Velocity Field Measurement of Supersonic Free Jet Expansion of R245fa Gas at Organic Rankine Cycle Operating Condition

orc2019 Tracking Number 176

Turbomachinery is designed and evaluated based on Computational Fluid Dynamics (CFD) simulations, which use the ideal gas law to model the fluid thermodynamic properties. This assumes that the deviation between a real gas and an ideal gas is very small. When turbomachinery operates in regions where this assumption does not hold, real gas effects should be considered. This deviation from an ideal gas particularly occurs in Organic Rankine Cycle (ORC) expanders, where the Mach number in the expander nozzles goes up to 1 which makes the flow supercritical. Up to date, CFD simulations have been validated in a case with ideal gas law which is not reliable. R245fa is classified as a frequent ORC working fluid which act as a dense gas in high-pressure regions which real-gas effects are dominant. Therefore, having a real experimental benchmark for validation of CFD models are crucial. To the best of author’s knowledge, there is no published document related to the R245fa flow structures in supersonic or even subsonic conditions. To extend a benchmark for the future CFD simulation a supersonic free jet of R245fa in the supersonic region is presented. To visualize the flow structures of jet an ORC is modified with replacing the expander with a Laval nozzle. Particle Image Velocimetry (PIV) has been used to quantitate the velocity field and study the flow structures inside the jet. The PIV system includes a PIVCAM 10-15 CCD camera, a double-pulsed Nd-Yag laser with a maximum power of 200 mJ/pulse, a TSI 610032 synchronizer, and a computer. The time difference between two consecutive images for capturing a suitable flow image near the model changes from 1 μs while the frequency of laser pulse was 3 Hz indicating the time difference between each double pulses. In this study, the working fluid fogs have been used tracking particles. The results showed that a Mach number of 1.6 has been reached using the current design of the nozzle.