Deposition of aerosol particles from turbulent flow onto rough pipe wall

Abstract

Out of many different theoretical studies describing the deposition of small particles in different engineering situations, very little work has accounted for the surface roughness. An approach suitable for estimating deposition velocities of small particles on rough surfaces is presented in this paper. This approach has been applied to estimate the rate of deposition of particles onto a rough pipe wall during turbulent flow. The surface roughness is represented by the average height of pipe surface roughness, K. The friction velocity has been calculated by applying the empirical formula developed by Bennet and Myers in terms of roughness ratio ( K/ D) and the flow Reynolds number. Provisions have been taken to account for the particle eddy diffusivity as a contribution to fluid eddy diffusivity as proposed by Liu et al. The velocity of deposition for this model has been computed numerically by means of the three eighth roots method. The effect of relative roughness, particle size, particle density and flow Reynolds number on the deposition velocity has been examined. It is concluded that the wall roughness has a large effect on particle deposition velocity of a diameter smaller than 5 μm. This effect diminishes for particles of 10 μm. For a given relative roughness and Reynolds number, the particle density has nearly no effect on deposition velocity of particles of less than 0.1 μm. The results of the present approach are compared with the available experimental results as well as the theoretical predictions. Good agreement with experimental results is obtained.