regenerate the filter in the second mode. Further, the first mode and the second mode can be switched by use of the switching means. Consequently, the air purification apparatus in accordance with the present invention is capable of making both air purification and filter regeneration by use of the single electrostatically atomizing device. Therefore, it is possible to downsize the air purification apparatus, and to reduce a production cost. In addition, in the first mode, a mist of charged minute water particles is discharged out from the duct not through the filter. Thus, it is possible to prevent occurrence of a decrease of an amount of a mist of charged minute water particles discharged out from the duct caused by the filter. As a result, it is possible to provide an enough amount of a mist of charged minute water particles discharged out from the duct. Moreover, since the filter can be regenerated in the second mode, it is possible to reduce replacement frequency of filter. Thus, maintenance need not be made for a long time. 
     In a preferred embodiment, the electrostatically atomizing device is configured to discharge a mist of charged minute water particles into a space formed inside of the duct between the filter and the outlet. The switching means includes a changing means and a controlling means configured to control the changing means. The changing means is configured to change a discharge direction where the electrostatically atomizing device discharges a mist of charged minute water particles. The controlling means is configured to direct the discharge direction toward the outlet when the first mode is selected. The controlling means is configured to direct the discharge direction toward the filter when the second mode is selected. 
     With the preferred embodiment, it is possible to easily and successfully select one of the first mode and the second mode. 
     In a preferred embodiment, the electrostatically atomizing device is configured to discharge a mist of charged minute water particles into a space formed inside of the duct between the filter and the outlet. The fan is configured to operate in an air supply mode of sending air from the inlet to the outlet, and an exhaust mode of sending air from the outlet to the inlet. The switching means includes a controlling means configured to control the fan. The controlling means is configured to control the fan to operate in the air supply mode when the first mode is selected, and to control the fan to operate in the exhaust mode when the second mode is selected. 
     With the preferred embodiment, it is possible to easily and successfully select one of the first mode and the second mode. 
     In a preferred embodiment, the electrostatically atomizing device is placed inside of the duct. The duct includes, between the outlet and the electrostatically atomizing device, a first air passage devoid of the filter and a second air passage provided with the filter. The switching means includes a shutter configured to block the first air passage and the second air passage selectively. The switching means includes a controlling means configured to control the shutter. The controlling means is configured to control the shutter to block the second air passage when the first mode is selected. The controlling means is configured to control the shutter to block the first air passage when the second mode is selected. 
     With the preferred embodiment, it is possible to easily and successfully select one of the first mode and the second mode. 
     In a preferred embodiment, the electrostatically atomizing device is configured such that an amount of a mist of charged minute water particles generated per unit time is greater in the second mode than in the first mode. 
     With the preferred embodiment, it is possible to shorten time necessitated for regenerating the filter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a schematic explanatory view illustrating an air purification apparatus of a first embodiment operating in a first mode, 
         FIG. 1B  is a schematic explanatory view illustrating the air purification apparatus of the first embodiment operating in a second mode, 
         FIG. 2  is a schematic explanatory view illustrating an electrostatically atomizing device of the above air purification apparatus, 
         FIG. 3  is an explanatory view illustrating a modification of the above air purification apparatus, 
         FIG. 4A  is a schematic explanatory view illustrating an air purification apparatus of a second embodiment operating in a first mode, 
         FIG. 4B  is a schematic explanatory view illustrating the air purification apparatus of the second embodiment operating in a second mode, 
         FIG. 5A  is a schematic explanatory view illustrating an air purification apparatus of a third embodiment operating in a first mode, 
         FIG. 5B  is a schematic explanatory view illustrating the air purification apparatus of the third embodiment operating in a second mode, and 
         FIG. 6  is an explanatory view illustrating a modification of the above air purification apparatus. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     As shown in  FIGS. 1A and 1B , an air purification apparatus of the present embodiment includes a duct  10 , a filter  20  for air purification, an electrostatically atomizing device  30 , a fan  40 , and a switching device (switching means)  50 . 
     The duct  10  is mounted on a housing which is a casing of the air purification apparatus. The duct  10  is shaped into a cylindrical shape, for example. A first axial opening (right opening, in  FIGS. 1A and 1B ) of the duct  10  is defined as an inlet  11 . The inlet  11  is used for introducing air into the duct  10  from the outside. A second axial opening (left opening, in  FIGS. 1A and 1B ) of the duct  10  is defined as an outlet  12 . The outlet  12  is used for discharging air to the outside from the inside of the duct  10 . 
