Transient velocity and temperature distributions in a water drop evaporating on a non-isothermal substrate

The particle image velocimetry (PIV) technique and an infrared camera were used to measure a water drop’s transient velocity and the surface temperature distributions undergoing evaporation. The drop’s bulk temperature was measured using a thermistor. The drop was placed on a substrate, and its initial temperature was varied compared to that of the substrate, which changed the thermo-capillary force acting on the drop. The drop’s bulk and surface temperatures initially varied rapidly with time and then reached a steady value. The time a drop takes to attain the steady value depends on the substrate’s conductivity and, as expected, increased with increasing drop volume.