Research On The Key Theory And Technology Of Particle Size Classifi-Cation Based On Differential Mobility

Aerosols are particulate matter suspended in the air and have important effects on human health,semiconductor processing,and other aspects.Traditional aerodynamic detection equipment and laser dust particle detection equipment rely on optical sensor performance and have limited particle size detection capability.Electric mobility-based detection methods are based on the principle of different mobility of particles of different sizes of an electric field,with better particle size classification capabilities.This paper studies the particle size classification method based on differential electromobility,uses a cylindrical structure to design a differential mobility analyzer,studies a venturi-based differential pressure flow meter to achieve accurate control of sampling flow,and conducts related experiments,which include the following parts:The overall structure of the differential mobility analyzer was studied,and the sampling gas path and sheath gas path were designed.The orifice plate and venturi gas flow measurement methods were analyzed,and Fluent fluid simulation software was applied to carry out simulation analysis and actual flow measurement experiments.In terms of to flow control,a closed-loop control process is performed for the vacuum gas pump using the PID algorithm,and it is necessary to combine real-time environmental parameters for flow compensation,and then to achieve precise regulation of flow.The flow prototype was developed and experimental studies were carried out.Based on the experimental results,the venturi flowmeter was selected for sheath gas flow measurement.As the core components of the electromobility analyzer,the performance of the charger and electrostatic classification chamber directly determines the effect of particle size classification.In terms of the charger,this paper designs a corona discharge type charger with a needle tip-circular arc structure to charge the aerosol particles by using the corona discharge principle.In the electrostatic classification chamber,a cylindrical electrostatic classification chamber is designed,and the key parts of the electrostatic classification chamber structure are analyzed by fluid simulation to determine the rationality of the structure design.At the same time,with the help of simulation software,the trajectory of particle motion inside the two-dimensional model classification chamber under the joint action of sheath gas flow and electric field is observed,and the relationship between different particle sizes and sheath gas flow and deflection voltage is reasoned and theoretically calculated according to the designed structure parameters.A high-voltage control module was designed to provide the required voltages for the corona discharge type charger and the cylindrical electrostatic classification chamber.The prototypes of corona discharge type charger and differential mobility analyzer were developed and experimental studies were carried out,and high voltage output control,flow output control,partial particle size classification test and charger comparison experiments were conducted respectively.In the experimental tests with the particle counter,it was found that the differential mobility analyzer designed in this paper is relatively effective in classifying aerosol particles of 0.2 μm and 0.3 μm,and relatively ineffective in classifying aerosol particles of 0.5 μm.In the comparative test experiment of the charger,the results of the corona discharge type charger test showed the same trend of particle size distribution as that of the soft X-ray test.