Condensation particle counter and particle number concentration measurement method

Abstract

To accurately detect fine particles without complicating a device configuration.SOLUTION: The condensation particle counter includes a supply unit configured to supply a working fluid to a periphery of an inlet of a condensation tube through which an aerosol containing sample particles flows, a saturation unit configured to saturate the aerosol with vapor of the working fluid, and a control unit configured to condense and grow the aerosol into droplets using the sample particles as nuclei and extract the aerosol containing the droplets from a center axis of a condensation-growth tube connected to the condensation tube. A condensation and growth section that and exhausts excess working fluid that has flowed down an inner wall of a condensation and growth tube, vapor of the working fluid that has condensed on the inner wall, and water vapor together with excess aerosol, a flow rate control section that controls a flow rate of the aerosol flowing through a capillary tube that the aerosol containing droplets after condensation and growth at a minute flow rate, a double cylindrical sheath flow that positions the aerosol that has passed through the capillary tube on an extension line of a central axis of the capillary tube, and a droplet counting section that counts the droplets contained in the aerosol based on the droplets flowing through the capillary tube, wherein the working fluid contains an alkane having a carbon number of 14 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a condensation particle counter and a method for detecting particle number concentration. [Background technology]

[0002] A mixture of gas and tiny liquid or solid particles suspended in a gas is called an aerosol. Condensation particle counters (CPCs) are known to measure the particle number concentration in aerosols (see Non-Patent Document 1). Existing CPCs can only measure particles with a diameter larger than approximately 3 nm.

[0003] To address this issue, a PSM (Particle Size Magnifier) ​​was developed that can measure particles with a diameter of 3 nm or less. The PSM is installed in front of the CPC. The PSM can increase the particle diameter by condensing and growing particles, thereby improving the particle detection accuracy of the CPC. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Aerosol Research / Japanese Society of Aerosol Science Editorial Office, Aerosol Science Basic Course: Measurement (1) Condensation Particle Counter, 31(3), p.212-217 (2016) Summary of the Invention [Problem to be solved by the invention]

[0005] Existing PSMs are designed to be used in conjunction with a CPC, and since PSMs cannot be used without a CPC, the reality is that PSMs are not widely used.

[0006] On the other hand, optical particle counters (OPCs) are used in many industrial fields. By placing a PSM before an OPC, particle detection sensitivity in the low-sensitivity particle size range of the OPC can be improved, and the use of PSMs is expected to become more widespread.

[0007] However, it is known that existing systems using PSM and CPC (PSM-CPC systems) cannot detect carbon-based particles with a diameter of 2 nanometers or less, and there is a demand for a device that can accurately detect these carbon-based particles.

[0008] Therefore, one embodiment of the present invention provides a condensation particle counter and a particle number concentration detection method that can accurately detect particles with particle diameters on the order of nanometers, which cannot be detected by CPC, without complicating the device configuration. [Means for solving the problem]

[0009] In order to solve the above problems, according to one embodiment of the present invention, there is provided a method for measuring aerosol concentration by using a supply unit that supplies a working liquid to a periphery of an inlet of a saturation tube through which an aerosol containing sample particles flows; a saturation section that heats the working fluid by permeating it into the wall of the saturation tube and saturates the aerosol with vapor of the working fluid; a condensation growth section that cools the aerosol to reduce the saturated vapor pressure of the working fluid, thereby condensing and growing droplets using the sample particles contained in the aerosol as nuclei, extracts the aerosol containing the droplets from a central axis of a condensation growth tube connected to the saturation tube, and sucks and exhausts the excess working fluid that has flowed down the inner wall of the condensation growth tube, the vapor of the working fluid that has condensed on the inner wall, and water vapor together with the excess aerosol; a capillary tube that draws in a minute flow rate of the aerosol containing the droplets after condensation growth from a downstream side of the condensation growth tube; a flow rate control unit that controls the flow rate of the aerosol flowing through the capillary tube and supplies a clean sheath flow around the capillary tube outlet; and a double cylindrical sheath flow that positions the aerosol that has passed through the capillary tube on an extension of the central axis of the capillary tube. a droplet counting unit that counts the droplets contained in the aerosol based on the droplets flowing through the capillary tube whose flow rate of the aerosol is controlled by the flow rate control unit, The hydraulic fluid comprises an alkane having a carbon number of 14 or less. A condensation particle counter is provided.

[0010] The supply section, the saturation section, the condensation growth section, the capillary tube, the double cylindrical sheath flow, and the droplet counting section may be arranged in this order in the direction of gravity.

[0011] The alkane may have 14 or 13 carbon atoms.

[0012] A working fluid extraction unit may be provided downstream of the condensation growth tube, surrounding the capillary tube, for sucking and exhausting the working fluid vapor and water vapor condensed on the inner wall of an outlet tube covering at least a part of the capillary tube, together with excess aerosol, in the radially outward direction using a non-metallic porous filter.

[0013] The flow rate control unit may adjust the flow rate of the aerosol flowing through the capillary tube so that the number of droplets per unit time introduced into the droplet counting unit does not exceed the counting rate of the droplet counting unit.

[0014] The droplet counter may be an OPC (Optical Particle Counter).

