Heterogeneous flashing in water drops

This paper is concerned with the vaporization of superheated water drops. When calculating the heat and mass transfer from drops in this condition, it is not known to what temperatures the drops will superheat before they react through explosive flashing. An experimental study has been carried out in which water drops with diameters between 1 and 3 mm have been suspended on a thermocouple junction in a saturated steam environment within a vessel at pressures up to 9 bar abs. By rapidly depressurizing the vessel at different rates so that the drop superheated, it was possible to measure the temperature of the drop and to observe its reaction. For superheat temperatures up to 5°C the drops experienced only quiescent surface evaporation. For superheat temperatures between 5 and - 18° C, the drops reacted through internal boiling but did not disintegrate. For temperatures above about 18°C the drops reacted by flashing explosively. © 1991