Thermophoresis in an absorbing aerosol

Abstract

Several one-dimensional model problems have been solved for the temperature and concentration profiles of an aerosol allowed both to absorb external radiation and to move under the influence of thermophoresis. Since the aerosol absorbs radiation, the quantity of energy deposited is proportional to concentration. The effects of aerosol radiation and natural convection have been neglected. Analytical results are possible for steady uniform irradiation of plane and circular geometries in the large Schmidt number limit with a reflecting wall boundary condition, while numerical techniques are employed for the transient case. The problems studied are distinguished by the strong non-linear coupling between concentration and temperature that is effected by thermophoresis. It is shown that relatively small amounts of energy are required to produce large changes in aerosol concentration in the case of uniform external radiation, that Gaussian irradiation is capable of burning a ‘hole’ in the concentration profile and that ‘donut’ made radiation may trap particles temporarily. The results for uniform radiation also apply to an aerosol with internal heat generation as may be experienced, for example, during radioactive decay.