[0015] supplying a working liquid around an inlet of a saturated tube through which an aerosol containing sample particles flows; a step of heating the working liquid by permeating the wall of the saturation tube to saturate the aerosol with vapor of the working liquid; a step of cooling the aerosol to reduce the saturated vapor pressure of the working liquid, thereby condensing and growing droplets using the sample particles contained in the aerosol as nuclei, extracting the aerosol containing the droplets from the central axis of a condensation growth tube connected to the saturation tube, and sucking out the excess working liquid that has flowed down the inner wall of the condensation growth tube, and the vapor of the working liquid and water vapor that have condensed on the inner wall, together with the excess aerosol; a step of controlling a flow rate of the aerosol flowing through a capillary tube that draws in the aerosol containing the droplets after condensation growth at a minute flow rate from a downstream side of the condensation growth tube; a step of positioning the aerosol that has passed through the capillary tube on an extension of the central axis of the capillary tube by a double cylindrical sheath flow; and counting the droplets contained in the aerosol based on the droplets flowing through the capillary tube in which the flow rate of the aerosol is controlled; The working fluid contains an alkane having 14 or less carbon atoms. A particle number concentration detection method is provided. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram showing the overall configuration of a condensation particle counter according to an embodiment of the present invention; [Figure 2] FIG. 10 is a diagram showing the measurement results of particle number concentration of atmospheric aerosols measured by the condensation particle counter according to this embodiment and an existing CPC. [Figure 3] 1 is a graph in which the vertical axis represents the particle number concentration measured by the condensation particle counter according to the present embodiment divided by the particle number concentration measured by an existing CPC. [Figure 4] 5A to 5C are diagrams showing the results of measuring various particles using the condensation particle counter according to the present embodiment. [Figure 5] Diagram showing the molecular structure of tetradecane. [Figure 6] A diagram showing the molecular structure of the hydraulic fluid used in existing PSMs and CPCs. [Figure 7] A graph showing the counting efficiency curve of an existing OPC. [Figure 8]FIG. 10 is a diagram showing the particle size distribution of droplets after condensation growth when tetradecane is used as the working liquid in the condensation particle counter according to the present embodiment. [Figure 9] FIG. 2 is a diagram showing the cross-sectional structure of the outlet pipe of the condensation growth section and the working fluid extraction section and its surroundings. [Figure 10] FIG. 2 is a diagram showing the cross-sectional structure of a saturated region and a condensation growth region. [Figure 11] FIG. 2 is a diagram showing the cross-sectional structure of a suction / exhaust section of the condensation growth section, a porous filter provided in the working fluid extraction section, and a flow rate control section. [Figure 12] FIG. 1 shows the relationship between particle number concentration and the fraction of countable particles for each of three aerosol flow rates. [Figure 13] FIG. 10 is a diagram showing the detection efficiency of the condensation particle counter according to the present embodiment, the existing Model 3775 manufactured by TSI, and the existing PSM(DEG)-CPC System. [Figure 14] FIG. 10 is a diagram showing the transition of the flow rate of the aerosol in the capillary tube controlled by the flow rate control unit. [Figure 15A] This figure shows an example of the inner wall surface of a condensation growth tube, showing an acid-cleaned stainless steel tube and an unacid-cleaned stainless steel tube. [Figure 15B] This is a diagram showing an example in which diethylene glycol is used as a working fluid and is dropped onto an acid-cleaned stainless steel pipe and an unacid-cleaned stainless steel pipe. [Figure 15C] This is a diagram showing an example in which dimethyl phthalate is used as a working fluid and is dropped onto an acid-cleaned stainless steel pipe and an unacid-cleaned stainless steel pipe. [Figure 15D] FIG. 10 is a diagram showing an example in which tetradecane is used as a working fluid and is dropped onto an acid-cleaned stainless steel pipe and an unacid-cleaned stainless steel pipe. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of a condensation particle counter and a particle number concentration measurement method will be described with reference to the drawings. The following description will focus on the main components of the condensation particle counter, but the condensation particle counter may include components and functions that are not shown or described. The following description does not exclude components and functions that are not shown or described.

[0018] Fig. 1 is a diagram showing the overall configuration of a condensation particle counter 1 according to one embodiment of the present invention. The condensation particle counter 1 shown in Fig. 1 includes a working liquid supply unit 2, a saturation unit 3, a condensation growth unit 4, a capillary tube 5, a flow rate control unit 6, a double-cylindrical sheath flow 23, and a droplet counting unit 7.

[0019] The working fluid supply unit 2, saturation unit 3, condensation growth unit 4, capillary tube 5, double-cylindrical sheath flow 23, and droplet counting unit 7 are arranged in this order in the direction of gravity. The direction of gravity here refers to the arrangement of the working fluid supply unit 2, saturation unit 3, condensation growth unit 4, capillary tube 5, double-cylindrical sheath flow 23, and droplet counting unit 7 in a direction that allows the working fluid to flow down the inner wall of the condensation growth tube, and is not necessarily limited to the normal (vertical) direction relative to the ground. Of these, the working fluid supply unit 2, saturation unit 3, condensation growth unit 4, capillary tube 5, flow rate control unit 6, and double-cylindrical sheath flow 23 constitute the PSM 8.

[0020] The working fluid supply unit 2 supplies the working fluid to the periphery of the saturation unit 3. The working fluid supply unit 2 supplies the working fluid at a predetermined cycle, for example, every 20 to 30 minutes. The working fluid supply unit 2 has a liquid trap container (hereinafter simply referred to as the container) 9 that stores the working fluid, and a liquid feed pump 10 that sucks the working fluid from the container 9 and supplies it to the saturation unit 3. A gas pump (not shown) is provided downstream of the valves 14, 17, and 21. The flow rate of the aerosol introduced into the saturation unit 3 is controlled taking into account the amount of suction and exhaust by this gas pump.

[0021] Although the specific material of the sample particles is not important, this embodiment is characterized by the ability to selectively detect carbonaceous particles with a particle size of 2 nm or less. The working liquid in this embodiment is an alkane with a carbon number of 14 or less. More preferably, in this embodiment, an alkane with a melting point of 6°C or less is used as the working liquid. One specific example of an alkane is tetradecane (C 14 H 30 The physical properties of tetradecane will be discussed later.

[0022] The saturation unit 3 heats the working fluid by permeating it through the walls of the saturation tube, saturating the aerosol with vapor of the working fluid. More specifically, a membrane with the ability to absorb the working fluid is placed on the walls of the saturation tube, and the working fluid is uniformly permeated through this membrane, heating it and saturating the aerosol containing sample particles with vapor of the working fluid. From a safety standpoint, it is undesirable to raise the temperature of the saturation unit 3 extremely high. The temperature of the saturation unit 3 is set to 90°C or below, for example, 86°C.

