Experimental analysis of flashing front propagation in superheated water - Effects of degree of superheat, tube inclination, and secondary nucleation

Abstract

A comprehensive experimental investigation on free surface flashing and flashing front (FF) propagation after sudden depressurization of stagnant water is reported. Elaborate high-speed imaging and some limited pressure and temperature recording have been made using two experimental facilities. A new rupture mechanism has been developed, which offers a simple operation where the amount of depressurization can be controlled easily and precisely. For the first time, we have quantified the decrease in delay time with the degree of superheat. Facilities have been designed meticulously to cover a reasonable range of operating parameters and to eliminate spurious nucleations. We recorded the evolution and propagation of the free surface FF over the entire length of the test section (500 mm) and observed the propagation to be linear with a strong dependence on the degree of superheat. For the first time, we also reported the effect of secondary nucleation on the FF with elaborate imaging. Finally, we report our observation of FF dynamics in tubes for the entire range of inclinations for which to date no information is available. Our study reveals many unexplored aspects regarding flashing and more crucially pinpoints some important directions in which meticulous experiments are to be conducted in the future to understand this complex phenomenon better.