JPH0733994B2 - Particle counter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a particle counting device for counting the number of minute particles contained in air, and in particular, to a particle capable of accurately measuring the number of particles regardless of room temperature. The present invention relates to a counting device.

[Prior art]

As a particle counting device used to measure the collection efficiency of a conventional filter or a test of a clean working environment, an aerosol in a measurement region is extracted and ejected from a nozzle into a predetermined measurement region, where a laser beam or the like is emitted. There is known a fine particle counting device that counts the number of particles on the basis of the presence or absence of scattered light. According to such a conventional particle counting device, it is difficult to measure the particles in the submicron order region, and there is a problem that the measurable particle size is limited by the speed at which the particles are ejected to the measurement region.

Therefore, for example, as shown in JP-A-57-42839,
A particle detection device that guides an aerosol containing fine particles to a high temperature saturated vapor chamber and a saturated vapor chamber and mixes them to condense vapor with aerosol fine particles as nuclei and expand the particle size for optical detection. It has been known.

[Problems to be solved by the invention]

However, according to such a conventional fine particle counting device, an aerosol containing fine particles is guided to a saturated vapor chamber and a high temperature saturated vapor chamber, and a solvent such as alcohol is used so as to maintain a constant temperature in the high temperature saturated vapor chamber. Is heated to high temperature saturated steam. However, in a clean room, etc., the room temperature, that is, the temperature of the aerosol is kept almost constant, but in other facilities, the room temperature is not always constant, and even if the temperature of the high temperature saturated steam chamber is constant, the temperature of the other saturated steam chamber is room temperature. Therefore, the mixing conditions vary depending on the room temperature. Therefore, there is a problem that the fine particles cannot be sufficiently grown, or conversely, they may be condensed even if there are no particles serving as nuclei. There is also a problem that water vapor adheres to the pipe wall before the aerosol particles passing through the saturated vapor chamber enter the mixing section. Further, since it is necessary to heat the solvent in the high temperature saturated steam chamber to a temperature considerably higher than room temperature, for example, about 70 to 90 ° C., which is higher than room temperature by 50 ° C., there is a drawback that the consumption amount of the solvent is extremely large and the efficiency is low.

The present invention has been made in view of the problems of such a conventional particle counting device, and it is possible to always expand the particle size of the particles under the same conditions regardless of the room temperature and to reduce the consumption of the solvent. Is a technical issue.

[Means for solving problems]

The present invention has a laser light source for generating a laser beam, an optical means for focusing the laser beam, and a particle diameter enlarging means for enlarging the particle diameter of the fine particles, and a fine particle passing through the focal position of the laser beam. A fine particle counting device for counting the number of particles based on scattered light, as shown in FIG.
The particle size enlarging means includes an air cooling chamber for cooling air at room temperature to keep it at a constant temperature, a filter portion for removing fine particles contained in low temperature air obtained from the air cooling chamber, and a heating means for heating the solvent to a predetermined temperature. It has a high temperature saturated steam chamber that generates a high temperature saturated steam that is higher than the cooling temperature of the air cooling chamber by being guided by the measurement aerosol, and a high temperature saturated steam obtained from the high temperature saturated steam chamber and a low temperature provided by the filter unit. And a diffusion chamber for expanding the particle size of the fine particles of the air cooled by the mixing section together with the air cooling chamber.

[Action]

According to the present invention having such a feature, the air at room temperature is cooled to maintain a constant low temperature, and the cooled air is guided to the mixing chamber through the filter. On the other hand, the aerosol for measurement is introduced into a high temperature saturated vapor chamber, which is higher than the temperature of the cooling chamber by a predetermined temperature, to obtain high temperature saturated vapor, and they are introduced together into the mixing chamber.

[Explanation of Examples]