[0023] The condensation growth unit 4 cools the aerosol and reduces the saturated vapor pressure of the working fluid, causing the sample particles contained in the aerosol to condense and grow into droplets from nuclei. The condensation growth unit 4 also extracts the aerosol containing droplets from the central axis of the condensation growth tube connected to the saturation tube, and sucks out the excess working fluid that has flowed down the inner wall of the condensation growth tube, the vapor of the working fluid that has condensed on the inner wall, and water vapor, together with the excess aerosol.

[0024] The temperature of the condensation-growth section 4 is set to a temperature higher than 0°C, for example, 11°C, in order to prevent the working fluid and moisture in the air from freezing. By using, for example, tetradecane as the working fluid, the sample particles can be condensed and grown into droplets with a diameter of 2 to 6 μm. More preferably, the condensation-growth section 4 according to this embodiment condenses and grows the sample particles into droplets with a diameter of, for example, 5 μm or less.

[0025] An outlet pipe 4b is arranged downstream of the condensation growth section 4. This outlet pipe is a pipe that extracts the aerosol containing droplets after condensation growth from the central axis of the condensation growth pipe and introduces it into the capillary tube 5.

[0026] An intake / exhaust section 11 is provided below the condensation growth section 4, which sucks and exhausts excess working liquid that has flowed down the wall of the condensation growth tube, and the vapor of the working liquid and water vapor that have condensed on the wall of the condensation growth tube, together with excess aerosol. The intake / exhaust section 11 has a liquid trap container (hereinafter simply referred to as the container) 12 that contains the sucked working liquid, a filter 13, and a valve 14. By opening the valve 14, the vapor that has passed through the filter 13 is exhausted.

[0027] The working fluid extraction unit 22 is provided downstream of the condensation growth unit 4. The working fluid extraction unit 22 sucks and exhausts the working fluid vapor and water vapor condensed on the inner wall of the outlet pipe 4b of the condensation growth unit 4 together with excess aerosol. The working fluid sucked by the working fluid extraction unit 22 is stored in the liquid trap container 15 and then exhausted via the filter 16 and the valve 17. As will be described later, the working fluid extraction unit 22 has, for example, an aeration plastic tone, which is a type of non-metallic porous filter. This non-metallic porous filter is disposed so as to surround the capillary tube 5 and exhausts the working fluid radially outward from the capillary tube 5.

[0028] By providing the suction exhaust part 11 and the working fluid extraction part 22, condensation of the working fluid on the inner walls of the capillary tube 5 and the condensation growth tube can be suppressed, and the droplets can flow more easily through the capillary tube 5.

[0029] The flow rate control unit 6 controls the flow rate of the aerosol flowing through the capillary tube 5. The flow rate control unit 6 is connected to the lower part of the working fluid extraction unit 22. Alternatively, the flow rate control unit 6 may be connected to the lower part of the working fluid extraction unit 22 via flexible piping. The flow rate control unit 6 includes an MFC (Mass Flow Controller) 18 and a filter 19. The MFC 18 controls the aerosol flow through the capillary tube 5 to a predetermined flow rate. A complementary clean air flow that has passed through the filter 19 is supplied to the conduit. By surrounding the aerosol that has passed through the capillary tube 5 with the clean air flow, the aerosol continues to flow on an extension of the central axis of the capillary tube 5 even after passing through the capillary tube 5. This allows the droplets 34 in the aerosol to be transported to the droplet counting unit 7 without loss. The clean air flow surrounding the aerosol described above is called a double-cylindrical sheath flow. As will be described later, the droplet counting unit 7 counts the droplets contained in the aerosol based on the droplets flowing through the capillary tube 5. Specifically, the droplet counting unit 7 is a light scattering airborne particle counter (OPC). A commercially available general-purpose OPC can be used. As will be described later, the particle number concentration of the aerosol can be calculated from the count value of the droplets counted by the droplet counting unit 7.

[0030] A filter 20 and a valve 21 are provided downstream of the droplet counting unit 7 to suck and exhaust the aerosol flowing from the PSM 8 to the droplet counting unit 7 .

[0031] Figure 2 shows the measurement results of particle number concentration of atmospheric aerosols measured using the condensation particle counter 1 according to this embodiment and an existing CPC. The horizontal axis of Figure 2 represents time [days], and the vertical axis represents particle number concentration. The black plots in Figure 2 represent the measurement results using the condensation particle counter 1 according to this embodiment, and the gray lines represent the measurement results using the existing CPC, Model 3775 CPC manufactured by TSI.

[0032] As shown in FIG. 2, the measurement results of the condensation particle counter 1 according to this embodiment and the existing TSI Model 3775 CPC are almost identical for more than 20 days, which indicates that the condensation particle counter 1 according to this embodiment has long-term stability equivalent to that of the TSI Model 3775 CPC.

[0033] 3 is a graph in which the vertical axis represents the particle number concentration measured by the condensation particle counter 1 according to this embodiment divided by the particle number concentration measured by an existing CPC, Model 3775 CPC manufactured by TSI, and the horizontal axis represents time (days), as in FIG.

[0034] The value on the vertical axis in Fig. 3 is 1 when the particle number concentration measured by the condensation particle counter 1 according to this embodiment matches the particle number concentration measured by the Model 3775 CPC manufactured by TSI. As shown in Fig. 3, the vertical axis rarely becomes 1 or less, but there are periodic times when the value becomes much greater than 1. This measurement result shows that the condensation particle counter 1 according to this embodiment can measure a higher particle number concentration than the existing Model 3775 CPC manufactured by TSI, specifically, it can measure a particle number concentration closer to the true value.

