JP2011012977A - Inertial filter for classifying fine particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus, capable of performing the process from the removal of coarse particles to the classification and collection of nano-particles by a small-sized lightweight structure and capable of measuring, for example, the exposure amount of fine particles in the breathing region of a worker with high accuracy.SOLUTION: This apparatus is constituted so that at least two first and second inertial filters 3 and 5 are respectively connected in series which are to be arranged on the upstream and downstream sides, in a solvent passing direction, and both inertial filters are respectively equipped with through-holes 3e2 and 5d2 filled with metal fibers 11 and 13. The first and second inertial filters are equipped with a structure that serve to establish the relation: D1<D2, L1<L2 and d1>d2, wherein D1 and D2 are the pore sizes of the mutual through-holes; L1 and L2 are the pore lengths of the mutual through-holes; and d1 and d2 are the fiber diameters of non-compressible fibers. The filling amount of the non-compressible fibers in the through-holes of the first inertial filter is adjusted so as to become more than that of the non-compressible fibers in the through-holes of the second inertial filter to set not only the first inertial filter as a coarse particle removing filter but also the second inertial filter as a nano-particle classifying filter.

Description

  The present invention relates to an inertial filter that collects particles by filling incompressible fibers in through holes.

  The cascade impactor type particle classifier is an apparatus in which impactors are connected in series in a plurality of stages in the vertical direction (see FIG. 1 of Patent Document 1). In this cascade impactor-type particle classifier, the lower the side impactor, the smaller the airflow passage nozzle diameter, the higher the airflow speed, and the higher the impact mass of each stage, the larger the inertial mass. It can be collected and classified. An impactor is a device that collects particles having an inertial mass that cannot follow the change in the direction of the airflow due to the inertial force when the direction of the airflow is changed. Thus, it is possible to classify the particles in descending order of particle size.

  In such a particle classifier, an air flow for classifying the particles inside the apparatus is generated by a pumping suction to reduce the internal pressure of the apparatus and generate an air pressure difference with the external pressure of the apparatus. With fine particles, it has become difficult to produce nozzle diameters with high accuracy, and classification of fine particles has been difficult.

  In Patent Document 1, the cascade impactor type particle classifier is arranged on the upper stage side to classify particles having a large particle size, while the inertia filter according to the invention of Patent Document 1 is installed on the lower stage side (see FIG. 2 of Patent Document 1). ) To enable classification of fine particles.

 This inertial filter includes a filter support portion having a through hole through which gas passes, and SUS fiber (conventional inertia filter) which is a breathable porous member disposed so as to close the through hole in the through hole. .

JP 2008-70222 A

  By the way, in the structure of a conventional inertia filter, when trying to classify nanoparticles by increasing the filling rate of metal fibers in the through hole and minimizing the porosity in the through hole, As a result of the significant decrease in air flow and an increase in pressure loss, it was necessary to use a large air flow suction pump. Therefore, in the particle classification device using the conventional inertial filter, the whole device becomes large and becomes an inconvenient device for portability. On the other hand, in consideration of portability, when sucking with a small pump with a small flow rate, the air velocity is reduced due to pressure loss in a small through hole with a low porosity, and the particle inertia effect required for classification is reduced. It becomes difficult to classify nanoparticles.

  The present invention aims to reduce the size and weight of the entire device by sucking a small flow rate of air inside with a portable pump, etc. An object to be solved is to provide an inertial filter capable of securing the porosity in the through-hole and classifying the nanoparticles in the through-hole.

  The inertial filter according to the present invention has a through-hole through which a fluid containing particles passes, and has a filter structure in which the incompressible fiber is filled in the through-hole. It is controlled by adjusting the filling amount of the compressible fiber.

  The inertial filter according to the present invention reduces the pressure loss in the through hole by controlling the porosity in the through hole by adjusting the filling amount of the incompressible fiber in the through hole even if a small flow rate is sucked into the through hole by the pump. As a result of being able to suppress and obtain an inertial mass effect that can contribute to particle classification, a structure of a small and lightweight nanoparticle classification filter can be obtained.

