Reconsideration of correlation for condensation outside a vertical tube in the presence of noncondensable gas

•We model an externally condensing vertical tube with temperature variation.•We estimate a correction factor of a condensation heat transfer coefficient.•The correction factor depends on the suction parameter.•We propose a simplified correlation without the heat and mass transfer analogy.•The variation of the correction factor can be explained by a double layer model. A correlation of the condensation heat transfer coefficient (HTC) on the exterior surface of a vertical tube in the presence of noncondensable gas is reconsidered taking into account temperature variation of the tube and the coolant. We derive a heat transfer model of the condenser tube by employing energy conservation and the HTCs of the outside and inside of the tube. For the condensation HTC, two different suction factors are examined. We estimate a correction factor of the condensation HTC by fitting a numerical solution of the model into experimental data. As a result, it is shown that the correction factor depends on the suction parameter. Furthermore, we show that the correction factor inevitably diverges at no subcooling because of the heat and mass transfer analogy (HMTA). To resolve this problem, we propose a simplified expression for the condensation HTC without HMTA. Finally, a double layer model, where the concentration boundary layer around the condensing surface is composed of viscous and diffusive sublayers, is developed as a generalization of the two suction factors. The variation of the correction factor against the suction parameter can be explained by the double layer model.