[0035] Note that a value of 1 or less on the vertical axis of Fig. 3 indicates that the particle number concentration measured by the condensation particle counter 1 according to this embodiment is lower than the particle number concentration measured by the TSI Model 3775 CPC, but this does not necessarily mean that the measurement accuracy of the condensation particle counter 1 according to this embodiment is low. The TSI Model 3775 CPC uses butanol as the working fluid, and if butanol has a better chemical affinity with atmospheric aerosol particles than tetradecane, which is used as the working fluid in the condensation particle counter 1 according to this embodiment, the value on the vertical axis of Fig. 3 may be less than 1. Therefore, information on the chemical composition of particles contained in atmospheric aerosols can be obtained from the value on the vertical axis of Fig. 3.

[0036] It is known that existing CPCs cannot count carbon-based particles with a particle size of 2 nanometers or less. In contrast, the condensation particle counter 1 according to this embodiment can accurately count carbon-based particles with a particle size of 1 nm or less.

[0037] Fullerene C, an example of a carbon-based particle with a particle size of less than 1 nm 60is a soccer ball-shaped carbon molecule. Fullerene C was synthesized using existing CPC and PSM8. 60 There have been no reported cases where the condensation particle counter 1 according to this embodiment has been able to count particles of this kind, and this fact also shows that the condensation particle counter 1 according to this embodiment is superior.

[0038] The condensation particle counter 1 according to this embodiment can also measure particles other than carbon-based particles with a particle size of 2 nanometers or less.

[0039] FIG. 4 is a diagram showing the results of measuring various particles using the condensation particle counter 1 according to this embodiment. The horizontal axis of FIG. 4 is particle diameter [nm], and the vertical axis is the value obtained by dividing the particle number concentration measured by the condensation particle counter 1 according to this embodiment by the particle number concentration measured by an existing system consisting of a PSM and a CPC (hereinafter referred to as a PSM-CPC system). The existing PSM-CPC system in FIG. 4 is a system that uses diethylene glycol (hereinafter referred to as DEG) as the working fluid. In FIG. 4, fullerene C is used as the sample particle. 60 The plot shows the measurement results for silver, sodium chloride, and sodium iodide. These particle materials were heated and cooled to form aerosols, and a differential electric mobility classifier was used to extract test particles of uniform size from the aerosol for evaluation. Therefore, the particle size is defined as the mobility particle size.

[0040] As can be seen from Figure 4, for sample particles with a particle size of 2 nm or more, the particle number concentration measured by the condensation particle counter 1 according to this embodiment is comparable to the particle number concentration measured by the existing PSM-CPC system. 60 For sample particles other than fullerene C, when the particle size is less than 2 nm, the particle number concentration measured by the condensation particle counter 1 according to this embodiment is lower than the particle number concentration measured using the existing PSM(DEG)-CPC system. 60For particle diameters of less than 2 nm, the particle number concentration measured by the condensation particle counter 1 according to this embodiment is much greater than the particle number concentration measured by the existing PSM(DEG)-CPC system.

[0041] As can be seen from the measurement results in Figure 4, the condensation particle counter 1 according to this embodiment has the same measurement accuracy as the existing PSM(DEG)-CPC system for sample particles with a particle size of 2 nm or more, regardless of the type of sample particle. Also, for sample particles with a particle size of less than 2 nm, the measurement accuracy is as high as that of the existing PSM(DEG)-CPC system. 60 In the case of silver, sodium chloride, and sodium iodide sample particles, the measurement accuracy is lower than that of the existing PSM(DEG)-CPC system.

[0042] FIG. 5 is a diagram showing the molecular structure of tetradecane used as the working fluid by the condensation particle counter 1 according to this embodiment, and may be expressed in a simplified form as shown on the right side of FIG.

[0043] Tetradecane is a non-polar linear alkane. The condensation particle counter 1 according to this embodiment is characterized by its use of a non-polar working fluid such as tetradecane, allowing it to detect particle species that could not be detected by existing PSMs and CPCs.

[0044] Alkanes have the general formula C n H 2n+2 Alkanes are saturated chain hydrocarbons expressed as follows. Alkanes are liquids with a relatively high vapor pressure. As the number of carbon atoms increases, the vapor pressure decreases. Therefore, it is important to use alkanes with as many carbon atoms as possible to prevent the droplet size from becoming excessively large after condensation growth.

[0045] According to the inventors' investigations, tetradecane, an alkane with 14 carbon atoms, is optimal as a working fluid. The melting point of tetradecane is approximately 6°C. If the number of carbon atoms in the alkane exceeds 14, the melting point becomes too high, and there is a risk that the working fluid will freeze inside the condensation growth section 4. It is also possible to use alkane molecules with fewer than 13 carbon atoms as a working fluid, but as the carbon number decreases, the vapor pressure of the alkane molecules increases, and the droplet diameter after condensation growth is expected to significantly exceed 5 μm. If the droplets significantly exceed 5 μm, the probability that the droplets will pass through the capillary tube of the condensation growth section 4 and reach the optical system of the droplet counting section 7 is expected to significantly decrease, but the droplets themselves can still be counted.

[0046] Figure 6 shows the molecular structure of the working fluid used in existing PSMs and CPCs. Figure 6A shows water (H2O) and Figure 6B shows butanol (CH4). 10 O, Figure 6C shows diethylene glycol CH 10 O3, Figure 6D shows dibutyl phthalate C 16 H 22 It is O4.

[0047] Figure 7 shows the counting efficiency curve w3 of an existing OPC. The horizontal axis of Figure 7 represents the particle size [μm] of the sample particle, and the vertical axis represents the counting efficiency of the OPC. The counting efficiency curve w3 in Figure 7 allows particles with diameters ranging from 0.3 μm to 10 μm to be counted. The counting efficiency curve w3 in Figure 7 indicates the percentage of particles that the OPC can count relative to the total number of particles sampled by the OPC.

