Simulation of condensation flow in a rectangular microchannel

The condensation flow of the refrigerant FC-72 in a rectangular microchannel with a 1-mm hydraulic diameter is numerically studied using the volume of fluid (VOF) model. The heat transfer related to the condensation is taken into account by a thermal equilibrium model assuming the interface temperature is at saturation. The numerical method is validated against experiments from the literature and well predicts the flow patterns along the microchannel. The vapor phase in the microchannel forms a continuous column with a decreasing diameter from upstream to downstream. Slugs are periodically generated at the head of the column. Decreasing the wall cooling heat flux or increasing the flow mass flux increases the vapor column length. Waves along the interface cause necks in the column and locally increase the vapor velocity and decrease the pressure, facilitating breakage of the vapor column into slugs. The liquid temperature is close to saturation near the interface and lower downstream and in the thin liquid layer close to the cooling surface. The initial bubble size increases with increasing flow mass flux or decreasing cooling heat flux.