Drop impact on a heated pre-wetted wall: deposition-on-crater splash regime

TL;DR

This study investigates the impact of a liquid drop on a heated, pre-wetted wall, revealing a new splash regime where only the wall film produces splashes and deposits, with implications for spray cooling modeling.

Contribution

It introduces a novel impact regime where the drop deposits without splashing, and the wall film alone causes splashes, supported by high-speed imaging and temperature measurements.

Findings

Drop deposits at the crater base, not splashing.

Wall film alone causes corona and splashes.

Validated models for cold spot diameter and temperature.

Abstract

The impact of a liquid drop with high Reynolds and Weber numbers on a wet solid surface typically results in the emergence, rising, and expansion of a corona-like thin jet. This phenomenon is explained by the propagation of a kinematic discontinuity within the wall film. Conventional theories suggest that the corona-forming liquid jet comprises material from the impacting drop and wall film. In this study, the impact of a drop on a wall film is observed using a high-speed video system. Simultaneously, the distribution of the contact temperature at the substrate surface is measured with a high-speed infrared system. The results reveal that heat transfer predominantly occurs within the thin thermal boundary layers in the drop and substrate. Moreover, our experiments show that under our specific conditions, the drop deposits at the base of the crater while only the wall film produces the corona and splashes. Correspondingly, the secondary drops consist only of the heated material of the wall film. This regime has not been previously reported in the literature. The validated models for the diameter of the cold spot, the characteristic time, and the contact temperature developed in this study can be potentially useful for reliable modeling of spray cooling.