An investigation of microscale explosive vaporization of water on an ultrathin Pt wire

The explosive vaporization of water close to its superheat limit was invest igated at the microscale level using a short (I mm in length) and ultrathin (10 mum in diameter) Pt wire. It was possible to obtain novel visualizatio ns and simultaneously pressure and temperature measurements in the vapor mi croregion, thus accomplishing a step forward in understanding the complex b ehavior of explosive vapor nucleation, growth, and subsequent collapse, des pite experimental difficulties posed by the very short time and length scal es of the phenomena. The temperature results verify (to the best of our kno wledge, for the first time) the limit of superheat reported in the classica l work of Skripov. The nucleation temperature increases with heating rate u ntil a maximum limit is reached. The maximum heating rate was 86 x 10(6) K/ s and a maximum nucleation temperature of 303 degreesC could be obtained. F or the visualization of the very rapid boiling process, a strobe microscopy technique was developed and employed. A clear difference in the mode (homo geneous vs. heterogeneous) of vapor nucleation between high and moderate he ating rates was observed. A fast pressure transducer allowed to capture the acoustic emission from the expanding vapor volume. From these data, the pr essure inside the growing vapor layer and the mechanical energy released by its rapid expansion could be estimated. (C) 2001 Published by Elsevier Sci ence Ltd.