Experiment on local convective heat transfer for successive droplets impacting on heated cylindrical surface

Abstract

An experiment was conducted to investigate the underlying heat transfer mechanism when successive droplets impacting on the heated cylindrical surface. The hydrodynamics of droplets were captured by visual method and the local convective heat transfer characteristics were obtained by combining direct measurement and numerical solution of three-dimensional differential equation of heat conduction. The influences of impact frequency, impact velocity and input heat flux were experimentally discussed. It is found that, based on the evolution of local wall temperature, there are three zones along the circumference, i.e., impingement zone, heat diffusion zone and tail detachment zone. Increasing the impact frequency and input heat flux enhances the convective heat transfer performance. However, when the impact frequency is high enough, continuously increasing the impact frequency, the degree of convective heat transfer improvement gradually decreases. The increase of impact velocity mainly enhances the convective heat transfer on the impingement zone and heat diffusion zone, but has little effect on the tail detachment zone. The continuous increase of impact velocity results in the splashing phenomenon and the decrease of convective heat transfer performance. Furthermore, some dimensionless correlations were proposed for predicting the droplet splashing threshold and the local convective heat transfer performance along circumference, respectively.