Numerical study of flow and direct contact condensation of entrained vapor in water jet eductor

Eductors are multi-functional devices that can be used for pumping, mixing, and heat transfer, and hence for commercially available eductors, optimum operational point for one function is not clearly defined. This paper computationally studies two-phase flow and mass transfer in a water jet eductor, involving liquid water as primary fluid and water vapor as secondary fluid. It has been prepared with the objective of study of thermal-fluid behavior within eductor and shares the detailed computational process for other similar applications. This work focuses on the performance of eductor as condenser along with identification of critical operational variables. This research studies eductor as a combined vacuum pump and condenser for thermal desalination, where water vapor is produced using a low-temperature heat source (below 95 °C). The Eulerian approach with thermal phase change model was used to predict direct contact condensation (DCC) with ANSYS-Fluent. The results demonstrated enhanced flow entrainment due to secondary fluid condensation which also causes unstable flow. In general, it was observed that the increase in back pressure decreased the flow entrainment, but this also helped maintain complete condensation within the eductor which helps reduce pressure shocks in the system. The computational model used demonstrated that it can be an effective solution to industrial problems of phase change, especially for comparative optimization processes.