Patent Publication Number: US-2023151984-A1

Title: Electrostatic dust collection apparatus and air purifier comprising such electrostatic dust collection apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This utility application claims priority to Taiwan Application Serial Number 110142817, filed Nov. 17, 2021, which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an electrostatic dust collection apparatus and an air purifier including such electrostatic dust collection apparatus, and more in particular, to an electrostatic dust collection apparatus capable of preventing contamination of discharge electrodes and an air purifier including such electrostatic dust collection apparatus and being capable of being miniaturized easily. 
     2. Description of the Prior Art 
     The operation of a general electrostatic dust collection apparatus is to ionize the air to be treated by the principle of corona discharge, such that the suspended particles in the air to be treated are charged by the ion impact. The charged suspended particles move to the collection electrode and are removed from the air to be treated, so as to achieve the purpose of purifying the air to be treated. 
     But, the discharge electrode in the electrostatic dust collection apparatus of the prior art is disposed in the air passage, such that the discharge electrode will be adsorbed by the suspended particles in the air to be treated to gradually reduce the discharge efficiency of the discharge electrode. This results in that the particle interception rate of the electrostatic dust collection apparatus of the prior art will also gradually decrease. 
     Referring to TW patent issue no. 1579052, a prior art prior art of reducing contamination of discharge electrodes is disclosed. The prior art discloses a plate-shaped high voltage conductive unit, a plurality of needle-shaped discharge electrodes, and several insulative members. The insulative members are formed on the plate-shaped high voltage conductive unit, and are respectively located at different positions in the air flow direction. In the direction of air flow, the plurality of needle-shaped discharge electrodes are shielded by the insulative members. Because the insulative members can block the air to be treated from directly flowing to the needle-shaped discharge electrodes, an air stagnation area will occur around the needle-shaped discharge electrodes shielded by the insulative members. However, the insulative members disclosed by the prior art cannot shield all of the needle-shaped discharge electrodes. Moreover, the plate-shaped high voltage conductive unit and the plurality of needle-shaped discharge electrodes disclosed in the prior art are obviously expensive to manufacture. 
     In addition, the plate-shaped collection electrode in most of the electrostatic dust collection apparatus of the prior art only use one surface itself to collect charged suspended particles, and do not fully utilize the whole surface of the plate-shaped collection electrode, which is not beneficial to the miniaturization of the air purifier using the electrostatic dust collection apparatus of the prior art. 
     SUMMARY OF THE INVENTION 
     Accordingly, one scope of the invention is to provide an electrostatic dust collection apparatus capable of preventing contamination of discharge electrodes and an air purifier including such electrostatic dust collection apparatus. The air purifier according to the invention utilizes the whole surface of the collection electrode, which is beneficial to its miniaturization. 
     An electrostatic dust collection apparatus according to a first preferred embodiment of the invention includes a sheet collection electrode, an insulative bearing member, a plurality of discharge electrodes and a high voltage device. The sheet collection electrode has a first surface formed into a plane or an arc surface. The insulative bearing member has a second surface and a plurality of grooves formed on the second surface. The plurality of grooves are formed across the second surface of the insulative bearing member. The plurality of grooves are parallel to one another. The insulative bearing member is disposed so that the second surface of the insulative bearing member faces and is parallel to the first surface of the sheet collection electrode. An air passage is defined between the sheet collection electrode and the insulative bearing member, and allows an air to be treated to pass through. Each discharge electrode corresponds to one of the grooves, and is disposed in the corresponding groove. The high voltage device has a ground terminal and a discharge terminal. The ground terminal of the high voltage device is electrically connected to the sheet collection electrode. The discharge terminal of the high voltage device is electrically connected to the plurality of discharge electrodes such that a potential difference exists between the sheet collection electrode and the plurality of discharge electrodes. The plurality of discharge electrodes charge a plurality of suspended particles in the air to be treated. The sheet collection electrode collects the plurality of charged suspended particles. 
     In one embodiment, a distance between two adjacent grooves in the plurality of grooves ranges from 1 mm to 20 mm. 
     In one embodiment, an included angle between the second surface of the insulative bearing member and a sidewall of each groove ranges from 90 degrees to 335 degrees. 
