Local heat transfer during reflux condensation mode in a U-tube with and without noncondensible gases

A series of experiments was performed to investigate the local heat transfer phenomenon inside a U-tube in a reflux condensation mode. A total of 477 data (108 for pure steam flow conditions and 369 for steam–air flow conditions) for the local heat transfer coefficients were obtained for various inlet flow rates of steam and air under atmospheric conditions. Based on the steam–air experimental results, a new correlation applicable to the reflux condensation mode is developed using the degradation factor. The new correlation includes the effects of the flow rates of the condensate and the noncondensible gases (air) on the heat transfer coefficient. Most of our data agree with the predicted values with a RMS error of 27.4%.