Molecular Study on Phase Transition of Fluid by a Shock Tube

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The present in vestigators have developed a new method to make a simultaneous measurement of both the phase-transition rate from a vapor to liquid phase and the vapor temperature in a thermodynamic nonequilibrium condition at the vapor-liquid interface.Focussing on the rapid growth of the liquid film formed on the shock tube endwall behind a reflected shock wave, the phase-transition from the vapor to liquid phase and the vapor temperature at the interface have been measured by using optical methods. The phasetransition of methanol vapor and the temperature have been measured from energy reflectance of lights which varies with changes of the liquid film thickness and of the refractive index of the vapor at the interface. A thoeritical analysis of the liquid film growth has also been made by solving one-dimensional gas dynamics equations for the vapor and thermal equations for the liquid film and the endwall. The condensation coefficient of the methanol vapor has been deduced from the conformity between the experiment and the theory.It has been clarified that the condensation coefficient is greatly influenced by thermodynamic states of the vapor, e.g., supersaturated, saturated and superheated states. This phenomenon has been explained by the introduction of the concept of molecular exchange between vapor and liquid. The present results are found to be in good agreement with those of molecular dynaics computer simulation of dynamical processes of evaporation and cindensation.