Simple and general correlation for heat transfer during flow condensation inside plain pipes

•A general heat transfer coefficient model for flow condensation was developed.•HTC is correlated by the sum of the liquid and vapor superficial Reynolds number.•The condensation HTC model is equivalent to the single-phase flow HTC model. This work proposes a new general and simple model to determine the local flow condensation heat transfer coefficient inside plain pipes. The model considers two regimes corresponding to high mass fluxes and/or high thermodynamic qualities and low mass fluxes and/or low thermodynamic qualities. For each region, a new model is suggested which resembles the single-phase heat transfer coefficient model but defining an equivalent Reynolds number in terms of the sum of the superficial liquid and vapour Reynolds numbers. The models consider that the superficial vapour Reynolds number plays a major role in controlling the heat transfer coefficient. The model is able to predict the heat transfer coefficient from channels with a hydraulic diameter of 67 μm up to pipes with a hydraulic diameter of 20 mm for several fluids. No noticeable effect of the diameter of the channel, shape or fluid properties on the heat transfer coefficient has been observed for the studied cases.