Droplet dynamics and heat transfer enhancement via dropwise condensation on helically-finned hydrophobic tube

Abstract

The dropwise condensation is presented on a helically-finned hydrophobic tube that has been fabricated through a facile annealing method, and the condensed droplet dynamics and corresponding heat transfer have been systematically investigated via droplet patterns and heat transfer coefficients (HTCs), respectively. Findings reveal that the HTC increment of helically-finned hydrophobic tube is up to 327% compared with smooth hydrophilic tube at the heat flux of 145 kW/m2 and simultaneously the HTC decreases from 64.2 kW/(m2•K) to 41.5 kW/(m2•K) as the subcooling temperature increases from 2.3 °C to 6.3 °C. This reduction is particularly induced by the dynamic growth of droplet and dripping frequency of the hanging droplet at the bottom of tube which are slower in comparison with droplet nucleation and transport at higher subcooling temperatures. In all, the heat transfer performance of helically-finned hydrophobic tube outperforms the rest of test tubes, which is ascribed to the effective droplet nucleation and coalescence. The grooves of helically-finned hydrophobic tube accelerate the coalescence and sweeping of droplets, shorten growth time of droplets and facilitate the efficient dripping from the bottom of tube. This study provides the technological insights that can help improve the heat transfer performance of industrial condensers.