Burnett Simulations Of Gaseous Flows In Slip/Transition Regime

Prediction of gas flow through microfluidic and nanofluidic devices isimportant to enable the design and development of complex MEMS/NEMS. In microand nano-scale gas flows, the flow falls into the slip or transition regime. The gasdeviates from the equilibrium state and the Navier-Stokes equations fail to describethe gas flow in this regime. The DSMC method converges slowly and requires plentyof computational time. The MD method is not suitable for rarefied gas. The Burnettequations are the second-order approximation, which of the Chapman-Enskogsolution to the Boltzmann equation. As a result, the Burnett equations are widelyused to study the gas flow characteristics in slip/transition regime.The augmented Burnett equations and slip boundary conditions are used to studythe gas flow characteristics of micro-filter flow, three dimensional Poiseuille flowand micro-nozzle flow. The results of the Burnett equations agree much better withDSMC results than those of the Navier-Stokes equations. Power requirements andpressure drop through the microfilters are important properties. It can be found thatthe power dissipation is a function of the opening factor, the ratio of the filterthickness to the hole diameter, and the Reynolds number. The pressure deviationsfrom linear distribution under different pressure ratios and Knudsen numbers are thenanalyzed in three dimensional Poiseuille flow. The tendency of pressure’s nonlineardistribution increases with the increase of pressure ratio and decrease of Knudsennumber. The nonlinear is increased by the compressibility and decreased by therarefied effect. The different scales of micro-nozzle have been analyzed, it can befound that the sonic points moved away from the throat along the channel with theincrease of Knudsen number. Thrust force and specific impulse are two importantparameters of micro-nozzle. The thrust force increases with the increase of inletpressure, but the increase of specific impulse is slight. The effects of differentcontraction ratios and expansion ratios on the thrust and specific impulse are alsoanalyzed.