Aerosol Deposition Measurements as a Function of Reynolds Number for Turbulent Flow in a Ninety-Degree Pipe Bend

An experimental and numerical investigation of the effect of the Reynolds number (Re) on the deposition of aerosol particles in a 90° pipe bend for turbulent flow was performed. Deposition fraction data were measured for a range of Stokes numbers (Stk) at different flow Re (10,250, 20,500, and 30,750) higher than those of most previous studies where Re was ?10,000. The data show good agreement with previous studies for Stk > 0.4, demonstrating that increased Re does not significantly alter the trend of deposition fraction with Stokes number (Stk) in this range. However, a noticeable increase in deposition was detected for 0.1 ? Stk ? 0.4. At Stk = 0.15, an increase in Re from 10,250 to 30,750 caused a factor of 2.6 increase in deposition fraction from 0.14 to 0.36. Numerical simulations were completed, using the Reynolds Averaged Navier-Stokes (RANS) equations with the Shear Stress Transport turbulence model. Modeling with inertial impaction only (i.e., neglecting turbulent dispersion), the results accurately reproduced the general trends seen in the experimental data; however, they failed to detect the Re effect at low Stk seen experimentally. The inclusion of turbulent particle tracking in the RANS simulation via an eddy interaction model did not improve the results. However, an analytical analysis of the particle tracking equation drawing data from the numerical results, showed that the experimentally observed effect of Re at low Stk can be attributed to damped particle response to velocity fluctuations at the eddy frequency scale.