Thermophoresis and photophoresis of cylindrical particles

An analytical study is presented for the thermophoresis and photophoresis of a cylindrical aerosol particle in the direction normal to its axis. The Knudsen number is assumed to be small so that the fluid flow is described by a continuum model with a temperature jump, a thermal slip, and a frictional slip at the particle surface. In the limit of small Peclet and Reynolds numbers, the energy and momentum equations governing these problems are solved at steady state. Expressions for the migration velocity of the particle are obtained in simple closed forms for the cases of thermophoresis in a uniformly prescribed bulk-gas temperature gradient and of photophoresis subjected to an intense light beam. The results indicate that the thermophoretic mobility of a cylindrical particle is smaller than that of a sphere, keeping the properties of the gas and particle unchanged. On the other hand, the photophoretic mobility of a cylindrical particle can be greater or smaller than that of a sphere, depending on the ratio of particle-to-gas thermal conductivities and the relative magnitude of the temperature jump coefficient at the gas/particle interface.