An experimental study of annular film flow condensation in a micro-fin tube with high mass flux

In the work, the annular liquid film and flow condensation heat transfer of R134a inside four horizontal micro-fin tubes were experimentally studied under mass fluxes of 500-1100 kg m(-2) s(-1). The biggest difference of the tested tubes in geometry is essentially tube diameter and fin helical angle. The influencing mechanisms of mass flux, vapor quality, saturation temperature, fin helical angle, tube diameter, etc., on the heat transfer property were firstly revealed through the liquid film variation. In other words, the transformation rules of the heat transfer coefficient with the experimental variable can be further explained by the liquid film thickness and flow variations. The measured heat transfer coefficients, subsequently, were compared with the calculated values of some existing correlations. After verification, all correlations reported in the researches underestimate the heat transfer coefficient at high mass flux, and the experimental variables, particularly mass flux and vapor quality, have a great effect on the correlation prediction accuracy. To achieve a high-accuracy prediction for the heat transfer coefficient, therefore, on the basis of the theoretical analysis of the continuity, momentum and energy processes in the liquid film, a new correlation was proposed and it can predict the experimental data with an average deviation of 1.61 %.