表面特性对棘齿型Knudsen泵气体分离特性影响的模拟研究

Simulation Study of the Effect of Surface Properties on Gas Separation Characteristics for Ratchet-type Knudsen Pumps

Knudsen泵作为一种微型泵,在微机电系统(MEMS)中具有广泛应用。本文提出了一种具有不同表面反射系数的棘齿型Knudsen泵,通过直接模拟蒙特卡罗(DSMC)方法对该泵内He-Xe混合气体流动特性进行了数值模拟研究。结果表明:表面反射特性对Knudsen泵内的流场特性和气体分离特性影响巨大,不同的表面反射特性导致了Knudsen泵内不同的热驱流动机理;三角形倾斜边的α_(n)=σ_(t)=0时Knudsen泵内主要热驱流动为辐射流,有利于气体分离,而α_(n)=σ_(t)=1时Knudsen泵内主要热驱流动为热边缘流,对气体分离没有明显有利作用;三角形倾斜边的α_(n)=σ_(t)=0时He和Xe的速度和扩散速度在三角形棘齿上顶点附近差异最大,而α_(n)=σ_(t)=1时在三角形棘齿左侧顶点附近差异最大;越轻的气体流动速度和扩散速度越快。本文可为实际工程应用中微型气体分离装置的设计和生产提供理论依据。

The Knudsen pump,a type of micro-pump,is widely used in microelectromechanical systems(MEMS).The paper proposes a ratchet-type Knudsen pump with varied surface accommodation coefficients.The gas flow characteristics of this pump are simulated numerically by using the direct simulation Monte Carlo(DSMC)method.The results show that surface accommodation characteristics significantly influence the flow field and gas separation features.Distinct surface reflection characteristics give rise to varying thermally induced flow mechanisms within the Knudsen pump.The primary thermally induced flow in the Knudsen pump atα_(n)=σ_(t)=0 of the inclined edge of the triangle is the radiometric flow,which is advantageous for gas separation.Atα_(n)=σ_(t)=1 of the triangular inclined edge,the primary thermally induced flow is the thermal edge flow,which is not clearly advantageous for gas separation.The velocity difference and diffusion velocity difference between He and Xe are greatest near the upper vertex of triangular ratchet atα_(n)=σ_(t)=0 of the triangular inclined edge,while the differences are greatest near the left vertex of triangular ratchet atα_(n)=σ_(t)=1.Moreover,the flow velocity and diffusive velocity increase as the gas becomes lighter.This paper may establish a theoretical foundation for creating and producing miniature gas separation devices applicable in practical engineering contexts.