     An electrostatic dust collection apparatus according to a second preferred embodiment of the invention includes a sheet collection electrode, an insulative bearing member, a plurality of discharge electrodes and a high voltage device. The sheet collection electrode has a first surface formed into a plane or an arc surface. The insulative bearing member has a second surface, a third surface opposite to the second surface and a plurality of grooves formed on the third surface and a plurality of through holes formed on the second surface. The plurality of grooves are formed across the third surface of the insulative bearing member. The plurality of grooves are parallel to one another. The insulative bearing member is disposed so that the second surface of the insulative bearing member faces and is parallel to the first surface of the sheet collection electrode. Each through hole corresponds to one of the plurality of grooves, and communicates with the corresponding groove. An air passage is defined between the sheet collection electrode and the insulative bearing member, and allows an air to be treated to pass through. Each discharge electrode corresponds to one of the grooves, and is disposed in the corresponding groove. The high voltage device has a ground terminal and a discharge terminal. The ground terminal of the high voltage device is electrically connected to the sheet collection electrode. The discharge terminal of the high voltage device is electrically connected to the plurality of discharge electrodes such that a potential difference exists between the sheet collection electrode and the plurality of discharge electrodes. The plurality of discharge electrodes charge a plurality of suspended particles in the air to be treated. The sheet collection electrode collects the plurality of charged suspended particles. 
     In one embodiment, a distance between two adjacent grooves in the plurality of grooves ranges from 1 mm to 20 mm. 
     In one embodiment, an included angle between the second surface of the insulative bearing member and a sidewall of each groove ranges from 90 degrees to 335 degrees. 
     An air purifier according to a third preferred embodiment of the invention includes a tubular collection electrode, an insulative outer tubular bearing member, an insulative inner tubular bearing member, a connecting member, an outer discharge electrode, an inner discharge electrode, and a high voltage device. The tubular collection electrode has a first outer surface and a first inner surface. The insulative outer tubular bearing member has a second outer surface, a second inner surface, a first groove formed on the second outer surface and a plurality of through holes formed on the second inner surface. The first groove extending helically on the second outer surface of the insulative outer tubular bearing member. The tubular collection electrode is disposed in the insulative outer tubular bearing member so that the second inner surface of the insulative outer tubular bearing member faces and is parallel to the first outer surface of the tubular collection electrode. Each through hole communicates with the first groove. A first air passage is defined between the tubular collection electrode and the insulative outer tubular bearing member. The insulative inner tubular bearing member has a third outer surface and a second groove formed on the third outer surface. The second groove extending helically on the third outer surface of the insulative inner tubular bearing member. The insulative inner tubular bearing member is disposed in the tubular collection electrode so that the third outer surface of the insulative inner tubular bearing member faces and is parallel to the first inner surface of the tubular collection electrode. A second air passage is defined between the tubular collection electrode and the insulative inner tubular bearing member. The connecting member connects a first top of the insulative outer tubular bearing member and a second top of the insulative inner tubular bearing member such that a downstream of the first air passage communicates with an upstream of the second air passage. The first air passage and the second air passage allow an air to be treated to pass through. The outer discharge electrode is disposed in the first groove, and extends along the first groove. The inner discharge electrode is disposed in the second groove, and extends along the second groove. The high voltage device has a ground terminal and a discharge terminal. The ground terminal of the high voltage device is electrically connected to the tubular collection electrode. The discharge terminal of the high voltage device is respectively electrically connected to the outer discharge electrode and the inner discharge electrode such that a first potential difference exists between the tubular collection electrode and the outer discharge electrode, and a second potential difference exists between the tubular collection electrode and the inner discharge electrode. The outer discharge electrode and the inner discharge electrode charge a plurality of suspended particles in the air to be treated. The tubular collection electrode collects the plurality of charged suspended particles. 
     In one embodiment, a first distance between two adjacent first groove sections in the first groove ranges from 1 mm to 20 mm. A second distance between two adjacent second groove sections in the second groove ranges from 1 mm to 20 mm. 
     In one embodiment, a first included angle between the third outer surface and a first sidewall of the second groove ranges from 180 degrees to 270 degrees. A second included angle between the second inner surface and a second sidewall of each through hole ranges from 90 degrees to 335 degrees. 
     In one embodiment, the first top of the insulative outer tubular bearing member and the second top of insulative inner tubular bearing member can exhibit a circle, an ellipse, a rectangle, a triangle, a trapezoid, a polygon with more than 4 sides, a half circle, a half ellipse, or other geometric shape. 
