Two-phase flow pressure-drop type and thermal oscillations

Abstract

This work focuses on the theoretical investigation of thermal pressure-drop type instabilities in forced convection boiling in a vertical single channel system, with Freon-11 as the working fluid. Experiments with two nichrome tubes of 7.5 mm inner diameter and 9.5 mm outer diameter, one bare and one coated with Linde High-Flux coating, have been carried out. One series of experiments was conducted with constant fluid inlet temperature and various heat inputs, and another with constant heat input and varying inlet liquid temperature. Under the experimental conditions of the study, pressure-drop type and thermal oscillations, as well as pressure-drop type oscillations with superimposed density-wave oscillations, have been observed. A numerical model has been developed to predict the steady-state characteristics of the forced convective two-phase flow and the pressure-drop type and thermal oscillations in a boiling single channel. The drift-flux model is used for numerical predictions. Good agreement between the theory and experiments is obtained.