Abstract:
A multi-filter PM 10-PM 2.5 sampler which enable the simultaneous collection of four PM 10 and four PM 2.5 samples is disclosed. The sampler is provided with a PM 10 impactor to remove coarse particles and operates at 33.4 L/min. After the PM 10 impactor, the aerosol flow is divided by half by a branch pipe. Half of the flow is directed into four PM 10 cassettes, while the other half is directed into four PM 2.5 cassettes after the aerosols are further classified by a PM 2.5 impactor. To ensure the aerosol flow uniformly passes through each of the four PM 10 or four PM 2.5 cassettes, an orifice plate is assembled behind each of the filter cassettes to increase the pressure drop, such that the flow rates of eight sampling lines are nearly equal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to an aerosol sampler, and more particularly, to a multi-filter sampler for collecting PM 10 and PM 2.5 samples simultaneously. 
         [0003]    2. Description of the Related Art 
         [0004]    U.S. patent application Ser. No. 2010/0089183 disclosed a multi-filter sampler, which classifies particles by means of an impaction separator. Coarse particles with the aerodynamic diameter of 2.5-10 μm are led to pass through a first separation assembly and are collected by a 102 mm filter paper and three 47 mm filter papers, while fine particles having an aerodynamic diameter smaller than 2.5 μm pass through a second separation assembly and are collected by an 8×10 inch filter and four 47 mm filters. The user is consequently able to obtain the ambient air quality information by analyzing the filters. However, the filter cassettes have different flow rates from one another, so it is inconvenient to calibrate or operate the sampler, which results in inaccurate sampling. 
       SUMMARY OF THE INVENTION 
       [0005]    The primary objective of the present invention is to provide a multi-filter PM 10-PM 2.5 sampler, which is capable of collecting PM 10 and PM 2.5 samples simultaneously and has a better accuracy. 
         [0006]    The foregoing objective of the present invention is attained by the multi-filter PM 10-PM 2.5 sampler composed of a PM 10 impactor, a branch pipe, a PM 10 flow splitter, a plurality of PM 10 filter devices, a PM 2.5 impactor, a PM 2.5 flow splitter, a plurality of PM 2.5 filter devices, a conflux assembly, a plurality of flow uniformization devices, and an air pump. The branch pipe includes a top end, a left end, and a right end. The PM 10 impactor is connected with the top end of the branch pipe. The PM 10 flow splitter includes an inlet and a plurality of outlets. The inlet of the PM 10 flow splitter is connected with the left end of the branch pipe and the outlets are connected with the PM 10 filter devices separately. The PM 2.5 impactor is connected with the right end of the branch pipe. The PM 2.5 flow splitter includes an inlet and a plurality of outlets. The inlet of the PM 2.5 flow splitter is connected with the PM 2.5 impactor. The PM 2.5 filter devices are connected with the outlets of the PM 2.5 flow splitter. The flow uniformization devices are connected between the PM 10 filter devices and the conflux assembly and between the PM 2.5 filter devices and the conflux assembly, which make the flow rates even by reducing the perssure drop differences among the filter devices of the PM 10 and PM 10 filter devices. The air pump is connected with the conflux assembly. 
         [0007]    In one of the preferred embodiments of the present invention, each of the PM 10 impactor and the PM 2.5 impactor includes an external housing, a nozzle, and an impact plate. The external housing has a chamber and an exit. The nozzle is mounted to the external housing and has an acceleration passage communicating with the chamber. The impact plate is mounted inside the chamber and located on an imaginary axis extension line of the acceleration passage. The multi-filter PM 10-PM 2.5 sampler further includes a protective mesh mounted to a top end of the PM 10 impactor. The multi-paper PM 10-PM 2.5 sampler further includes a plurality of flow uniformization devices mounted between the PM 10 filter devices and the conflux assembly or between the PM 2.5 filter devices and the conflux assembly. The uniformization device includes an upper member, an orifice plate and an lower member. The upper member has an axial hole including a smaller-diameter portion, a threaded portion, and a larger-diameter portion located between the smaller-diameter portion and the threaded portion for receiving the orifice plate. The lower member has a threaded portion and an axial hole, the axial hole being located inside the threaded portion, the threaded portion engaging with the threaded portion of the axial hole of the upper member, the axial hole of the lower member communicating with the smaller-diameter portion of the axial hole via a through hole of the orifice plate. The conflux assembly includes a PM 10 conflux device, a PM 2.5 conflux device, and a terminal conflux device. The PM 10 conflux device has a plurality of entrances and an exit. Each of the entrances of the PM 10 conflux device is connected with one of the PM 10 filter devices. The PM 2.5 conflux device has a plurality of entrances and an exit. Each of the entrances of the PM 2.5 conflux device is connected with one of the PM 2.5 filter devices. The terminal conflux device is connected among the exit of the PM 10 conflux device, the exit of the PM 2.5 conflux device, and the air pump. The multi-filter PM 10-PM 2.5 sampler further includes two mass flow controllers, a pressure sensor, a temperature sensor, and a control PC. The mass flow controller, the pressure sensor, the temperature sensor, and the air pump are electrically connected with the control PC. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic view of a preferred embodiment of the present invention. 
           [0009]      FIG. 2  is a perspective view of a part of the preferred embodiment of the present invention, illustrating a flow splitter. 
           [0010]      FIG. 3  is a perspective view of parts of the preferred embodiment of the present invention, illustrating a filter device and a flow uniformization device. 
           [0011]      FIG. 4  is a sectional exploded view of the preferred embodiment of the present invention, illustrating the flow uniformization device. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0012]    Referring to  FIG. 1 , a multi-filter PM 10-PM 2.5 sampler  10  constructed according to a preferred embodiment of the present invention is composed of a PM 10 impactor  20 , a branch pipe  22 , a PM 10 flow splitter  24 , four PM 10 filter devices  26 , a PM 2.5 impactor  28 , a PM 2.5 flow splitter  30 , four PM 2.5 filter devices  32 , a protective mesh  36 , a conflux assembly  40 , a flow control system  50 , and a plurality of flow uniformization devices  60 . The detailed descriptions and operations of these elements as well as their interrelations are recited in the respective paragraphs as follows. 
         [0013]    The PM 10 impactor  20  includes an external housing  201 , a nozzle  205 , and an impact plate  207 . The external housing  201  has a chamber  202  and an exit  204 . The nozzle  205  is mounted to the external housing  201  and has an acceleration passage  206  in communication with the chamber  202 . The impact plate  207  is mounted inside the chamber  202  and located on an imaginary axis extension line A of the acceleration passage  206 . 
         [0014]    The branch pipe  22  is composed of two tubular members  221  and includes a top end  224 , a left end  226 , and a right end  228 . The top end  224  is connected with the exit  204  of the PM 10 impactor  20  for dividing the airflow passing through the PM 10 impactor  20  into two parts. 
