Local heat transfer during reflux condensation at subatmospheric pressure and with and without non-condensable gases for power plant application

Reflux condensation heat transfer of steam–air flow has been studied experimentally and theoretically. Effect reflux and co-current flow configurations and flow pressure on condensation heat transfer are investigated. Particular attention was paid to phenomena occurring at the interface and produced by the high steam velocity when the system runs at very low pressure. A total of 200 data points were used to analyze the average condensation heat transfer. An analytical model based on diffusion layer theory, momentum balance and combination of heat and mass transfer, has been developed. A good accuracy was obtained between model predictions and measurements at low pressure. The heat transfer coefficient for the reflux condensation is lower than the co-current flows, because of a thicker condensate film. Comparison between experimental results and predictions shows that the wavy film and non-condensable gas effects are very pronounced for condensation at low pressure. A new equation of the Fwave factor is proposed.