An experimental device for testing the performance of a differential electromobility analyzer

Abstract

The application discloses an experimental device for testing the performance of a differential electrical mobility analyzer. The application comprises a first differential electrical mobility analyzer, a second differential electrical mobility analyzer, a first condensation particle counter, a second condensation particle counter and a high-voltage power supply module. The first differential electrical mobility analyzer is operated at a fixed flow rate and voltage to sieve out approximately monodisperse aerosol particles, and the aerosol particle number concentration N1 at this time is detected. Then, the second differential electrical mobility analyzer is operated at a fixed flow rate and a scanning voltage, and the flow direction of the gas circuit is selected by adjusting a three-way valve. One route can directly flow to the downstream condensation particle counter, and the concentration is recorded as N3. The other route first passes through the differential electrical mobility analyzer to be detected, and then flows to the downstream condensation particle counter, and the concentration is recorded as N2. If the number concentration N1 does not fluctuate significantly during this period, the performance parameters of the second differential electrical mobility analyzer can be obtained through the concentration ratio of N3 and N2.

Description

Technical Field

[0001] The invention relates to an experimental device for testing the performance of a differential mobility analyzer. Background Art

[0002] The performance of existing differential mobility analyzers is expressed through a transfer function. This is achieved by connecting two identical differential mobility analyzers in series and applying a series of complex deconvolution schemes to solve the true transfer function. However, the transfer function only represents the performance of the differential mobility analyzer within its effective classification range and does not account for losses at the aerosol inlet and outlet, nor does it factor in the influence of the differential mobility analyzer's inherent geometric parameters and manufacturing and assembly processes. Summary of the Invention

[0003] The purpose of the present invention is to solve the deficiencies of the prior art and to provide an experimental device for testing the performance of a differential mobility analyzer. The performance parameters of the differential mobility analyzer can be obtained by using the device and based on the theoretical diffusion transfer function.

[0004] The technical solution adopted by the present invention to solve the technical problem is:

[0005] The present invention comprises a first differential mobility analyzer, a second differential mobility analyzer, a first condensation particle counter, a second condensation particle counter and a high-voltage power supply module.

[0006] Approximately monodisperse aerosol particles are screened out by the first differential mobility analyzer. One path of the aerosol particles enters the first condensation particle counter, which measures the aerosol particle number concentration N1 at that time. The other path is divided into two branches by a three-way valve. The aerosol particles in one branch enter the second differential mobility analyzer; the aerosol particles in the other branch enter the second condensation particle counter, and the aerosol particle number concentration N3 measured by the second condensation particle counter is recorded. The three-way valve can select the airflow direction.

[0007] The second differential mobility analyzer scans in multiple voltage intervals, wherein the high-voltage power supply module provides multiple voltage intervals; the approximately monodisperse outlet of the second differential mobility analyzer is connected to the second condensation particle counter, and the number concentration N2 of the aerosol particles measured by the second condensation particle counter at this time is recorded;

[0008] The first differential mobility analyzer is a commercial differential mobility analyzer with known performance. Within a certain period, when the number concentration N1 does not fluctuate significantly, the parameters characterizing the performance of the second differential mobility analyzer are obtained through the concentration ratio of N3 and N2 and the diffusion transfer function: penetration efficiency and multiplication factor.

[0009] Furthermore, it also includes an aerosol generator, an aerosol neutralizer and a laminar flow meter. The polydisperse aerosol particles generated by the aerosol generator enter the aerosol neutralizer through the trachea; the radioactive source of the aerosol neutralizer is KR85, which is a bipolar diffusely charged radioactive source and provides a stable charge number distribution for the aerosol particles; the outlet of the aerosol neutralizer is connected to the first differential mobility analyzer through a laminar flow meter.

[0010] Furthermore, the multiple voltage intervals are 0V-500V, 500V-2000V, 2000V-5000V and 5000V-8000V respectively.

[0011] Furthermore, the first differential mobility analyzer maintains fixed voltage, sheath gas flow rate, and aerosol flow rate when in operation.

[0012] Furthermore, the inlet sheath gas flow rate of each differential mobility analyzer is equal to the residual gas flow rate, and the inlet aerosol flow rate is equal to the approximately monodisperse outlet aerosol flow rate.

[0013] Furthermore, the two branches after passing through the three-way valve are of equal length, and both branches use anti-static hoses.

[0014] Furthermore, when the flow rate and geometric parameters in the second differential mobility analyzer are fixed, the penetration efficiency and the multiplication factor are solved using nonlinear least square fitting.

