JPH0692929B2 - Airborne microparticle characteristics measurement device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the particle size distribution of solid or liquid fine particles suspended in a gas.

[0002]

2. Description of the Related Art In measuring the particle size distribution of liquid particles,
A general method is to eject aerosol (a system in which dust and mist are suspended in a gas) at high speed from a nozzle directed downward and collect the aerosol on a disk-shaped collision plate provided directly below the nozzle. That is, the particles in the aerosol are 2
An inertial force proportional to the power of the square is obtained, and only particles having an inertial force above a certain level collide with and adhere to this collision plate. A device called a mist cascade impactor is a device for collecting the droplets collected on each collision plate provided immediately below the column for each stage and weighing them to determine the particle size and distribution amount.

However, the above-mentioned device stores the liquid particles to be measured in the collision plate for a certain period of time, then takes them out to the outside and weighs them.
There is a problem in that an accurate particle size distribution cannot be obtained because evaporation or re-scattering phenomenon may cause a drop in liquid particles during the collection of the liquid particles.

The light-scattering measuring device used for measuring the particle size distribution of fog is easy to operate, but it also measures solid particles (dust) to form liquid particles (mist) which is the main body of the fog. Can't get information about. Liquid particles can be measured by applying a hot-wire anemometer, but solid particles are not possible, and existing solid particles and liquid particles are mixed in the existing particle size distribution measuring device. It was difficult to measure the particle size distribution of.

[0005]

The problem to be solved is that it is possible to distinguish between solid and liquid particles and to measure the distribution of particle size.

[0006]

[Means for Solving the Problems] Since liquid particles are fluid and generally volatile, the aerosol in which solid particles and liquid particles are mixed is collected on a collision plate and heated to collect the aerosol. By forcibly evaporating the collected liquid droplets and measuring the mass of the collision plate before and after the evaporation, the liquid mass, that is, the mass of the collected liquid particles is obtained. Furthermore, if the mass of the collision plate before collection is measured, the mass of solid, that is, the mass of solid particles can be known from the difference between the mass after evaporation and the mass before collection. Here, the amount of increase in the mass of the collision plate can be obtained from the change in the frequency of the glass tubular detection element.

The present invention pays attention to this point and, in contrast to the above-mentioned conventional cascade impactor device, which is provided with several stages of nozzles and collision plates to measure the particle size distribution at each stage, the suction flow rate of aerosol By gradually changing the above, the entire apparatus is made compact with only one set of nozzles and a collision plate.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS This apparatus comprises a particle collecting and mass detecting section, an electronic circuit section, and an aerosol suction section. The outline

FIG. 1 shows. The particle collecting and detecting unit is housed in the detection box 11, and the aerosol is guided to the nozzle 1 of the detection box by the operation of the suction pump 4 and enters from the nozzle 1 toward the collision plate 5. A nichrome plate 5 is fixed as a collision plate to the tip of the detection element 3 of a tapered glass tube, and both electrodes necessary for heating the nichrome plate 5 are connected to an external power source 8 and the detection element 3 The widened other end of is fixed to the bottom. A pair of electrodes 6 and 6 ′ for vibrating the element 3 and an optical system (light emitting element 7 and light receiving element 7 ′) for measuring the frequency are opposed to the center of the element 3 in the direction perpendicular to the electrodes. Are arranged. The frequency of the element 3 is determined by the mass of the nichrome plate 5 at the tip and the physical characteristics of the detection element. On the nichrome plate 5,

Particles having a particle size equal to or larger than the particle size calculated by the inertial collision equation of [Equation 1] collide with the nichrome plate 5 regardless of solid or liquid particles and are collected. As the particles are trapped and the mass increases, the frequency decreases at a constant rate. By measuring the frequency with an optical system, on the contrary, the increased mass on the nichrome plate can be determined.

[0009]

[Equation 1] D _p = [(18 ・ μ ・ D _n・ ψ ₅₀ ) / (C ・ ρ _p・ v)] ^1/2

In the above equation, v is the average flow velocity in the nozzle 1, ρ _p is the particle density, D _p is the particle diameter, C is the Cunningham correction coefficient, μ is the gas viscosity coefficient, and D _n is the nozzle diameter. , Ψ ₅₀ is a coefficient (= 0.14) at a particle size with an effective collection efficiency of 50%.

