PARTICLE TRANSPORT AS A STOCHASTIC PROCESS OF TURBULENT BOUNDARY LAYER FLOW

摘要

The viscous sublayer approach concept, which is consistent with the visualization studies, is extended to simultaneously solve the particle continuity and momentum conservation equations for quantitatively estimating the deposition rate of particles. An expression for the mean part of particle flux is used to reflect three distinct categories that are a typical variation in the experimentally measured deposition rate with particle relaxation time. During the lifetime of an individual eddy element, the mean concentration distribution of particles is derived from Laplace transform schemes. The comparable mechanism of mean components that dominates the transport processes is automatically considered on the average growth period of viscous sublayer by formulating the mean distributions as a stochastic process with the aid of exponential distributed density function. This procedure leads to an analytical solution that offers a simple computation tool of practical use to aerosol engineers. The variations of particle deposition velocity with the particle relaxation time agree with experimental data providing support to the usefulness of the proposed model, which can further extend by including appropriate forces in the analytical formulation through the equilibrium among acceleration terms. In turbulent flows with thermal gradients, the calculations show that the thermophoresis significantly affects the intensity of Brownian motion between colder and hotter regions of a fluid, and its effects are dispersed just about the inertial impaction of particles on the surface to take effect and vanished at the high particle impaction velocities.