[0015] The beneficial effects of the present invention are:

[0016] 1. The present invention is based on the diffusion transfer function and adopts the nonlinear least squares method to fit and solve the penetration efficiency and multiplication factor of the differential mobility analyzer, which has the advantages of high precision and simple data inversion.

[0017] 2. The first condensation particle counter provided in the present invention serves to detect the concentration of upstream aerosol particles to explain any concentration fluctuations of the test aerosol during the N2 and N3 measurements, thereby improving the accuracy of data inversion.

[0018] 3. The present invention uses four high-voltage power supplies with different voltage ranges. Since the voltage operating range of the differential mobility analyzer to be tested is wide, if a single high-voltage power supply is used, it will cause large errors when outputting a small voltage range, affecting the accuracy of the experiment.

[0019] 4. The aerosol particle path uses an anti-static hose, which starts at the three-way valve and ends at the second condensation particle counter. The distance between the two anti-static hoses is the same, which can reduce experimental errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1A schematic diagram of an experimental setup for testing the performance of a differential mobility analyzer;

[0021] Figure 2 This is the result of fitting the numerical simulation transfer function using the nonlinear least squares method. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] like Figure 1 As shown, the device of this embodiment includes an aerosol generator, an aerosol neutralizer, a commercial differential mobility analyzer with known performance, two condensation particle counters, a differential mobility analyzer (DMA) to be tested, four mass flow meters, two laminar flow meters, a high-voltage power supply module, two air pumps, three filters, and two dryers.

[0024] The aerosol generator is a low-concentration generation source to prevent airway blockage and damage to the instrument. The aerosol particles generated by the aerosol generator enter the aerosol neutralizer through the trachea.

[0025] The radioactive source of the aerosol neutralizer is KR85, which is a bipolar diffusely charged radioactive source and can provide a stable charge number distribution for aerosol particles.

[0026] The differential mobility analyzer with known performance is an instrument that can accurately screen out particles of approximately single particle size.

[0027] The high-voltage power supply module includes 4 EMCO C series high-voltage modules and 2 DC power supplies, namely C05, C20, C50, C80, a low-precision DC power supply, and a high-precision DC power supply.

[0028] The filter has a filtration efficiency of 3nm or more, which prevents ultrafine aerosol particles from overflowing, causing environmental pollution and harming the health of experimenters.

[0029] The air inlet and the air outlet of the air pump are both connected to filters to ensure that clean sheath gas is provided to the differential mobility analyzer, while preventing the inside of the air pump from being contaminated by external particles.

[0030] The flowmeter is connected to each outlet and inlet of the differential mobility analyzer to control its flow rate.

[0031] The commercial differential mobility analyzer with known performance (i.e., the first differential mobility analyzer) maintains fixed voltage, sheath gas flow, and aerosol flow in the working state. The classified approximately monodisperse aerosol particles enter the condensation particle counter 1 (i.e., the first condensation particle counter) along the trachea. The condensation particle counter 1 reads the number concentration of the aerosol particles, and the concentration is recorded as N1.

[0032] The differential mobility analyzer to be tested (i.e., the second differential mobility analyzer) maintains a scanning voltage when in working state, and the approximately monodisperse aerosol particles screened out upstream enter its aerosol inlet channel, and the scanning voltage range is from 0V to the maximum voltage upper limit, and finally enter the condensation particle counter 2 (i.e., the second condensation particle counter) from its approximately monodisperse aerosol outlet along the trachea. The condensation particle counter 2 reads the number concentration of the aerosol particles, and the concentration is recorded as N2; the approximately monodisperse aerosol particles screened out upstream on the other path directly enter the condensation particle counter 2, and the condensation particle counter 2 reads the number concentration of the aerosol particles, and the concentration is recorded as N3.

[0033] Furthermore, the flow rate controlled by the flow meter is specifically expressed as the inlet sheath gas flow rate Q c Equal to the remaining gas flow Q m , inlet aerosol flow Q a Equal to the approximately monodisperse outlet aerosol flow Q s , so that its resolution reaches the maximum value.

