SYSTEM AND METHOD FOR COUNTING AEROSOL PARTICLES IN ATMOSPHERE WITH RESPECT TO EACH PARTICLE SIZE BY APPROPRIATELY SETTING RATIO OF FLOW RATE OF SAMPLE GAS AND SHEATH GAS IN DMA

• US 20130085706A1
• Filed: 09/06/2012
• Published: 04/04/2013
• Est. Priority Date: 09/07/2011
• Status: Active Grant

• Current Assignee: RION Company Limited
• Original Assignee: RION Company Limited
• Inventors: TSUNODA, Chiryo
• Granted Patent: US 9,534,998 B2
• Time in Patent Office: Days
• US Class Current: 702/128
• CPC Class Codes: B03C 2201/24 for measuring or calculating of parameters, e.g. efficiency
• CPC Class Codes: B03C 3/145 Inertia
• CPC Class Codes: B03C 3/155 Filtration
• CPC Class Codes: G01F 1/56 by using electric or magnetic effects G01F1/66 takes precedence
• CPC Class Codes: G01N 15/0266 with electrical classification
• CPC Class Codes: G01N 15/0656 using electric, e.g. electrostatic methods or magnetic methods by investigating individual particles G01N15/1031, G01N15/12
• CPC Class Codes: G06F 15/00 Digital computers in general details G06F1/00 – G06F13/00; Data processing equipment in general

Abstract

A maximum number of charges on aerosol particles which are measurement targets is decided as a natural number x equal to or larger than 2. First and second electrical mobility groups are derived based on x. The first group includes electrical mobility Zc(U) and electrical mobilities having voltage values equal to a voltage U multiplied by values from 2 to x respectively, and the second group includes electrical mobilities having respective voltage values equal to voltage U multiplied by irreducible fractions which are coprime to each other among values with regularity. A ratio of flow rate with which range corresponding to the electrical mobilities included in the first group do not interfere with one another and the range corresponding to the electrical mobilities included in the first group and range corresponding to the electrical mobilities included in the mobility group do not interfere with one another is calculated.

Claims

1. A ratio of flow rate deciding method in which, when a sample fluid containing charged aerosol particles and a clean fluid comprised of clean air are made to flow in a DMA (Differential Mobility Analyzer) which classifies the charged aerosol particles in a predetermined electric field based on electrical mobility, a ratio of flow rate equal to a flow rate of the sample fluid divided by a flow rate of the clean fluid is calculated, the method comprising:

a maximum charge number deciding step of deciding a maximum number of charges on aerosol particles being measurement targets among the charged aerosol particles as a natural number x equal to or larger than 2;

a reference electrical mobility defining step of defining electrical mobility which is ability of aerosol particles whose number of charges is 1 among the aerosol particles being the measurement targets to move in the electric field, as Zc(U) expressed with a voltage value U supplied to form the is electric field;

an electrical mobility group deriving step of deriving a first electrical mobility group and a second electrical mobility group based on x decided in the maximum charge number deciding step, the first electrical mobility group including the electrical mobility Zc(U) and electrical mobilities expressed with voltage values equal to the voltage value U multiplied by values from 2 to x respectively, and the second electrical mobility group including electrical mobilities expressed with respective voltage values equal to the voltage value U multiplied by irreducible fractions which are coprime to each other among values with regularity which arc x/(x−

1), x/(x−

2), . . . x/2, (x−

1)/(x−

2), (x−

1)/(x−

3), (x−

1)/2, (x−

2)/(x−

3), (x−

2)/(x−

4) . . . (x−

2)/2, . . . and 3/2;

a converting step of expressing each of the electrical mobilities by using Zc(U) defined in the reference electrical mobility defining step, regarding all the electrical mobilities included in the first electrical mobility group and the second electrical mobility group derived in the electrical mobility group deriving step;

a range defining step of, if a range where a given electrical mobility is variable by adjusting a ratio of flow rate is defined as a range corresponding to the relevant electrical mobility, defining the range corresponding to all the electrical mobilities included in the first electrical mobility group and the second electrical mobility group derived in the electrical mobility group deriving step. after the converting step; and

a final calculating step of calculating the ratio of flow rate with which the range corresponding to the electrical mobilities included in the first electrical mobility group, which range are defined in the range defining step, do not interfere with one another and the range corresponding to the electrical mobilities included in the first electrical mobility group and the range corresponding to the electrical mobilities included in the second electrical mobility group do not interfere with one another.

2. A size-classified particle size distribution measuring method comprising:

(A) a step of putting aerosol particles into a charged equilibrium state;

(B) a step of classifying the aerosol particles charged in the step (A) in a predetermined electric field based on electrical mobility while making a sample fluid containing the aerosol particles charged in the step (A) and a clean fluid comprised of clean air flow in the electric field based on the ratio of flow rate calculated by the ratio of flow rate deciding method according to claim 1, the step being a step of initially setting a reference voltage supplied to form the electric field to a voltage value U and executing the first classifying of the aerosol particles under the supplied voltage having the initially set voltage value U;

(C) a step of measuring the aerosol particles classified out in the step (B), by an electrical or/and optical measuring method and outputting a result of the measurement;

(D) a step of confirming whether or not a predetermined condition is satisfied, based on the measurement result output in the step (C); and

(E) a step of, when confirming in the step (D) that the condition is satisfied, calculating particle size distribution with respect to each particle size from the measurement result output in the step (C), and when confirming that the aforesaid condition is not satisfied, executing;

