Void fraction and flow regime of in-tube condensation in a vapor-compression system

In vapor-compression systems, superheated vapor condenses with temperature gradient. A “3-zone” (superheated, two-phase and subcooled) approach is not fully representative of the process because condensation happens earlier and later than bulk quality 1 and 0 respectively. The new approach, which is “5-zone” (additional condensing superheated and condensing subcooled), addresses those issues by capturing the non-equilibrium effects. Void fraction and flow regime measured in 4 and 6 mm smooth horizontal round tubes are used to validate the new approach in the range: mass flux from 50 to 400 kg m^-2 s^-1; heat flux 5 to 15 kW m^-2; condensing temperatures 30 and 50^oC. The refrigerants explored are R32, R134a, R1234ze(E), R245fa and R1233zd(E). Comparing to the “3-zone” approach, the new void fraction correlation and flow regime map expend the prediction range by finding the real onset and end of condensation, providing grounds for new heat transfer and pressure drop models.