[0034] Furthermore, the bias voltage for the EMCO C series is provided by a low-precision DC power supply with a DC voltage range between 11.5V and 16V. Different EMCO C series models have different DC voltage amplification factors, resulting in different voltage errors. (For example, the EMCO C05 has a voltage output range of 0-500V, a programmable input voltage range of 0-5V, and a voltage amplification factor of 100. However, due to the tolerance of the DC voltage source, the programmable input voltage will fluctuate within the set value and rarely reach the same state as the set value. Therefore, this error is also amplified by 100 times in the EMCO C05. Similarly, the C80 has a voltage amplification factor of 1600, so the error is also amplified by 1600 times.) The programmable DC voltage of the EMCO C series is provided by a high-precision DC power supply. The programmable DC voltage range is between 0V and 5V. The EMCO C05 provides a voltage of 0V-500V, the EMCOC20 provides a voltage of 500V-2000V, the EMCO C50 provides a voltage of 2000V-5000V, and the EMCO C80 provides a voltage of 5000V-8000V.

[0035] Furthermore, the approximately monodisperse aerosol outlet pipe of a commercial differential mobility analyzer with known performance and the condensation particle counter 1 are connected by a three-way socket.

[0036] Furthermore, another route of the three-way socket is connected to a three-way valve, and the other two routes of the three-way valve are respectively connected to the aerosol inlet of the differential mobility analyzer to be tested and the condensation particle counter 2. The direction of the airflow can be selected through the three-way valve.

[0037] Furthermore, anti-static hoses are used in the pipes through which the charged aerosol particles flow, minimizing the loss of aerosol particles in the pipes.

[0038] Furthermore, the distance between the two anti-static hoses is the same, starting from the three-way valve and ending at the condensation particle counter 2.

[0039] Furthermore, when the number concentration N1 has no significant fluctuation (the fluctuation range is within plus or minus 100 per cubic centimeter), the flow direction of the gas path is selected by adjusting the three-way valve, and the performance parameters of the differential mobility analyzer are obtained through N2 and N3.

[0040] The working process of this device is as follows: pure gas enters the aerosol generator, and the gas carries polydisperse particles into the aerosol neutralizer. The Kr85 radioactive source performs bipolar diffusion charging on the aerosol particles. The charged polydisperse aerosol particles are charged with Q a1 The flow rate is fed into a commercial differential mobility analyzer with known performance. c1 The flow rate also flows into the commercial differential mobility analyzer, and the remaining gas and the approximately monodisperse outlet aerosol flow rate are expressed as Q m1 and Q s1 In the operating state, a commercial differential mobility analyzer with known performance is maintained at a fixed voltage. In this mode, approximately monodispersed aerosol particles are screened out, and the condensation particle counter 1 measures the number concentration N1 of the aerosol particles at this time.

[0041] The sieved aerosol particles are approximately monodispersed and are expressed as Q a2 The flow rate enters the differential mobility analyzer to be tested, and at the same time passes through the sheath gas with Q c2 The flow rate of the remaining gas and the approximately monodisperse outlet aerosol flow are Q m2 and Q s2 When the differential mobility analyzer to be tested is in working state, its voltage is scanned between 0V and the maximum voltage upper limit. The EMCO C05 provides a voltage of 0V-500V, the EMCO C20 provides a voltage of 500V-2000V, the EMCO C50 provides a voltage of 2000V-5000V, and the EMCO C80 provides a voltage of 5000V-8000V.

[0042] The other path is connected to the three-way valve through the three-way socket. The direction of the gas flow is selected by adjusting the three-way valve. One path can flow directly to the condensation particle counter 2, and the concentration is recorded as N3. The other path first passes through the differential mobility analyzer to be tested, and then flows to the condensation particle counter 2, and the concentration is recorded as N2. If there is no significant fluctuation in the number concentration N1 within a certain period, the concentration ratio of N3 to N2 is used to fit η using the nonlinear least squares method. pen and f σ .

[0043] The theoretical basis for calculating the performance parameters of the differential mobility analyzer is given below:

[0044] The diffusion transfer function of this embodiment is given by the following formula:

[0045]

[0046] Where ε is an error equation containing a Gauss error function, and β is the ratio of the aerosol flow rate to the sheath gas flow rate of the differential mobility analyzer:

[0047]

[0048] Among them, Q a is the aerosol inlet flow rate, Q s is the approximately monodisperse outlet aerosol flow rate, Q c is the sheath gas flow rate, Q m is the residual gas flow (i.e., the mixed gas of the aerosol and sheath gas that has not been separated).

[0049] δ is the normalized flow imbalance factor:

[0050]

[0051] Usually the DMA aerosol inlet and the approximately monodisperse outlet aerosol flow rates are equal, so δ = 0.

