Abstract:
A portable nanoparticle sampler for collecting respirable particulate matters and nanoparticles is composed of a tangential flow cyclone, a multi-microorifice impactor and a filter cassette. The tangential flow cyclone can remove the microparticles with cutoff aerodynamic diameter (dpa) larger than 4 μm and guide the airflow to the multi-microorifice impactor located below the cyclone. The multi-microorifice impactor includes a multi-orifice nozzle and a rotary impaction plate for enabling the microparticles with dpa from 100 nm to 4 μm to be uniformly collected on a silicon-oil-coated impaction substrate. The remanent microparticles with dpa smaller than 100 nm are collected by the filter cassette. Therefore, compared with the prior art, the portable nanoparticle sampler is characterized by low pressure loss and accurate microparticle sizing to meet the requirement of nanoparticle sampling at workplaces.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a microparticle sampler and more particularly, to a portable nanoparticle (NP) sampler. 
         [0003]    2. Description of the Related Art 
         [0004]    According to many studies, inhaled NPs pose a high adverse effect on human health. To assess the occupational health risk due to the exposure to the NPs in workplaces, it is necessary to collect the NPs of various diameters for further analysis of their ingredients. 
         [0005]    A variety of NP samplers have been commercially available, including electric low-pressure impactor (ELPI), low-pressure impactor (LPI), microorifice uniform deposition impactor (MOUDI), and nano micro-orifice uniform deposition impactor (Nano-MOUDI). However, such samplers are too large and too heavy. Besides, the flow rate and the pressure loss are too high in the process of sampling to make the samplers work with small portable pumps. Thus, they could only be put at a fixed location for collecting NPs. 
         [0006]    To measure the particle concentration at the actual workplaces more accurately, the inventors of the present invention successfully developed a personal NP sampler as disclosed in U.S. Pat. Laid-open No. 2009/0272202. The personal NP sampler is composed of a per-classifier, a nozzle, a particle-sizing filter pack, and a final filter pack from bottom to top for guiding an airflow from bottom to top to enable the airflow to be filtered by a particle-sizing filter and the final filter. Although such personal NP sampler can collect the NPs of different diameters via two stages and be applied to the small pump, the cutoff diameter of the particle-sizing filter is related to the flow rate of the airflow thereat and the flow rate is subject to the invariable number of the pores of the particle-sizing filter in such a way that a deviation happens between the cutoff diameter thereat and the default. 
         [0007]    In other words, the aforesaid personal NP sampler though has had preferable portability but the cutoff diameter is subject to slight inaccuracy, so it still needs further improvement. 
       SUMMARY OF THE INVENTION 
       [0008]    The primary objective of the present invention is to provide an NP sampler, which is portable and precise at the same time. 
         [0009]    The foregoing objective of the present invention is attained by the NP sampler composed of a tangential flow cyclone, a multi-microorifice impactor located below the tangential flow cyclone, and a filter cassette located below the multi-microorifice impactor. 
         [0010]    The tangential flow cyclone includes a cyclone body and an outflow duct. The cyclone body is formed of an annular portion, a top plate, and a bottom plate. The top plate and the bottom plate are mounted to a top side and a bottom side of the annular portion, respectively. A first chamber is defined between the annular portion, the top plate, and the bottom plate. An inlet is formed on the annular portion for communication with the first chamber. The outflow duct runs through the bottom plate and is provided with an entrance and an exit. The entrance is located inside the first chamber and higher than the inlet in elevation. The outflow duct allows a gas entering the first chamber to downwardly pass through the entrance and the exit and then to exit the tangential flow cyclone. 
         [0011]    The multi-microorifice impactor includes an impaction body, a nozzle base, and an impaction plate. The impaction body defines a second chamber. The nozzle base has multiple microorifice nozzles communicating with the exit and the second chamber. The impaction plate is located inside the second chamber and right beneath the nozzle base. 
