Thermophoretic properties of nonspherical particles and large molecules

The Knp ≫ 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 αT should increase approximately linearly with particle (molecule) length.