[0052] is the normalized electrical mobility, which is equal to the particle electrical mobility Z P The mobility Z screened by the differential mobility analyzer P * Ratio:

[0053]

[0054] Where L is the length of the effective grading area of ​​DMA, R1 is the outer radius of the inner electrode of DMA, and R2 is the inner radius of the outer electrode of DMA.

[0055] σ Ω is the dimensionless diffusion parameter:

[0056]

[0057] where K B is the Boltzmann constant, T is the temperature, q is the number of particles charged, e is the elementary charge, and V is the voltage applied to the DMA. G is a coefficient that depends on the geometry of the DMA and the flow field:

[0058]

[0059] Among them I γ (x) depends on the velocity field and is expressed as follows under fully developed laminar flow:

[0060]

[0061] Therefore, we can get:

[0062]

[0063] where η pen is the penetration efficiency, which represents the efficiency of particles of a certain size passing through the entrance and exit areas of the differential mobility analyzer (i.e., the loss of the entrance and exit), f σ is a multiplicative factor, indicating that in addition to particle diffusion, the transfer function may also be affected by instrument imperfections, electrode defects and misalignments (caused by the processing and assembly process), and other factors that may affect the flow or electric field.

[0064] Furthermore, when the flow rate and geometric parameters in the differential mobility analyzer are fixed, equation (8) becomes a function of particle size, so a nonlinear least squares fit can be used to solve for η pen and f σ .

[0065] like Figure 2 The figure is the result of fitting the numerical simulation transfer function using the nonlinear least squares method; in theory, η pen and f σ are all equal to 1, and the η of the fitted curve pen and f σ are all close to 1, indicating that this method is feasible.

Claims

1. An experimental device for testing the performance of a differential mobility analyzer, comprising a first differential mobility analyzer, a second differential mobility analyzer, a first condensation particle counter, a second condensation particle counter, and a high-voltage power supply module, characterized in that: Approximately monodisperse aerosol particles are screened out by the first differential mobility analyzer. One path of the aerosol particles enters the first condensation particle counter, which measures the aerosol particle number concentration N1 at that time. The other path is divided into two branches by a three-way valve. The aerosol particles in one branch enter the second differential mobility analyzer; the aerosol particles in the other branch enter the second condensation particle counter, and the aerosol particle number concentration N3 measured by the second condensation particle counter is recorded. The three-way valve can select the airflow direction. The second differential mobility analyzer scans in multiple voltage intervals, wherein the high-voltage power supply module provides multiple voltage intervals; the approximately monodisperse outlet of the second differential mobility analyzer is connected to the second condensation particle counter, and the number concentration N2 of the aerosol particles measured by the second condensation particle counter at this time is recorded; The first differential mobility analyzer is a commercial differential mobility analyzer with known performance. In a certain period, when the number concentration N1 does not fluctuate significantly, the concentration ratio of N3 and N2 and the diffusion transfer function are used to determine the difference between the two. Obtain the parameter that characterizes the performance of the second differential mobility analyzer: penetration efficiency : The multiple voltage intervals are 0V-500V, 500V-2000V, 2000V-5000V and 5000V-8000V respectively; The two branches after passing through the three-way valve are of equal length, and both branches use anti-static hoses.

2. The experimental device for testing the performance of a differential mobility analyzer according to claim 1, characterized in that: It also includes an aerosol generator, an aerosol neutralizer and a laminar flow meter. The polydisperse aerosol particles generated by the aerosol generator enter the aerosol neutralizer through the trachea; the radioactive source of the aerosol neutralizer is KR85, which is a bipolar diffusely charged radioactive source and provides a stable charge number distribution for the aerosol particles; the outlet of the aerosol neutralizer is connected to the first differential mobility analyzer through a laminar flow meter.

3. The experimental device for testing the performance of a differential mobility analyzer according to claim 1, characterized in that: The first differential mobility analyzer maintains fixed voltage, sheath gas flow rate, and aerosol flow rate when in operation.

4. The experimental device for testing the performance of a differential mobility analyzer according to claim 1, characterized in that: The inlet sheath gas flow rate of each differential mobility analyzer is equal to the residual gas flow rate, and the inlet aerosol flow rate is equal to the approximately monodisperse outlet aerosol flow rate.

5. The experimental device for testing the performance of a differential mobility analyzer according to claim 1, characterized in that: When the flow rate and geometric parameters in the second differential mobility analyzer are fixed, the penetration efficiency is calculated using a nonlinear least squares fitting method.

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