The velocity field behavior and the nature of deposition of microparticles in a thin layer of colloidal solution at wall heating from one and two laser beams

Abstract

To date, heat transfer, convection and particle deposition have been mainly investigated for the case of homogeneous wall heating. Convection and particle deposition during local heating, when there are one or more local heating sources, have not been practically studied. Experimental studies of free convection and particle deposition in a layer of colloidal solution have been carried out. Convection was created by heating the liquid using one and two laser beams. The colloidal solution consisted of water and microscopic TiO2 particles. The novelty of the work is the demonstration of the effectiveness of local heating in creating high rates of convection and particle deposition at low energy costs. With two-point laser heating, the convection rate is higher than with single-point heating. When using two laser beams, the Marangoni number increases in comparison with single-point laser heating. As a result, the Bo number becomes lower than the critical value and the stability of the velocity field increases. In contrast to single-point heating, the use of two laser beams does not change the vortex flow pattern with increasing layer height. The particle deposition rate is higher when using a single laser beam than when using two beams and is two orders higher than the deposition without convection. An expression linking the deposition rate with time, layer height and fluid velocity is derived. The obtained results on the use of local heating sources are applicable for enhancing convection, as well as in technologies for cleaning solutions from solid impurities.