     Distinguishable from the prior arts, the electrostatic dust collection apparatus according to the invention can prevent the contamination of the overall polarized electrode, and the overall manufacturing cost of the electrostatic dust collection apparatus is low. The air purifier according to the invention utilizes the whole surface of the collection electrode, which is beneficial to its miniaturization. 
     The advantage and spirit of the invention may be understood by the following recitations together with the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE APPENDED DRAWINGS 
         FIG.  1    is a partial cross-sectional view and a functional block diagram of some devices of an electrostatic dust collection apparatus according to the first preferred embodiment of the invention. 
         FIG.  2    is a flow field simulation analysis diagram of an example of the electrostatic dust collection apparatus according to the first preferred embodiment of the invention. 
         FIG.  3    is a potential simulation analysis diagram of the example of the electrostatic dust collection apparatus according to the invention shown in  FIG.  2   . 
         FIG.  4    is a flow field simulation analysis diagram of another example of the electrostatic dust collection apparatus according to the first preferred embodiment of the invention. 
         FIG.  5    is a potential simulation analysis diagram of the example of the electrostatic dust collection apparatus according to the invention shown in  FIG.  4   . 
         FIG.  6    is a partial enlarged view of a flow field simulation analysis diagram of another example of the electrostatic dust collection apparatus according to the first preferred embodiment of the invention. 
         FIG.  7    is a partial cross-sectional view and a functional block diagram of some devices of an electrostatic dust collection apparatus according to the second preferred embodiment of the invention. 
         FIG.  8    is an explosive view of the members and devices of an air purifier according to the third preferred embodiment of the invention. 
         FIG.  9    is a cross-sectional view taken along line A-A of the air purifier shown in  FIG.  8    after being assembled. 
         FIG.  10    is another cross-sectional view taken along line A-A of the air purifier shown in  FIG.  8    after being assembled. 
         FIG.  11    is an explosive view of the members and devices of a modification of the air purifier according to the third preferred embodiment of the invention. 
         FIG.  12    is a photograph of the appearance of the discharge electrode of the electrostatic dust collection apparatus according to the invention after operating for 1000 hrs. 
         FIG.  13    is a photograph of the appearance of the discharge electrode of the electrostatic dust collection apparatus of the prior art in which the discharge electrode is disposed in the air passage after operating for 24 hrs. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Some preferred embodiments and practical applications of this present invention would be explained in the following paragraph, describing the characteristics, spirit, and advantages of the invention. 
     Referring to  FIG.  1   ,  FIG.  1    schematically shows an electrostatic dust collection apparatus  1  according to the first preferred embodiment of the invention with a partial cross-sectional view and a functional block diagram of some device. 
     As shown in  FIG.  1   , the electrostatic dust collection apparatus  1  according to the first preferred embodiment of the invention includes a sheet collection electrode  10 , an insulative bearing member  12 , a plurality of discharge electrodes  14  and a high voltage device  16 . 
     The sheet collection electrode  10  has a first surface  102  formed into a plane or an arc surface. In the example shown in  FIG.  1   , the first surface  102  of the sheet collection electrode  10  is a plane. 
     The insulative bearing member  12  has a second surface  122  and a plurality of grooves  124  formed on the second surface  122 . The plurality of grooves  124  are formed across the second surface  122  of the insulative bearing member  12 . The plurality of grooves  124  are parallel to one another. The insulative bearing member  12  is disposed so that the second surface  122  of the insulative bearing member  12  faces and is parallel to the first surface  102  of the sheet collection electrode  10 . 
     An air passage P 1  is defined between the sheet collection electrode  10  and the insulative bearing member  12 . The air passage P 1  allows an air to be treated to pass through. In the example shown in  FIG.  1   , the air inlet of the air passage P 1  is located at the top of the electrostatic dust collection apparatus  1  according to the invention, and the air outlet of the air passage P 1  is located at the bottom of the electrostatic dust collection apparatus  1  according to the invention. The arrows marked in the air passage P 1  represent the direction of air flow. 
     Each discharge electrode  14  corresponds to one of the grooves  124 , and is disposed in the corresponding groove  124 . In one embodiment, each discharge electrode  14  is a metal wire, e.g., stainless steel wire, copper wire, tungsten wire, etc. Compared with the electrostatic dust collection apparatus of the prior art, obviously, the electrostatic dust collection apparatus  1  according to the first preferred embodiment of the invention has a simple structure of the discharge electrode  14  and low manufacturing cost. 
