Effect of vapour velocity on condensation of atmospheric pressure steam on integral-fin tubes

New experimental data are presented for forced-convection condensation of steam on a set of five single, integral-fin tubes. The tubes had identical geometry except for fin spacing, which was varied from 0.25 to 2 mm. The data covered vapour velocities between 2.3 and 10.2 m/s and a wide range of heat fluxes. The best finned tube was that with a fin spacing of 0.25 mm, despite the fact that this tube was fully flooded with retained condensate between the fins. This result, however, is in line with simple theory for condensation of quiescent vapour. The effect of vapour velocity on the heat-transfer coefficients for the finned tubes was somewhat less than for a plain tube, leading to a decrease in vapour side, enhancement ratio with increasing vapour velocity. The data were in poor agreement with a simple, semi-empirical model. The poor agreement was thought due to the fact that the empirical constants in the model were found using data for refrigerants.