Alcohol-induced elevation in the dynamic Leidenfrost point temperature for water droplet impact

In the present study, an experimental investigation is conducted to explore the alcohol additive effect on water droplet impact on a smooth red copper surface and to construct impact regime maps. The observations show that the alcohol additives can effectively facilitate droplet atomization and breakup, and increase the dynamic Leidenfrost point temperature. An interesting phenomenon is noted that the dynamic Leidenfrost point temperatures of alcohol-added water droplets at lower impact velocities are obviously elevated compared with pure water at higher impact velocities. In other words, the addition of a small amount of alcohol additive can effectively compensate for the decrease in the dynamic Lei-denfrost point temperature caused by smaller impact momentum. A new triggering mechanism of the dynamic Leidenfrost effect is proposed with the surface roughness effect taken into consideration. An ap-proximation model based on the pressure balance criterion is then developed to discuss the underlying physics of the alcohol-induced elevation in the dynamic Leidenfrost point temperature. Combining the scaling analysis of vapor layer thickness, a scaling relation of the dynamic Leidenfrost point temperature is derived, and the predictions agree well with present and previous data. It is concluded that the present findings provide an effective method to expedite the transformation from film boiling to transition boil-ing for heat transfer improvement with an increased dynamic Leidenfrost point temperature, simply by adopting alcohol additives to regulate the droplet thermophysical properties. & COPY; 2023 Elsevier Ltd. All rights reserved.

Automated summary

In this study, the impact of alcohol additives on water droplets on a smooth red copper surface was experimentally investigated. The results showed that alcohol additives can enhance droplet atomization and breakup, as well as increase the dynamic Leidenfrost point temperature. It was observed that the dynamic Leidenfrost point temperature of alcohol-added water droplets at lower impact velocities was higher than that of pure water at higher impact velocities, indicating that alcohol additives can compensate for the decrease in the dynamic Leidenfrost point temperature caused by smaller impact momentum. A new triggering mechanism of the dynamic Leidenfrost effect was proposed, taking into account the surface roughness effect. An approximation model based on the pressure balance criterion was developed to explain the underlying physics of the alcohol-induced elevation in the dynamic Leidenfrost point temperature. The findings of this study provide an effective method for improving heat transfer by regulating the thermophysical properties of droplets with alcohol additives.