Evaporation of Lubricant Films Subjected to Laminar and Turbulent Boundary Layers

This work investigates experimentally the effects of grid-generated turbulence on the evaporation of thin oil films subjected to laminar, transitional, and turbulent boundary layers. Particle image velocimetry (PIV) is used to characterize flow development within a rectangular duct (20 mm x 40 mm) with a length of 1 m (similar to 40D(h)). The inlet turbulence intensity is manipulated using wire meshes, and experiments are performed for Reynolds numbers based on the duct hydraulic diameter of 10,650, 17,750, and 35,500. Mass transfer measurements are conducted under the characterized boundary layers for oil films with initial thicknesses of 50 mu m at a constant substrate temperature of 150 degrees C. The Reynolds number is shown to have a significant impact on the evaporation rate, whereas varying near-wall turbulence intensity is shown to have little effect for the parameters investigated in this study. This implies that mean wall shear and transport within the viscous sublayer are the predominant parameters governing the convection-limited mass transfer considered in this investigation.