Dropwise cooling in single-phase evaporation: Infrared experiments on single- and multi-droplet configurations

A large variety of applications in engineering and physics is based on evaporative cooling of solid surfaces: this phenomenon is commonly generated through a spray of water droplets. A quite relevant background is currently available in the field, with specific regard to impingement and heat-transfer mechanisms. However, the thermal transient at the solid-liquid interface still requires some deeper understanding, together with the thermal interac-tion among a certain number of droplets and the solid substrate. The present study work has been aimed at ex-perimentally investigating these physical aspects under single-phase evaporation regime, which is ultimately re-lated to temperatures of the solid surface lower than 100 °C at atmospheric pressure. Moreover, the droplets have been gently deposited (Weber number lower than 30), thus allowing to neglect impact phenomena affect-ing their initial shape. Single- and multi-droplet configurations (two droplets) have been considered to carry out a quantitative investigation of thermal interaction among subsequently released droplets and then refer and com-pare this case to the classic cooling effect induced by a single droplet. Infrared thermography has been here em-ployed to evaluate evaporation and thermal recovery transients at the solid-liquid interface: an experimental apparatus has been built and a suitable methodology has been developed to perform fully non-intrusive meas-urements. Thermal trends are finally expressed as functions of both time and space, thus thoroughly represent-ing the thermal behavior of the considered configurations.