Thermal creep Knudsen pumps are made up of micro/nanochannels subjected to a temperature gradient. In such a combination, the fluid flows from the cold side to the hot side based on the thermal creep phenomenon. Due to the widespread use of Knudsen pumps in various applications, much research has been done to improve their technology. In this work, the effects of wall surface roughness on the flow field characteristics are investigated using the molecular-based direct simulation Monte Carlo method. The surface roughness is modeled by square bumps on the wall. The roughness parameters, including relative roughness, roughness aspect ratio, and roughness distance, are studied in a wide range, that is, 0 ≤ ε ≤ 10, 0.5 ≤ ξ ≤ 2, and 3 ≤ χ ≤ 10, respectively. It is concluded that the existence of roughness, no matter how small, has a significant effect on the flow conditions; so that the subminiature roughness of ε = 0.5% results in a 24% decrease in the mass flow rate. This emphasizes the importance of considering the role of surface roughness in the calculation of the performance of Knudsen pumps. Furthermore, the results indicate that the mass flow rate is independent of the relative roughness and the roughness distance for ε ≤ 1.25% and χ ≤ 5, respectively.

The numerical simulation of different types of nose cone shapes involving conical, Bi-conic, parabolic, spherical Blunt cone and tangent ogive in high Knudsen numbers flow and for three different mixtures O2-N2, He-Ar and He-Xe are investigated in this article. A computer code based on the method of Direct Simulation Monte Carlo (DSMC) has been developed to study numerically the supersonic flow around these cone shapes in rarefaction condition. In order to verify the computer code, the flow field in the slip regime is solved and compared with the results of Navier Stokes equation with the slip boundary condition. The results obtained in the supersonic flows regime show that the parabolic and tangent ogive nose shapes have the least mean shear stress distribution and lowest tip temperature.

In this study, a computational technique is used to investigate the ability of a new Micro Electro-Mechanical System (MEMS) gas actuator Microscale In-plane Knudsen Radiometric Actuator (MIKRA) for detecting and sensing gas mixture. In this actuator, the temperature difference of two arms in a rectangular domain in a rarefied condition induces a Knudsen force which is associated with physical properties of the gas. Both 2D and 3D approaches were applied to simulating the ow inside the model. In order to de ne the ow feature of low-pressure gas inside the micro gas actuator, a high-order equation of Boltzmann should be solved to attain reliable results. Since the domain of this micro gas is non-equilibrium, Direct Simulation Monte Carlo (DSMC) method was applied to the simulation of the model. According to obtained results, the three-dimensional model achieved more reliable results and the existence of a gap for the three-dimensional model clearly demonstrated the impact of this parameter on the effective Knudsen force.

Effects of Knudsen number, lid velocity and velocity ratio are investigated on the flow features of single lid driven cavity with an aspect ratio of one and double lid driven cavity of aspect ratio two. Knudsen numbers studied are 0. 01(early slip regime), 0. 1 (slip regime) and 1 (transitional regime). Lid velocities investigated are 100 m/s, 200 m/s and 500 m/s. The velocity ratios explored are 1 and-1. Knudsen number was found to have a huge impact on the flow rigidity. Lid velocity tends to shift the central vortex to the top left of the cavity for a cavity with aspect ratio of one and shifts the upper vortex to the top left of the cavity for a cavity with aspect ratio of two. Lid velocity does not affect the slip to a great extent on the lid. Changing the velocity ratio from 1 to-1 leads to the reversal of the relative vorticity in the top and bottom half of the cavity.