Journal of Fluid Mechanics



Evaporation waves in superheated dodecane


J. R. SIMÕES-MOREIRA a1 and J. E. SHEPHERD a2c1
a1 Departamento de Engenharia Mecânica, SISEA – Alternative Energy Systems Laboratory, Escola Politécnica da USP, caixa postal 61548, S˜o Paulo, SP, Brazil; e-mail: jrsimoes@usp.br
a2 Graduate Aeronautical Laboratory, California Institute of Technology, Pasadena, CA 91125, USA; e-mail: jeshep@galcit.caltech.edu

Abstract

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.

(Received February 3 1997)
(Revised September 18 1998)


Correspondence:
c1 Author to whom correspondence should be addressed.


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