     The filter  20  is placed inside of the duct  10 . For example, the filter  20  is a deodorization filter configured to remove offensive odor substances from air utilizing an activated carbon. 
     The fan  40  is placed close to the inlet  11  within the duct  10 . The fan  40  is configured to operate in two working modes, one being an air supply mode and the other being an exhaust mode. The fan  40  sends air from the inlet  11  to the outlet  12  in the air supply mode. The fan  40  sends air from the outlet  12  to the inlet  11  in the exhaust mode. In the present embodiment, based on a situation where the fan  40  operates in the air supply mode, a side of the inlet  11  of the duct  10  is defined as an upstream side, and a side of the outlet  12  of the duct  10  is defined as a downstream side. 
     The electrostatically atomizing device  30  is configured to generate a mist of charged minute water particles by means of electrostatically atomizing phenomenon and discharge the same into the duct  10 . In the present embodiment, the electrostatically atomizing device  30  is placed between the filter  20  and the outlet  12  in the duct  10 . Consequently, the electrostatically atomizing device  30  discharges a mist of charged minute water particles into a space formed inside of the duct  10  between the filter  20  and the outlet  12 . 
     As shown in  FIG. 2 , the electrostatically atomizing device  30  includes a housing  310 . 
     The housing  310  is made of a dielectric material and is shaped into a cylindrical shape. The first axial opening (lower opening shown in  FIG. 2 ) of the housing  310  is covered with a cooling plate  311 . The housing  310  houses a discharge electrode  320 . 
     The discharge electrode  320  is shaped into a bar shape having a sharp tip. The discharge electrode  320  has its base end thermally coupled to the cooling plate  311 . 
     There is an opposed electrode  330  which is placed inside of a second opening (upper opening shown in  FIG. 2 ) of the housing  310 . 
     The opposed electrode  330  is shaped into a plate shape having enough dimensions to cover the second opening of the housing  310 . The opposed electrode  330  is provided with a spray hole  331  in its center. 
     The tip of the discharge electrode  320  is visible from the outside of the housing  310  via the spray hole  331 . 
     A peltier unit  340  having a peltier element (not shown) is attached to the first opening side of the housing  310 . 
     The peltier unit  340  is used for cooling the discharge electrode  320 . Therefore, the peltier unit  340  has its cooling side thermally coupled to the discharge electrode  320  through the cooling plate  311 . The pettier unit  340  has its heat dissipation side attached to a heat dissipation unit  350  having plural fins  351 . 
     The electrostatically atomizing device  30  includes, as circuit components, a voltage application unit  360 , an ammeter  370 , a cooling control unit  380 , and a control circuit  390 . 
     The voltage application unit  360  is configured to apply a voltage (DC voltage) between the discharge electrode  320  and the opposed electrode  330 . For example, the voltage application unit  360  is an AC/DC converter which is configured to apply a voltage between the discharge electrode  320  and the opposed electrode  330  by use of power received from a commercial AC source. 
     The ammeter  370  is configured to measure a current flowing between the discharge electrode  320  and the opposed electrode  330 . 
     The cooling control unit  380  is configured to energize the peltier element of the peltier unit  340 . The cooling control unit  380  has a function of adjusting a voltage applied to the peltier element. 
     The control circuit  390  is constructed by use of a microcomputer, for example. 
     The control circuit  390  is configured to control the cooling control unit  380  to cool the discharge electrode  320  below a dew point of circumambient air. When the discharge electrode  320  is cooled below the aforementioned dew point, moisture in the circumambient air is condensed on the surface of the discharge electrode  320 . Consequently, dew is produced on the surface of the discharge electrode  320 . That is, the electrostatically atomizing device  30  of the present embodiment is configured to supply water (dew condensation water) to the discharge electrode  320  utilizing dew condensation (surface condensation). 
