Abstract:
A personal nanoparticle sampler is disclosed to include a pre-classifier, a nozzle, a connector and a final filter pack. The connector and the final filter pack respectively accommodate a particle-sizing filter and a final filter to collect nanoparticles smaller than a diameter. The pre-classifier removes large particles to avoid clogging of the connector. The nozzle raises the airflow velocity to reduce the cut-off diameter of the particle-sizing filter without increasing the total flowrate, allowing the personal nanoparticle sampler to be used with a personal sampling pump.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to air pollutant sampling equipments and more particularly, to a personal nanoparticle sampler for sampling workplace nanoparticles. 
     2. Description of the Related Art 
     In recent years, many researches and health-related studies show the impact of nanoparticle inhalation on human health. Further, nanoparticles of different compositions or particle sizes may have different impacts to human health. 
     In order to evaluate the impacts of nanoparticles to workers at the workplaces, it is necessary to collect nanoparticles smaller than a certain diameter, which is typically less than 100 nm, for laboratory analysis. Many nanoparticle sampling equipments are commercially available, including ELPI (Electrical Low-Pressure Impactor, Dekati Ltd. Model 3935), LPI (Low Pressure Impactor, Andersen model 20-930), MOUDI (Micro-Orifice Uniform Deposition Impactor, MSP model 100), and Nano-MOUDI (Nano Micro-orifice Uniform Deposition Impactor, MSP model 110). However, these equipments usually are large and heavy, and sample nanoparticles at a high flowrate and high pressure drop. They are not suitable to use with a personal pump. Therefore, they are merely used for fixed-location sampling. However, workers are usually moving among different areas having different particle concentrations. Sampling nanoparticles at fixed locations cannot reflect accurate exposure of workers to nanoparticles. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is the main objective of the present invention to provide a personal nanoparticle sampler, which collects nanoparticles smaller than a certain diameter which is typically less than 100 nm. 
     Another objective of the present invention is to provide a personal nanoparticle sampler, which has a low pressure drop and low flowrate, and can be used with a personal sampling pump carried by a worker to sample surrounding nanoparticles for further analysis. 
     To achieve these objectives of the present invention, the personal nanoparticle sampler comprises a pre-classifier, a nozzle, a connector, and a final filter pack. The pre-classifier comprises a first chamber and an air inlet. The air inlet extends from the first chamber to the outside of the pre-classifier. The nozzle is connected to the pre-classifier, comprising a passage disposed in communication with the first chamber of the pre-classifier. The passage has a cross section gradually reducing in direction apart from the first chamber. The connector is connected to one end of the nozzle opposite to the pre-classifier, comprising a second chamber disposed in communication with the passage of the nozzle. The final filter pack is connected to the connector, comprising a third chamber and a suction passage. The third chamber is disposed in communication with the second chamber of the connector. The suction passage extends from the third chamber to the outside of the final filter pack. 
     Further, the pre-classifier can be a cyclone separator. Further, the first chamber is comprised of a conical portion and a cylindrical portion. The connector further comprises a filter support mounted in the second chamber. The filter support has a plurality of perforations. The final filter pack comprises a top cover, a bottom cover, and a connector. The top cover and the bottom cover are fastened together, defining therein the third chamber. The connector defines therein the suction passage. 
     The personal nanoparticle sampler further comprises a rack. The rack comprises a top plate, two sliding rods, a bottom plate, and two springs. The top plate is stopped outside the final filter pack. The sliding rods are connected in parallel to the top plate. The bottom plate is coupled to the periphery of the pre-classifier and movable along the sliding rods. The springs are bilaterally connected between the top plate and the bottom plate. 
     The personal nanoparticle sampler further comprises a particle-sizing filter mounted in the second chamber of the connector, and a final filter mounted in the third chamber of the final filter pack. Further, the particle-sizing filter can be a polycarbonate track etch membrane. 
     Further, the passage of the nozzle has a circular cross section, and an outlet disposed at one end thereof remote from the first chamber. The outlet has a diameter smaller than 1.5 mm, preferably within 0.6 mm˜1 mm. Further, the outlet has an airflow velocity of 85 m/sec˜165 m/sec, preferably within 110 m/sec˜115 m/sec. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is the perspective view of the assembly of the personal nanoparticle sampler in accordance with the present invention. 
