The research concerns the experimental and theoretical studies of the flow of a predominantly liquid two-phase fluid in nozzles and diffusers, undertaken as part of a longrange program dealing with the development of a gas-driven jet pumpt for rocket engines. The physical description of the flow is based on momentum, heat, and mass transfer phenomena, droplet mechanics, and the influence of flow geometry and operating conditions. As the mass ratio of one of the components is increased, it is imperative to consider at least some aspects of the discreteness of the component of lower volume in mass and energy transfer processes in a theoretical analysis for a first-order prediction of velocities, droplet diameters, and pressure for the flow in an accelerating or nozzle flow and a decelerating or diffuser flow. In the nozzle experiments, the total flow rate and the mass ratio of liquid to gas were varied to establish a series of design and performance parameters. The experimental investigation for diffusing flows was performed employing a conical diffuser and a predominantly liquid medium with the gas in the form of small bubbles dispersed in the liquid. The objects of the research were to determine the feasibility of diffusing a free jet to liquid and the effect of gas entrained in the flowing liquid. (Author).