Thermophoretic properties of nonspherical particles and large molecules

Abstract

Abstract The Kn p ≫ 1 gas‐kinetic approach of Waldmann (1959, 1961) is extended to predict the thermophoretic properties of nonspherical aerosol particles , and massive nonspherical gas molecules . Calculations are presented for sphero‐cylindrical particles (molecules) of arbitrary aspect ratio, L / R , predicting that in a local temperature gradient grad T they will thermophoretically drift: (i) more rapidly when their major axis is aligned with − grad T ; (ii) at a velocity different from that of a sphere of radius R equal to the cylinder radius; (iii) at an angle with respect to − grad T when their major axis is not parallel to, nor perpendicular to, − grad T ; and (iv) without a net torque tending to orient the particle with respect to − grad T . Important corollaries are that nonspherical particles in a temperature gradient should also experience new thermophoretically‐induced coagulation mechanisms. We predict that the orientation‐averaged thermal diffusion factor α T should increase approximately linearly with particle (molecule) length.