         [0015]    The PM 10 flow splitter  24 , as shown in  FIG. 2 , includes an inlet  241 , four outlets  243 , and four channels  245 . The channels  245  are arranged equiangularly and communicate with the inlet  241  and the outlet  243  for dividing the airflow into four parts. 
         [0016]    Each of the PM 10 filter devices  26 , as shown in  FIG. 3 , is connected with one of the outlets  243  of the PM 10 flow splitters  24  and internally includes a filter cassette  261 , in which a 37 mm filter paper is provided, for collecting PM 10 particle samples. 
         [0017]    The PM 2.5 impactor  28  likewise includes an external housing  281 , a nozzle  285 , and impact plate  287 . The external housing  281  has a chamber  282  and an exit  284 . The nozzle  285  is mounted to the external housing  281  and has an acceleration passage  286  communicating with the chamber  282 . The impact plate  287  is mounted inside the chamber  282  and located on an axis extension line of the acceleration passage  286 . The PM 2.5 impactor  28  and the PM 10 impactor  20  are structurally similar to each other but different in size and cutoff aerodynamic diameter; the cutoff aerodynamic diameter of the former is 2.5 pm and the latter 10 μm. 
         [0018]    The PM 2.5 flow splitter  30  ( FIG. 2 ) is similar to the PM 10 flow splitter  24  in structure and size, likewise having an inlet  301 , four outlets  303 , and four channels  305  arranged equiangularly and communicating with the inlet  301  and the outlets  303 . 
         [0019]    Each of the PM 2.5 filter devices  32  ( FIG. 3 ) is connected with one of the outlets  303  of the PM 2.5 flow splitter  30  and internally includes a filter cassette  321 , in which a 37 mm filter paper is provided, for collecting PM 2.5 particle samples. 
         [0020]    The protective mesh  36  is made of metal and mounted to a top end of the PM 2.5 impactor  20  for preventing any insect or other foreign matter from entering the PM 10 impactor  20 . 
         [0021]    The conflux assembly  40  includes a PM 10 conflux device  42 , a PM 2.5 conflux device  44 , and a terminal conflux device  46 . The PM 10 conflux device  42  includes a plurality of entrances  421  and an exit  423 . Each of the entrances  421  is connected with one of the PM 10 filter devices  26 . The PM 2.5 conflux device  44  likewise includes a plurality of entrances  441  and an exit  443 . Each of the entrances  441  is connected with one of the PM 2.5 filter devices  32 . The terminal conflux device  46  is connected among the exit  423  of the PM 10 conflux device  42  and the exit  443  of the PM 2.5 conflux device  44 . 
         [0022]    The flow control system  50  includes an air pump  52 , two mass flow controllers  54 , a pressure sensor  56 , a temperature sensor  58 , and a control PC  59 . The air pump  52  is connected with the terminal conflux device  46  for providing pumping power for the sampler  10 . One of the mass flow meters  54  is connected between the PM 10 conflux device  42  and the terminal conflux device  46  and the other is connected between the PM 2.5 conflux device  44  and the terminal conflux device  46 . The control PC  59  is electrically connected with the air pump  52 , the mass flow controllers  54 , the pressure sensor  56 , and the temperature sensor  58 . The standard flow rate of mass flow controllers  54  is adjusted automatically based on the ambient temperature and pressure obtained by the pressure sensor  56 , and the temperature sensor  58 . 
         [0023]    The flow uniformization devices  60  ( FIGS. 3-4 ) are connected between the PM 10 filter devices  26  and the PM 10 conflux device  42  or between the PM 2.5 filter device  32  and the PM 2.5 conflux device  44 . Each of the flow uniformization devices  60  includes an upper member  62 , an orifice plate  64 , and a lower member  66 . The upper member  62  is connected with the filter device  26  or  32  and has an axial hole  621  with a smaller-diameter portion  623 , a larger-diameter portion  625 , and a threaded part  627 . The larger-diameter portion  625  is located between the smaller-diameter portion  623  and the threaded part  627  for receiving the orifice plate  64 . The orifice plate  64  has a small through hole  641 . The lower member  66  has a threaded portion  661  and an axial hole  663 . The threaded portion  661  engages with the threaded part  627  of the axial hole  621  of the upper member  62 . The axial hole  663  of the lower member  66  communicates with the smaller-diameter portion  623  of the upper member  62  via the through hole  641  of the orifice plate  64 . 
         [0024]    While the air pump  52  is operated, aerosols are guided into the sampler  10  at 33.4 L/min via an annular slot inlet  21 . After the inlet  21 , the PM 10 impactor  20  is used to remove particles greater than 10 μm in aerodynamic diameter. Aerosol flow is then divided into two stream of equal flow rate of 16.7 L/min by the smooth branch pipe  22 , one stream is led to four PM 10 filter devices  26  behind the PM 10 flow splitter  24 , and the other is introduced into the PM 2.5 impactor  28 . After the PM 2.5 impactor  28 , the aerosol stream is divided by the PM 2.5 splitter  30  into four PM 2.5 filter devices. The flow control system  50  is used to control the total actual sampling flow rate of both PM 10 and PM 2.5 at 16.7 L/min using the feedback signals of ambient temperature and pressure. 
         [0025]    The PM 10 filter devices  26  and the PM 2.5 filter device  32  are able to collect four PM 10 filter samples and four PM 2.5 filter samples at the same time for further analysis, such as gravimetric analysis, organic carbon analysis, elemental carbon analysis, metallic element analysis, ionic analysis, etc., thus avoiding the inaccuracy resulting from cutting the filter paper and saving the cost caused by installing multiple samplers. 
         [0026]    When filters of different types are used, the pressure drops of the filter devices  26  and  32  are not equal due to the differences in filter porosity and thickness, and therefore the flow rates of the filter devices  26  and  32  are different. The orifice plate  64  of the flow uniformization device  60  is provided to enhance the pressure drop of each sampling channel of the filter devices  26  and  32  to lower the relative difference of pressure drop resulting from different filters. Table 1 show that when the orifice plates  64  are not used, the maximum relative difference in the pressure drop created by Teflon filters is 10.3%, which is large due to the differences in the filters. The flow rates between sampling lines are shown to be non-uniform with a maximum relatively difference of 9.1%. However, after the orifice plates  64  with the diameter of 1.1 mm are assembled behind the filter cassettes  261  and  321 , the pressure drop in each sampling line is increased by nearly the same amount of about 40 cm H 2 O, which reduces the relatively differences in the pressure drop to less than 1.9%. Since the pressure drop differences are reduced, the flow rate uniformity between four sampling channels is achieved with a relatively difference of less than 1.7%. The flow rates of all of the filter devices  26  and  30  are nearly the same to enable the sampler  10  to be calibrated or operated more easily and to enhance the accuracy of collection. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Comparison of difference of pressure drops and flow rates of filter 
               
