Thermophoretic deposition in crossflow over a cylinder

tions.4 The pressure gradient to be used in the momentum equation is found either from the potential flow solution over the cylinder or from the best fit for the experimental data.4 The temperature gradient established in the thermal boundary layer drives the particles either toward or away from the cylinder surface. The velocity acquired by the small parti- cles relative to the gas velocity is known as the thermophoretic velocity vt. Following the standard assumptions,5 the conser- vation law for particle concentration, with the help of the continuity equation, reduces to HERMOPHORESIS causes small particles to be driven away from a hot surface and toward a cold one. This phenomenon has many practical applications. It affects the removal of small particles from gas streams, determines ex- haust gas particle trajectories from combustion devices, and helps in studying the particulate material deposition on turbine blades. It is also of importance in the manufacture of fumed silica, carbon black, and titania particles for the paint industry. All studies of thermophoreti c deposition in external flow (except Homsy et al.1 and Alam and Mehrotra2) are either for a zero pressure gradient in the boundary layer or for cases for which similarity solution is possible. Practical applications of thermophoresis in external flow, however, involve a nonzero pressure gradient for which no similarity solution is possible. Therefore, we study the thermophoretic deposition of aerosol particles in crossflow over a circular cylinder. Both theoretical and experimental pressure distributions in the hydrodynamic boundary layer over the cylinder are considered, unlike those in Homsy et al. 1 and Alam and Mehrotra,2 where only the former is studied. A finite-differe nce method is used for the solution. The working fluid is taken to be air.