Confined Evaporation-Mediated Enhanced Residence Time of Levitated Water Drops over Deep Oil Pools.

We observe the impact of bouncing and floating of water drops on a pool of immiscible volatile oil pools at low Weber numbers. The residence time of the impacting drop ranges from a few milliseconds to a few seconds before it sinks into the lighter oil phase. It is hypothesized that the confined evaporation from the volatile oil pool replenishes the thin film draining and results in prolonged floating and delayed sinking of drops into the oil pool. Water drops are released from a low height to impact on volatile hydrocarbon oil deep pools of various volatilities. The floating dynamics and residence times are captured using high-speed imaging. A theoretical model for the residence time has been developed to evaluate the hypothesis. The drop residence time is found to be directly proportional to the volatility of the oil pool in accordance with the hypothesis. The mathematical model incorporating the coupled confined evaporation and film draining dynamics is found to be in well agreement with the experimentally observed residence time. The bouncing-sinking regime map has been developed based on the experimental data.