Transient film condensation on upward-facing horizontal surfaces

Both analytical and experimental results are presented for a wide range of conditions for transient film condensation on an upward-facing horizontal surface, including the effect of condensate run-off. The appropriate conservation equations are simplified by using several approximations valid for a variety of physical circumstances of interest, and the resulting ordinary nonlinear differential equations are integrated numerically. The theoretical results are shown to depend on a single new dimensionless group. The importance of run-off increases as this parameter increases, and the no-run-off case results when the parameter is zero. The theory correctly predicts zero film thickness for large times and nonzero values of the run-off parameter. A comparison of the predicted transient temperature response with those obtained in the associated experiments suggests the range of validity of the theroetical results. We find fair agreement for nonzero values of the run-off parameter and excellent agreement for zero values of the run-off parameter. Finally, heat-transfer results are presented and the various approximations used are scrutinized. The experimental results suggest that the film thickness is a relatively weak function of time.