Droplet impact and Leidenfrost dynamics on a heated post

TL;DR

This paper experimentally investigates how a heated post structure influences droplet impact dynamics, Leidenfrost temperature, and cooling efficiency, revealing improved heat transfer and droplet control compared to flat surfaces.

Contribution

It introduces the effect of a heated post structure on droplet impact and Leidenfrost dynamics, demonstrating enhanced cooling and breakup behavior over flat substrates.

Findings

Post substrate shortens droplet lifetime.

Post increases Leidenfrost temperature by 20°C.

Post improves cooling capacity and prevents droplet bouncing.

Abstract

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 lifetime, 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{\deg}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 provides 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 successfully 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 relatively 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.