Transient Boiling of a Droplet Stream Quenching Microstructured Surfaces

We experimentally investigate the transient flow boiling that takes place when a stream of ethanol droplets starts impinging on a heated copper plate. If the initial surface temperature is sufficiently high, the flow boiling develops from film boiling, to transition boiling and then nucleate boiling, while the flow behavior development shows repelling, contacting, and pooling stages. Copper plates with laser-ablated surface microstructures are used in the tests to investigate the effects of surface microstructures on the boiling regimes. It is found that film boiling can be achieved on microstructured surfaces with lower initial temperatures as compared to the smooth surface. This observation is supported by boiling curve analysis, which noticeably shows the Leidenfrost temperature decreases with increasing surface roughness. It is also found that surface microstructures slightly reduce the Nukiyama temperature. This work is relevant to two-phase spray cooling in high temperature boiling regimes. (C) 2020 Elsevier Ltd. All rights reserved.