Experimental study on the interfacial heat transfer of sessile droplet evaporation using temperature-sensitive paint

The present work is aimed at analyzing changes in the interfacial temperature distribution and interfacial heat flux distribution during sessile droplet evaporation. In particular, two kinds of nonintrusive measurement techniques, temperature-sensitive paint (TSP) and infrared imaging were used simultaneously. TSP was used to capture the interfacial temperature distribution, and then a one-dimensional unsteady transient model was established to obtain the heat flux distribution. An infrared camera was applied to observe the thermal patterns during droplet evaporation from the top view. Three kinds of liquids, pentane, HFE-7100 and hexane, were used during our experiments, and the experimental results show that the contact line profile captured by TSP was consistent with that captured by an infrared camera. Three stages could be observed during droplet evaporation: initial droplet heating, convection cell evaporation and thin film evaporation. Convection cells could be observed in the infrared images during the second stage, and an obvious temperature gradient at the contact surface could also be seen from the images captured by TSP. In addition, the heat flux at the contact line was higher than that at the centre. Finally, the heat dissipation due to droplet evaporation could also be obtained by double integration of interfacial heat flux data with contact area and evaporation time, which further demonstrated the soundness of the present experimental and calculated methods.