Orientation-frozen and coupled motion of nonspherical particles in vertical stagnation flows

Abstract

ORIENTATION-FROZEN AND COUPLED MOTION OF NONSPHERICAL PARTICLES IN VERTICAL STAGNATION FLOWS D. Broday, M. Shapiro, M. Fichman, and C. Gutfinger, Faculty of Mechanical Engineering, Technion - Israel Institute of Technology Haifa 32000, Israel Deposition of submicrometer and micrometer aerosol particles in stagnation flows is important in relation to several applications, including flows in impactors and in clean rooms over workbenches• In the latter case calculation of particle deposition rates is necessary for understanding the roles of technological and environmental factors in fabrication of VLSI. This study is focused at investigation of the nonspherical particle shape as a factor governing the deposition rate. To determine the latter we calculate trajectories of prolate spheroidal particles on a horizontal surface (workbench) in a vertical, laminar-fiow clean room. Motion of micrometer-sized aerosol particles is affected by inertia, hydrodynamic drag and gravity forces. Calculation of trajectories of nonspherical particles involves integration of coupled equations of their rotational and translational motions - a task, which oftentimes requires significant computational efforts. A specific goal of this study is investigating the circumstances in which these computations may be simplified. Towards this goal we calculate the trajectories of spheroids of various aspect ratios fl by assuming that their orientation at any time is frozen and equal to their initial orientation 00 in the undisturbed flow far above the workbench (see Fig. 1). With this simplification only the equation of translational particle motion should be integrated. The orientation-frozen trajectories are compared with the true particle trajectories, obtained by numerical integration of the coupled equations of motion. Y