[0048] Condensation particle counter 1 according to this embodiment uses tetradecane as the working liquid, and is therefore capable of forming droplets that have condensed and grown to a particle size of 2 to 6 μm, which is the range indicated by the arrow line y1 in Fig. 7. Furthermore, an existing CPC that uses butanol or water as the working liquid can form droplets that have condensed and grown to a particle size of 5 to 10 μm, which is the range indicated by the arrow line y2 in Fig. 7. On the other hand, an existing PSM that uses diethylene glycol as the working liquid can form droplets that have condensed and grown to a particle size of 0.05 to 0.2 μm.

[0049] If the particle size of droplets that have condensed and grown from sample particles as nuclei exceeds 5 μm, the probability that droplets in the aerosol will collide with the inner wall of the OPC increases while the aerosol is being transported from the inlet of the OPC to the optical system. This probability increases as the diameter of the droplets increases. Therefore, when tetradecane is used as the working liquid in the condensation particle counter 1 according to this embodiment, it is ideal to keep the particle size of the droplets after condensation growth within the range of 1 to 5 μm, at which point the counting efficiency is maximized.

[0050] Fig. 8 is a diagram showing the particle size distribution of droplets after condensation growth when tetradecane is used as the working liquid in condensation particle counter 1 according to this embodiment. The horizontal axis of Fig. 8 represents the average particle size [nm] of droplets after condensation growth, and the vertical axis represents the frequency of droplet appearance. As shown in Fig. 8, the average particle size of droplets after condensation growth is in the range of approximately 2 to 5 µm, which is within the ideal range of 1 to 5 µm mentioned above, and it is clear that using tetradecane as the working liquid is appropriate.

[0051] As shown in FIG. 1, the condensation particle counter 1 according to this embodiment has a suction and exhaust section 11 in the condensation growth section 4 for sucking and exhausting the working fluid, and also has a working fluid extraction section 22 near the outlet of the condensation growth section 4 for sucking and exhausting the working fluid.

[0052] Figure 9 shows the cross-sectional structure of the condensation growth section 4 and the working fluid extraction section 22, and Figure 10 shows the cross-sectional structure of the saturation section 3 and the condensation growth section 4. As shown in Figures 9 and 10, an outlet pipe 4b is provided downstream of the condensation growth section 4. The outlet pipe 4b is arranged to cover the upper end of the capillary tube 5. The capillary tube 5 extends vertically from the outlet pipe 4b to the working fluid extraction section 22. The flow rate control section 6 controls the flow rate of the aerosol 24 passing through the capillary tube 5, and a clean air flow compensates for the deficiency in the sample flow rate of the droplet counting section. This clean air flow becomes a double-cylindrical sheath flow 23, which positions the aerosol 24 that has passed through the capillary tube on an extension of the central axis of the capillary tube. This transports droplets 34 in the aerosol 24 to the droplet counting section 7 without loss.

[0053] As shown in Figure 10, a membrane 3b that absorbs a portion of the working fluid flowing through the saturation tube 3a is disposed on the wall of the saturation tube 3a in the saturation section 3. A portion of the working fluid is permeated through this membrane 3b and heated, saturating the aerosol with vapor of the working fluid. Figure 10 shows a schematic diagram of an aerosol 24 containing sample particles 32 introduced into the saturation tube 3a, an aerosol 24a containing sample particles 32 and vapor 33 of the working fluid inside the saturation tube 3a, and an aerosol 24b containing droplets 34 that have condensed and grown inside the condensation growth tube 4a.

[0054] The saturation tube 3a of the saturation section 3 is connected to the condensation growth tube 4a of the condensation growth section 4. In this embodiment, when the membrane 3b is arranged on the tube wall of the saturation tube 3a, the inner diameter of the saturation tube 3a and the inner diameter of the condensation growth tube 4a are made the same. Therefore, when the membrane 3b is not arranged, the inner diameter of the saturation tube 3a is made larger than the inner diameter of the condensation growth tube 4a by about 1 mm. As a result, when the membrane 3b is arranged on the tube wall of the saturation tube 3a, no difference in level occurs between the inner wall surface of the saturation tube 3a and the inner wall surface of the condensation growth tube 4a, allowing the aerosol to flow smoothly from the saturation tube 3a to the condensation growth tube 4a.

[0055] In addition, since the working fluid is injected from the outer surface of the membrane 3b arranged in the saturated pipe 3a, the working fluid passes through the membrane 3b and is introduced into the saturated pipe 3a, so that the force of the injected working fluid does not cause splashes of the working fluid inside the saturated section 3.

[0056] A heat exchanger 31 is connected to the tube wall of the condensation growth tube 4a, and the aerosol 24a inside the condensation growth tube 4a is cooled by this heat exchanger 31. By cooling the aerosol 24a in the condensation growth tube 4a, the saturated vapor pressure of the vapor of the working liquid decreases, and the aerosol 24a condenses and grows into droplets 34 with sample particles 32 contained in the aerosol 24b as nuclei.

[0057] Because there is a risk that the working fluid vapor 33 may condense on the inner walls of the condensation growth section 4 and the outlet pipe 4b of the condensation growth tube 4a, a suction and exhaust section 11 is provided below the condensation growth section 4 to suck and exhaust the excess working fluid that has flowed down the wall of the condensation growth tube 4a and the working fluid vapor 33 and water vapor that have condensed on the wall, together with the excess aerosol. In addition, because there is a risk that the working fluid vapor 33 and water vapor may condense on the inner wall downstream of the outlet pipe 4b of the condensation growth tube 4a, a working fluid extraction section 22 (see FIG. 1) is provided downstream of the outlet pipe 4b of the condensation growth tube 4a to suck and exhaust the condensed working fluid vapor 33 and water vapor together with the excess aerosol.

[0058] The working fluid extraction unit 22 according to this embodiment has a non-metallic porous filter 26 (see FIG. 9) arranged along the inner wall surface of the working fluid extraction unit 22. The working fluid extraction unit 22 sucks and exhausts the working fluid vapor 33 and water vapor condensed on the inner wall of the outlet pipe 4b of the condensation growth unit, together with excess aerosol, to the radially outer side of the capillary tube 5 via the porous filter 26.