     Especially, the control circuit  390  of the present embodiment adjusts the temperature of the discharge electrode  320  to either a first configuration temperature or a second configuration temperature. Both the first configuration temperature and the second configuration temperature are selected to be not greater than the above dew point. The second configuration temperature is lower than the first configuration temperature. Therefore, the discharge electrode  320  develops the dew on its surface in a greater amount when it is at second preset temperature than at the first preset temperature. 
     The control unit  390  is configured to control the voltage application unit  360  with reference to a detection result of the ammeter  370  in order to apply a predetermined voltage (e.g., 5000V) between the discharge electrode  320  and the opposed electrode  330 . Therefore, water held by the discharge electrode is atomized, and then a mist of charged minute water particles is generated. A mist of charged minute water particles is discharged out of the housing  310  via the spray hole  331  of the opposed electrode  330 . A principle of the electrostatically atomizing is well known, and no explanation thereof is deemed necessary. 
     The air purification apparatus of the present embodiment is configured to operate in two operation modes, one being a first mode and the other being a second mode. In the first mode, the air purification apparatus sends a mist of charged minute water particles from the electrostatically atomizing device to the outlet  12  not through the filter  20  (see  FIG. 1A ). In the second mode, the air purification apparatus sends a mist of charged minute water particles from the electrostatically atomizing device to the filter  20  (see  FIG. 1B ). Besides, arrows respectively shown in  FIG. 1A  and  FIG. 1B  indicate a direction of air. 
     The switching device  50  is configured to switch one of the first mode and the second mode. 
     The switching device  50  includes an electric motor  51 , a control unit  52 , and a manipulation unit  53 . 
     The electric motor  51  is a stepping motor, for example. The electric motor  51  has a stator (not shown) fixed to the duct  10 . The electric motor  51  includes a rotation axis  511  configured to rotate with a rotor (not shown). The rotation axis  511  has its tip fixed to the electrostatically atomizing device  30 . A discharge direction M in which the electrostatically atomizing device  30  discharges a mist of charged minute water particles is perpendicular to an axial direction of the rotation axis  511 . Therefore, with a rotation of the rotation axis  511 , the discharge direction M is changed. In the present embodiment, the electric motor  51  is defined as a changing means configured to change the discharge direction M. 
     The manipulation unit  53  is used for making the switching one of the first mode and the second mode by manual operation, for example. The manipulation unit  53  is constructed by use of a switch or button, for example. 
     The control unit  52  is configured to control the electric motor  51 , the fan  40 , and the control circuit  390  in accordance with the operation mode of the air purification apparatus. The control unit  52  is configured to switch one of the first mode and the second mode corresponding to manual operation of the manipulation unit  53 . The control unit  52  is constructed by use of a microcomputer, for example. 
     When the first mode is selected, the control unit  52  rotates the rotation axis  511  of the electric motor  51  to direct the discharge direction M toward the outlet  12  (downstream side). In addition, the control unit  52  controls the fan  40  to operate in the air supply mode. Further, the control unit  52  controls the control circuit  390  to adjust the temperature of the discharge electrode  320  to the first configuration temperature. 
     Therefore, in the first mode, a mist of charged minute water particles is discharged from the electrostatically atomizing device  30  towards the outlet  12 . Further, since the fan  40  sends air towards the downstream side, a mist of charged minute water particles is moved towards the outlet  12  as being carried on an air flow. 
     As seen from the above, the first mode is defined as a purification mode (external space purification mode) of discharging out a mist of charged minute water particles via the outlet  12  without passing through the filter  20 . When discharged into the external space, the mist of charged minute water particles remains floating in the air for a long time, and spread through every corner of the space. Thus, radical species contained in a mist of charged minute water particles removes offensive odor substances from the external space. 
     When the second mode is selected, the control unit  52  rotates the rotation axis  511  of the electric motor  51  to direct the discharge direction M toward the filter  20  (upstream side). In addition, the control unit  52  controls the fan  40  to operate in the exhaust mode. Further, the control unit  52  controls the control circuit  390  to adjust the temperature of the discharge electrode  320  to the second configuration temperature. Besides, in the second mode, the fan  40  may be deactivated instead of operating in the exhaust mode (it is sufficient that the fan  40  does not operate in the air supply mode). 
     Therefore, in the second mode, a mist of charged minute water particles is discharged from the electrostatically atomizing device  30  towards the filter  20 . Further, since the fan  40  sends air towards the upstream side, a mist of charged minute water particles is moved towards the filter  20  as being carried on an air flow. 
