Numerical investigation of gas separation via thermally induced flows in ratchet-like patterned microchannels

Abstract

Gas separation can be achieved via thermally induced flows inside a microchannel. To obtain the optimum parameters for the best gas-separation efficiency, the direct simulation Monte Carlo (DSMC) method is used to numerically simulate a ratchet-like patterned microchannel with triangular hot plates. The analysis is based on the molar fraction of binary gas mixtures (He–Xe) in a steady state. The influence of temperature, Knudsen number, surface accommodation coefficient, and geometric parameters of the microchannel on its gas separation efficiency are studied using the controlled variable method. Results show that the separated heavier gas species (Xe) is mainly accumulated in wide or narrow microchannel at the last stage of the microchannel. The gas-accumulating position can be controlled by changing the microchannel width, microchannel length, and ratchet angle. The lighter gas moves from the cold to the hot side and concentrates in the hot region, while the heavier gas concentrates in the cold region. The gas separation efficiency improves as the temperature difference increases and the surface accommodation coefficient of the inclined surface decreases. The surface accommodation coefficient directly affects the transition between the thermal edge flow and radiometric flow near the upper tip of the triangle in the microchannel. The gas separation efficiency with a radiometric flow at the upper tip of the triangle is better than that with a thermal edge flow. In addition, the study gives the optimum parameter values for the best gas separation efficiency. These results can be applied to the realization and design of gas separators in various industry fields.