Film condensation of water in a vertical tube with countercurrent vapour flow

In this experimental investigation of condensation heat transfer, the effec ts of film Reynolds number Re-F, Prandtl number Pr-F and interfacial shear stress tau (V) have been studied independently. For condensation without co nsiderable interfacial shear stress tau (V), correlations from the literatu re are confirmed. In the case of increasing values of tau (V) a reduction i n heat transfer coefficients is found for Re-F < 10 and an increase for 20 < Re-F < 670. With turbulent film the influence of the shear stress disappe ars. Apparently two opposite tendencies which balance each other are respon sible for this: with low film Reynolds numbers, holding back the downward f low of liquid causes a deterioration of the heat transfer; with high Reynol ds numbers, the intensification of waves and turbulent fluctuations causes an improvement. A correlation is suggested which predicts very well the inf luence of the vapour flow on the heat transfer as a function of tau (V) and Re-F. For the friction factor of the two-phase flow, correlations from the literature can be confirmed. (C) 2001 Elsevier Science Ltd. All rights res erved.