Intube Flow Boiling of R-407C and R-407C/Oil Mixtures. Part 1: Microfin Tube

Intube evaporation tests for R-407C and R-407C/oil are reported for a microfin tube. The tests were run at a nominal inlet pressure of 6.45 bar (93.5psia) at mass velocities of 100, 200 and 300 kg/m2s (73581, 147162 and 220743 lb/h ft2) over nearly the entire vapor quality range. Pure R-407C performed similar to previous pure R-134a tests at the highest mass velocity, but lower for the other mass velocities, at similar operating conditions. Any amount of oil tended to decrease local R-407C micorfin heat transer coefficients, especially at high vapor qualities where degradations of as much as 50% or more occurred. Two-phase pressure drops were increased by the presence of oil, especially at high vapor qualities. Buildup of the local oil mass fraction in the microfin test sections was observed at high vapor qualities together with the formation of slowly flowing viscous liquid films, a phenomenon becoming more acute at lower mass velocities.