Jet dynamics during vaporization of water drops in hot oil films

We experimentally investigate the vaporization of water droplets immersed in a hot oil film, with moderate temperaturedifferentials of 30-50 degrees C. In this regime, only a fraction of the water droplet vaporizes, but results in a symmetric vertical jet of oil. We provide detailed high-speed imaging of the physical process and quantitatively describe the vapor bubble growth, jet formation, jet speed and satellite droplets resulting from the jet break-up. The principal findings are that the jet speeds (nu(jet) similar to O(1) m/s) are inversely correlated to the oil film thickness (delta similar to O(1) mm), whilst the surface tension-driven break-up results in primary satellite droplets whose normalized diameters also scale inversely with film thickness. Lastly, we provide observations of a water 'peeling' mechanism which occurs inside the vapor bubble, leading to a re-entrant jet that ultimately causes a secondary vaporization event.