Deposition of aerosols from turbulent pipe flow

Abstract

Several approaches to the calculation of the rate of deposition of particles from a turbulent fluid stream on to the boundary walls are discussed. In a turbulent flow system containing suspended particles, the need to consider the relationship between the particle eddy diffusivity and the fluid eddy diffusivity in calculating the deposition rate, has been indicated. A quantitative estimation is made of the effect of temperature gradients between the fluid and the wall surface in inducing a radially-directed thermophoretic velocity on the particles.

A flow system is described in which a turbulent air stream passes through a cylindrical duct. The flow was assumed to be two-dimensional and was characterized by measuring the mean velocities and the fluctuating turbulent velocities of the fluid in the axial and radial directions, and also the shear stress profile in the radial direction. From the latter measurement the eddy diffusivity of the fluid was determined. The measurements were carried out at Reynolds numbers of 1.27 × 10⁵ and 2.67 × 10⁴ and at several duct wall temperatures between 279 and 317 K. Droplets of approximately 1 µm diam. were injected into the turbulent fluid and the results indicate the effect of the flow conditions and wall temperatures on the particle deposition rates.