Effect of vane thickness on radiometric force

A numerical and experimental study of radiometric forces on vanes of different thickness is presented for the flow regime where the radiometric force is near its maximum. For single- and multi-vane geometries, it is shown that radiometric force decreases by only ∼10–15 % when the vane thickness-to-height ratio increases fourfold from 0.5 to 2. For a single-vane geometry, the shear force on the lateral side of the vane is attributed to a vortex flow generated by the interaction of cold chamber walls and heated walls of the vane. In that case, it always acts to reduce the total radiometric force governed by the pressure difference between the hot and the cold sides of the vane. For a multi-vane geometry, represented by a perforated vane, the shear force becomes positive for larger thickness-to-height ratios and lower pressures, primarily due to strong vane-driven transpiration flow through the gaps.