  In addition, the inertial filter according to the present invention includes, for example, at least two first and second inertial filters connected in series on the upstream side and the downstream side of the fluid passage, respectively, and the incompressibility in the through holes of the two inertial filters. By adjusting the filling amount of the fiber, the porosity in the through hole in the first inertial filter on the upstream side is set to a porosity corresponding to the removal of coarse particles having a predetermined particle size or more, and the second inertial filter in the downstream side in the through hole. Nanoparticles can be classified using the porosity corresponding to the classification of nanoparticles having a predetermined particle size or less.

  In a preferred embodiment of the present invention, the incompressible fiber is a stainless fiber.

  In the present invention, a preferable aspect is that the through hole includes a diameter-enlarged through hole on the upstream side of the fluid and a constant-diameter through hole on the downstream side of the fluid. A through-hole whose inner diameter gradually increases in the lateral direction, and the constant-diameter through-hole is a through-hole having a constant inner diameter from the upstream side to the downstream side, and the inside thereof is filled with the incompressible fiber. That's it.

  In the present invention described above, by adjusting the filling amount of the incompressible fibers in the through holes of the first and second inertial filters to ensure a predetermined through hole porosity, the flow rate is reduced to a small flow rate. Although the pressure loss increases almost in proportion to the increase in the filling amount of the compressible fiber, both of the pressure loss can be suppressed to be extremely small, and particles having a large and small particle diameter can be collected. As a result, even if suction is performed with a small flow rate pump, the particle inertia effect necessary for classification can be obtained by suppressing the pressure loss to a small level, and in combination with downsizing of the pump, the entire apparatus can be reduced in size and weight. .

  According to the present invention, it is possible to provide an apparatus that can remove coarse particles and classify nanoparticles with low-pressure loss, while having a structure that reduces the size and weight of the entire apparatus, such as sucking a small flow rate with a portable pump.

FIG. 1 is a diagram showing a conceptual configuration of a particle classification device according to an embodiment of the present invention as viewed from the side. 2A is an enlarged view of the first inertia filter in the apparatus of FIG. 1, and FIG. 2B is an enlarged view of the second inertia filter in the apparatus. FIG. 3A and FIG. 3B are diagrams showing the metal fiber filling amount versus pressure loss of the first inertia filter and the second inertia filter, respectively. 4 (a) and 4 (b) show the particle diameters in which the horizontal axis is the particle size (μm) and the vertical axis is the particle collection efficiency (%) in the first inertia filter and the second inertia filter, respectively. It is a figure which shows the relationship of (micrometer) versus collection efficiency (%). FIG. 5 is a view showing a modification of the particle classifying apparatus according to the embodiment.

  Hereinafter, an inertial filter according to an embodiment of the present invention and a particle classifier using the same will be described with reference to the accompanying drawings. In the embodiment, the particles are assumed to be particles floating in a gas as an example of a solvent. However, the particles are not limited to particles floating in a gas, and may include other solvents such as particles floating in a liquid or others. it can. Referring to FIGS. 1 and 2 (a) and 2 (b), a particle classification device 1 according to an embodiment is a first inertia filter that is a coarse particle removal filter as a pre-inert filter from the air flow upstream side to the air flow downstream side. 3. As the inertial filter, a second inertial filter 5 that is a nanoparticle classification filter, a backup filter 7 for collecting nanoparticles, and an exhaust unit 9 that exhausts the airflow inside the inertial filter to the outside.

  The first inertia filter 3 includes a disk-shaped plate 3a, a cylindrical plate 3b, and a columnar plate 3c, and forms a filter space 3d therein.

 The disc-like plate 3a is arranged as a filter plate on the upstream side of the airflow, has a number of airflow suction holes (not shown), and from the airflow suction hole by the action of an airflow suction pump (not shown) arranged on the downstream side of the airflow. Airflow can be inhaled inside. The disk-shaped plate 3a is not always essential and can be omitted. The cylindrical plate 3 b has the same outer diameter as that of the disk-shaped plate 3 a and constitutes the side surface of the first inertia filter 3. The columnar plate 3c has an axial through hole 3e at the center of the plate. The through-hole 3e has an enlarged through-hole 3e1 whose inner diameter gradually increases downward from the upper side to the lower side, a constant-diameter through-hole 3e2 that is continuous with the lower end of the enlarged-diameter through-hole 3e1, and has a constant inner diameter, Consists of

  This constant diameter through hole 3e2 is filled with a metal fiber, preferably SUS (stainless steel) fiber 11, which hardly changes in volume even when a high-speed airflow passes as an incompressible fiber, in a state of being densely entangled. The metal fiber is not limited to SUS fiber, and may be one or more metal fibers selected from aluminum fiber, copper fiber, and other metal fibers. Further, the fibers are not limited to metal fibers as long as they are fibers that are incompressible and hardly change in volume even when a high-speed airflow passes through them.