         [0012]    The filter cassette defines a third chamber and includes a guide passage, an outlet, and a filter. The filter is mounted inside the third chamber and partitions the third chamber into a filtration chamber and an outtake chamber. The guide passage communicates with the second chamber and the filtration chamber. The outlet communicates with the outtake chamber. 
         [0013]    The output airflow exiting the tangential flow cyclone through the exit is downward and the multi-microorifice impactor is employed, so the NP sampler of the present invention has lower pressure loss for working with a small pump. Besides, the cutoff diameter of the respirable particulate mass (RPM) collected by the multi-microorifice impactor at the second stage can be precisely maintained to the default without any deviation to help further analysis and comparison to reach the aforesaid objective of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is an exploded view of a preferred embodiment of the present invention. 
           [0015]      FIG. 2  is a sectional view of the preferred embodiment of the present invention. 
           [0016]      FIG. 3  is a top view of a nozzle base of the preferred embodiment of the present invention. 
           [0017]      FIG. 4  is an enlarged view of a part of the preferred embodiment of the present invention, illustrating the nozzle base and the impaction plate. 
           [0018]      FIG. 5  is a schematic view of the preferred embodiment of the present invention at work. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    Referring to  FIGS. 1-2 , a portable NP sampler constructed according to a preferred embodiment of the present invention is composed of a tangential flow cyclone  10 , a multi-microorifice impactor  20  located below the tangential flow cyclone  10 , and a filter cassette  30  located below the multi-microorifice impactor  20 . The detailed descriptions and operations of these elements as well as their interrelation are recited in the respective paragraphs as follows. Note that the phrases “top”, “bottom”, “high”, “lower”, and “upper” are defined while the portable NP sampler is erect on the ground, i.e. according to the relative positions in gravity. 
         [0020]    The tangential flow cyclone  10  includes a cyclone body  11  and an outflow duct  12 . The cyclone body  11  has an annular portion  111 , a top plate  112  mounted to a top side of the annular portion  111 , and a bottom plate  113  mounted to a bottom side of the annular portion  111 . A first chamber  114  is defined between the annular portion  111 , the top plate  112 , and the bottom plate  113 . An inlet  115  is formed on the annular portion  111  for communication with the first chamber  114  and axially parallel to an imaginary tangential direction of an internal surface of the annular portion  111 . The outflow duct  12  runs through the bottom plate  113  and has an entrance  121  and an exit  122 . The inlet  121  is located inside the first chamber  114  and higher than the inlet  115  in elevation, so the outflow duct  12  can allow the airflow entering the first chamber  114  to downwardly exit the tangential flow cyclone  10  through the entrance  121  and the exit  122 . In this embodiment, the inlet  115  has a square cross-section; on the premise that the flow rate keeps constant at 2 L/min, the diameter of the inlet  115  is 2.1 mm×2.1 mm, the cutoff diameter of the tangential flow cyclone is 4 μm. 
         [0021]    To facilitate cleaning the first chamber  114 , the bottom plate  113  can be designed to be detachably mounted to a bottom end of the annular portion  111  by threaded connection or alternative proper means. The outflow duct  12  is combined to the bottom plate  113 , so when the bottom plate  113  and the annular portion  111  are separated from each other, the outflow duct  12  can be detached apart from the annular portion  111 . 
         [0022]    The multi-microorifice impactor  20  includes an impaction body  21 , a nozzle base  22 , and an impaction plate  23 . The impaction body  21  defines a second chamber  24  therein and is formed of an upper half part  211  and a lower half part  212 . The nozzle base  22  is arranged between the impaction body  21  and the outflow duct  12 . As shown in  FIG. 3 , the nozzle base  22  includes multiple nozzles  221  communicating with the exit  122  and the second chamber  24 , respectively. The impaction plate  23  is located inside the second chamber  24  and right beneath the nozzle base  22 . A predetermined gap is formed between a peripheral edge of the impaction plate  23  and a peripheral wall of the second chamber  24 . 