               
                 channels before he orifice plate is installed. 
               
             
          
           
               
                   
                 No Orifice Plate Installed 
                 Orifice Plate Installed 
               
             
          
           
               
                   
                 ΔP 
                   
                 ΔP 
                   
               
               
                 Channel No. 
                 (cmH 2 O)* 
                 Q a  (L/min)** 
                 (cmH 2 O)* 
                 Q a  (L/min)** 
               
               
                   
               
               
                 1 
                 13.75 
                 3.90 
                 54.68 
                 4.12 
               
               
                 2 
                 14.37 
                 3.75 
                 54.99 
                 4.07 
               
               
                 3 
                 13.03 
                 4.09 
                 53.95 
                 4.14 
               
               
                 4 
                 13.54 
                 3.97 
                 54.37 
                 4.13 
               
               
                 Max Relative 
                 10.3% 
                 9.1% 
                 1.9% 
                 1.7% 
               
               
                 Difference 
               
               
                   
               
               
                 Note: 
               
               
                 *The standard flow rate of each filter channel is controlled at 4.17 L/min. 
               
               
                 **The standard flow rate sum of each filter channel is controlled at 16.7 L/min. 
               
             
          
         
       
     
         [0027]    Although the present invention has been described with respect to a specific preferred embodiment thereof, it is in no way limited to the specifics of the illustrated structures but changes and modifications may be made within the scope of the appended claims.