Abstract: 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 at α_n=σ_t=0 of the inclined edge of the triangle is the radiometric flow, which is advantageous for gas separation. At α_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 at α_n=σ_t=0 of the triangular inclined edge, while the differences are greatest near the left vertex of triangular ratchet at α_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.

Key words: Knudsen pump, gas separation, surface properties, thermally induced flow, ratchet-type microchannels, DSMC method, MEMS