Theory of thermophoresis of large aerosol particles

Abstract

Onsager's principle of kinetic coefficient symmetry is used to build a uniform theory of motion of aerosol particles and gases in the presence of temperature gradients. Only the transport heat in the bulk of the gas is taken into account; the heat of transport in the Knudsen layer is neglected as insignificant. The basis for this is Derjaguin and Bakanov's calculations of the velocity distribution of the gas molecules in the Knudsen layer when a surface is streamlined by a flow of gas. The formulas obtained for the thermomolecular pressure difference in capillaries whose width is large relative to the path length of the molecules are in good agreement with available experimental data, in contrast to Maxwell's formula based on the expression he obtained for the thermal slip. A formula has also been obtained for the velocity of thermophoresis of large and moderately large aerosol particles, with allowance for the temperature jump at the particle surfaces, this formula being a refinement of the Derjaguin-Bakanov formula.