Thermophoretic Transport of Submicron Particles in Pulsating Surface Sublayers 2012-01-1950
EGR coolers are widely used in reciprocating engines to reduce NOx emission. Thermophoresis-an important transport mechanism for submicron particles such as soot-drives gas-suspended particles from hot regions towards cool surfaces and is responsible for soot deposition and build-up in EGR coolers and related devices. Although much is known about thermophoresis in steady flow, little is known about soot deposition in flows with oscillatory heat and mass transfer. In this paper we present new results for the model problem of thermophoretic particle transport in a thin pulsatile shear layer above a flat, cold wall. The transport equations for this sublayer flow with oscillating shear have been solved numerically and, in the case of steady flow, are in excellent agreement with the exact solution for the steady wall shear. Results describing the effect of pulsation on heat and particle mass transfer show that it has only a small effect which is consistent with the experimental measurements. It follows that steady-flow results can be used to describe accurately the average behavior of devices with unsteady pulsating laminar flows.