Infrared experiments of dropwise cooling: Single- and multi-droplet configurations in single-phase evaporation

A wide number of engineering applications is based on evaporative cooling, which is usually performed through a spray of water droplets: the scientific background in the field is considerable, notably about heat-transfer mechanisms. This work has been focused on investigating dropwise cooling of hot solid surfaces under single-phase evaporation regime (i.e.: temperature of the solid substrate lower than 100 °C at atmospheric pressure). The droplet Weber number has been kept lower than 30 (gently deposited), thus yielding to negligible impact phenomena on the initial shape of the droplets. Both single- and multi-droplet configurations (two droplets) are here considered to quantitatively investigate the thermal interaction among droplets subsequently released and compare this latter case to the cooling effect induced by a single droplet. The thermal transient during evaporation and subsequent recovery process has been here experimentally evaluated by infrared thermography: an experimental apparatus has been built and a suitable methodology has been developed to measure the solid-liquid interface temperature. The thermal trends are then expressed as functions of both time and space, thus allowing to determine the thermal behavior of the considered configurations.