Diffuser Studies with Single-and Two-Phase Flows

Abstract : An experimental investigation was conducted of two problems of diffuser flow which are encountered in a gas-driven jet pump. The first was concerned with determining the feasibility of diffusing a free jet of liquid. The second was concerned with determining the effect of entrained gas in the flowing liquid upon the diffusion process. In all of the experiments, conical diffusers were employed with water and air as the working fluids. It was found that up to 86.5% of the kinetic energy of the free jet could be recovered by employing the proper type and size of diffuser inlet, with the appropriate back pressure. Flow rate and the distance from the nozzle exit to the diffuser inlet had little effect on the energy recovery. The experiments indicated that when a gas is entrained in a liquid being diffused, the pressure recovery of the diffuser is reduced, the amount of reduction depending on the volume of entrained air and the static pressure at the throat of the diffuser. A theoretical analysis indicates that the reduction in pressure recovery due to gas entrainment should become smaller as the entrance velocity to the diffuser is increased. The experiments indicated, however, the possibility that compressibility effects may seriously reduce the pressure recovery for high velocity, two-phase flow in a diffuser.