Separate Effects of Surface Roughness, Wettability and Porosity on the Leidenfrost Temperature of Water

Abstract

Quenching phenomena play a key role in LWR safety, particularly in the reflood phase of a large-break LOCA. It is well known that quenching phenomena are affected by the physico-chemical characteristics of the hot surface, such as surface roughness, wettability and porosity. However, while some general qualitative trends are known, there is a lack of quantitative data on the relative importance and magnitude of these effects. Therefore, we have conducted water-droplet Leidenfrost Point (LFP) tests using custom-fabricated surfaces for which roughness, wettability and porosity were controlled accurately and separately at the nanoscale. This approach reveals that nanoporosity is the crucial feature in efficiently increasing the LFP temperature by initiating heterogeneous nucleation of bubbles during short-lived solid-liquid contacts, which results in disruption of the vapor film.