Hydrodynamic Characteristics of a Gas-Inducing Impeller

Gas-inducing impellers use the relative velocity between the bulk liquid and the impeller, and the acceleration of the liquid phase over the blades, to locally reduce the pressure at an orifice on the blade and induce a flow of gas from the headspace, through a hollow shaft. In this paper a theoretical model based on a blade slip factor and a pressure coefficient is developed to predict the reduction in the pressure at the gas outlet. The model has been used to predict the critical impeller speed marking the onset of induction, and also the rate of gas induction at higher impeller speeds. The model predictions are in good agreement with experimental observations for cylindrical, aerofoil and flat paddle impeller shapes.