A Computational Study of Two Novel Non-steady Pressure Exchange Ejectors with Environmental Benefits and Energy Efficiency

ABSTRACT The latest progress on the design and performance of two different types of novel supersonic pressure exchange ejectors for thermally driven ejector refrigeration systems are presented. One is an axial rotor-vane pressure-exchange ejector whose main component parts are a supersonic nozzle, a rotor with some wedged vanes, and a shroud diffuser. The other is a radial rotor-nozzle pressure-exchange ejector that includes a rotor with some canted nozzles, and two disc-shaped diffusers. The energy exchange, which occurs between the fluids throughout the pressure exchange ejectors, is shown by computational simulation with two commercial CFD packages, Tascflow and Fluent. This paper shows how the supersonic aerodynamics is managed to provide the desirable flow induction characteristics through computational study for both radial-flow and axial-flow supersonic pressure exchange ejectors. For axial-flow supersonic rotor-vane pressure exchange ejectors, three different spin-angles, 0 o , 10 o , and 20 o are used to better understand aerodynamic performance of three-dimensional, complex, supersonic pressure-exchange ejectors and to enhance a strong foundation for the problem at hand. Even though the larger spinangle and the more number of rotor vane produce better flow induction and mixing between primary flow and secondary flow, the rotor rotating speed closer to free spinning one is more essential to produce better flow induction and mixing between primary flow and secondary flow. Meanwhile practically severe mechanical difficulties were observed with supersonic radialflow pressure exchange ejectors whose design concept was turned out aerodynamically great by computational study that allowed one to make some idealized assumption on it. Because of its radial vaneless diffuser, a supersonic pressure-exchange ejector with a free-spinning rotor can be aerodynamically highly desirable. It is less likely to have strong shocks, which is a source for detrimental effects on the ejector. The radial configuration provides the opportunity for utilizing yet another mode of energy exchange "extended pressure exchange" that has been newly re-identified. INTRODUCTION Ejectors boast of being one of the simplest direct contact flow induction devices that exchange energy and momentum between a high-energy primary fluid and a relatively low energy secondary fluid to produce a discharge of intermediate specific energy level. As a novel form of ejectors, pressure-exchange ejector is a device, which uses a high primary pressure fluid, "driving fluid", to entrain a secondary fluid lower pressure, "driven fluid", by transferring energy from a high velocity to a lower one. This is a direct fluid-fluid energy transfer from a high kinetic energy primary flow to a secondary fluid. The transfer of momentum gives rise to an increase in the stagnation pressure of the secondary fluid and enables the ejector to function as a compressor. In an ejector, momentum can be imparted from the primary fluid to the secondary fluid by tw