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 9,534,998 B2
• Filed: 09/06/2012
• Issued: 01/03/2017
• Est. Priority Date: 09/07/2011
• Status: Active Grant

• Current Assignee: RION Company Limited
• Original Assignee: RION Company Limited
• Inventors: Tsunoda, Chiryo
• Primary Examiner(s): Satanovsky, Alexander
• Assistant Examiner(s): CORDERO, LINA M
• Application Number:
  US13/605,236
• Publication Number:
  US 20130085706A1
• Time in Patent Office: 1,580 Days
• Field of Search: 702/128
• US Class Current: 1/1
• CPC Class Codes: B03C 2201/24 for measuring or calculating parameters, efficiency, etc.
• 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 size-classified particle size distribution measuring method comprising:

(A) a step of, when a sample fluid containing charged aerosol particles and a clean fluid comprised of clean air are made to flow in a predetermined electric field and when the charged aerosol particles are classified in the electric field based on electrical mobility by using a Differential Mobility Analyzer, calculating a ratio of flow rate necessary for increasing accuracy of the classification, the ratio of flow rate being a ratio between a flow rate of the sample fluid and a flow rate of the clean fluid, the step comprising;

(a) a procedure to decide 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;

(b) a procedure to define 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) by using a voltage value U supplied to form the electric field;

(c) a procedure to derive a first electrical mobility group and a second electrical mobility group based on x decided in the procedure (a), 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 are 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;

(d) a procedure to express each of the electrical mobilities by using Zc(U) defined in the procedure (b), regarding all the electrical mobilities included in the first electrical mobility group and the second electrical mobility group derived in the procedure (c);

(e) a procedure to, if a range where a given electrical mobility is variable by adjusting the ratio between the flow rates of the sample fluid and the clean fluid which are made to flow in the electric field is defined as a range corresponding to the electrical mobility, define the ranges corresponding to all the electrical mobilities included in the first electrical mobility group and the second electrical mobility group derived in the procedure (c), after the procedure (d); and

(f) a procedure to calculate the ratio between the flow rate of the sample fluid and the flow rate of the clean fluid, with which the ranges corresponding to the electrical mobilities included in the first electrical mobility group, which ranges are defined in the procedure (e), do not interfere with one another and the ranges corresponding to the electrical mobilities included in the first electrical mobility group and the ranges corresponding to the electrical mobilities included in the second electrical mobility group do not interfere with one another, whereby the sample fluid and the clean fluid are made to flow in the electric field at respective flow rates whose ratio is the calculated ratio;

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

(C) a step of classifying the aerosol particles charged in the step (B) in the predetermined electric field based on the electrical mobility while making the sample fluid containing the aerosol particles charged in the step (B) and the clean fluid comprised of clean air flow in the electric field based on the ratio of flow rate calculated in the step (A), the step (C) being a step of initially setting a reference voltage supplied to form the electric field to the voltage value U used for classifying aerosol particles with a predetermined particle size whose number of charges is 1, and executing a first classifying of the aerosol particles under the supplied voltage having the initially set voltage value U;

(D) a step of measuring the aerosol particles classified out in the step (C), by an electrical or/and optical measuring method and outputting a result of the measurement as a first measurement result M1; and

(E) a step of re-setting the voltage supplied to form the electric field, and supplying the voltage having the re-set voltage value to execute re-classifying of the aerosol particles, the step comprising;

(g) a procedure to re-set the voltage supplied to form the electric field to nU (the voltage value U multiplied by n) for an n^th classifying which is a sum of the voltage value of the voltage supplied in a previous classifying (previous value) and the voltage value U, and supply the voltage having the re-set voltage value to execute the re-classifying of the aerosol particles based on an electrical mobility Zc(nU);

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

(i) a procedure to calculate a ratio of the measurement result Mn, which is output in the procedure (h), to the first measurement result M1; and

(j) a procedure to, when the ratio calculated in the procedure (i) is larger than a prescribed value, execute the procedures (g), (h), and (i), and when the ratio calculated in the procedure (i) is equal to or smaller than the prescribed value, calculate the number of the aerosol particles with respect to each particle size from the measurement result to output a particle size distribution based on a charging probability for the aerosol particles to be charged in the step (B).

2. The size-classified particle size distribution measuring method according to claim 1, wherein in the step (C), based on that the ratio of flow rate calculated in step (A) 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 that is more than three times as high as the flow rate of the sample fluid.

3. The size-classified particle size distribution measuring method according to claim 1, wherein in the step (C), based on that the ratio of flow rate calculated in the step (A) 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 that is more than seven times as high as the flow rate of the sample fluid.

