Numerical Simulation of the Effects of High Content Noncondensable Gases in a Wide Space on the Direct Contact Condensation of Steam

Abstract

Abstract. This study investigates the effects of noncondensable gas (NCG) content (0–9%) on the steam direct contact condensation process in a large space using the volume of fluid (VOF) multiphase flow model and the realizable k–ε turbulence model. Phase change and heat and mass transfer are simulated by incorporating a user-defined function (UDF). The results demonstrate that NCG markedly suppresses steam condensation, leading to a transition in the morphology of the vapor plume from periodic contraction to stable ejection, accompanied by bubble detachment phenomena. As the NCG content increases, the axial penetration of the vapor plume is enhanced, and the flow field characteristics undergo significant changes. Downstream of the ejector, the fluctuations in temperature and velocity become more pronounced, while the pressure fluctuation frequency at the throat increases and the mass transfer rate decreases. The thrust performance, quantified by specific impulse, exhibits a nonmonotonic trend with increasing NCG content: it first increases and then decreases, peaking at 7% NCG. This study provides a theoretical basis for the optimized design of steam ejectors and condensers under high NCG conditions.