Pressure and power generation during explosive vaporization on a thin-filmmicroheater

When a liquid is superheated above its boiling point to temperatures near o r at the homogeneous nucleation limit, the energy released could create a s o-called explosive vaporization, if a significant fraction of this energy i s manifested in the form of vapor expansion. In this study, a thin-film mic roheater (100 mu m x 110 mu m) was placed on the underside of a water layer . The surface temperature of the heater was rapidly (6 mu s) raised electri cally, well above the boiling point of water. As a result, rapid vaporizati on took place. Due to its rapid growth, the vapor volume performs mechanica l work on its surrounding and emits acoustic pressure waves. By measuring t he acoustic emission from an expanding volume, the dynamic growth of the va por microlayer is reconstructed where a linear expansion velocity up to 17 m/s was reached. Using the Rayleigh-Plesset equation? an absolute pressure inside the vapor volume of 7 bar was calculated from the data of the acoust ic pressure measurement. The amount of extractable mechanical energy produc ed from the explosive expansion of a vapor microlayer on a thin-film microh eater surface? its rate of production, and the energy conversion efficiency was also quantified in this work. (C) 1999 Elsevier Science Ltd. All right s reserved.