THEORETICAL REDUCTION OF RATE OF DEPOSITION OF SUSPENSIONS IN TURBULENT FLOW OVER A TILTED FLAT PLATE BY APPLYING AN EXTERNAL ELECTRIC FIELD

Particle deposition from turbulent flow of suspensions on inclined surfaces, is related to many practical problems such as attenuation of solar energy collected by solar flat plate collectors due to dust deposition. In this paper, the effect of external electric field on the deposition of suspensions in turbulent flow over a tilted flat plate is investigated. The external electric field is obtained by a number of equally spaced parallel cylinders having the same voltage and height above the plate. The case of a constant external electric field is also considered. A mathematical model for the flow of suspensions using the combined equation of continuity of fluid and particulate phases with the application of Fick's law and the equations of Poisson, external electric field and rate of deposition along with the proper boundary conditions are given. Numerical solution is obtained using the finite difference method. The effects of the intensity of the external electric field, the number of charged cylinders and their height above the plate on the rate of deposition of the solid particles are studied. The theoretical results indicate that an externally applied electric field obtained by an array of charged cylinders placed parallel to the plate can considerably reduce the rate of particle deposition from turbulent flow of suspensions over a tilted flat plate if the potential on the electrodes of the charged cylinders has an opposite polarity with respect to the polarity of the charge on the particles. In addition, increasing the number of the cylinders for the same applied voltage results in more reduction in rate of deposition. Moreover, for a given applied voltage, there is an optimum height of the array of cylinders that minimizes the total rate of deposition.