Numerical study on thermophoresis of highly absorbing, emitting particles in laminar tube flow

Abstract

The effect of the radiation on thermophoresis phenomenon due to the presence of highly absorbing, emitting particles such as soot, fly ash and pulverized coal suspended in a two phase flow system is investigated numerically for a laminar tube flow. An analysis of conservation equations for a gas-particle flow system is performed on the basis of a two-fluid model from a continuum Eulerian viewpoint. In addition, the P-1 approximation method is used to evalute a non-linear radiation source term involved in a coupled energy equation. In part I, it is found that under a strong radiative effect, the rate of thermophoretic particle deposion becomes considerably low. furthermore, the effects of thermal loading ratio and the Stokes number on thermophoresis are to be predicted. In part II, thermophoresis of radiating particles in combined forced and free convection flows in analyzed in a long vertical tube. The gravitational body force affects the hydrodynamic and thermal characteristic of a forced flow. When the radiative effect is couple with a combined forced and free convection flow system, the radiative effect decreases a buoyancy driven effect on thermophoresis phenomenon. At $\tau_0$=0, as the buoyant effect is increased, the cumulative collection efficiency is decreased compared with that of Gr=0. For larger optical radius, E(x) in a buoyant-affected flow becomes a bit larger than that at Gr=0.