     As seen from the above, the second mode is defined as a regeneration mode (filter regeneration mode) of spraying the mist of charged minute water particles into the filter  20  for regeneration thereof. When contacting with the filter  20 , the charged minute water particles have its radical species functioning to remove offensive odor substances from the filter  20  for regeneration thereof. 
     As described in the above, the air purification apparatus of the present embodiment includes the duct  10 , the filter  20 , the electrostatically atomizing device  30 , the fan  40 , and the switching device  50 . The duct  10  has the inlet  11  and the outlet  12 . The filter  20  is placed the inside of the duct  10 . The electrostatically atomizing device  30  is configured to generate a mist of charged minute water particles by means of electrostatically atomizing phenomenon and discharge the same into the duct  10 . The fan  40  is configured to send air from the inlet  11  to the outlet  12 . The switching means  50  is configured to switch one of the first mode and the second mode. The air purification apparatus sends a mist of charged minute water particles from the electrostatically atomizing device  30  to the outlet  12  not through the filter  20  in the first mode. The air purification apparatus sends a mist of charged minute water particles from the electrostatically atomizing device  30  to the filter  20  in the second mode. 
     Thus, the air purification apparatus of the present embodiment can purify air in the first mode, and can regenerate the filter  20  in the second mode. Further, the switching device  50  can switch one of the first mode and the second mode. 
     Consequently, the air purification apparatus of the present embodiment is capable of making both purification of air and regeneration of the filter  20  by use of the single electrostatically atomizing device  30 . Therefore, it is possible to downsize the air purification apparatus, and to reduce a production cost. In addition, in the first mode, a mist of charged minute water particles is discharged out from the duct  10  not through the filter  20 . Thus, it is possible to prevent occurrence of a decrease of an amount of a mist of charged minute water particles discharged out from the duct  10  caused by the filter  20 . As a result, it is possible to provide an enough amount of a mist of charged minute water particles discharged out from the duct  10 . Moreover, since the filter  20  can be regenerated in the second mode, it is possible to reduce replacement frequency of filter  20 . Thus, maintenance need not be made for a long time. 
     Especially, the electrostatically atomizing device  30  is configured to discharge a mist of charged minute water particles into the space formed inside of the duct  10  between the filter  20  and the outlet  12 . 
     The switching device  50  includes the electric motor  51  as the changing means, and the control unit  52  configured to control the electric motor  51 . The electric motor  51  is configured to change the discharge direction M. The control unit  52  is configured to direct the discharge direction M toward the outlet  12  when the first mode is selected, and to direct the discharge direction M toward the filter  20  when the second mode is selected. 
     Accordingly, it is possible to easily and successfully select one of the first mode and the second mode. 
     Additionally, in the second mode, the discharge electrode  320  has the second configuration temperature. Therefore, dew generated on the surface of the discharge electrode  320  is greater in the second mode than in the first mode. As a result, a generation amount of a mist of charged minute water particles is increased. 
     In other words, the electrostatically atomizing device  30  is configured such that an amount of a mist of charged minute water particles generated per unit time is greater in the second mode than in the first mode. 
     Therefore, in contrast to a situation where an amount of a mist of charged minute water particles generated per unit time is the same in the second mode as in the first mode, it is possible to shorten time necessitated for regeneration of the filter. 
     Beside, a large amount of ozone is generated while a large amount of a mist of charged minute water particles is generated. However, since both ozone and a mist of charged minute water particles come into contact with the filter  20 , the filter  20  prevents both ozone and a mist of charged minute water particles from being discharged out. Therefore, it is possible to assure safety of the air purification apparatus. 
       FIG. 3  shows a modification of the air purification apparatus of the present embodiment. Besides, the circuit components of the electrostatically atomizing device  30  are not shown in  FIG. 3 . 
     In the modification shown in  FIG. 3 , the duct  10 A is provided in its inner surface with a storing recess  13  configured to receive the electrostatically atomizing device  30 . The storing recess  13  is located between the outlet  12  and the filter  20 . 
     The electrostatically atomizing device  30  is accommodated within the storing recess with its spray hole  331  directed towards an opening of the storing recess  13 . 
