A comprehensive investigation of two-phase flow in off-design operating condition of ejector performance by using entropy generation analysis

The steam ejector works in two operating conditions: on-design and off-design. The overall best ejector's performance is achieved at the on-design operating condition, but the ejector enters the off-design condition due to certain conditions, and its performance decreases. This study has been conducted with the aim of investigating the liquid phase's behavior produced by the nucleation phenomenon in the off-design condition. The pressures for the ejector output are selected to achieve this purpose so that the ejector performance curve is in the off-design condition. Then, the impact of each of these pressures on temperature, nucleation rate, Mach number (MN), liquid mass fraction (LMF), droplet radius, entrainment ratio (ER), and production entropy was investigated. According to the results, the behavior of all mentioned parameters with the outlet pressure changes is different in the diffuser and the same in the primary nozzle. No change can be seen in the nucleation rate with outlet pressure changes, but the production entropy and outlet temperature enhance with the increase in outlet pressure, and a decreasing trend is seen in outlet MN and ER. As the outlet pressure increases from 6.5 kPa to 7 kPa, the production entropy increases by about 3.6%.