Pitot and static pressure measurement and CFD simulation of a co-flowing steam jet

Condensation in the primary nozzle of a steam ejector changes the steam jet properties during the nozzle expansion process and affects the mixing rate of the primary and secondary streams and thus the performance of steam ejectors. Only limited experimental data is available for the mixing of wet steam jets at conditions relevant to steam ejectors. The present work provides static and pitot pressure measurements within a wet supersonic steam jet which mixes with a low pressure co-flowing secondary stream. High pressure steam was delivered to the primary nozzle at a stagnation pressure and temperature of 270 kPa and 406 K, respectively. The primary nozzle throat diameter was 3.2 mm and its exit diameter was 13.6 mm. Pitot and static pressure measurements were obtained on the mixing jet centreline from the nozzle exit to a downstream location of 185 mm in the mixing chamber. Radial profiles of pitot and static pressure were also measured at positions of 5, 20, 35, 85, 135 and 185 mm downstream of the nozzle exit. With the mixing chamber pressure maintained at approximately 1.3 kPa, the mixing jet was in an under-expanded condition. CFD simulations with a non-equilibrium wet steam model also demonstrate the under-expanded jet structure. The pitot pressure profiles at the furthest locations downstream (135 and 185 mm) show reasonable agreement between experiments and simulations in terms of the spreading of the jet due to turbulent mixing. However, there are significant differences between the experimental and simulated pitot and static pressures profiles in the transverse and axial directions. Contributions to these differences are likely to arise because the simulated static pressures in the under-expanded wet steam jet core are lower than the triple point for water (0.61 kPa), so potential exists for liquid-solid and vapour-solid phase transitions that are not currently modelled in the simulations.