     The high voltage device  16  has a ground terminal  162  and a discharge terminal  164 . The ground terminal  162  of the high voltage device  16  is electrically connected to the sheet collection electrode  10 . The discharge terminal  164  of the high voltage device  16  is electrically connected to the plurality of discharge electrodes  14  such that a potential difference exists between the sheet collection electrode  10  and the plurality of discharge electrodes  14 . The plurality of discharge electrodes  14  charge a plurality of suspended particles in the air to be treated. The sheet collection electrode  10  collects the plurality of charged suspended particles. The electrostatic dust collection apparatus  1  according to the first preferred embodiment of the invention is created based on the boundary layer effect of fluid. Regarding the boundary layer effect of the fluid, the fluid is affected by the viscous force and will form a thin boundary layer at the edge of the device or member. Within the thin boundary layer, the flow velocity at the fixed surface is zero, and the flow velocity increases further from the edge of the device or member. 
     Referring to  FIG.  2   ,  FIG.  2    is a flow field simulation analysis diagram of an example of the electrostatic dust collection apparatus  1  according to the first preferred embodiment of the invention. In the flow field simulation analysis case of  FIG.  2   , the width of the air passage P 1  is 5 mm. The enlarged view of the electrostatic dust collection apparatus  1  according to the invention is shown in  FIG.  2    together and marked with an ellipse area with a dotted line. As shown in  FIG.  2   , the denser the streamline density in the air passage P 1  represents the lower the flow velocity there. The flow field simulation analysis diagram of  FIG.  2    confirms that the air flow in the grooves  124  of the insulative bearing member  12  is in a stagnant state. Thereby, the plurality of discharge electrodes  14  can reduce from being fouled by suspended particles. 
     In one embodiment, a distance d 1  between two adjacent grooves  124  in the plurality of grooves  124  ranges from 1 mm to 20 mm. The distance d 1  between two adjacent grooves  124  in the plurality of grooves  124  also represents the distance between two adjacent discharge electrodes  14  in the plurality of discharge electrodes  14 . The smaller the distance d 1  between the two adjacent grooves  124 , the higher the distribution density of the discharge electrodes  14 , and the increase of the spatial ionization region of the air passage P 1 . 
     Referring to  FIG.  3   ,  FIG.  3    is a potential simulation analysis diagram of an example of the electrostatic dust collection apparatus  1  according to the invention shown in  FIG.  2   . Regarding the potential simulation analysis case in  FIG.  3   , the level of potential is represented by the level of gray scales, the plurality of discharge electrodes  14  are electrically connected to the high voltage device  16  of 5 kV, the distance d 1  between two adjacent grooves  124  is 10 mm, and the flow velocity of the air is 2 m/s. The potential simulation analysis diagram of  FIG.  3    confirms that the air flow in the grooves  124  of the insulative bearing member  12  is in a stagnant state. Thereby, the potential of the grooves  124  where the plurality of discharge electrodes  14  are located is the highest, and the potential of the first surface  102  of the sheet collection electrode  10  is 0 V as it is closer to the sheet collection electrode  10 . 
     Referring to  FIG.  4   ,  FIG.  4    is a potential simulation analysis diagram of another example of the electrostatic dust collection apparatus  1  according to the invention. Regarding the potential simulation analysis case in  FIG.  4   , the level of potential is also represented by the level of gray scales, the plurality of discharge electrodes  14  are electrically connected to the high voltage device  16  of 5 kV, the distance d 1  between two adjacent grooves  124  is 5 mm, and the flow velocity of the air is 2 m/s. Likewise, the potential simulation analysis diagram of  FIG.  4    confirms that the air flow in the grooves  124  of the insulative bearing member  12  is in a stagnant state. Thereby, the potential of the grooves  124  where the plurality of discharge electrodes  14  are located is the highest, and the potential of the first surface  102  of the sheet collection electrode  10  is 0V as it is closer to the sheet collection electrode  10 . But, compared to the example shown in  FIG.  3   , in  FIG.  4   , the distribution density of the discharge electrodes  14  is higher. Therefore, the potential simulation analysis diagram of  FIG.  4    confirms that the potential of the region between the two adjacent grooves  124  is also quite high, which also represents an increase in the spatial ionization region of the air passage P 1 . 
     Referring to  FIG.  5   ,  FIG.  5    is a flow field simulation analysis diagram of the example of the electrostatic dust collection apparatus  1  according to the invention shown in  FIG.  4   . In the flow field simulation analysis case of  FIG.  5   , the width of the air passage P 1  is 5 mm. It should be explained first that in the flow field simulation analysis diagram shown in  FIG.  2   , the distance d 1  between two adjacent grooves  124  is 10 mm. In  FIG.  5   , the distance d 1  between two adjacent grooves  124  is 5 mm. As shown in  FIG.  5   , the denser the streamline density in the air passage P 1  represents the lower the flow velocity there. The flow field simulation analysis diagram of  FIG.  5    confirms that the air flow in the grooves  124  of the insulative bearing member  12  is in a stagnant state. Thereby, the plurality of discharge electrodes  14  can reduce from being fouled by suspended particles. 
     In one embodiment, also as shown in  FIG.  1   , an included angle θ 1  between the second surface  122  of the insulative bearing member  12  and a sidewall of each groove ranges from 90 degrees to 335 degrees. 
