Experimental dropwise condensation of unsaturated humid air - Influence of humidity level on latent and convective heat transfer for fully developed turbulent flow

Dropwise condensation is experimentally studied on the lower surface of a 0.03 m × 0.3 m rectangular test section. Turbulent flow develops along an isothermal horizontal 2 m-long section before single-sided condensation is initiated over a 0.1 m × 0.2 m cooled surface. The relative humidity level of unsaturated moist air is controlled by steam injection and ranges from 13% to 94%. Drop size and its distribution are followed from small droplets up to puddle formation just before the appearance of a liquid film. The latent contribution of condensation is determined from instantaneous condensed mass data. Comparison between latent and global heat flux demonstrates that drop growth has secondary effects on the condensation rate and that mass rises almost linearly for dropwise condensation. In addition, transition from droplets to large drops and puddles plays a direct role in global heat flux density and strongly influences convective heat transfer contribution.