  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.