     In one embodiment, the cross-section of each groove  124  can exhibit triangular (as shown in  FIG.  2   , the base of which is located at the second surface  122 ), trapezoid (the long base of which is located at the second surface  122 ), a groove with an arc-shaped bottom is (referring to  FIG.  6   ), etc.  FIG.  6    is a partial enlarged view of a flow field simulation analysis diagram of another example of the electrostatic dust collection apparatus  1  according to the first preferred embodiment of the invention. In the flow field simulation analysis case of  FIG.  6   , the width of the air passage P 1  is 5 mm. The width of the gas flow channel P 1  is 5 mm. The local area shown in  FIG.  6    is marked with the ellipse area with a dotted line similarly as shown in  FIG.  2   . In  FIG.  6   , the bottom of the groove  124  is arc-shaped, and the included angle θ 1  between the second surface  122  of the insulative bearing member  12  and the sidewall of each groove  124  is 270 degrees. Likewise, the flow field simulation analysis diagram of  FIG.  6    confirms that the air flow in the grooves  124  of the insulative bearing member  12  is in a stagnant state. Thereby, the plurality of discharge electrodes  14  can reduce from being fouled by suspended particles. 
     Referring to  FIG.  7   ,  FIG.  7    schematically shows an electrostatic dust collection apparatus  2  according to the second preferred embodiment of the invention with a partial cross-sectional view and a functional block diagram of some device. 
     As shown in  FIG.  7   , the electrostatic dust collection apparatus  2  according to the second preferred embodiment of the invention includes a sheet collection electrode  20 , an insulative bearing member  22 , a plurality of discharge electrodes  24  and a high voltage device  26 . 
     The sheet collection electrode  20  has a first surface  202  formed into a plane or an arc surface. In the example shown in  FIG.  7   , the first surface  202  of the sheet collection electrode  20  is a plane. 
     The insulative bearing member  22  has a second surface  220 , a third surface  222  opposite to the second surface  220  and a plurality of grooves  224  formed on the third surface  222  and a plurality of through holes  226  formed on the second surface  220 . The plurality of grooves  224  are formed across the third surface  222  of the insulative bearing member  22 . The plurality of grooves  224  are parallel to one another. The insulative bearing member  22  is disposed so that the second surface  220  of the insulative bearing member  22  faces and is parallel to the first surface  202  of the sheet collection electrode  20 . Each through hole  226  corresponds to one of the plurality of grooves  224 , and communicates with the corresponding groove  224 . In one embodiment, one groove  224  corresponds to some through holes  226 . 
     An air passage P 2  is defined between the sheet collection electrode  20  and the insulative bearing member  22 . The air passage P 2  allows an air to be treated to pass through. In the example shown in  FIG.  7   , the air inlet of the air passage P 2  is located at the bottom of the electrostatic dust collection apparatus  2  according to the invention, and the air outlet of the gas flow channel P 2  is located at the top of the electrostatic dust collection apparatus w according to the invention. The arrows marked in the air passage P 2  represent the direction of air flow. 
     Each discharge electrode  24  corresponds to one of the grooves  224 , and is disposed in the corresponding groove  224 . 
     In one embodiment, each discharge electrode  24  is a metal wire, e.g., stainless steel wire, copper wire, tungsten wire, etc. Compared with the electrostatic dust collection apparatus of the prior art, obviously, the electrostatic dust collection apparatus  2  according to the second preferred embodiment of the invention has a simple structure of the discharge electrode  24  and low manufacturing cost. 
     The high voltage device  26  has a ground terminal  262  and a discharge terminal  264 . The ground terminal  262  of the high voltage device  26  is electrically connected to the sheet collection electrode  20 . The discharge terminal  264  of the high voltage device  26  is electrically connected to the plurality of discharge electrodes  24  such that a potential difference exists between the sheet collection electrode  20  and the plurality of discharge electrodes  24 . The plurality of discharge electrodes  24  charge a plurality of suspended particles in the air to be treated. The sheet collection electrode  20  collects the plurality of charged suspended particles. 
     Similarly, the electrostatic dust collection apparatus  2  according to the second preferred embodiment of the invention is created based on the boundary layer effect of fluid. Regarding the boundary layer effect of the fluid, the fluid is affected by the viscous force and will form a thin boundary layer at the edge of the device or member. Within the thin boundary layer, the flow velocity at the fixed surface is zero, and the flow velocity increases further from the edge of the device or member. 
     In one embodiment, the sides of the plurality of through holes  226  corresponding to the same groove  224  adjacent to the second surface  220  of the insulative bearing member  22  can be connected in series. Thereby, the insulative bearing member  22  can still maintain a certain strength, and the internal air flow in all of the through holes  226  can be in a stagnant state. The parts of the plurality of polarized electrodes  24  exposed to all of the through holes  226  can be reduced from being contaminated by suspended particles. 
