Study On Air Flow Characteristics And Cutting Performance Of Single Stage Impact Sampler Cutting Head

In the study of atmospheric particles,particles are usually classified according to different sizes.There are many sampling methods for atmospheric particulate matter,among which inertial impact sampling is the most widely used because of its wide range,high efficiency,high sensitivity and easy operation.The principle of inertial impact sampling is to use the inertial effect of particles in air flow to separate them according to size.The cutting head is a very important component in the sampler.Its main function is to use its special structure to make the particles deflect 90to 180 degrees,so that the particles larger than the cutting particle size impact on the impact plate,and the particles smaller than the cutting particle size can pass smoothly.Inertial impact sampling can be divided into single-stage inertial impact sampling and multi-stage inertial impact sampling.The multi-stage inertial impact sampling can be used to sample the particles step by step.The sampling instrument is large and the principle is complex.The portable impact sampler is usually a single-stage impact sampler.When measuring the particle concentration of a certain equivalent diameter,it is necessary to replace the cutting head corresponding to the particle size.Different cutting heads have certain differences in pipe diameter and impact distance.In this thesis,the single-stage inertial impact sampling cutting head is taken as the research object,and two kinds of cutting heads,flush nozzle and convex nozzle,are proposed.By adjusting the impact distance and inlet speed,different cutting heads can be used to measure different cutting particle sizes without changing different types of cutting heads.The effects of impact distance,nozzle diameter and inlet velocity on the flow field,particle trajectory and particle size in the cutting head of flush nozzle and convex nozzle sampler were studied by CFD.The research contents are as follows:（1）This thesis introduces the basic principle of particulate matter collection,describes the numerical simulation theory of gas phase flow field and discrete phase flow field in the cutting head,and verifies the accuracy of the numerical method by simulating the PM_2.5 cutting head of DUSKTR^TMⅡdust analyzer.（2）Taking the cutting head of flush nozzle as the research object,the influence of impact distance,nozzle diameter and inlet velocity on the internal flow field,particle trajectory and cutting particle size of the cutting head was studied by numerical simulation method,and the influencing factors of particle capture were analyzed.（3）Taking the convex nozzle cutting head as the research object,the numerical simulation method was used to study the influence of impact distance,nozzle diameter and inlet velocity on the flow field,particle trajectory and particle size of the cutting head.The influencing factors of particle capture were analyzed,and the air flow characteristics and particle size cutting performance of the two cutting heads were compared and analyzed.