  The second inertia filter 5 is continuously arranged immediately downstream of the air flow with respect to the first inertia filter 3 and is connected to the first inertia filter 3. The second inertia filter 5 includes a cylindrical plate 5a having the same outer diameter as that of the first inertia filter 3 and a columnar plate 5b, and these constitute a filter space 5c. The columnar plate 5b has an axial through hole 5d at the center of the plate. The through-hole 5d has an enlarged through-hole 5d1 whose inner diameter gradually increases downward from the upper side to the lower side, a constant-diameter through-hole 5d2 that is continuous with the lower end of the first through-hole portion 5d1, and has a constant inner diameter. Is composed of.

  The constant-diameter through hole 5d2 of the second inertia filter 5 is filled with metal fibers, preferably SUS (stainless steel) fibers 13. Also in this case, in the same manner as described above, the constant-diameter through hole 5d2 of the second inertia filter 5 is densely made of metal fibers, preferably SUS (stainless) fibers 13, which hardly change in volume even when a high-speed air flow passes as incompressible fibers. It is filled in a tangled state. The metal fiber is not limited to SUS fiber, and may be one or more metal fibers selected from aluminum fiber, copper fiber, and other metal fibers. Further, the fibers are not limited to metal fibers as long as they are fibers that are incompressible and hardly change in volume even when a high-speed airflow passes through them.

  The backup filter 7 is continuously disposed immediately downstream of the air flow with respect to the second inertia filter 5 and is connected to the second inertia filter 5 for collecting nanoparticles. The backup filter 7 includes a cylindrical plate 7a having the same outer diameter as that of the second inertia filter 5, and a disk-like plate 7b. The disk-like plate 7b acts as a filter plate, and thereby the inside. A filter space 7c is configured.

  The exhaust unit 9 exhausts the airflow from the inside of the apparatus to the outside, and the exhaust is performed by a suction pump (not shown).

  In the above configuration, the airflow flows from the first inertia filter 3 on the upstream side of the airflow to the exhaust part 9 on the downstream side of the airflow, and coarse particles are removed when passing through the filters 3, 5, 7. The nanoparticles are classified and collected.

  In the embodiment, the constant diameter through holes 3e2 of the first inertia filter 3 and the constant diameter through holes 5d2 of the second inertia filter 5 are filled with the metal fibers 11 and 13, respectively. The metal fibers 11 and 13 are SUS fibers in the embodiment.

  The fiber diameter (μm) of the metal fiber 11 in the constant diameter through hole 3e2 of the first inertia filter 3 is d1, and the fiber diameter (μm) of the metal fiber 13 in the constant diameter through hole 5d2 of the second inertia filter 5 is d2. Then, there is a relationship of d1> d2. The filling amounts (mg) of the metal fibers 11 and 13 in the constant diameter through hole 3e2 of the first inertia filter 3 and the constant diameter through hole 5d2 of the second inertia filter 5 are m1 and m2, respectively, and the metal fiber filling amount m1. , M2 are ΔP1 and ΔP2, respectively.

  In the above configuration, the diameter-enlarged through-hole 3e1 of the first inertial filter 3 decreases in diameter toward the downstream side of the airflow, so that the airflow gradually accelerates and then passes through the constant-diameter through-hole 3e2 at a constant speed. During this passage, coarse particles are collected.

  Since the constant diameter through hole 3e2 has a filter structure in which the metal fibers 11 are layered, the Stokes number Stk and the Peclet number Pe that can be used for selecting the gas flow velocity and fiber diameter are applied. Can do. The Stokes number Stk is a dimensionless value representing the followability of particles to a gas flow in a filter having a metal fiber structure. The formula is omitted. The Stokes number Stk is proportional to the flow velocity and particle density, is proportional to the square of the particle diameter, and is inversely proportional to the fiber diameter.

