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AbstractKnudsen force acting on a heated microbeam adjacent to a cold substrate in a rarefied gas is a mechanical force created by unbalanced thermal gradients. The measured force has its direction pointing towards the side with a lower thermal gradient and its magnitude vanishes in both continuum and free-molecule limits. In our previous study, negative Knudsen forces were discovered at the high Knudsen regime before diminishing in the free-molecule limit. Such a phenomenon was however not observed in the experiment. In this paper, the existence of such a negative Knudsen force is further confirmed using both numerical simulation and theoretical analysis. The asymptotic order of the Knudsen force near the collisionless limit is analyzed and the analytical expression of its leading term is provided, from which approaches for the enhancement of negative Knudsen forces are proposed. Copyright © 2012 by ASME.
CitationZhu T, Ye W, Zhang J (2012) Size Dependent Orientation of Knudsen Force. ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer. Available: http://dx.doi.org/10.1115/mnhmt2012-75237.
SponsorsThis work is supported in part by Award No. SA-C0040/UKC0016,made by King Abdullah University of Science andTechnology, and in part by Hong Kong Research GrantsCouncil under Competitive Earmarked Research Grant 621408.