Simulation of R-245fa Vapor Condensation in an Inclined Tube Using the VOF Method in Conjugate Problem Statement

For designing facilities operating on organic working fluid according to the Rankine cycle, reliable methods for calculating organic coolant condensation processes in channels, including inclined ones, are required. In this regard, the problem of special importance is to determine condensation heat transfer in the cases when the heat transfer intensity on the coolant side is commensurable with that on the condensation side. The article describes the results of the activity aimed at studying the condensation of R-245fa (considered as a promising coolant) in horizontal and inclined tubes using the Volume of Fluid (VOF) method. By using this method, supplemented with the model of heat and mass transfer at the phase interface, one can visualize the flow structure and obtain data on the local heat transfer characteristics. The prediction results are compared with the experimental data obtained on the experimental setup at the CJSC Turbokon, intended for studying heat and mass transfer processes during condensation of various promising working media. The predicted data have been compared with the experimental data obtained in condensation regimes in a 2 m long copper tube 32 × 2 mm in diameter at mass fluxes up to 27 kg/(m2 s) and tube inclination angles up to ‒24.3°. For simulating the processes at the phase interface, the Lee model was used with automatically calculating the relaxation constant based on the working fluid properties and computation mesh parameters. All calculations were carried out using the in-house CFD code ANES. The article presents data on the distribution of heat transfer coefficients along the tube inner surface. The prediction results are in good agreement with the experimental data, which have shown that the heat transfer coefficient increases significantly even at a small tube inclination. The accomplished study helps gain deeper insight into the condensation heat transfer processes in horizontal and inclined tubes, which is of importance for designing heat transfer apparatuses, such as air and water cooled condensers of the vapors of refrigerants, petroleum products, and other chemical substances. The obtained results can be used for improving the accuracy of engineering calculations and elaborating new design solutions for condensers with taking into account local flow features.