Deposition of glass fiber particles from turbulent air flow in a pipe

Abstract

A novel experimental technique is developed and used for measuring the deposition velocities of nonspherical particles from turbulent air flow in a horizontal pipe. The deposition velocities of glass fiber cylindrical particles of diameters 0.6–2.5 μm and lengths of up to 50 μm are measured in wide ranges of the flow Reynolds number and particles' aspect ratio for upward, downward and sideward orientations of the deposition surface. It is found that the deposition velocity of particles, characterized by intermediate values of the effective relaxation time, is significantly affected by the nonspherical particles' shape via the interception mechanism. Known correlations proposed for the deposition velocity of spherical particles are shown to significantly underestimate the experimental data for glass fibers, if these correlations are employed using the fibers' aerodynamically equivalent diameters. The latter diameter is, thus, shown to be inappropriate for predicting deposition velocities of nonspherical particles. A turbulent-interception model for deposition of nonspherical particles is proposed to correlate the experimental data obtained for glass fibers. Several formulas for the deposition velocity of cylindrical particles in turbulent pipe flows are proposed.