(A) semi-empirical heat transfer coefficient for laminar and turbulent film condensation on a vertical surface

Abstract

A new average film-wise condensation heat transfer correlation applicable for both laminar and turbulent film-wise condensation is obtained from published experimental data on a ertical surface without non-condensible gas and with negligible interfacial friction between vapor and condensate film. The functional form of the present correlation is based on the representative existing correlatons for laminar or turbulent film-wise condensation. The least squares method is used to determine the coefficients and the exponents of the present correlation. A non-linear equations system, which comes from the derivatives of sum of square errors of the proposed correlation with respect to each coefficients and exponents, is solved by a variation of Newton``s method which uses a finite difference approximation to the Jacobian matrix. This correlation is compared with experimental data and the representative correlations for laminar or turbulent film-wise condensation The results show that the present correlation agrees well with experimental data. With 95% confidence level, fractional errors of the present correlation lie between -39.2% and 36.3%. The comparison of correlations shows that the present correlation is superior to the existing correlations in the whole range The comparison of correlations for each subdivided regions(laminar, transition-laminar, transition-turbulent, turbulent) also show that the present correlation is superior to the bestperforming correlation in each sub-region. The present correlation is recommanded to be used for the range of 1.75<Pr<5.0 and Re $3.1×10^4$, which involves laminar and turbulent film flow regimes. Especially, the present correlation may be conveniently used in the transition region, where the extrapolated values from the correlations for laminar or turbulent film flow have been used. The present correlation is applied to a model for the reflux condensation. This model is developed to predict the condensation length of the refl...