     The switching device  50 A shown in  FIG. 3  includes the electric motor  51 A, the control unit  52 , the manipulation unit  53 , a pipe  54 , and a bearing plate  55 . 
     The pipe  54  is shaped into a cylindrical shape. The pipe  54  is provided with a first opening  541  in its first axial end, and provided with a second opening  542  in its second axial end. The pipe  54  has an arc-shaped axis having a central angle of 90 degree. Therefore, the first opening  541  has its central axis perpendicular to a central axis of the second opening  542 . 
     The bearing plate  55  is attached to the duct  10 A to cover the storing recess  13 . The bearing plate  55  bears the pipe  54  such that the first opening  541  and the spray hole  331  communicate with each other. Additionally, the bearing plate  55  is configured to hold the pipe  54  rotatively around a rotation axis A (see  FIG. 3 ). The rotation axis A is aligned with the central axis of the first opening  541 . 
     The electric motor  51 A is configured to rotate the pipe  54  around the rotation axis A. The electric motor  51 A is a stepping motor, for example. The electric motor  51 A has a stator (not shown) fixed to the bearing plate  55 . The electric motor  51 A includes a rotor (not shown) which is mechanically coupled to the pipe  54  such that the pipe  54  rotates with a rotation of the rotor. 
     In the instance shown in  FIG. 3 , a mist of charged minute water particles is discharged into the duct  10  from the electrostatically atomizing device  30  through the pipe  54 . A direction toward which the second opening  542  is directed is defined as the discharge direction M. The discharge direction M is perpendicular to the rotation axis A, because of that the discharge direction M is aligned with the central axis of the second opening  542 . 
     Consequently, the discharge direction M is changed with a rotation of the pipe  54 . In the instance shown in  FIG. 3 , the electric motor  51 A, the pipe  54 , and the bearing plate  55  constitute the changing means configured to change the discharge direction M. 
     In addition, as described in the above, the storage recess  13  is located between the outlet  12  and the filter  20 . Therefore, the electrostatically atomizing device  30  discharges a mist of charged minute water particles into the space formed inside of the duct  10  between the filter  20  and the outlet  12 . 
     The control unit  52 A is configured to control the electric motor  51 A, the fan  40 , and the control circuit  390  in accordance with the operation mode of the air purification apparatus. Besides, the control unit  52 A controls the fan  40  and the control circuit  390  in a similar manner as seen in the control unit  52 , and no explanation thereof is deemed necessary. 
     When the first mode is selected, the control unit  52 A rotates the pipe  54  to direct the discharge direction M toward the outlet  12 . Thus, in the first mode, a mist of charged minute water particles is discharged toward the outlet  12  from the electrostatically atomizing device  30 . Further, since the fan  40  sends air towards the downstream side, a mist of charged minute water particles is moved towards the outlet  12  as being carried on an air flow. 
     When the second mode is selected, the control unit  52 A rotates the pipe  54  to direct the discharge direction M towards the filter  20 . Thus, in the second mode, a mist of charged minute water particles is discharged from the electrostatic atomizing device  30  towards the filter  20 . Further, since the fan  40  sends air towards the upstream side, a mist of charged minute water particles is moved towards the filter  20  as being carried on an air flow. 
     Accordingly, the modification of the air purification apparatus shown in  FIG. 3  also can provide the same effect as the instance shown in  FIG. 1 . 
     Besides, the air purification apparatus of the present embodiment and the following second and third embodiments is defined as an apparatus having at least an air purification function, and therefore may be an air conditioner of cooling and/or heating air, a humidifier, a dehumidifier, a humidification and air purification apparatus, a vacuum cleaner, or a fan heater. 
     In addition, the filter  20  used in the present embodiment and the following second and third embodiments is not limited to a deodorization filter. The filter  20  may be a dust collection filter (e.g., HEPA filter) configured to collect particles floating in the air, or a sterilization filter designed to remove bacteria and viruses. Alternatively, the filter  20  may have both a function of deodorization and a function of removing dusts, bacteria, and viruses. A filter having a desired function can be adopted as the filter  20 . Moreover, a mist of charged minute water particles can regenerate a sterilization filter, because of that a mist of charged minute water particles inactivates bacteria and viruses. 
