10-04-2017, 08:36 PM
Thermophoresis is a phenomenon of the movement of small particles in a gas with a temperature gradient towards the cooler region of the gas. Small particles, such as dust, when suspended in a non-isothermal gas, experience a force in the direction opposite to the temperature gradient. This force, known as the thermophoretic force plays an important role in the mass transfer mechanism of several devices involving sub-micron and micron sized particles and a large thermal gradient, and it is often cited as an important one influence the efficiency of air filters and aerosols scrubbers. Thus the net velocity got to the particle due to the thermophoretic force is called the thermophoretic velocity. The phenomenon of thermophoresis may be of important in the fouling of heat exchanger surfaces, in combustion phenomena involving small particles (e.g. fly ash in coal combustion), and in process involving the deposition of small particle on cold surfaces following chemical reaction (e.g. manufacture of optical fibre performs). The subject of the thermophoretic deposition of radioactive particle is currently one of important in view of its relevance to postulate accidents reactors. In the work explained here, thermophoretic transport of small particles is analyzed numerically for a laminar parallel plate channel flow. Two-dimensional forced convection boundary layer type equations are used with appropriate boundary conditions. The governing equations are solved using finite difference scheme. A marching solution procedure is employed where by velocity, temperature and particle concentration at any down stream location are determined knowing the flow field upstream of that location. Solution is thus obtained in a series of steps covering the complete flow field starting from the stagnation point. The effect of additional heating of the field on the particle deposition trend has been analyzed. The effect of the ratio of the wall-to gas-temperature, thermophoretic co-efficient, and Schmidt number on the particle concentration has been studied. It can be observed from the results that concentration of particles can be increased on the channel walls by reducing the wall-to gas-temperature ratio. Also additional heating of flow field gives a higher particle deposition on the walls.