     In one embodiment, also as shown in  FIG.  7   , a distance d 2  between two adjacent grooves  224  in the plurality of grooves  224  ranges from 1 mm to 20 mm. The distance d 2  between two adjacent grooves  224  in the plurality of grooves  224  also represents the distance between two adjacent discharge electrodes  24  in the plurality of discharge electrodes  24 . The smaller the distance d 2  between the two adjacent grooves  224 , the higher the distribution density of the discharge electrodes  24 , and the increase of the spatial ionization region of the air passage P 2 . 
     In one embodiment, an included angle θ 2  between the second surface  220  of the insulative bearing member  22  and a sidewall of each groove  224  ranges from 90 degrees to 335 degrees. 
     Referring to  FIG.  8   ,  FIG.  9    and  FIG.  10   , those drawings schematically illustrate an air purifier  3  according to the third preferred embodiment of the invention.  FIG.  8    schematically shows the air purifier  3  according to the third preferred embodiment of the invention with an explosive view of devices and members.  FIG.  9    is a cross-sectional view taken along line A-A of the air purifier  3  shown in  FIG.  8    after being assembled.  FIG.  10    is another cross-sectional view taken along line A-A of the air purifier  3  shown in  FIG.  8    after being assembled. 
     As shown in  FIG.  8   ,  FIG.  9    and  FIG.  10   , the air purifier  3  according to the third preferred embodiment of the invention includes a tubular collection electrode  30 , an insulative outer tubular bearing member  31 , an insulative inner tubular bearing member  32 , a connecting member  33 , an outer discharge electrode  34 , an inner discharge electrode  35 , and a high voltage device  36 . 
     The tubular collection electrode  30  has a first outer surface  302  and a first inner surface  304 . 
     The insulative outer tubular bearing member  31  has a second outer surface  310 , a second inner surface  312 , a first groove  314  formed on the second outer surface  310  and a plurality of through holes  316  formed on the second inner surface  312 . The first groove  314  extending helically on the second outer surface  310  of the insulative outer tubular bearing member  31 . The tubular collection electrode  30  is disposed in the insulative outer tubular bearing member  31  so that the second inner surface  312  of the insulative outer tubular bearing member  31  faces and is parallel to the first outer surface  302  of the tubular collection electrode  30 . Each through hole  316  communicates with the first groove  314 . A first air passage P 3  is defined between the tubular collection electrode  30  and the insulative outer tubular bearing member  31 . In the example shown in  FIG.  9    and  FIG.  10   , the air inlet of the first air passage P 3  is located at the bottoms of the insulative outer tubular bearing member  31  and the tubular collection electrode  30 , and the air outlet of the first air passage P 3  is located at the tops of the insulative outer tubular bearing member  31  and the tubular collection electrode  30 . 
     The insulative inner tubular bearing member  32  has a third outer surface  320  and a second groove  322  formed on the third outer surface  320 . The second groove  322  extending helically on the third outer surface  320  of the insulative inner tubular bearing member  32 . The insulative inner tubular bearing member  32  is disposed in the tubular collection electrode  30  so that the third outer surface  320  of the insulative inner tubular bearing member  32  faces and is parallel to the first inner surface  304  of the tubular collection electrode  30 . A second air passage P 4  is defined between the tubular collection electrode  30  and the insulative inner tubular bearing member  32 . In the example shown in  FIG.  9    and  FIG.  10   , the air inlet of the second air passage P 4  is located at the tops of the insulative inner tubular bearing member  32  and the tubular collection electrode  30 , and the air outlet of the second air passage P 4  is located at the bottoms of the insulative inner tubular bearing member  32  and the tubular collection electrode  30 . 
     As shown in  FIG.  9    and  FIG.  10   , the connecting member  33  connects a first top of the insulative outer tubular bearing member  31  and a second top of the insulative inner tubular bearing member  32  such that a downstream of the first air passage P 3  communicates with an upstream of the second air passage P 4 . The first air passage P 3  and the second air passage P 4  allow an air to be treated to pass through. The arrows marked in the first air passage P 3  and the second air passage P 4  represent the direction of air flow. 
     As shown in  FIG.  8    and  FIG.  9   , the outer discharge electrode  34  is disposed in the first groove  314 , and extends along the first groove  314 . For the convenience of description, in  FIG.  9   , the outer discharge electrode  34  is only shown as a winding track, and the inner discharge electrode  35  is not shown, so as to clearly show the winding track of the outer discharge electrode  34 . 
     As shown in  FIG.  8    and  FIG.  10   , the inner discharge electrode  35  is disposed in the second groove  322 , and extends along the second groove  322 . For the convenience of description, in  FIG.  10   , the inner discharge electrode  35  is only shown as a winding track, and the outer discharge electrode  34  is not shown, so as to clearly show the winding track of the inner discharge electrode  35 . 
