Influence of Nozzle Divergent Part Length and Throat Diameter on Vortex Control of Initially Subcooled Flashing Flow

Expansion work recovery by two-phase ejector is known to be beneficial to vapor compression cycle performance. However, one of the biggest challenges with ejector vapor compression cycle is that the ejector cycle performance is sensitive to working condition changes which are common in many applications, including automotive AC systems. Different working conditions require different ejector geometries to achieve maximum performance. Slightly different geometries may result in substantially different COPs under the same conditions. Ejector motive nozzle throat diameter (motive nozzle restrictiveness) is one of the key parameters that can significantly affect COP. This paper presents the experimental investigation of a new motive nozzle restrictiveness control mechanism for two-phase ejectors used in vapor compression cycles, which has the advantages of being simple, potentially less costly and less vulnerable to clogging. The redesigned ejector utilizes an adjustable vortex at the motive inlet to control the nozzle restrictiveness on the flow expanded in the motive nozzle. Adjustable nozzles based on this new control mechanism were designed and manufactured for experiments with R134a. The influence of nozzle divergent part length and throat diameter on the vortex control of initially subcooled flashing flow is presented. Visualization results of the two-phase flow inside the nozzle are also provided.