         [0023]    To reduce the circumstances that the nozzles  221  are jammed by microparticles, each of the nozzles  221  is provided with a smooth annular wall, a longitudinal cross-section of which is arc-shaped, and has an upper opening  223  and a lower opening  224 , as shown in  FIG. 4 . The lower opening  224  is smaller than the upper opening  223  in diameter. To avoid or reduce particle bounce, the multi-microorifice impactor  20  further includes an impaction substrate  25  disposed on a top side of the impaction plate  23  and coated with silicon oil  251 . To prevent the silicon oil  251  from dispersion resulting from air jet and to further avoid particle bounce, the impaction substrate  25  can preferably be a Teflon filter with a pore size of 10 μm, having a plurality of pores  252  for preventing dispersion of the silicon oil and effectively avoiding particle bounce. Alternatively, the impaction substrate  25  can be excluded from the present invention. Besides, to facilitate weighing after sampling, an aluminum foil  26  or a thin support piece made of other material can be mounted between the impaction substrate  25  and the impaction plate  23 . In this way, the aluminum foil  26 , the impaction substrate  25 , and the silicon oil  251  can be weighed as well as collected microparticles after the sampling. 
         [0024]    Let reference character W denote the diameter of the lower opening  224  of each nozzle  221 . Let reference character S denote the distance between the lower opening  224  and the top side of the impaction plate  23  because the surface of the impaction substrate  25  is regarded as the extension of the top side of the impaction plate  23  and the silicon oil  251  is subject to dispersion resulting from the air jet to be appressed onto the surface of the impaction substrate  25 . The number of the nozzles  221  is  137  as an example. When the specific value (S/W) is 13.8, the cutoff diameter of the multi-microorifice impactor  20  is about 100 nm, i.e. the microparticles with diameters of 100 nm to 4 μm will be collected by the multi-microorifice impactor  20 . The cutoff diameter of the multi-microorifice impactor  20  can be precisely controlled by change of the aforesaid specific value. In practice, the cutoff diameter of the multi-microorifice impactor  20  is not limited to 100 nm. 
         [0025]    In addition, to make the distribution of the microparticles be more uniform, the multi-microorifice impactor  20  can further include a fastening plate  27  and a motor  28 , both of which are located inside the second chamber  24 . The fastening plate  27  partitions the second chamber  24  into an upper chamber  241  and a lower chamber  242 . The fastening plate  27  includes an axial hole  271  and a U-shaped flow guide hole  272  communicating with the upper and lower chambers  241  and  242 . The motor  28  includes a rotary shaft  281  inserted into the axial hole  271  and synchronically rotatably connected to the impaction plate  23 . The impaction plate  23  and the motor  28  are located inside the upper and lower chambers  241  and  242 , respectively. When the rotary shaft  281  of the motor  28  is rotated, the impaction plate  23  can be driven for rotation together at a predetermined 1 rpm in such a way that the microparticles can be distributed preferably uniformly on the impaction substrate  25  to effectively avoid particle bounce occurring when the microparticles are centered to particular positions. 
         [0026]    The filter cassette  30  defines a third chamber  31  therein and includes a guide passage  32 , an outlet  33 , and a filter  34 . The filter  34  is mounted to the third chamber  31  to partition the third chamber  31  into a filtration chamber  311  and an outtake chamber  312  for collecting the remanent microparticles indicating those with a size smaller than 10 nm in this embodiment. The guide passage  32  communicates with the lower chamber  242  and the filtration chamber  311 . The outlet  33  communicates with the outtake chamber  312  and is connected with a piping communicating with a suction pump, which is portable, such as portable high-pressure-loss pump (Model No. XR5000) developed by SKC Inc., PA, USA, 8 cm (Length)×6 cm (Width)×10 cm (Height), 1054 g (Weight; battery included); its size and weight facilitate a user to carry it with himself or herself. Besides, to increase the flow rate of the airflow from the second chamber  24  to the third chamber  31 , the second chamber  24  can have a taper-shaped bottom side. However, the bottom side of the second chamber  24  is not limited to taper in shape. 
