Effects of the surface roughness on the entrainment heights of oil–gas mixture impingement on the vertical wall

The entrainment of oil–gas mixture from the wall significantly affects the performances of inertial separators. By spraying the oil–gas mixture onto a vertical wall, the effect of surface roughness on entrainment height is investigated in this study. The oil droplet size distribution on the impingement surface is measured using a Malvern particle size analyser, whereas the impingement velocity field is measured using particle image velocimetry technique. The impingement and entrainment profiles are captured through high-speed photography, and the entrainment height is identified from digital image processing. Results show that the entrainment heights range from 2 to 12 mm on the surface with a roughness of 0.3-4.5 μm when the impinge velocity is 3–5 m/s and the Sauter mean diameter of the impinging droplets is approximately 40 μm. The lowest entrainment height in all operating conditions is obtained at the surface roughness level of 1.1 μm.