(Structure of Embodiment) FIG. 1 is a sectional view showing the entire structure of an embodiment of a particle counting apparatus according to the present invention, and FIG. 2 is a side view thereof. As shown in FIG. 1, in this embodiment, the grain size expanding portion is integrally formed. That is, in this figure, the high temperature saturated steam chamber 2 is provided below the particle size expanding portion 1. At the side of the high temperature saturated steam chamber 2, there is an inlet portion 3 through which measurement air is introduced. The high temperature saturated steam chamber 2 is filled with alcohol such as ethylene glycol as a solvent, and its inner wall is covered with the felt 4. A seat heater 5 is attached to the outer periphery of the high temperature saturated steam chamber 2 as shown in the drawing, and heats the high temperature saturated steam chamber 2 from the side wall. A temperature sensor 6 protruding from the side wall is provided in the high temperature saturated steam chamber 2 as shown in the figure. The temperature sensor 6 detects the temperature of high-temperature saturated steam, and its output is transmitted to the temperature control unit 7. The temperature control unit 7 controls the heating amount of the seat heater 5 and maintains the temperature of the high temperature saturated steam chamber 2 at a predetermined temperature.
A cooling chamber 8 is attached to the upper portion of the high temperature saturated steam chamber 2 as shown in the figure. The cooling chamber 8 is provided at one end with a pump 9 that guides the air inside the cooling chamber 8 and has a large number of fins 10 inside.
Is installed. Then, on the side wall of the cooling chamber 8, for example, an electronic cooler 11a for performing electronic cooling utilizing the Peltier effect,
A plurality of 11b are attached, and a heat sink 12
Are thermally coupled. A temperature sensor 13 for detecting the room temperature is provided in the cooling chamber 8 and a temperature control unit 14 is connected thereto. The temperature control unit 14 controls the electronic coolers 11a and 11b, and keeps the temperature in the cooling chamber at a predetermined temperature slightly higher than 0 ° C, for example, 5 ° C. If the temperature is lower than 0 ° C, water vapor in the air is frozen and the filter is clogged, so the temperature should be maintained at a low temperature of 0 ° C or higher. Cooling room 8
A filter unit 15 is provided below the. The filter unit 15 removes the fine particles contained in the cooled air to remove the fine particles from the mixing chamber 16
It leads to. The mixing chamber 16 is provided between one end of the high temperature saturated steam chamber 2 and the diffusion chamber 17 at the upper portion as shown in the drawing. The side wall of the mixing chamber 16 has a ventilation part 18 formed in an annular shape for guiding the cool air from the filter part 15 as shown in the figure,
A large number of openings are provided in the side wall of the mixing chamber 16 from the ventilation part 18 so that cold air is ejected into the mixing chamber 16. Further, one end of the high temperature saturated steam chamber 2 has an opening toward the mixing chamber 16. The mixing chamber 16 is a part for mixing the high temperature saturated vapor containing the aerosol and the low temperature clean air, and the high temperature saturated vapor chamber 2
Is kept at about the same temperature as. Further, a drain 19 is provided beside the mixing chamber 16 to release alcohol generated during mixing. The inner wall of the diffusion chamber 17 above the mixing chamber 16 is covered with a heat insulating material 20 and is formed in a cylindrical shape. The mixing chamber 16 rapidly cools the temperature of the saturated steam by precipitating the steam by mixing the cooled air with the fine particles in the high temperature saturated steam as nuclei,
This is a part for adhering to the fine particles to increase the particle size. A nozzle chamber 21 having an inner wall formed in a tapered shape and having a nozzle hole 21a at the tip thereof is provided above the diffusion chamber 17 as shown in the figure.

On the other hand, in the light source chamber 31, a laser light source 32 such as a laser diode is arranged as shown in the drawing, and a collimator lens 33 and a convex lens 34 for expanding the light diameter into parallel light are arranged on the optical axis thereof. The convex lens 34 is a lens that focuses the laser light on the measurement area. A glass plate 35 is attached to the front surface of the light source chamber 31 except for a central laser beam transmitting portion. And glass plate 35
A measurement chamber 36 is formed along the optical path via the. Measurement room
Reference numeral 36 is an area in which an aerosol in which the particle diameter of the fine particles is expanded is jetted at a predetermined speed in the optical path of the laser beam to scatter light, in order to maintain the expanded particle diameter and reduce dark noise due to stray light. Use a closed structure. On the right side of the measurement chamber 36, a light detection chamber 37 is further arranged along the optical path. The light detection chamber 37 is a part that collects scattered light and converts it into an electric signal, and on its front surface, condenser lenses 38 and 39 that collect scattered light are provided. A photoelectric converter 40 such as a PIN diode is provided at the focal position of the condenser lens 39, and converts scattered light into an electric signal corresponding to the received light level thereof. Further, a flow meter 42 and a pump 43 are provided above the measurement chamber 36 via an exhaust duct 41 so as to suck the aerosol at a predetermined speed.

