Design Of Differential Mobility Analyzer Based On Integrated Response Model And Its Data Analysis Method

Aerosol pollution is one of the major environmental problems in our country.It has an important impact on visibility reduction,climate change,and human health.Aerosol particle size spans multiple orders of magnitude,and its size distribution is an important feature of aerosol,which determined the physical and chemical characteristics of aerosols,which affected environment and health.Therefore,it is of great significance to accurately measure aerosol particle size distribution.Differential Mobility Analyzer(DMA)is a standard classification tool for studying submicron particles.The performance of classification can be characterized by transfer function.By building DMA transfer function and integral response model,the performance of classification and output responses can be effectively simulated and analyzed.(1)In this study,the high-order moments of the transfer function was calculated,and its relative widths of particle sizes(S[Dp]/E[Dp])was deduced based on transfer function model.The influence of the key parameters such as diffusion coefficient,sample flow rate,and the ratio of sheath flow rate to sample flow rate on the transfer function was studied,it shows that increasing the sample flow rate can improve the performance of the DMA,and the over large ratio of sheath flow rate to sample flow rate will reduce the transmission efficiency,but the small ratio reduce the size resolution.In a word the ratio can be set to 5?25.Although the input aerosol particle size distribution causes disturbance to the output size distribution spectrum,the DMA transfer function is the main influence factor of the output size distribution spectrum.(2)A DMA integral response model was established,which can output the concentration based on the function of the input aerosol particle size distribution.The inversion method of DMA data was studied,including the particle size inversion based on the table of voltage and particle size,and the method of particle concentration inversion based on lognormal approximation of transfer function.These methods were applied to the processing of DMA output data.(3)Based on the transfer function and the integral response model,the key parameters such as sample flow rate,the ratio of sheath flow rate to sample flow rate were set.The DMA peripheral control circuits were designed including sample flow control circuit,sheath flow control circuit,inner cylinder high voltage control circuit and data processing circuit.The DMA experimental platform was set up to test the performance of the DMA size classification and measurement,including the particle size accuracy,the dispersion of monodisperse aerosols,and the measurement of size distribution.The experimental results shthan ow that the particle concentration calculated by the integral response model is lower the experimental results,but it has a good correlation,and the correlation coefficient R2 is 0.98,which shows that the integral response model can simulate the classification performance of DMA well.The particle size measured by DMA and the predicted particle size have a good correlation,the correlation coefficient R2 is 0.99,and its relative error is within 5.0%.Otherwise,the scattered level of the output monodisperse particle size distribution is relatively low,and its relative width of the particle size(S[Dp]/E[Dp])is less than 2.5.the Particle Size Distribution of monodisperse and polydisperse aerosol measured by the differential mobility analyzer and SMPS are similar,which shows that the data inversion method have a good performance in data processing of the DMA.