Droplet impact and Leidenfrost dynamics on a heated post

This study experimentally explores fluid breakup and Leidenfrost dynamics for droplets impacting a heated millimetric post. Using high-speed optical and infrared imaging, we investigate the droplet life-time, breakup and boiling modes, as well as the cooling performance of different substrates. The post substrate leads to a shorter droplet lifetime and a 20 degrees C higher Leidenfrost temperature compared to a flat substrate, attributed to mixed boiling modes along the height of the post and additional pinning. For temperatures below the Leidenfrost point, in the nucleate boiling regime, the post substrate also pro-vides a larger maximum temperature drop than its flat counterpart. The enhanced cooling capacity can be attributed to better droplet pinning and an enlarged droplet-substrate contact area. The post's superior cooling performance becomes especially clear for impact on an inclined surface, where the post success-fully prevents the rolling and bouncing of the droplet, providing a 51% to 180% increase in the maximum local temperature drop. Interestingly, at temperatures slightly above the Leidenfrost point and for a rel-atively narrow range of Weber numbers, droplets on the post substrate rebound rather than break up due to a complex interplay of inertial, capillary, and bubble (thin film) dynamics. Overall, the findings show that a large-scale structure increases the Leidenfrost temperature and enhances droplet breakup and interfacial heat transfer efficiency during non-isothermal droplet impact.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

This study experimentally investigates the fluid breakup and Leidenfrost dynamics for droplets impacting a heated millimetric post. The findings show that the post substrate leads to a shorter droplet lifetime, a higher Leidenfrost temperature, and enhanced cooling capacity compared to a flat substrate.