Next, FIG. 3 is a circuit diagram of an electric signal processing unit for processing the output of the photoelectric converter 40 of the photodetection chamber 37 according to the present invention. As shown in the figure, the output of the photoelectric converter 40 is given to the comparator 52 via the amplifier 51. The comparator 52 has a predetermined reference level Vref
For converting a signal exceeding the reference level into a square wave signal, the output of which is transmitted to the counter 53. The counter 53 counts the given number of pulses, and its output is given to the display 54 for display.

(Operation of Embodiment) The laser light oscillated by the laser light source 32 in the light source chamber 31 is focused by the lenses 33 and 34. This laser beam is given to the measurement chamber 36 and focused on the upper part of the nozzle 21a. Then, by operating the pump 43, the air in the mixing chamber 16 and the diffusion chamber 17 is sucked from the exhaust duct 41. Therefore, the measurement air is introduced into the high temperature saturated steam chamber 2 via the inlet 3. The high temperature saturated steam chamber 2 is controlled to have a temperature higher than the cooling chamber 8 by a predetermined temperature, for example, 45 ° C., and is introduced into the mixing chamber 16 as high temperature saturated steam. On the other hand, the air in the room is guided to the cooling room 8 and controlled to a predetermined temperature, for example, 5 ° C. as described above. Therefore, if the humidity of the air in the room is high, it will be dehumidified at the same time, and will be introduced into the mixing chamber 16 via the filter unit 15 as low-temperature air. Therefore, clean cooling air having a temperature difference of 40 ° C. and high temperature saturated steam are mixed in the mixing chamber 16. Therefore, the steam in the high temperature saturated steam chamber 2 is rapidly cooled. And diffusion room 17
Then, since the precipitated alcohol vapor adheres to the fine particles of the aerosol, the particle size of the fine particles is expanded. The fine particles whose particle size has been expanded in this way are sucked into the nozzle 21a of the nozzle chamber 21, pass through the measurement chamber 36, and are ejected to the discharge duct 41. Then, when the fine particles pass through the focal point of the laser beam, the laser light is scattered. The scattered light is condensed by the condenser lenses 38 and 39, transmitted to the photoelectric converter 40, and converted into an electric signal.

Next, the characteristics of the grain size enlargement portion 1 will be described. The particle size expansion in the mixing chamber 16 and the diffusion chamber 17 is determined by the total heat balance and material balance, because the flow rate and temperature of high temperature saturated vapor and the flow rate and temperature of aerosol are important factors. FIG. 4 shows these relationships on the temperature-vapor amount diagram. Now, the temperature of the high temperature saturated steam provided from the high temperature saturated steam chamber 2 is
_Assuming that T _{sh is} the amount of steam, H _sh is the temperature of the low temperature air _supplied to the mixing chamber 16, and T _{sL is} the temperature of the low temperature air, H _sL is the high temperature saturated steam supplied from the high temperature saturated steam chamber 2 as shown in FIG. Is on the saturation curve A, and the low temperature air is usually located on the curve A because the relative humidity increases due to cooling. Then, when these are mixed in the mixing chamber 16, immediately after that, a supersaturated state is reached, and as shown in the figure, the temperature reaches the point _i where the temperature is T _i and the vapor amount is H _i . If there are sufficient condensation nuclei in the supersaturated air, the point i changes adiabatically due to the condensation process and reaches the point f on the saturation curve A by the Kelvin effect after a predetermined time. Let T _{sf be} the temperature and H _sf be the amount of steam. Now, at this time, the difference ΔH (= H _i −
H _sf ) is the vapor condensation amount, and the ratio of the saturated vapor pressures at T _i and T _sf is the supersaturation degree S (= P _i −P _sf ), the supersaturation degree S and the condensed vapor amount ΔH are obtained. And the flow rate of high temperature saturated steam
Let Q _{sh be} the flow rate of low temperature air and Q _sL be the mixing ratio R _h (= Q _sh /
(Q _sh + Q _sL )) is determined. 5 (a), (b),
(C) is 50 ℃, 45 ℃ of high temperature saturated steam T _sh when the temperature T _sL of the air supplied at low temperature is changed to 10 ℃, 5 ℃ and 1 ℃.
3 is a graph showing the respective mixing ratios R _h and the degree of supersaturation S at 40 ° C. and 40 ° C. Further, FIG. 6 is a graph showing the value of the condensed vapor amount ΔH with respect to 50 ° C., 45 ° C. and 40 ° C. of the high temperature saturated vapor when the temperature of the low temperature air is 5 ° C.
Figure (b) shows that the temperature of the aerosol on the low temperature side is 25 ° C and the temperature of the high temperature saturated vapor is 90 ° C, 80 ° C.
6 is a graph showing changes in the supersaturation degree S and the condensed vapor amount ΔH with respect to the mixing ratio R _h at 70 ° C.

