Flow excursions and pressure drop oscillations in boiling two-phase channel

Abstract

The present work aims to study different types of flow instabilities in two-phase flow heated channel. These flow instabilities have an important effect on the performance of the systems with such channels. A methodology is developed to find the regions in the parametric space where different types of instabilities occur. Three types of instabilities, namely, Ledinegg instability or flow excursion, pressure drop oscillations (PDO) and flow excursion with compressible volume (FECV), are considered here. The first two instabilities, Ledinegg instability, and PDO are quite well known. However, the instability termed here as FECV is rarely studied in the literature. Although FECV is a flow excursion, it has several significant differences from the Ledinegg instability. First of all, Ledinegg instability can lead the system to two alternate equilibrium points depending on the resultant of the perturbation; however, for the system having FECV only one alternative equilibrium point exists. Moreover, the existence of FECV requires the presence of compressible volume in the system, again a feature similar to PDO and in contrast with Ledinegg instability. A detailed physical explanation of these instabilities in terms of the interaction of internal pressure drop and external curves included in this paper. Using bifurcation theory, namely, Hopf and pitchfork bifurcations are identified as the PDO and Ledinegg instability, respectively. Furthermore, FECV is identified by Hopf bifurcation (a feature similar to PDO). Moreover, numerical simulations are carried out at different locations in the parameter space to understand the dynamics of the system. These simulations are presented as time evolution of the variables as well as by trajectories in the phase space.