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In the last decade, researchers working on direct contact condensation (DCC) have focused their attention on studying the effect of liquid cross-flow, in contrast to the conventional stagnant liquid pool condensers. Currently, the major applications of DCC in liquid cross-flow include the sterilization process of milk and the mixing of oxygen-rich turbine drive gas with liquid oxygen (LOX) at the booster turbopump exit of a typical staged combustion cycle-based rocket engine. In this work, attempt has been made to develop and validate a two-fluid two-phase model for predicting the complex phenomena of steam injection into a cross-flow of subcooled water. A correlation for interaction length scale has been developed for DCC cases. The correlation includes the effect of all the critical operating parameters such as liquid subcooling, steam mass flux, and liquid velocity, which hitherto has not been available in the literature. The unstable nature of steam plumes has been investigated, and critical Weber numbers for predicting stable to unstable transition in a DCC cycle have been computed. The associated pressure and temperature oscillations due to unstable nature of plume have been studied. The critical design parameters for direct contact condenser such as the heat transfer coefficients and dimensionless vapor penetration lengths have been quantified and analyzed.

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Direct contact condensation occurs when a vapor comes in contact with the liquid of the same fluid and is accompanied by very high heat transfer coefficients compared to the conventional heat exchanging processes. Many researchers have investigated the direct contact condensation of steam jets in a pool of subcooled water. In the last decade, the potential of flowing liquid as an enhanced heat transfer medium in comparison with the stationary pool of liquid was explored by various researchers. Also, in some configurations of staged combustion cycle based rocket engine, the oxygen-rich gas is injected into flowing liquid oxygen to improve the heat transfer characteristics. Hence, there is a need to investigate the direct contact condensation of vapor jets in a cross flow of liquid. A two-fluid particle based multiphase formulation with thermal phase change model has been implemented in the present investigation to capture the direct contact condensation phenomena. The data obtained from numerical simulations are validated with the experimental results of Clerx et al., [1]. Further, studies on plume shapes, interfacial area and pressure amplitudes are reported.

Cryogenic turboexpanders for nitrogen refrigeration and liquefaction cycles operating near liquefaction conditions are vulnerable to droplet formation. The turboexpander must be devoid of any traces of droplets, as this may cause damage to the blades and also result in performance deterioration. Hence, a multiphase flow analysis was conducted, based on the droplet condensation model in Ansys CFX®, to identify any possible droplet sites and its nature of propagation. A single-phase steady state simulation of the turboexpander was performed initially to identify the regions susceptible to droplet formation, followed by a multiphase analysis to study the flow field behavior and to characterize the droplet nucleation and growth. It has been observed that the low-pressure regions like vortices and wakes are susceptible to sub-cooling and thereby in droplet formation. Also, major geometrical parameters that affect the droplet nucleation have also been identified.