     Second Embodiment 
     As shown in  FIG. 4 , the air purification apparatus of the present embodiment is mainly different from that of the first embodiment in the switching device  50 B. Besides, with regard to components common to the present embodiment and the first embodiment, no detailed explanations are deemed necessary. 
     In the air purification apparatus of the present embodiment, like the instance shown in  FIG. 3 , the electrostatically atomizing device  30  is accommodated within the storage recess  13  of the duct  10 A. 
     The electrostatically atomizing device  30  is accommodated within the storing recess with its spray hole  331  directed towards the opening of the storing recess  13 . Therefore, the electrostatically atomizing device  30  discharges a mist of charged minute water particles to the space formed inside of the duct  10  between the filter  20  and the outlet  12 . 
     The switching device  50 B includes the control unit  52 B and the manipulation unit  53 . 
     The control unit  52 B is configured to control the fan  40  and the control circuit  390  in conformity with the operation mode of the air purification apparatus. The control unit  52 B selects one of the first mode and the second mode in response to manual operation of the manipulation unit  53 . Besides, the control unit  52 B controls the fan  40  and the control circuit  390  in a similar manner as seen in the control unit  52  of the first embodiment, and no explanation thereof is deemed necessary. 
     When the first mode is selected, the control unit  52 B controls the fan  40  to operate in the air supply mode (see  FIG. 4A ). Therefore, in the first mode, the fan  40  sends air towards the downstream side. Thus, a mist of charged minute water particles discharged between the outlet  12  and the filter  20  is moved towards the outlet  12  as being carried on an air flow. Accordingly, in the first mode, a mist of charged minute water particles is discharged out from the outlet  12  without contacting with the filter  20 . 
     When the second mode is selected, the control unit  52 B controls the fan  40  to operate in the exhaust mode (see  FIG. 4B ). Therefore, in the second mode, the fan  40  sends air towards the upstream side. Thus, a mist of charged minute water particles discharged between the outlet  12  and the filter  20  is moved towards the filter  20  as being carried on an air flow. Accordingly, in the second mode, a mist of charged minute water particles contacts with the filter  20 . 
     As seen from the above, the switching device  50 B of the present embodiment includes the control circuit  52 B defined as a control means configured to control the fan  40 . The control circuit  52 B controls the fan  40  to operate in the air supply mode when the first mode is selected, and controls the fan  40  to operate in the exhaust mode when the second mode is selected. 
     As described in the above, in the air purification apparatus of the present embodiment, the electrostatically atomizing device  30  is configured to discharge a mist of charged minute water particles into the space formed inside of the duct  10  between the filter  20  and the outlet  12 . The fan  40  is configured to operate in the air supply mode of sending air from the inlet  11  to the outlet  12 , and the exhaust mode of sending air from the outlet  12  to the inlet  11 . The switching device  50 B includes the control circuit  52 B configured to control the fan  40 . The control circuit  52 B is configured to control the fan  40  to operate in the air supply mode when the first mode is selected, and to control the fan  40  to operate in the exhaust mode when the second mode is selected. 
     Consequently, the air purification apparatus of the present embodiment also produces the same effect as the air purification apparatus of the first embodiment. Especially, in the present embodiment, the first mode and the second mode are switched by only switching the working mode between the air supply mode and the exhaust mode. Therefore, it is possible to easily and successfully select one of the first mode and the second mode. In addition, it is possible to reduce the production cost, because of that the electric motor  51  is unnecessary. 
     Third Embodiment 
     As shown in  FIG. 5 , the air purification apparatus of the present embodiment is mainly different from the first embodiment in the configurations of the duct  10 C and the switching device  50 C. Besides, with regard to components common to the present embodiment and the first embodiment, no detailed explanations are deemed necessary. 
     The duct  10 C is provided with a first inlet  111  and a second inlet  112 . The duct  10 C has a main channel  14  connecting the first inlet  111  to the outlet  12 . The duct  10 C has an auxiliary channel  15  connecting the second inlet  112  to the outlet  12 . The duct  10 C includes a first confluent opening  161  and a second confluent opening  162  respectively connecting the main channel  14  to the auxiliary channel  15 . 