[0059] The inventors conducted repeated trial and error experiments to select a material for radially extracting the working fluid. Metallic porous filters prevent condensed working fluid from passing through the porous filter stably, resulting in an unstable suction and exhaust flow rate. It was discovered that polypropylene plastic tones used for aquarium aeration have a high porosity and excellent chemical resistance. By using a non-metallic porous filter 26 made of plastic tones for aquarium aeration, the suction and exhaust flow rate of condensed working fluid could be stabilized.

[0060] Ports 27, 28 for measuring the minute differential pressure of the working liquid are provided between the condensation growth section 4 and the working liquid extraction section 22, and between the working liquid extraction section 22 and the droplet counting section 7, respectively. These minute differential pressure measurement ports 27, 28 are connected to a minute differential pressure gauge 29 via piping. The minute differential pressure measured by the minute differential pressure gauge 29 is input to a mass flow controller 30. The mass flow controller 30 controls the flow rate control section 6 based on the measured minute differential pressure.

[0061] 11 is a diagram showing the cross-sectional structure of the porous filter 26 provided in the suction / exhaust section 11, the capillary tube 5, and the working fluid extraction section 22 of the condensation growth section 4. The numbers in brackets in FIG. 11 are the numbers in FIG. 1. The complementary clean air flow from the flow rate control section 6 positions the aerosol 24, which has become the double-cylindrical sheath flow 23 and passed through the capillary tube 5, on an extension of the central axis of the capillary tube 5, thereby transporting the droplets 34 in the aerosol 24 to the droplet counting section 7 without loss.

[0062] In this embodiment, the aerosol 24 is sucked from a position further downstream of the droplet counter (OPC) 7, which is disposed downstream of the capillary tube 5. Originally, the OPC is designed to suck particles in the sub-micrometer particle size range (particle size of 0.3 μm or more) at a high flow rate in a clean environment with a low particle number concentration C.

[0063] That is, because OPCs are often used for cleanliness control in clean environments, they are not designed to count particles at high speeds, and even the fastest OPC has a counting speed F of approximately 25,000 particles / second.

[0064] On the other hand, particles in the atmosphere have a high particle number concentration C, so a higher counting rate is required than when using an OPC in a clean environment. To accurately measure particle numbers with an OPC, the counting rate must be reduced, which requires a lower aerosol flow rate.

[0065] If the aerosol flow rate sucked into the OPC is Q, the following equation (1) holds true:

[0066] C=F / Q …(1) To enable measurements at high particle number concentrations C even at low counting rates, the aerosol flow rate Q needs to be reduced by about two orders of magnitude.

[0067] The particle number concentration C is expressed by the following formula (2) using the count value N of the droplets counted by the droplet counter (OPC) 7. C=N / (Δt×Q) …(2)

[0068] As shown in equation (2), if the droplet count value N counted by the droplet counter (OPC) 7, the aerosol flow rate Q sucked into the droplet counter (OPC) 7, and the sample time Δt are known, the particle number concentration C can be easily calculated.

[0069] Figure 12 shows the relationship between particle number concentration and the proportion of countable particles for each of three types of aerosol flow rates. The horizontal axis of Figure 12 shows the particle number concentration (particles / cm 3 ), and the vertical axis is the percentage of countable particles. Curves w11, w12, and w13 are plotted at an aerosol flow rate of 30 cm 3 (30mL) / min, 300cm 3 (0.3L) / min, 2830cm 3 (2.83L) / min.

[0070] 12, the smaller the aerosol flow rate, the higher the particle number concentration can be counted over a wider range of particle number concentrations. Therefore, in this embodiment, the aerosol flow rate flowing through the working fluid extraction unit 22 to the droplet counter (OPC) 7 is set to 30 cm 3 The flow rate of the aerosol 24 passing through the capillary tube 5 is adjusted by the flow rate control unit 6 so that the flow rate is 1 / min.

[0071] FIG. 13 shows the results of the PSM (C 14 H 30 The horizontal axis of Figure 13 shows the detection efficiency of the PSM (DEG)-OPC System, the existing TSI Model 3775, and the existing PSM (DEG)-CPC System. -3 ], and the vertical axis represents the particle number concentration detected by the droplet counter (OPC) 7 divided by the reference particle number concentration. The reference particle number concentration is measured using, for example, a Faraday Cup Aerosol Electrometer (FCAE).

[0072] As shown in FIG. 13, the condensation particle counter 1 according to this embodiment has a 5×10 4 pieces / cm3 At particle number concentrations below 5 x 10, a relationship can be obtained to determine the true particle number concentration from the count value by OPC and the particle number concentration measured from the flow rate through the capillary tube. 4 pieces / cm 3 The particle number concentration in the aerosol can be measured in the following ranges:

[0073] Figure 14 is a diagram showing the transition of the flow rate of the aerosol 24 passing through the capillary tube 5 controlled by the flow rate control unit 6. The horizontal axis of Figure 14 is time [days], and the vertical axis is the flow rate of the aerosol 24 in the capillary tube 5. By controlling the flow rate with the flow rate control unit 6, it is possible to maintain the flow rate of the aerosol 24 passing through the capillary tube 5 at a substantially constant value over a period of approximately 20 days.

[0074] Although the main technical features of the condensation particle counter 1 according to this embodiment have been described above, there are several other technical features in addition to those described above. The following lists the other technical features of the condensation particle counter 1 according to this embodiment.

[0075] In the condensation particle counter 1 according to this embodiment, the inner wall of the condensation growth tube 4a is roughened by acid cleaning or sandblasting, thereby preventing the working fluid 25 and condensed water vapor from pooling on the inner wall surface.