         FIG. 2  is an exploded view of the personal nanoparticle sampler in accordance with the present invention. 
         FIG. 3  is a sectional view of the personal nanoparticle sampler in accordance with the present invention. 
         FIG. 4  is a particle collection efficiency curve of the personal nanoparticle sampler according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1˜3 , a personal nanoparticle sampler  10  in accordance with the present invention is shown comprised of a pre-classifier  20 , a nozzle  30 , a connector  40 , a particle-sizing filter  50 , a final filter pack  60 , a final filter  70 , and a rack  80 . 
     The pre-classifier  20  is a cyclone separator, having a first chamber  22  and an air inlet  24 . The first chamber  22  comprises a conical portion  221  and a cylindrical portion  223 . The air inlet  24  extends from the cylindrical portion  223  of the first chamber  22  to the outside of the pre-classifier  20 . According to the present preferred embodiment, the cylindrical portion  223  has an inner diameter of 17 mm. When the flowrate is at 5.3 L/min, the cut-off aerodynamic diameter of the cyclone separator  20  is about 3 μm. 
     The nozzle  30  is connected to the pre-classifier  20 , having a passage  32  connected to the first chamber  22  of the pre-classifier  20 . The cross section of the passage  32  reduces gradually in direction apart from the first chamber  22 . The nozzle  30  comprises an air outlet  321  located on one end of the passage  32  remote from the first chamber  22  of the pre-classifier  20 . The diameter of the air outlet  321  is also called the nozzle diameter. According to the present preferred embodiment, the cross section of the passage  32  has a circular shape and the air outlet  321  has a diameter of 1 mm. 
     The connector  40  is connected to one end of the nozzle  30  opposite to the pre-classifier  20 , comprising a second chamber  42  and a filter support  44 . The second chamber  42  is disposed in communication with the passage  32  of the nozzle  30 . The filter support  44  is mounted in the second chamber  42 , having a plurality of perforations  441 . 
     The particle-sizing filter  50  is a PCTE (polycarbonate track etch) membrane arranged on the upstream side of the filter support  44  of the connector  40  within the second chamber  42 . The particle-sizing filter  50  can be selected from, but not limited to, a PCTE (polycarbonate track etch) membrane of pore size 8 μm, 10 μm or 20 μm. Further, two or more particle-sizing filters  50  may be stacked up to reduce the cut-off aerodynamic diameter. 
     The final filter pack  60  comprises a top cover  62 , a bottom cover  64 , a connector  66 , and a supporting pad  68 . The top cover  62  and the bottom cover  64  are fastened together, defining a third chamber  69 . The third chamber  69  is disposed in communication with the second chamber  42  of the particle-sizing filter pack  40 . The connector  66  is installed on the top cover  62 , defining therein a suction passage  661 . The suction passage  661  extends from the third chamber  69  to the outside of the final filter pack  60 . The connector  66  is connected to a suction pump (not shown) so that the inner of the first chamber  22 , the passage  32 , the second chamber  42  and the third chamber  69  of the personal nanoparticle sampler  10  are kept in a negative pressure condition for enabling surrounding particles to be sucked into the inside of the personal nanoparticle sampler  10  through the air inlet  24  of the pre-classifier  20 . The supporting pad  68  is accommodated in the third chamber  69 . 
     The final filter  70  is accommodated in the third chamber  69  of the final filter pack  60  and arranged on the upstream side of the supporting pad  68 . The final filter  70  can be selected from, but not limited to, Teflon filter, quartz filter or MCE (mixed cellulose ester) membrane. 
     The rack  80  comprises a top plate  82 , two sliding rods  84 , a bottom plate  86 , and two springs  88 . The top plate  82  is stopped outside the final filter pack  60 . The sliding rods  84  have the respective top ends respectively fastened to the top plate  82 . The bottom plate  86  is coupled to the periphery of the pre-classifier  20  and movable along the sliding rods  84 . The two springs  88  are bilaterally connected between the top plate  82  and the bottom plate  86 . Under the effect of the spring force of the springs  88 , the pre-classifier  20 , the nozzle  30 , the connector  40  and the final filter pack  60  are held together. 