  According to the equation of Stokes number Stk, as the gas flow rate increases, it becomes impossible to follow the movement of the gas in order from the suspended particle having the larger particle size, and the gas flows out of the gas flow path and collides with the metal fiber. With reference to the Stokes number Stk, the particle size of the particles to be collected can be selected by controlling the gas flow rate and selecting the fiber diameter. In the embodiment, since the fiber diameter of the metal fiber is extremely small, it is not necessary to increase the flow velocity as much as the impactor. Further, metal fibers can collect particles not only by the inertia of the particles but also by collection mechanisms such as interception, gravity, electrostatic force, and diffusion.

  The Peclet number Pe is a number that represents the ratio between the effect of carrying particles by an air flow and the effect of carrying particles by diffusion, and is proportional to the flow velocity and fiber diameter and inversely proportional to the diffusion coefficient. In order to reduce the influence of diffusion, it is necessary to increase the Peclet number Pe. The smaller the particle size, the larger the diffusion coefficient and the smaller the fiber diameter selected, so it can be seen that increasing the flow rate is preferable for increasing the particle size selectivity. From the above, the target particles can be collected or classified by metal fibers by selecting the flow rate, fiber diameter, and the like.

  In the embodiment, in particular, the porosity in the constant diameter through hole 3e2 of the first inertia filter 3 is adjusted by adjusting the filling amount of the metal fiber 11 in the constant diameter through hole 3e2 of the first inertia filter 3. As a result of the fact that the air flow in the constant-diameter through hole 3e2 is not greatly reduced by the fiber diameter d1 of the metal fiber 11, the pressure loss is suppressed to a small level, so that coarse particles can be removed even if a small air flow suction pump is used to suck a small flow rate. To obtain the particle inertia effect necessary for this.

  Similarly, by adjusting the filling amount of the metal fiber 13 in the constant diameter through hole 5d2 of the second inertia filter 5, the porosity in the constant diameter through hole 5d2 of the second inertia filter 5 is adjusted. Even if the filling rate is reduced and the porosity in the constant diameter through hole 5d2 is increased, the air flow in the constant diameter through hole 5d2 is not significantly reduced by selecting the diameter d2 of the metal fiber 13 to be small. The airflow suction pump is also small, and even when suctioned at a small flow rate, the particle inertia effect necessary for nanoparticle classification can be obtained while suppressing the pressure loss to a small level.

 When specific numerical values are applied to the above embodiment, the constant diameter through hole 3e2 of the first inertia filter 3 and the constant diameter through hole 5d2 of the second inertia filter 5 have the hole diameters D1 and D2 of 3 mm and 6 mm, respectively, and the hole length. The lengths L1 and L2 are 4.5 mm and 5 mm, respectively, and the fiber diameters d1 and d2 of the metal fibers 11 and 13 are 12 μm and 8 μm, respectively. Further, the airflow generated by the airflow suction pump has the same flow rate Q1 and Q2 of a small flow rate of 6 liters per minute.

  FIG. 3A and FIG. 3B show the relationship between the metal fiber filling amounts m1 and m2 and the pressure losses ΔP1 and ΔP2 under the above conditions. FIG. 3A shows the relationship between the horizontal axis indicating the metal fiber filling amount m1 (mg) in the constant-diameter through hole 3e2 of the first inertia filter 3 and the vertical axis indicating the pressure loss ΔP1 (kPa). 3 (b) shows the relationship between the horizontal axis representing the metal fiber filling amount m2 (mg) in the constant diameter through hole 5d2 of the second inertia filter 5 and the vertical axis representing the pressure loss ΔP2 (kPa).

  As shown in FIGS. 3A and 3B, the pressure loss ΔP1 of the constant-diameter through hole 3e2 of the first inertia filter 3 is 0.3-0 in the adjustment range where the metal fiber filling amount m1 is 10-20 mg. The pressure loss ΔP2 of the constant-diameter through hole 5d2 of the second inertial filter 5 is 1.5-2 kPa in the adjustment range where the metal fiber filling amount m2 is 3-4 mg.

  As is clear from these FIGS. 3 (a) and 3 (b), the metal fibers 11 in the first inertia filter 3 and the second inertia filter 5, 13 By adjusting the porosity by adjusting the respective filling amounts, the first inertia filter 3 can remove coarse particles and the second inertia filter 5 can classify nanoparticles with low pressure loss. As a particle classifier, it is possible to measure the exposure of fine particles in the breathing area of the worker with high accuracy.

