Single-droplet vapor-explosion experiments

Single-droplet vapor explosions on contact of hot molten material and a colder liquid are studied. In the five baseline experiments laser-melted iron-oxide droplets of about 0.1 gm at 19000C are injected into a large water pool of about 4 kg at 150C. As the molten iron-oxide droplet enters the water, stable film boiling is established. When a pressure pulse is applied, the vapor film is collapsed and the fuel fragments rapidly resulting in an explosive vapor generation. Pressure and bubble-diameter histories during the explosion are obtained along with the high-speed motion pictures. The work done by the expanding steam explosion bubble is estimated and its thermal-to-mechanical efficiency is 1 to 6%. Debris from the explosion are collected and analyzed. Most of the debris are spherical and 1 to 200 microns in diameter. Based on the methodology developed in the baseline experiments, the effect of variation in the coolant viscosity is studied together with the trigger pressure. The explosion efficiency is decreased as the collant viscosity is increased, and the trigger pressure is decreased. The debris from these tests are also analyzed using the EDS (Energy Dispersive Spectrometer) and the optical micrographs. To explain the experimental result, the well-known theory of a linear Taylor instability is applied. The effect of the coolant viscosity and the trigger pressure on the triggerability of the explosion is discussed