Numerical investigation of curved channel Knudsen pump performance

Thermal creep driven flows in curved micro-channels, commonly referred to as Knudsen pumps, are investigated across a range of rarefaction levels with particular focus on the effects of realistic gas coefficients and geometric configuration on performance. Two base geometries are investigated consisting of a previously proposed curved-straight channel and a newly developed double-curved channel with no straight sections. Use of the S-model kinetic equations enables investigation with realistic values of the Prandtl number and viscosity index for argon and nitrogen as well as for Maxwell molecules. For each gas, the pumping performance and flow structure of each base geometry are investigated for three channel aspect ratios and an array of Knudsen numbers finely spaced between 0.1 and 2.0 to allow performance extrema to be identified. The influence of Prandtl number is found to be significant with increased maximum mass flow rates for argon and nitrogen. The impact of viscosity index is found to be comparatively minor. The double-curved geometry is found to generate over twice the mass flow rate. Both geometries are also tested in pumping array configurations involving multiple sections with the newly introduced geometry again providing superior performance.