Study Of PIV Experiment On Low Pressure Gas Flow

Under the development of aerospace industry,the study of the flow of low pressure rarefied gas attaches more and more attentions in vacuum field.The condition of vacuum rarefied gas is clean and pollution-free which advantage for precision parts processing and applied in many industries such as integrated circuit(IC),micro-electron mechanical systems(MEMS)and so forth.Therefore,the study of low pressure gas flow has great significance.Particle image velocity(PIV)technology is one of the most important methods to conduct the fluid mechanics experiment,which uses the movement of the tracer particles in the fluid to indirectly reveal the velocity distribution of the flow field,so the followability of the tracing particles has the decisive influence on the experimental measurement accuracy.The flow field measuring becomes more and more difficult while the gas density changes and the vacuum degree increases in the vacuum system.It is necessary to analyze the choice,distribution and the followability of the tracing particles in the PIV experiment under the condition of rarefied gas,in order to notarize the range,condition and method while the PIV experiments are applied in the field of vacuum technology.In this paper,a set of experimental devices which can adjust the vacuum degree was established,which gradually reduced the pressure from the barometric pressure,and a series of PIV experiments of rarefied gas flows were carried out.Before the experiment,the tracing particles were selected in the experiment.Five kinds of tracer particles were carried out under different pressure conditions by PIV experiment in this project,to obtain the suitable experimental test environment of different kinds of particles and the pressure range of PIV experiment.The experimental results of several particles were analyzed,and cigarette smoke was finally selected as the experimental tracing particle for low-pressure gas flow.By the CFD simulation of the flow field,the results showed that flow field in central area has the large flow rate of about 4 m/s under the atmospheric pressure,but the rate decrease at the outlet of the chamber due to the rebound caused by the flow field colliding with the wall.Compared with the experimental results of PIV,the simulation results were in good agreement with the experimental results,and the error was within the acceptable range.Using the selected particles and reducing the degree of the vacuum system,the PIV experiment was carried out under the conditions of different vacuum degrees,e.g.101kPa,90kPa,80kPa,70kPa,60kPa,50kPa,40kPa,30kPa,20kPa,10kP and 0.5kPa.The conclusion was drawn from the experiment that the smoke particles can reflect the flow pattern of flow filed under the pressure from 60kPa to 101kPa where the flow filed can greatly carry the particles;the particles can fully reflect the flow pattern of flow field under the pressure from 30kPa to 60kPa but the rate of the flow filed decreases;the measured pattern of the flow field is incomplete under the pressure from 10kPa to 30kPa,where the minimum velocity decreases to 1.5m/s which is different from the actual flow rate;0.5kPa was the minimum pressure of this experiment when the flow filed cannot carry the tracing particles any more.The research methods and the analysis results of paper can provide reference for the experimental research of low pressure rarefied gases.