The problem of the contact temperature in droplet-solid heat transfer: experimental analysis

The present work is aimed at analyzing the cooling of hot solid surfaces induced by liquid sprays. In particular, the study is focused on the measurement of the transient contact temperature between impinging droplets and hot solid surfaces.An experimental apparatus was built and setup in order to approach the non-trivial problem of the non-intrusive measurement of a solid-liquid interface temperature after droplet impingement. The solid-liquid interface temperature was monitored from below through a transparent-to-infrared, zero-emissivity material. That material had been coated with a very thin layer of high-emissivity, opaque paint on its upper side, so that it could effectively respond to the infrared camera located below.The experiences collected up to now are described, with particular regard to the approaches used to coat the transparent solid. The results of a few preliminary tests are also reported here, together with considerations about the effectiveness of the proposed method and about the improvements that are currently being implemented to get new and more accurate interface temperature measurements. The obtained results are comparable with the predictions of the theoretical contact temperature equation, which is available in literature.