Effect of contact angle on spreading of refrigerant mixture over the vertical cylinder

Abstract

The paper presents 3D numerical modeling of spreading dynamics of R21 (mol. fraction: 0.9) and R114 refrigerant mixture film. We considered an outer flow along a round vertical cylinder at Reynolds numbers of 50 and 104 and contact angles of 10°, 30°, 50°, 70° and 90°. The simulation was performed in OpenFOAM software on the basis of the volume of fluid (VOF) method. Main simulated results are presented in the form of velocity fields of liquid that allow evaluating both wetting dynamics and local characteristics of the liquid film. We obtained that the contact angle has a key effect on the wetted area due to the change of liquid spreading modes over the cylinder. At that, we distinguished the following flow modes: the continuous film, the stable jet mode, the cascade jet mode, the mode of the massive jet, the jet-droplet mode and the drying mode. These modes are similar ones for horizontal tubes. In some flow modes over the vertical cylinder we demonstrated the existence of the noticeable transversal velocity at the wetting front, that leads to moving of jets sources, and the back liquid flow between jets, directed against gravity.