[0076] 15A is an example of a simulated inner wall surface of a condensation growth tube 4a, with the left side being an acid-cleaned stainless steel tube and the right side being an unacid-cleaned stainless steel tube. Figures 15B-D show examples in which a liquid used as a PSM working fluid was dripped onto the stainless steel tube in Figure 15A. For the stainless steel tube in Figure 15A, diethylene glycol was used as the working fluid in Figure 15B, dimethyl phthalate in Figure 15C, and tetradecane in Figure 15D. As shown in the left images of Figures 15B-15D, it can be seen that the use of an acid-cleaned tube can prevent the formation of pools of working fluid.

[0077] Furthermore, in the condensation particle counter 1 according to this embodiment, the piping and liquid pump that supply the aerosol 24 containing sample particles to the saturation section 3 are made of a material resistant to alkanes, specifically polyurethane. Existing PSMs and CPCs often use transparent chemical-resistant tubing made of Tygon 2375, but this tubing is insufficient in terms of chemical resistance. When nylon piping, an inexpensive material with high chemical resistance, was tried, it was confirmed that when an alkane was used as the working fluid, the plasticizer components of the nylon precipitated.

[0078] On the other hand, when polyurethane piping was used, no plasticizer precipitation occurred. Polyurethane is inexpensive and has excellent chemical resistance to alkanes, so in this embodiment, polyurethane was used as the material for the piping that transports the working fluid 25 made of alkanes.

[0079] In the above-described embodiment, an example was described in which an alkane (particularly tetradecane) was used as the working liquid 25 in the condensation particle counter according to this embodiment. However, tridecane C having 13 carbon atoms may be used instead of tetradecane. 13 H 28 Tridecane has a higher vapor pressure than tetradecane, so the droplets can become larger, but by lowering the temperature of the saturation section 3, it may be possible to control the droplet diameter after condensation growth to 5 micrometers or less.

[0080] As described above, the condensation particle counter 1 according to this embodiment is a combination of the PSM 8 and the droplet counter (OPC) 7, and uses an alkane (specifically, tetradecane) as the working fluid 25 of the PSM 8, so that it can accurately count carbon-based particles with a particle size of 2 nanometers or less, which could not be measured by existing condensation particle counters.

[0081] In addition, the PSM8 according to this embodiment has a working fluid supply unit 2, a saturation unit 3, a condensation growth unit 4, a working fluid extraction unit 22, a capillary tube, a double-cylindrical sheath flow, and a droplet counting unit 7 arranged in the direction of gravity. The capillary tube 5 extends from the outlet tube 4b of the condensation growth unit 4 to the working fluid extraction unit 22, and the outlet tube 4b is arranged to surround the capillary tube 5. A suction / exhaust unit 11 is provided in the condensation growth tube 4a to suction / exhaust the working fluid 25, and a working fluid extraction unit 22 is provided downstream of the condensation growth unit 4 to suction / exhaust the working fluid 25. A flow rate control unit 6 is also provided to control the aerosol 24 flowing through the capillary tube 5 to a predetermined flow rate. This allows measurement at a high particle number concentration by reducing the flow rate of the aerosol 24 flowing through the capillary tube 5. Furthermore, the aerosol 24 that has passed through the capillary tube 5 is positioned on an extension of the central axis of the capillary tube 5 by the double cylindrical sheath flow 23, so that the droplets 34 in the aerosol 24 are transported to the droplet counting unit 7 without loss.

[0082] The technology related to the above-described embodiment can be summarized as follows. (1) a supply unit that supplies a working fluid around the inlet of a saturation tube through which an aerosol containing sample particles flows; a saturation section that heats the working fluid by permeating it into the wall of the saturation tube and saturates the aerosol with vapor of the working fluid; a condensation growth section that cools the aerosol to reduce the saturated vapor pressure of the working fluid, thereby condensing and growing droplets using the sample particles contained in the aerosol as nuclei, extracts the aerosol containing the droplets from a central axis of a condensation growth tube connected to the saturation tube, and sucks and exhausts the excess working fluid that has flowed down the inner wall of the condensation growth tube, the vapor of the working fluid that has condensed on the inner wall, and water vapor together with the excess aerosol; a capillary tube that draws in a minute flow rate of the aerosol containing the droplets after condensation growth from a downstream side of the condensation growth tube; a flow rate control unit that controls the flow rate of the aerosol flowing through the capillary tube; a double cylindrical sheath flow that positions the aerosol that has passed through the capillary tube on an extension of the central axis of the capillary tube; a droplet counting unit that counts the droplets contained in the aerosol based on the droplets flowing through the capillary tube whose flow rate of the aerosol is controlled by the flow rate control unit, The working fluid contains an alkane having 14 or less carbon atoms. Condensation particle counter. (2) the supply section, the saturation section, the condensation growth section, the capillary tube, the double cylindrical sheath flow, and the droplet counting section are arranged in this order in the direction of gravity; (1) A condensation particle counter according to (1). (3) The particle size of the droplets is 5 μm or less. A condensation particle counter according to (1) or (2). (4) The sample particles are carbon-based particles having a particle size of 2 nm or less. A condensation particle counter according to any one of (1) to (3). (5) The melting point of the alkane is 6°C or lower. A condensation particle counter according to any one of (1) to (4). (6) The alkane has 13 or 14 carbon atoms. A condensation particle counter according to any one of (1) to (5). (7) A working liquid extraction unit is provided downstream of the condensation growth tube so as to surround the capillary tube, and sucks and exhausts the vapor of the working liquid and water vapor condensed on the inner wall of an outlet tube covering at least a part of the capillary tube, together with excess aerosol, in an outward radial direction using a non-metallic porous filter. A condensation particle counter according to any one of (1) to (6). (8) The flow rate control unit adjusts the flow rate of the aerosol flowing through the capillary tube so that the number of droplets introduced into the droplet counting unit per unit time does not exceed the counting rate of the droplet counting unit. A condensation particle counter according to any one of (1) to (7). (9) The supply unit supplies the working fluid to the periphery of the capillary tube through a pipe made of polyurethane. A condensation particle counter according to any one of (1) to (8). (10) The droplet counting unit is an OPC (Optical Particle Counter), A condensation particle counter according to any one of (1) to (9). (11) supplying a working liquid around the inlet of the saturation tube through which the aerosol containing the sample particles flows; a step of heating the working liquid by permeating the wall of the saturation tube to saturate the aerosol with vapor of the working liquid; a step of cooling the aerosol to reduce the saturated vapor pressure of the working liquid, thereby condensing and growing droplets using the sample particles contained in the aerosol as nuclei, extracting the aerosol containing the droplets from the central axis of a condensation growth tube connected to the saturation tube, and sucking out the excess working liquid that has flowed down the inner wall of the condensation growth tube, and the vapor of the working liquid and water vapor that have condensed on the inner wall, together with the excess aerosol; a step of controlling a flow rate of the aerosol flowing through a capillary tube that draws in the aerosol containing the droplets after condensation growth at a minute flow rate from a downstream side of the condensation growth tube; a step of positioning the aerosol that has passed through the capillary tube on an extension of the central axis of the capillary tube by a double cylindrical sheath flow; and counting the droplets contained in the aerosol based on the droplets flowing through the capillary tube in which the flow rate of the aerosol is controlled; The working fluid contains an alkane having 14 or less carbon atoms. Particle number concentration detection method.