(a) a procedure to re-set the voltage supplied to form the electric field to a sum of the voltage value of the voltage supplied in the previous classifying executed in the step (B) (previous value)and the voltage value U, and supply the voltage having the re-set voltage value to execute re-classifying of the aerosol particles;

(b-1) a procedure to output a first measurement result M1 which is the measurement result of the aerosol particles that are classified out in the step (B) under the supplied voltage having the initially set voltage value U, and

(b-2) a procedure to output a new measurement result Mx which is the re-measurement result of the aerosol particles that are classified out, every time the re-classifying is executed in the procedure (a);

(c) a procedure to calculate a ratio of the measurement result Mx, which is output in the procedure (b-2), to the measurement result M1, which is output in the procedure (b-1); and

(d) a procedure to confirm that the condition is not satisfied yet when the ratio calculated in the procedure (c) is larger than a prescribed value, to execute the procedures (a), (b), and (c), while confirming that the condition is satisfied when the ratio calculated in the procedure (c) is equal to or smaller than the prescribed value; and

(e) a procedure to, when confirming that the condition is satisfied, calculate the particle size distribution with respect to each particle size from the measurement result based on a charging probability for the aerosol particles to be charged in the step (A).

3. The size-classified particle size distribution measuring method according to claim 2.

wherein in the step (B), based on that the ratio of flow rate calculated by the ratio of flow rate calculating method according to claim 1 when x being the maximum number of charges is 2 is 1/3, the flow rate of the clean fluid is set to a flow rate three times as high as the flow rate of the sample fluid.

4. The size-classified particle size distribution measuring method according to claim 2,

wherein in the step (B), based on that the ratio of flow rate calculated by the ratio of flow rate calculating method according to claim 1 when x being the maximum number of charges is 3 or 4 is 1/7, the flow rate of the clean fluid is set to a flow rate seven times as high as the flow rate of the sample fluid.

5. The size-classified particle size distribution measuring method according to claim 2,

wherein in the step (B), based on that the ratio of flow rate calculated by the ratio of flow rate calculating method according to claim 1 when x being the maximum number of charges is 5 or 6 is 1/11, the flow rate of the clean fluid is set to a flow rate eleven times as high as the flow rate of the sample fluid.

6. A particle size distribution measuring system comprising:

a neutralizer which puts aerosol particles into a charged equilibrium state;

a DMA (Differential Mobility Analyzer) which classifies the aerosol particles charged by the neutralizer in a predetermined electric field based on electrical mobility while making a sample fluid containing the aerosol particles charged by the neutralizer and a clean fluid comprised of clean air flow in the electric field based on the ratio of flow rate calculated by the ratio of flow rate deciding method according to claim 1, and which, in a state where a reference voltage supplied to form the electric field is initially set to a voltage value U, executes the first classifying of the aerosol particles under the supplied voltage having the initially set voltage value U;

an aerosol particle measuring device which measures the aerosol particles classified out by the DMA, by an electrical or/and optical measuring method and outputs a result of the measurement; and

a measurement result analyzing device which confirms whether or not a predetermined condition is satisfied, based on the measurement result output by the aerosol particle measuring device, and when confirming that the condition is satisfied, calculates particle size distribution with respect to each particle size from the measurement result output by the aerosol particle measuring device, and when confirming that the condition is not satisfied, executes;

(a) causing the DMA, in a state where the voltage supplied to form the electric field is re-set to a sum of the voltage value of the voltage supplied in the previous classifying (previous value) and the voltage value U, to execute re-classifying of the aerosol particles under the supplied voltage having the re-set voltage value;

(b) causing the aerosol particle measuring device

(b-1) to output a first measurement result M1 which is the measurement result of the aerosol particles that the DMA classifies out under the supplied voltage having the the initially set voltage value U, and

(b-2) to output a new measurement result Mx which is the re-measurement result of the aerosol particles that are classified out, every time the re-classifying is executed in the (a) by the DMA;

(c) calculating a ratio of the measurement result Mx, which the aerosol particle measuring device is caused to output in the (b-2), to the measurement result M1, which the aerosol particle measuring device is caused to output in the (b-1);

(d) confirming that the condition is not satisfied yet when the ratio calculated in the (c) is larger than a prescribed value, to execute the (a), (b), and (c), while confirming that the condition is satisfied when the ratio calculated in the (c) is equal to or smaller than the prescribed value; and

(e) when confirming that the condition is satisfied, calculating the particle size distribution with respect to each particle size from the measurement result based on a charging probability for the aerosol particles to be charged by the neutralizer.

7. The particle size distribution measuring system according to claim 6, wherein, as for the flow of the sample fluid and the clean fluid in the DMA,

based on that the ratio of flow rate calculated by the ratio of flow rate calculating method according to claim 1 when x being the maximum number of charges is 2 is 1/3, the flow rate of the clean fluid is set to a flow rate three times as high as the flow rate of the sample fluid.

8. The particle size distribution measuring system according to claim 6,

wherein, as for the flow of the sample fluid and the clean fluid in the DMA,

based on that the ratio of flow rate calculated by the ratio of flow rate calculating method according to claim 1 when x being the maximum number of charges is 3 or 4 is 1/7, the flow rate of the clean fluid is set to a flow rate seven times as high as the flow rate of the sample fluid.

9. The particle size distribution measuring system according to claim 6,

wherein, as for the flow of the sample fluid and the clean fluid in the DMA,

based on that the ratio of flow rate calculated by the ratio of flow rate calculating method according to claim 1 when x being the maximum number of charges is 5 or 6 is 1/11, the flow rate of the clean fluid is set to a flow rate eleven times as high as the flow rate of the sample fluid.