     The first confluent opening  161  connects the auxiliary channel  15  to the main channel  14  between the outlet  12  and the filter  20  (that is, downstream side). The second confluent opening  162  connects the auxiliary channel  15  to the main channel  14  between the first inlet  111  and the filter  20  (that is, upstream side). 
     In the present embodiment, the electrostatically atomizing device  30  is located inside of the auxiliary channel  15  while the spray hole  331  is directed toward the outlet  12 . In the present embodiment, the electrostatically atomizing device  30  is located in a center part of the auxiliary channel  15  not to occlude the auxiliary channel  15 . 
     In addition, the fan  40  is installed in the duct  10 C to send air from the second inlet  112  (upstream side) to the electrostatically atomizing device  30  (downstream side). 
     As seen from the above, in the air purification apparatus of the present embodiment, the duct  10 C has two air passages (that is, a first air passage and a second air passage) between the outlet  12  and the electrostatically atomizing device  30 . 
     The first air passage is defined by the auxiliary channel  15 , the first confluent opening  161 , and the main channel  14 . The first air passage is devoid of the filter  20  between the outlet  12  and the electrostatically atomizing device  30  (see  FIG. 5A ). 
     The second air passage is defined by the auxiliary channel  15 , the second confluent opening  162 , and the main channel  14 . The second air passage is provided with the filter  20  between the outlet  12  and the electrostatically atomizing device  30  (see  FIG. 5B ). 
     The switching device  10 C includes a shutter  56 , the control unit  52 C, and the manipulation unit  53 . 
     The shutter  56  is configured to move (slide) between a first position in which the shutter  56  close only the first confluent opening  161  and a second position in which the shutter  56  close only the second confluent opening  162 . In other words, the shutter  56  is defined as a switching valve configured to close the first air passage and the second air passage selectively. As apparent from the above, the air purification apparatus of the present embodiment is provided with a confluence selecting structure for selecting a confluence of the main channel  14  with the auxiliary channel  15  from which one of the points downstream and upstream of the filter  20 . 
     The control unit  52 C is configured to control the shutter  56  and the control circuit  390  in accordance with the operation mode of the air purification apparatus. The control unit  52 C selects one of the first mode and the second mode in response to manual operation of the manipulation unit  53 . Besides, the control unit  52 C controls the control circuit  390  in the same manner as the control unit  52  of the first embodiment, and therefore no explanation thereof is deemed necessary. The fan  40  operates in the air supply mode irrespective of selection of the first mode and the second mode. 
     The control unit  52 C places the shutter  56  in the second position when the first mode is selected (see  FIG. 5A ). Therefore, in the first mode, the second air passage is kept closed, and the first air passage is kept opened. Thus, a mist of charged minute water particles discharged from the electrostatically atomizing device  30  passes the first air passage. As a result, in the first mode, a mist of charged minute water particles is discharged into the external space via the outlet  12  not through the filter  20 . 
     The control unit  52 C places the shutter  56  in the first position when the second mode is selected (see  FIG. 5B ). Therefore, in the second mode, the first air passage is kept closed, and the second air passage is kept opened. Thus, a mist of charged minute water particles discharged from the electrostatically atomizing device  30  passes the second air passage. As a result, in the second mode, a mist of charged minute water particles is allowed to contact with the filter  20 . 
     Besides, irrespective of selection of the first mode and the second mode, air coming into the duct  10 C via the first inlet  111  is discharged out from the outlet  12  through the filter  20 . 
     As described in the above, in the air purification apparatus of the present embodiment, the duct  10 C includes the first air passage and the second air passage. The first air passage is not provided with the filter  20  between the outlet  12  and the electrostatically atomizing device  30 , and the second air passage is provided with the filter  20  between the outlet  12  and the electrostatically atomizing device  30 . The switching device  50 C includes the shutter  56  configured to shut the first air passage and the second air passage selectively, and the control unit  52 C configured to control the shutter  56 . The control unit  52 C is configured to control the shutter  56  to block the second air passage when the first mode is selected, and to control the shutter  56  to block the first air passage when the second mode is selected. 
     Accordingly, the air purification apparatus of the present embodiment also gives the same effect as the air purification apparatus of the first embodiment. Especially, in the present embodiment, the shutter  56  is moved to switch one of the first mode and the second mode. Therefore, it is possible to easily and successfully select one of the first mode and the second mode. 