[0083] The aspects of the present disclosure are not limited to the individual embodiments described above, but include various modifications that may be conceived by those skilled in the art, and the effects of the present disclosure are not limited to the above-described contents. In other words, various additions, modifications, and partial deletions are possible within the scope of the conceptual idea and spirit of the present disclosure, which is derived from the contents defined in the claims and their equivalents. [Explanation of symbols]

[0084] 1 condensation particle counter, 2 working liquid supply section, 3 saturation section, 4 condensation growth section, 4a condensation growth tube, 4b outlet tube, 5 capillary tube, 6 flow control section, 7 droplet counting section, 8 PSM, 9 liquid trap vessel, 10 pump, 11 suction exhaust section, 12 liquid trap vessel, 13 filter, 14 valve, 15 liquid trap vessel, 16 filter, 17 valve, 19 filter, 20 filter, 21 valve, 22 working liquid extraction section, 23 double cylindrical sheath flow, 24 aerosol, 25 working liquid, 26 porous filter, 27, 28 micro-differential pressure measurement port, 29 micro-differential pressure gauge, 30 mass flow controller

Claims

1. a supply unit that supplies a working liquid around the inlet of the saturation tube through which the aerosol containing the sample particles flows; a saturation section that heats the working fluid by permeating it into the wall of the saturation tube and saturates the aerosol with vapor of the working fluid; a condensation growth section that cools the aerosol to reduce the saturated vapor pressure of the working fluid, thereby condensing and growing droplets using the sample particles contained in the aerosol as nuclei, extracts the aerosol containing the droplets from a central axis of a condensation growth tube connected to the saturation tube, and sucks and exhausts the excess working fluid that has flowed down the inner wall of the condensation growth tube, the vapor of the working fluid that has condensed on the inner wall, and water vapor together with the excess aerosol; a capillary tube that draws in a minute flow rate of the aerosol containing the droplets after condensation growth from a downstream side of the condensation growth tube; a flow rate control unit that controls the flow rate of the aerosol flowing through the capillary tube; a double cylindrical sheath flow that positions the aerosol that has passed through the capillary tube on an extension of the central axis of the capillary tube; a droplet counting unit that counts the droplets contained in the aerosol based on the droplets flowing through the capillary tube whose flow rate of the aerosol is controlled by the flow rate control unit, The working fluid contains an alkane having 14 or less carbon atoms. Condensation particle counter.

2. the supply section, the saturation section, the condensation growth section, the capillary tube, the double cylindrical sheath flow, and the droplet counting section are arranged in this order in the direction of gravity.

10. The condensation particle counter of claim 1.

3. The alkane has 14 or 13 carbon atoms.

10. The condensation particle counter of claim 1.

4. a working liquid extraction unit disposed downstream of the condensation growth tube so as to surround the capillary tube, the working liquid vapor and water vapor condensed on the inner wall of an outlet tube covering at least a part of the capillary tube being sucked and exhausted in an outward radial direction together with excess aerosol using a non-metallic porous filter; 10. The condensation particle counter of claim 1.

5. the flow rate control unit adjusts the flow rate of the aerosol flowing through the capillary tube so that the number of droplets introduced into the droplet counting unit per unit time does not exceed the counting rate of the droplet counting unit.

10. The condensation particle counter of claim 1.

6. The droplet counting unit is an OPC (Optical Particle Counter). A condensation particle counter according to any one of claims 1 to 5.

7. supplying a working liquid around an inlet of a saturated tube through which an aerosol containing sample particles flows; a step of heating the working liquid by permeating the wall of the saturation tube to saturate the aerosol with vapor of the working liquid; a step of cooling the aerosol to reduce the saturated vapor pressure of the working liquid, thereby condensing and growing droplets using the sample particles contained in the aerosol as nuclei, extracting the aerosol containing the droplets from the central axis of a condensation growth tube connected to the saturation tube, and sucking out the excess working liquid that has flowed down the inner wall of the condensation growth tube, and the vapor of the working liquid and water vapor that have condensed on the inner wall, together with the excess aerosol; a step of controlling a flow rate of the aerosol flowing through a capillary tube that draws in the aerosol containing the droplets after condensation growth at a minute flow rate from a downstream side of the condensation growth tube; a step of positioning the aerosol that has passed through the capillary tube on an extension of the central axis of the capillary tube by a double cylindrical sheath flow; and counting the droplets contained in the aerosol based on the droplets flowing through the capillary tube in which the flow rate of the aerosol is controlled; The working fluid contains an alkane having 14 or less carbon atoms. Particle number concentration detection method.

Images