         [0027]    Furthermore, the NP sampler of the present invention can further include a plurality of fastening bars  40  for forcing the tangential flow cyclone  10  and the filter cassette  30  to approach toward the multi-microorifice impactor  20  for fixation. 
         [0028]    Referring to  FIG. 5 , in operation, when a suction pump is used for pumping the air, the airflow enters the first chamber  114  through the inlet  115  of the tangential flow cyclone  10  and firstly flows spirally downwardly along the internal wall of the annular portion  111  subject to the gravity and inertial action to enable the microparticles of larger diameters to be thrown to the internal wall of the annular portion  111  and then sunk on the bottom plate  113 . When flowing to the bottom plate  113 , the airflow can flow spirally upwardly along an external wall of the outflow duct  12  and finally exit the tangential flow cyclone  10  through the entrance  121  and exit  122  by order. In this embodiment, the cutoff diameter of the tangential flow cyclone  10  is about 4 μm. 
         [0029]    The airflow continues to pass through the nozzles  221 , flow along the gap between the impaction plate  23  and the impaction body  21 , and then veer; meanwhile, the larger microparticles impinge on the impaction plate  23  due to inertia to be collected by the impaction substrate  25  and the silicon oil  251  thereon. In this embodiment, the cutoff diameter of the multi-microorifice impactor  20  is 100 nm. 
         [0030]    At last, the airflow enters the third chamber  31  through the guide passage  32 , such that the microparticles with diameters smaller than 100 nm will be collected by the filter  34  and the clean airflow continue to exit the filter cassette  30  through the outlet  33 . 
         [0031]    After a predetermined time, stop the sampling and take out the impaction substrate  25  along with the aluminum foil  26  and the silicon oil  251  to weigh them, and then calculate the total weight of the RPMs with diameters of 4 μm to 100 nm; next, take out the filter  34  to weigh it and then calculate the total weight of the NPs with diameters smaller than 100 nm. In this way, exposure of workers to RPMs and NPs at the sampling place can be accessed. 
         [0032]    In light of the special design of the aforesaid embodiment, the NP sampler of the present invention is not only structurally compact and portable but the tangential flow cyclone, the multi-microorifice impactor, and the filter cassette have highly precise cutoff diameters, respectively. 
         [0033]    In particular, the evident difference between the tangential flow cyclone of the present invention and the conventional tangential flow cyclone lies in direction of output airflow. To effectively separate the microparticles from the airflow, the airflow in each of the conventional tangential flow cyclones disclosed on the textbooks or in practice is upward in direction as disclosed, for example, in aforesaid U.S. Pat. Laid-open No. 2009/0272202. For a long time, the upward output airflow of the tangential flow cyclone has become a technical prejudice in the art and is contrary to the input airflow required by the multi-microorifice impactor that should be downward in direction. Owing to such characteristic of congenital incompatibilty, none of any nanoparticle sampler composed of the tangential flow cyclone and the multi-microorifice impactor had been available. However, the inventors of the present invention become aware that if the direction of output airflow of the tangential flow cyclone is properly changed, it will not only reach the effect of separating the microparticles but be combined with the multi-microorifice impactor to become a low-pressure-drop two-stage microparticle separator, which is very applicable to the portable nanoparticle samplers stressing on portability. In this way, the precise and convenient microparticle sampling operation can be fulfilled. 
         [0034]    What are disclosed above is the preferred embodiment of the present invention only and the person skilled in the art can simply interchange or modify the structure, e.g. modifying the cutoff diameter of each component or respective components are connected by other means; modifying the U-shaped flow guide hole of the fastening plate to other shape; or further dividing it into a plurality of guide holes for communication with the upper and lower chamber. 
         [0035]    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.