Numerical Investigation into the Flow Characteristics of Gas Mixtures in Knudsen Pump with Variable Soft Sphere Model.

Chunlin Du,Xiaowei Wang,Zhijun Zhang,Feng Han,Xiaoyu Ren

doi:10.3390/mi11090784

Chunlin Du, Xiaowei Wang + Show 3 more

Open Access

https://doi.org/10.3390/mi11090784

Copy DOI

Abstract

In Knudsen pumps with geometric configuration of rectangle, gas flows are induced by temperature gradients along channel walls. In this paper, the direct simulation Monte Carlo (DSMC) method is used to investigate numerically the flow characteristics of H2–N2 mixtures in the Knudsen pump. The variable soft sphere (VSS) model is applied to depict molecular diffusion in the gas mixtures, and the results obtained are compared with those calculated from a variable hard sphere (VHS) model. It is demonstrated that pressure is crucial to affecting the variation of gas flow pattern, but the gas concentration in H2–N2 mixtures and the collision model do not change the flow pattern significantly. On the other hand, the velocity of H2 is larger than that of N2. The velocities of H2 and N2 increase if the concentration of H2 rises in the gas mixtures. The results of velocity and mass flow rate obtained from VSS and VHS models are different. Finally, a linear relation between the decrease of mass flow rate and the increase of H2 concentration is proposed to predict the mass flow rate in H2–N2 mixtures.

Highlights

Gas flows induced by temperature gradients are peculiar to rarefied gases and are an interesting research subject in rarefied gas dynamics [1,2,3,4]
The flow characteristics of H2–N2 mixtures in the rectangular Knudsen pump were studied by using the direct simulation Monte Carlo (DSMC) method
In order to depict the molecular diffusion in the gas mixtures, the variable soft sphere (VSS) model was used for the extension of the previous work [31]

Summary

Introduction

Gas flows induced by temperature gradients are peculiar to rarefied gases and are an interesting research subject in rarefied gas dynamics [1,2,3,4]. With the advancement of computational techniques and the increase of computational speed, Knudsen pump variants with complex structures can be simulated by the method of direct simulation Monte Carlo (DSMC) It is well-known that in order to accurately simulate the molecular collision process to obtain a reliable macroscopic quantity, the use of a more physically realistic collision model is crucial. Considering the background mentioned above, the DSMC method and VSS model are used in this paper to discuss the flow characteristics of two-component gas mixtures for different pressures and different gas concentration ratios in a Knudsen pump with rectangular layout.

Problem Statement

Theoretical Models and Numerical Method

Boundary Condition

Direct Simulation Monte Carlo Method and Solver

Results and Discussion

Temperature Distribution and Flow Characteristics

Velocity

Species Separation

Concluding Remarks