     During the operation of the personal nanoparticle sampler  10 , surrounding particles are moved with the intake flow of air into the first chamber  22 , and the intake flow of air is caused to spin helically therein. At this time, relatively greater particles are caused by the centrifugal force to move toward the inside wall of the pre-classifier  20  and deposit on the bottom side of the first chamber  22 , and therefore relatively greater particles are separated from the air flow. 
     When relatively greater particles are separated from the airflow spinning in the first chamber  22 , relatively smaller particles are moved with the spinning air flow through the passage  32  and the air outlet  321  to the upstream side of the particle-sizing filter  50 . Theoretically, when the filtration velocity of the particle-sizing filter  50  exceeds 72 m/sec, the cut-off diameter of the particle-sizing filter  50  will be reduced to below 200 nm. Because the air outlet  321  of the nozzle  30  is small, the filtration velocity of the particle-sizing filter  50  can be raised without increasing the total flowrate, thereby lowering the cut-off diameter of the particle-sizing filter  50 . The diameter of the air outlet  321  is suggested to be smaller than 1.5 mm, preferably within 0.6 mm˜1 mm. The particles which flow into the nozzle  30  move along an axis A of the passage  32  of the nozzle  30  until passing through the particle-sizing filter  50  and the perforations  441  of the filter support  44 . 
     Thereafter, nanoparticles greater than a certain size (or called cut-size) are removed from the airflow, and smaller nanoparticles are moved with the airflow through the particle-sizing filter  50  into the third chamber  69  of the final filter pack  60  and collected by the final filter  70 . After sampling, the exposure of workers to nanoparticles is determined by analyzing the composition and weight of the nanoparticles at the particle-sizing filter  50  and the final filter  70 . 
       FIG. 4  is a particle size-collection efficiency curve obtained experimentally. In this experiment, the range of the particle diameter is from 31.6 nm˜656.6 nm. The air flowrate of the personal nanoparticle sampler  10  is 5.3 L/min (i.e., the velocity of the air flow at the outlet  321  of the nozzle  30  is about 112.5 m/sec.), the diameter of the nozzle is 1 mm and the particle-sizing filter  50  has a pore diameter of 20 μm. 
     The inventor utilized a collision atomizer TSI model 3076 to generate polydisperse sodium chloride particles, and then utilized a diffusion dryer and an impactor to remove water vapor and large particles from the air respectively, and then utilized a DMA (differential mobility analyzer) to select monodisperse particles of a particular size, and then delivered the particles of a particular size into the personal nanoparticle sampler  10 , and then utilized a CPC (condensation particle counter) TSI model 3022 to measure the number concentration of the particles passing through the particle-sizing filter  50 . The number concentration of the particles passing through the particle-sizing filter  50  was compared with the number concentration of the particles before passing through the particle-sizing filter  50  to determine the particle collection efficiency. 
     As indicated in the experiment result, under the aforesaid experiment parameters, the cut-off diameter of the particle-sizing filter  50  of the personal nanoparticle sampler  10  is about 104 nm, i.e., particles greater than 104 nm can be removed by the particle-sizing filter  50 , and particles smaller than 104 nm can pass through the particle-sizing filter  50 . 
     The personal nanoparticle sampler  10  utilizes the nozzle  30  to accelerate filtration velocity, thereby lowering the cut-off diameter of the particle-sizing filter  50 , and therefore the personal nanoparticle sampler  10  can sample nanoparticles at a low flowrate. Additionally, the pressure drop of the personal nanoparticle sampler  10  is relatively lower than conventional nanoparticle samplers. Therefore, the personal nanoparticle sampler  10  can be used with a portable personal suction pump and carried by a worker to sample surrounding particles at the workplaces. 
     Further, the designer can change of the pore diameter of the particle-sizing filter  50  or modify the diameter of the air outlet  321  of the nozzle  30 , the distance between the outlet  321  of the nozzle  30  and the particle-sizing filter  50 , and/or the flowrate of the suction pump, thereby changing the cut-off diameter of the particle-sizing filter  50 . Further, the flow velocity at the outlet  321  of the nozzle  30  can be within 85 m/sec˜165 m/sec, preferably within 110 m/sec˜115 m/sec. 
     Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.