We have observed propagating adiabatic evaporation waves in superheated
liquid
dodecane, C12H26. 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.