4. The size-classified particle size distribution measuring method according to claim 1, wherein in the step (C), based on that the ratio of flow rate calculated in the step (A) 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 that is more than eleven times as high as the flow rate of the sample fluid.

5. A particle size distribution measuring system comprising:

a ratio of flow rate deciding device in which, when a sample fluid containing charged aerosol particles and a clean fluid comprised of clean air are made to flow in a predetermined electric field and when the charged aerosol particles are classified in the electric field based on electrical mobility by using a Differential Mobility Analyzer, a ratio of flow rate necessary for increasing accuracy of the classification, which ratio is a ratio between a flow rate of the sample fluid and a flow rate of the clean fluid, is calculated, wherein the ratio of flow rate deciding device calculates the ratio of flow rate by executing;

(A) a procedure to decide 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;

(B) a procedure to form the electric field by supplying a voltage, and define 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) by using a voltage value U of the supplied voltage;

(C) a procedure to derive a first electrical mobility group and a second electrical mobility group based on x decided in the procedure (A), 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 are 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;

(D) a procedure to express each of the electrical mobilities by using Zc(U) defined in the procedure (B), regarding all the electrical mobilities included in the first electrical mobility group and the second electrical mobility group derived in the procedure (C);

(E) a procedure to, if a range where a given electrical mobility is variable by adjusting the ratio between the flow rates of the sample fluid and the clean fluid which are made to flow in the electric field is defined as a range corresponding to the electrical mobility, define the ranges corresponding to all the electrical mobilities included in the first electrical mobility group and the second electrical mobility group derived in the procedure (C), after the procedure (D); and

(F) a procedure to calculate the ratio between the flow rate of the sample fluid and the flow rate of the clean fluid, with which the ranges corresponding to the electrical mobilities included in the first electrical mobility group, which ranges are defined in the procedure (E), do not interfere with one another and the ranges corresponding to the electrical mobilities included in the first electrical mobility group and the ranges corresponding to the electrical mobilities included in the second electrical mobility group do not interfere with one another, whereby the sample fluid and the clean fluid are made to flow in the electric field at respective flow rates whose ratio is the calculated ratio;

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

the Differential Mobility Analyzer which classifies the aerosol particles charged by the neutralizer in the predetermined electric field based on electrical mobility while making the sample fluid containing the aerosol particles charged by the neutralizer and the 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 device, and which, in a state where a reference voltage supplied to form the electric field is initially set to the voltage value U used for classifying aerosol particles with a predetermined particle size whose number of charges is 1, executes a 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 Differential Mobility Analyzer, by an electrical or/and optical measuring method and which outputs a result of the measurement as a first measurement result M1; and

a measurement result analyzing device which re-sets the voltage supplied to form the electric field, and supplies the voltage having the re-set voltage value to the Differential Mobility Analyzer to cause the Differential Mobility Analyzer to execute re-classifying of the aerosol particles, the measurement result analyzing device;

(a) causing the Differential Mobility Analyzer, in a state where the voltage supplied to form the electric field is re-set to nU (the voltage value U multiplied by n) for an n^th classifying which is a sum of the voltage value of the voltage supplied in a previous classifying (previous value) and the voltage value U, to execute the re-classifying of the aerosol particles based on an electrical mobility Zc(nU) under the supplied voltage having the re-set voltage value;

(b) causing the aerosol particle measuring device to output a new measurement result Mn 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 Differential Mobility Analyzer;

(c) calculating a ratio of the measurement result Mn, which the aerosol particle measuring device is caused to output in the (b), to the first measurement result M1; and

(d) when the ratio calculated in the (c) is larger than a prescribed value, executing the (a), (b), and (c), and when the ratio calculated in the (c) is equal to or smaller than the prescribed value, calculating the number of the aerosol particles with respect to each particle size from the measurement result to output a particle size distribution based on a charging probability for the aerosol particles to be charged by the neutralizer.

6. The particle size distribution measuring system according to claim 5, wherein, as for the flow of the sample fluid and the clean fluid in the Differential Mobility Analyzer, based on that the ratio of flow rate calculated by the ratio of flow rate deciding device 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 that is more than three times as high as the flow rate of the sample fluid.

7. The particle size distribution measuring system according to claim 5, wherein, as for the flow of the sample fluid and the clean fluid in the Differential Mobility Analyzer, based on that the ratio of flow rate calculated by the ratio of flow rate deciding device 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 that is more than seven times as high as the flow rate of the sample fluid.

8. The particle size distribution measuring system according to claim 5, wherein, as for the flow of the sample fluid and the clean fluid in the Differential Mobility Analyzer, based on that the ratio of flow rate calculated by the ratio of flow rate deciding device 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 that is more than eleven times as high as the flow rate of the sample fluid.