In the first step, a gas containing no solid and liquid fine particles is sucked at a constant suction flow rate, and the frequency of the nichrome plate 5 in this state is measured. Next, the aerosol containing solid and liquid fine particles is sucked into the box 11 at a constant suction flow rate for a certain period of time, the fine particles are collected on the nichrome plate 5 to measure the frequency, and the nichrome previously measured. The particle mass in the mixed state of solid and liquid particles is obtained by comparing with the frequency of only the plate. Next, by energizing the nichrome plate 5, the nichrome plate 5 is heated to evaporate only the liquid particles in the collected particles, and only the solid fine particles remain on the nichrome plate 5, and the particle mass at this time Is similarly obtained from the change in frequency. The mass of the liquid particles is obtained from the difference between the mass when the solid particles and the liquid particles are collected and the mass of the solid particles. Next, the mass of the collected solid particles is obtained from the mass before the aerosol is collected and after the liquid particles are evaporated.

As the second step, the suction flow rate is increased from the first step. By doing this,

Since the average flow velocity v of Eq. (1) becomes faster, the separated particle diameter D _p becomes smaller, and even fine particles having a smaller particle diameter than in the first step can be collected on the nichrome plate. Subsequent detection of solid and liquid particles repeats the same operation as the first step. Hereinafter, by increasing the suction flow rate one after another and obtaining the collection amounts of the solid and liquid particles in each step, the particle size distribution and mass concentration of the liquid and solid particles can be obtained.

[0013]

As described above, the apparatus for measuring the characteristics of airborne microparticles of the present invention employs the inertial collision method for measuring the particle size distribution and the method for distinguishing solid and liquid particles by heating. Therefore, there are advantages that the structure is relatively simple, it is solid, and there are no moving parts. This device can be easily applied to the measurement of the particle size distribution of aerosols containing solid and liquid particles such as fog in the atmosphere.

[0014]

[Brief description of drawings]

FIG. 1 is an overall schematic view of an apparatus for measuring characteristics of airborne microparticles.

FIG. 2 is a plan view of a central portion of a detection element of an apparatus for measuring characteristics of airborne microparticles.

FIG. 3 is a diagram showing a case where the nichrome plate heating method of the airborne microparticle characteristics measuring apparatus is an infrared heating method.

FIG. 4 is a diagram showing a case where a nichrome plate heating method of an airborne fine particle characteristic measuring apparatus is a high frequency electromagnetic heating method.

[Explanation of symbols]

 1 Nozzle 2 Discharge port 3 Detection element 4 Suction pump 5 Nichrome plate 6,6 'Vibration electrode 7,7' Light emitting element and light receiving element 8 Power supply 9 Drying agent 10 Detection element drive circuit 11 Detection box 12 Frequency detection circuit 13 Infrared lamp 14 high frequency oscillator

Claims (3)

[Claims] 1. A tapered glass tube-shaped detection element vibrating at a natural period in a box having a nozzle for introducing gas in which fine particles are suspended into the box and an exhaust hole for taking out gas in the box, The one with the larger detection element diameter is fixed to the bottom of the box directly below the nozzle, and the nichrome plate is fixed on the detection element on the nozzle side by connecting both ends to the power supply outside the box. Inhale gas containing particles,
The solid and liquid particles were collected on the nichrome plate by inertial collision, and the particle size distribution and particle size of the solid and liquid particles were calculated based on the frequencies before and after the collection and after the nichrome plate was electrically heated. A device that measures the mass concentration for each diameter category. 2. The apparatus for measuring characteristics of airborne microparticles according to claim 1, wherein the heating method by energizing the nichrome plate in claim 1 is a heating method by an infrared light bulb in the box. 3. An apparatus for measuring characteristics of airborne microparticles according to claim 1, wherein the heating method by energizing the nichrome plate in claim 1 is a high frequency electromagnetic heating method in a box.