IN-TUBE FLOW BOILING OF R-407C AND R-407C OIL MIXTURES PART I - MICROFIN TUBE/

In-tube 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 645 kPa (93.5 psia) at mass velocities of 100, 200 and 300 kg/(m(2).s) (20 .5 41, and 61 lb/s.ft(2)) over nearly the entire vapor quality range. At similar operating conditions, pure R-407C performed similarly to pr evious pure R-134a tests at the highest mass velocity, but lower than R-134a for the other mass velocities. Any amount of oil tended to decr ease local R-407C microfin heat transfer coefficients, especially at h igh vapor qualities where degradations of as much as 50% or more occur red. Two-phase pressure drops were increased by the presence of oil, e specially at high vapor qualities. Buildup of the local oil mass fract ion in the microfin test sections was observed at high vapor qualities , together with the formation of slowly flowing viscous liquid films, a phenomenon that became more acute at lower mass velocities.