     As shown in  FIG.  9    and  FIG.  10   , the high voltage device  36  has a ground terminal  362  and a discharge terminal  364 . The ground terminal  362  of the high voltage device  36  is electrically connected to the tubular collection electrode  30 . The discharge terminal  364  of the high voltage device  36  is respectively electrically connected to the outer discharge electrode  34  and the inner discharge electrode  35  such that a first potential difference exists between the tubular collection electrode  30  and the outer discharge electrode  34 , and a second potential difference exists between the tubular collection electrode  30  and the inner discharge electrode  35 . The outer discharge electrode  34  and the inner discharge electrode  35  charge a plurality of suspended particles in the air to be treated. The tubular collection electrode  30  collects the plurality of charged suspended particles. Obviously, the air purifier  3  according to the invention utilizes the whole surface of the tubular collection electrode  30 , which facilitates the miniaturization of the air purifier  3 . 
     The tubular collection electrode  30 , the insulative inner tubular bearing member  32 , the inner discharge electrode  35  and the high voltage device  36  disclosed in the air purifier  3  according to the invention are equivalent to the electrostatic dust collection apparatus  1  according to the first preferred embodiment of the invention. The tubular collection electrode  30 , the insulative outer tubular bearing member  31 , the outer discharge electrode  34 , and the high voltage device  36  disclosed in the air purifier  3  according to the invention are equivalent to the electrostatic dust collection apparatus  2  according to the second preferred embodiment of the invention. The outer discharge electrode  34  and the inner discharge electrode  35  both are a single metal wire, e.g., stainless steel wire, copper wire, tungsten wire, etc. The outer discharge electrode  34  and the inner discharge electrode  35  have a simple structure, and their manufacturing cost is low. 
     Also as shown in  FIG.  8   ,  FIG.  9    and  FIG.  10   , the air purifier  3  according to the third preferred embodiment of the invention further includes a fan  38  and a base  39 . The connecting member  33  also constitutes a bearing seat, and the fan  38  is fixed in the bearing seat. The air suction port of the fan  38  is located in the bearing seat, and communicates with the air outlet at the bottoms of the insulative inner tubular bearing member  32  and the tubular collection electrode  30 . The bottom of the tubular collection electrode  30  is disposed on the base  39 . 
     In one embodiment, a first distance d 3  between two adjacent sections of the first groove  314  ranges from 1 mm to 20 mm. The first distance d 3  also represents the distance between two adjacent turns of the outer discharge electrode  34  been wound. The smaller the first distance d 3 , the higher the distribution density of the outer discharge electrode  34 , and the increase of the spatial ionization region of the first air passage P 3 . A second distance d 4  between two adjacent sections of the second groove  322  ranges from 1 mm to 20 mm. The second distance d 3  also represents the distance between two adjacent turns of the inner discharge electrode  35  been wound. The smaller the second distance d 4 , the higher the distribution density of the inner discharge electrode  35 , and the increase of the spatial ionization region of the second air passage P 4 . 
     In one embodiment, a first included angle θ 3  between the third outer surface  320  of the insulative inner tubular bearing member  32  and a first sidewall of the second groove  322  ranges from 180 degrees to 270 degrees. A second included angle θ 4  between the second inner surface  312  of the insulative outer tubular bearing member and a second sidewall of each through hole  316  ranges from 90 degrees to 335 degrees. 
     In one embodiment, the first top of the insulative outer tubular bearing member  31  and the second top of the insulative inner tubular bearing member  32  can exhibit a circle (as shown in  FIG.  8   ), an ellipse, a rectangle, a triangle, a trapezoid, a polygon with more than 4 sides, a half circle, a half ellipse, or other geometric shape. 
     Referring to  FIG.  11   ,  FIG.  11    schematically illustrates a modification of the air purifier  3  according to the third preferred embodiment of the invention with an explosive view of devices and members. Obviously, the tops of the tubular collection electrode  30 , the insulative outer tubular bearing member  31  and the insulative inner tubular bearing member  32  all exhibit a rectangle. The devices and members in  FIG.  11    identical to those shown in  FIG.  8    are given the same numerical notations, and will be not described in detail herein. Due to the structure and arrangement of the collection electrode and the polarizing electrode, the air purifier of the prior art has its appearance limited to the design of a cube or a cylinder. The appearance design of the air purifier  3  according to the third preferred embodiment of the invention can have more choices to enhance the overall aesthetic feeling. 
     Table 1 lists the test results of the interception rate of suspended particles (PM2.5) of the air purifier according to the invention for different distances between two adjacent turns of the discharge electrodes and different flow velocities of the air. In this test case, the total length of the air passage of the air purifier according to the invention is 5 cm, the width of the air passage is 5 mm, the discharge electrodes are electrically connected to the high voltage device of 5 kV, and the original concentration of the suspended particles (PM2.5) of the air to be treated is 10,000 particles/m 3 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 velocity 
                   