       FIG. 6  shows a modification of the air purification apparatus of the present embodiment. 
     In the instance shown in  FIG. 6 , the duct  10 D includes the inlet  11  and the outlet  12 . 
     The electrostatically atomizing apparatus  30 D is located close to the inlet  11  within the duct  10 D. The electrostatically atomizing device  30  has its spray hole  331  directed toward the outlet  12 . The electrostatically atomizing device  30  shown in  FIG. 6  is provided with an air hole  312  in its side wall. Partial air coming into the duct  10 D via the inlet  11  comes into the housing  310  through the air hole  312 . 
     The duct  10 D shown in  FIG. 6  is provided with a partition wall  18  between the outlet  12  and the electrostatically atomizing device  30 . The partition wall  18  divides the inner space of the duct  10 D in two portions in order to form a first channel  191  and a second channel  192 . With regard to the instance shown in  FIG. 6 , the filter  20  is placed inside of the second channel  192 . 
     As apparent from the above, in the air purification apparatus shown in  FIG. 6 , the duct  10 D has two air passage (i.e., first air passage and second air passage) between the outlet  12  and the electrostatically atomizing device  30 . 
     The first air passage is defined by the first channel  191  in association with a space between the electrostatically atomizing device  30  and the partition wall  18 . The first air passage is not provided with the filter  20  between the outlet  12  and the electrostatically atomizing device  30 . 
     The second air passage is defined by the second channel  192  in association with the space between the electrostatically atomizing device  30  and the partition wall  18 . The second air passage is provided with the filter  20  between the outlet  12  and the electrostatically atomizing device  30 . 
     The switching device  50 D shown in  FIG. 6  includes the shutter  56 D, the control unit  52 D, and the manipulation unit  53 . 
     The shutter  56 D is attached to an end of the partition wall  18  adjacent to the inlet  11  so as to move (rotate) between a first position and a second position. 
     The first position is defined as a position (position of the shutter  56 D illustrated with broken lines in  FIG. 6 ) in which the shutter  56 D blocks a clearance between the partition wall  18  and a first end (lower end, in  FIG. 6 )  332  of the opposed electrode  330  in order to prevent a mist of charged minute water particles from coming into the first channel  191 . 
     The second position is defined as a position (position of the shutter  56 D illustrated with solid lines in  FIG. 6 ) in which the shutter  56 D blocks a clearance between the partition wall  18  and a second end (upper end, in  FIG. 6 )  333  of the opposed electrode  330  in order to prevent a mist of charged minute water particles from coming into the second channel  192 . 
     In brief, the shutter  56 D is defined as a switching valve configured to close one of the first air passage and the second air passage. As apparent from the above, the air purification apparatus of the present embodiment is provided with a confluence switching structure for selecting one of the first channel  191  and the second channel  192 . 
     The control unit  52 D is configured to control the shutter  56 D and the control circuit  390  in accordance with the operation mode of the air purification apparatus. The control unit  52 D selects one of the first mode and the second mode in response to manual operation of the manipulation unit  53 . Besides, the control unit  52 D controls the control circuit  390  in the same manner as the control unit  52  of the first embodiment, and therefore no explanation thereof is deemed necessary. 
     The control unit  52 D places the shutter  56 D in the second position when the first mode is selected. Therefore, in the first mode, the second air passage is kept closed, and the first air passage is kept opened. Thus, a mist of charged minute water particles discharged from the electrostatically atomizing device  30  passes the first air passage. As a result, in the first mode, a mist of charged minute water particles is discharged into the external space via the outlet  12  without said particles contacting with the filter  20 . 
     The control unit  52 D places the shutter  56 D in the first position when the second mode is selected. Therefore, in the second mode, the first air passage is kept closed, and the second air passage is kept opened. Thus, a mist of charged minute water particles discharged from the electrostatically atomizing device  30  passes the second air passage. As a result, in the second mode, a mist of charged minute water particles is allowed to contact with the filter  20 . 
     Besides, in both the first mode and the second mode, air coming into the duct  10 D via the inlet  11  is discharged out from the outlet  12  through the filter  20 . 
     The modification of the air purification apparatus shown in  FIG. 6  also provides the same effect as the air purification apparatus shown in  FIG. 5 .