Free jet expansion and gas entrainment characteristics of a plunging liquid jet

Abstract The change in effective jet diameter is measured as a function of free jet length for vertical liquid jets passing through air. The data are incorporated into a model to predict the rate of gas entrainment for a liquid jet plunging into a confined column of liquid. In the model it was assumed that the total gas entrainment rate included gas contained within (1) the effective diameter of the free jet at the plunge point and (2) an annular film adjacent to the surface of the jet, where the outer boundary of the film was defined to be the separating streamline between the entrained and unentrained components of the moving gas boundary layer. It was further assumed that the radial location of the separating streamline was independent of both liquid and gas flow rates and system geometry. Excellent agreement between model predictions and gas entrainment measurements were obtained once a number of experimental parameters were determined.