Numerical Investigation on the Heat and Mass Transfer Characteristics of Direct Contact Condensation in a Water-Driven Steam Ejector

A three-dimensional numerical model of a water-driven steam ejector was developed using the Euler-Euler two-fluid framework. A direct-contact condensation (DCC) heat and mass transfer model was employed to simulate the complex two-phase flow and energy exchange. The distributions of gas-liquid phases, pressure, and temperature were obtained to evaluate performance. Results indicate that within the investigated operating range (p_p = 140–160 kPa), the entrainment ratio (ER) and temperature rise (DT) are highly coupled, with DT varying from 5.33 to 11.49 K. The maximum temperature rise of 11.49 K was achieved at p_p = 140 kPa, T_p = 310 K, p_s = 100 kPa, and p_b = 92 kPa. It was found that a distinct pressure jump occurs at the throat, where the entrained steam is completely condensed, followed by rapid pressure recovery in the diffuser. The steam plume length and condensation zone are strongly governed by back pressure (p_b); Increasing p_b from 92 to 114 kPa leads to a continuous reduction in ER and shifts the peak condensation zone upstream. Furthermore, the study reveals that elevated back pressure suppresses steam entrainment and shortens the condensation length, eventually leading to flow reversal when a critical p_b is exceeded. This work provides detailed physical insight into DCC mechanisms and offers quantitative references for the design of ejector-assisted components in advanced energy systems.