Breakup of heterogeneous water drop immersed in high-temperature air

The enhancement of the evaporation rate of a heterogeneous water drop is experimentally investigated. A water drop encapsulating a solid graphite inclusion is instantaneously placed in the very hot air. Under action of the high ambient temperature and due to different thermal properties between water and solid inclusion, the initial drop explodes and creates numerous very small droplets. The vaporization rate of the water drop is strongly increased leading to a short time life of the drop. High speed video recording is used to detail the explosive breakup mechanism of a drop immersed in hot air when its temperature varies in the range between 1073 K and 1373 K. The target of the study is to determine the possible conditions for the increase of the water/air surface of the drop after breakup, i.e., the ratio of the final to initial surface, S_out/S_in, and to verify that this enlargement is responsible of the evaporation rate enhancement. For this purpose, we investigate drops of different initial volumes (5–15 µl) with graphite solid inclusions of different shapes and volumes: 2 × 2 × 1 mm, 2 × 2 × 2 mm, or 2 × 2 × 3 mm. The water surface ratio S_out/S_in is given as function of V_w/V_inc, which is the ratio of initial volume of water drop V_w to the volume of solid graphite inclusion V_inc. The study has shown that the maximum value of the ratio S_out/S_in ≈ 15 can be reached when V_w ∼ V_inc. When, the ratio of S_out/S_in varies in the range 1 to 15. The increase of the evaporating surface is of the highest interest to improve the heat transport and to be used and developed in heat technologies.