Measurement of static pressure profiles of vortex flashing R134a flow expanded through convergent-divergent nozzles

Vortex control is a novel two-phase convergent-divergent nozzle restrictiveness control mechanism which achieves flow control by adjustable nozzle inlet vortex strength. It can potentially provide flow control with less sacrifice of nozzle efficiency, which is important for two-phase ejector cooling cycle performance. It is also less vulnerable to clogging. However, the underlying mechanism behind vortex control is still unclear. In this study, static pressure profiles of vortex flashing R134a flow expanded through nozzles under various conditions have been measured. A 1D model for the estimation of vapor qualities in the initially subcooled flashing nozzle flow based on the measurement results was also developed. It was found that after the introduction of inlet vortex to the initially subcooled flashing nozzle flow, the pressure drop across the divergent part has been increased, which is caused by the increased vapor generation in the divergent part. The elevated nozzle throat pressure results in the nozzle behaving like being more restrictive. When the inlet vortex is applied to flashing nozzle flow with two-phase at the nozzle inlet or single-phase liquid nozzle flow, the influence of inlet vortex on the nozzle restrictiveness and the nozzle pressure profile is insignificant. The nozzle isentropic efficiency can be significantly increased by applying inlet vortex, which could be beneficial to ejector performance when the vortex nozzle is used in ejectors. In order to achieve satisfactory vortex control range and high nozzle isentropic efficiency, the vortex nozzle divergent part length as well as the divergent angle need to be appropriately sized. (C) 2019 Elsevier Ltd and IIR. All rights reserved.