               
            
           
           
               
               
               
            
               
                 distance 
                 1 m/s 
                 2 m/s 
               
               
                   
               
               
                 10 mm  
                 62.4%  
                 25.4% 
               
               
                 7 mm 
                 100% 
                 31.8% 
               
               
                 5 mm 
                 100% 
                  100% 
               
               
                   
               
            
           
         
       
     
     The results listed in Table 1 confirm that the interception rate of suspended particles (PM2.5) of the air purifier according to the invention is up to 100% under the condition of narrower distances between two adjacent turns of the discharge electrodes and lower flow velocities of the air. 
     Referring to  FIG.  12    and  FIG.  13   ,  FIG.  12    is a photograph of the appearance of the discharge electrode of the electrostatic dust collection apparatus according to the invention after operating for 1000 hrs. In contrast,  FIG.  13    is a photograph of the appearance of the discharge electrode of the electrostatic dust collection apparatus of the prior art in which the discharge electrode is disposed in the air passage after operating for 24 hrs. 
     The photograph of  FIG.  12    confirms that the discharge electrode disposed in the groove of the electrostatic dust collection apparatus according to the invention is in a stagnant state due to airflow, and the discharge electrode will not be contaminated by suspended particles even after long-term operation. On the contrary, the photograph of  FIG.  13    confirms that the prior art electrostatic dust collection apparatus disposes the discharge electrode in the air passage, and after a short time of operation, the discharge electrode is fouled by the suspended particles. 
     With detailed description of the invention above, it is clear that the electrostatic dust collection apparatus according to the invention can prevent the contamination of the overall polarized electrode, and the overall manufacturing cost of the electrostatic dust collection apparatus is low. The air purifier according to the invention utilizes the whole surface of the collection electrode, which is beneficial to its miniaturization. 
     With the example and explanations above, the features and spirits of the invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.