Maximum Spreading of Hydrofluoroether Drop Impacting on a Smooth Surface

Abstract

Hydrofluoroether is a dielectric, stable, and environmentally friendly fluid that has been identified as the most potential refrigerant for two-phase cooling and spray cooling. In this study, the impact of a hydrofluoroether droplet on a smooth surface is investigated to deepen the understanding of the droplet–wall interaction during spray cooling. Experimental results show that the impact of the hydrofluoroether droplet on a smooth surface is different from that of water and ethanol droplets. After maximum spreading, the rim formed at the droplet periphery reverses to the center. For the hydrofluoroether with a high boiling point, the inner edge of the rim contracts, but the outer edge is almost immobile. For the hydrofluoroether with a low boiling point, both the inner and outer edges of the rim contract to form a very thin lamella. The intense evaporation of the lamella region leads to the formation of some small droplets at a high impact velocity. Based on a large database collected from the present experiments and previous references, two models for the prediction of the maximum spreading ratio of various liquids in a broad range of impact velocities are developed by introducing the corrections determined by viscosity and surface tension. The present model is superior to the previous semiempirical models, predicting over 97.5% data points in the error bands of ±20% with an MAE of 5.7%.