J. Fluid Mech. (1999), vol. 382, pp. 63–86. Printed in the United Kingdom c  1999 Cambridge University Press 63 Evaporation waves in superheated dodecane By J. R. SIM ˜ OES-MOREIRA 1 AND J. E. SHEPHERD 2 † 1 Departamento de Engenharia Mecˆ anica, SISEA – Alternative Energy Systems Laboratory, Escola Polit´ ecnica da USP, caixa postal 61548, S˜ ao Paulo, SP, Brazil e-mail: jrsimoes@usp.br 2 Graduate Aeronautical Laboratory, California Institute of Technology, Pasadena, CA 91125, USA e-mail: jeshep@galcit.caltech.edu (Received 3 February 1997 and in revised form 18 September 1998) We have observed propagating adiabatic evaporation waves in superheated liquid dodecane, C 12 H 26 . Experiments were performed with a rapid decompression apparatus at initial temperatures of 180–300 ◦ C. Saturated dodecane in a tube was suddenly depressurized by rupturing a diaphragm. Motion pictures and still photographic images, and pressure and temperature data were obtained during the evaporation event that followed depressurization. Usually, a front or wave of evaporation started at the liquid free surface and propagated into the undisturbed regions of the metastable liquid. The evaporation wave front moved with a steady mean velocity but the front itself was unstable and fluctuating in character. At low superheats, no waves were observed until a threshold superheat was exceeded. At moderate superheats, subsonic downstream states were observed. At higher superheats, the downstream flow was choked, corresponding to a Chapman–Jouguet condition. At the most extreme superheat tested, a vapour content of over 90% was estimated from the measured data, indicating a nearly complete evaporation wave. Our results are interpreted by modelling the evaporation wave as a discontinuity, or jump, between a superheated liquid state and a two-phase liquid–vapour downstream state. Reasonable agreement is found between the model and observations; however, there is a fundamental indeterminacy that prevents the prediction of the observed wave speeds. 1. Introduction In certain situations, the pressure of a liquid may suddenly be reduced far below the saturation condition without immediate occurrence of boiling. As a result, the liquid becomes superheated or metastable. The superheat is characterized by the difference between the actual liquid temperature and the temperature of the saturated liquid at that pressure. Superheats of up to 200 ◦ C are possible. Following a brief incubation period, explosive evaporation results. Such steam or physical explosions are implicated (Reid 1976, 1983) in some types of industrial accidents. Under specific conditions, described below, a superheated liquid will evaporate in a wave-like process; that is, the phase change process is confined to a discrete and observable zone, which moves into the undisturbed metastable liquid and a two-phase mixture is observed downstream of the wave front (Terner 1962; Grolmes & Fauske 1974; Thompson et al. 1987; Hill 1991; Sim˜ oes-Moreira 1994; Sim˜ oes-Moreira & † Author to whom correspondence should be addressed.