In these figures, if the degree of supersaturation S is large, the particle size can be expanded even with small particles, and the value of the condensed vapor amount ΔH indicates the amount of vapor adhering to the particles at that time. Therefore, it is preferable that the supersaturation degree S is large in order to optically detect the fine particles. The condensed vapor amount ΔH indicates the consumption amount of the medium. Therefore, in this embodiment, for example, the temperature T _sh of the high temperature saturated steam is 45 ° C., the mixing ratio R _h is 0.3, and the supersaturation degree S is 3.2.
When a value that satisfies the above condition is selected, the value of the condensed vapor amount ΔH becomes sufficiently smaller than that of the conventional particulate counting device. In this way, the particle size can be expanded to the same level as that of the above-described conventional particle counting device, and the consumption of the medium can be greatly reduced. Further, in the present invention, since the temperature of the low temperature steam and the temperature of the high temperature saturated steam are set to predetermined values, the particle size can be increased by always mixing them under the same conditions regardless of the temperature of the measurement object or the room temperature.

〔The invention's effect〕

Therefore, according to the present invention, low-temperature clean air and high-temperature saturated vapor are mixed in the mixing chamber, and the particle size is expanded in the diffusion chamber. The temperature of the high temperature saturated steam and the temperature of the low temperature air are always constant and the temperature difference is also kept constant, so that the mixing conditions are always constant and the same particle size expansion can be performed. Further, since the temperature of the high temperature saturated steam chamber is set to a temperature higher than the temperature of the air cooling chamber by a predetermined value, it is not necessary to raise the temperature of the high temperature saturated steam chamber too much, and the amount of solvent used can be greatly reduced. You can also get the effect.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the particle counting apparatus according to the present invention, FIG. 2 is a side view thereof, FIG. 3 is a block diagram showing the electrical construction of this embodiment, and FIG. 5A, 5B, and 5C in the temperature-vapor amount diagram in Fig. 5 are the temperature of the air supplied at a low temperature and the high temperature saturated vapor chamber when ethylene glycol or the like is used as the solvent. 6 is a graph showing the change in supersaturation with temperature, FIG. 6 is a graph showing the amount of condensed vapor when low temperature air at 5 ° C. is used, and FIGS. 7 (a) and 7 (b) are propylene glycol as the solvent. It is a graph which shows the supersaturation degree and the amount of condensed vapor of the conventional particulate counting device at this time. 1 ... Particle size expansion unit, 2 ... High temperature saturated steam chamber, 5 ... Seat heater, 6,13 ... Temperature sensor, 7,14 ... Temperature control unit,
8 ... Cooling room, 11a, 11b ... Electronic cooler, 15 ... Filter section, 16 ... Mixing room, 17 ... Diffusion room, 31 ... Light source room, 36
…… Measuring room, 37 …… Light detection room

Claims (2)

[Claims] 1. A laser light source for generating a laser beam,
Fine particle counting for counting the number of particles based on the scattered light of the fine particles passing through the focal position of the laser beam, and having an optical means for focusing the laser beam and a particle diameter enlarging means for enlarging the particle diameter of the fine particles. In the apparatus, the particle size enlarging means is an air cooling chamber that cools air at room temperature to keep it at a constant temperature, a filter unit that removes fine particles contained in low temperature air obtained from the air cooling chamber, and a solvent at a predetermined temperature. A high temperature saturated steam chamber that has a heating means for heating, a measurement aerosol is introduced, and a high temperature saturated steam chamber that generates high temperature saturated steam that is higher than a cooling temperature of the air cooling chamber by a predetermined temperature, and a high temperature saturated steam obtained from the high temperature saturated steam chamber And a mixing chamber for mixing low-temperature air supplied from the filter unit, and diffusion for expanding the particle size of fine particles of the air cooled together with the air cooling chamber and mixed by the mixing unit. Particle counting apparatus characterized by having, when. 2. The particle counting device according to claim 1, wherein the air cooling chamber is kept at a predetermined low temperature higher than 0.degree.