Numerical simulation of thermal edge flow in ratchet-like periodically patterned micro-channels

Abstract

This paper presents a numerical analysis of a novel configuration of the Knudsen pump for rarefied gas flow. A basic unit of the ratchet-like periodically patterned micro-channel consists of two facing parallel cold walls with a triangular hot plate in the center. The gas flow is primarily triggered by the thermal edge flow formed by the dramatic variation in the temperature field near the tips of the triangular plate. The direct simulation Monte Carlo (DSMC) method is applied to study the influence of the operation conditions and geometric parameters on the gas flow, such as the temperature difference, Knudsen number, channel dimension, periodic length, geometric parameters of the triangular hot plate, and surface accommodation coefficients. The results demonstrate that the temperature difference of the walls is the basis for the gas flow. The mass flow rate increases nonlinearly with the temperature difference, and the maximum mass flow rate occurs when Kn is approximately 0.15. The pumping speed level can be improved by increasing the channel dimension appropriately; however, reverse gas flow occurs for exceedingly large channel dimensions. By simply adjusting the dimensions of the two triangular hot plates, the mass flow rate can be increased by 3.7 times. The mass flow rate reaches its maximum when the length-width ratio of the triangular hot plate is 2.0. In particular, by changing the surface accommodation coefficients of the inclined and vertical walls of the triangular plate, the pumping speed level can be maximally increased by approximately 35 times.