Boiling from liquid drops impact on a heated wall

• We identified different boiling morphologies near the Leidenfrost point.
• Boiling includes reflection and explosive rebound, explosive detachment.
• An empirical correlation for predicting the maximum spread factor was provided.
• A model was proposed to describe the dimensionless time scale in drop rebound.
• Preliminary analysis was undertaken for the drop detaching time from the wall.

With aid of high-speed imaging, boiling phenomena near the Leidenfrost point from a single liquid drop impact on a heated solid wall were identified, including reflection rebound, explosive rebound and explosive detachment. Wall temperature was ranging in 182–384 °C, and water, butanol, ethanol and 5.21% NaCl solution were adopted as the fluids due to their different properties. Transitions in the three boiling phenomena were determined concerning effects of Weber number and wall temperature, respectively. For the process of reflection rebound, the maximum spread factor and resident time of the drop are independent of wall temperature. With an increment in Weber number, the maximum spread factor rises, while its effect on the resident time is minor. Empirical correlations were acquired to predict the maximum spread factor and its corresponding dimensionless time as well as the dimensionless resident time. Moreover, formation of the central liquid jet was observed using the NaCl solution drop, which was interpreted by bubble entrainment with violent nucleating. Finally, preliminary discussions regarding drop detaching time in the explosive detachment process were undertaken. Results revealed that the drop detaching time decreases with Weber number, and wall temperature also can affect it.