Flow regimes during condensation in superheated zone

Heat transfer experiments with flow visualization were performed with R134a in a smooth horizontal tube in order to verify that condensation occurs outside the two-phase region. The visualization performed for this work is unusual in that a diabatic visualization section was used, more closely approximating the behavior of the fluid in an actual condenser than typical adiabatic visualization experiments. In addition to the flow visualization, liquid film thickness measurements were taken and used to determine the cumulative latent heat transferred from the refrigerant. The measured film thicknesses and recorded videos confirm the presence of liquid in the bulk superheated region. Condensate appeared first as droplets and rivulets on the tube wall and then formed a thin film. The flow later passed through misty annular and wavy flow regimes as the refrigerant transitioned to the two-phase region.