Numerical study of non-equilibrium condensing supersonic steam flow in a jet-pump based on supersaturation theory

Abstract

Condensation process in high velocity flowing steam inside jet-pumps and ejectors significantly affect the performance of these devices. The formation of droplets in the steam passed through the primary nozzle of a jet-pump, releases an amount of latent heat and numerous tiny particles which change the flow properties. Conventional CFD approaches of investigating ejectors consider steam as an ideal gas with a single-phase flow. In the present study, a robust mathematical model was developed to take into account the droplet formation phenomena in the flowing steam, wherein a large number of droplets are formed in the subcooled vapor through a non-equilibrium supersaturation phenomenon. Separately, the mathematical method was used to model the operating performance of a pilot-scale ejector and to investigate the deviation of the entrainment ratio and the compression ratio from the corresponding ideal-gas values. It was found that the error of the entrainment ratio substantially reduced from 10.0% for a single-phase steam to 1.69% for a two-phase steam, and the error of the compression ratio reduced from 7.3% to 3.52%, respectively. Moreover, effects of variations of the suction flow pressure and temperature on the two-phase steam flow velocity, density, pressure and temperature was investigated and thoroughly discussed. In addition, flow Mach number was introduced as a major characteristic to compare shock-wave patterns of supersonic flow in both steam assumptions. Finally, it was shown that the pressure-rise through the normal shock-wave in the two-phase flow simulation is considerably higher than that of the single-phase flow simulation.