  4 (a) and FIG. 4 (b), the first inertial filter 3 and the second inertial filter 5, respectively, have a horizontal axis of particle size (μm) and a vertical axis of particle collection efficiency (%). The relationship between diameter (μm) and collection efficiency (%) is shown. However, the hole diameters D1 and D2 in the constant diameter through holes 3e2 and 5d2 of the first inertia filter 3 and the second inertia filter 5 are 6 mm and 3 mm, respectively, and the hole lengths L1 and L2 are 3 mm and 4.5 mm, respectively. The fiber diameters d1 and d2 of the fibers 11 and 13 are 12 μm and 8 μm, respectively. Further, the airflow generated by the airflow suction pump has the same flow rate Q1 and Q2 of a small flow rate of 6 liters per minute.

  As shown in FIG. 4 (a), the first inertia filter 3 can have a particle separation diameter of around 0.5 μm, and the second inertia filter 5 has a particle separation diameter of about 190 nm as shown in FIG. 4 (b). It can be a separation diameter.

  The first inertia filter 3 and the second inertia filter 5 can also be configured as shown in FIG. FIG. 5 shows parts corresponding to those in FIG. In FIG. 5, the first inertial filter through hole 3e2 and the second inertial filter through hole 5d2 are continuous. The structure shown in FIG. 5 also has the same operation as FIG.

  As described above, in the present embodiment, the first and second inertial filters 3 are connected in series in the upper and lower stages of the airflow upstream side and the airflow downstream side, and the first and second inertial filters 3 are connected in series. , 5 are D1 <D2 and L1 <L2 where D1 and D2 are the hole diameters of the constant diameter through holes 3e2 and 5d2, L1 and L2 are the hole lengths, and d1 and d2 are the fiber diameters of the metal fibers 11 and 13. , D1> d2, and the filling amount of the metal fibers in the constant diameter through hole 3e2 of the first inertia filter 3 is larger than the filling amount of the metal fibers in the constant diameter through hole 5d2 of the second inertia filter 5. By adjusting so that the pressure loss in the constant diameter through hole 3e2 of the first inertia filter 3 can be set smaller than the pressure loss in the constant diameter through hole 5d2 of the second inertia filter 5, the first inertia filter 3 Then, the filling amount of the metal fiber 11 having a large fiber diameter in a small volume Even if the number is increased, the pressure loss can be suppressed as small as possible to efficiently collect coarse particles, and in the second inertia filter 5, the filling amount of the metal fibers 13 having a small fiber diameter in a large volume is reduced. As a result, it is possible to efficiently classify nanoparticles by suppressing the pressure loss as small as possible. Separating and collecting particles to nanoparticles.

3 First inertia filter 3e Through hole 11 Metal fiber 5 Second inertia filter 5d Through hole 13 Metal fiber

Claims (4)

  It has a through-hole through which a fluid containing particles passes, and has a filter structure filled with incompressible fibers in the through-hole, and the porosity in the through-hole adjusts the filling amount of the incompressible fibers. An inertial filter that is controlled by   The inertial filter according to claim 1, wherein the incompressible fiber is a stainless fiber.   The through hole is configured to include an enlarged diameter through hole on the upstream side of the fluid and a constant diameter through hole on the downstream side of the fluid, and the inner diameter of the enlarged diameter through hole gradually increases from the upstream side toward the downstream side. The through-hole which is a diameter, the constant-diameter through-hole is a through-hole having a constant inner diameter from the upstream side to the downstream side, and the inside thereof is filled with the incompressible fiber. Inertial filter.   The inertial filter according to any one of claims 1 to 3 is connected and arranged in series at each of the fluid passing upstream side and the downstream side, and each of the inertial filters has a through-hole diameter of D1. , D2, L1 and L2 of the hole length, and d1 and d2 of the fiber diameter of the incompressible fiber, the filter structure has a relationship of D1 <D2, L1 <L2, d1> d2, By adjusting the porosity in each through hole by adjusting the filling amount of the incompressible fiber, the pressure loss due to the passage of fluid in the through hole can be adjusted according to the purpose of use of each inertial filter, An inertial filter combination configuration characterized by that.

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