Modeling and Parametric Analysis of Two-Phase Fluid Stability in Boiling Process in a Thermal Channel

Two-phase flow instabilities are occurred in many systems such as turbo machinery, refrigeration systems, boiling water reactors, two-phase heat exchangers and nuclear reactors. Fluid flow parameters such as pressure drop, stability range in boiling process are the determining factors in design and operation condition of two-phase flow equipment. In this paper, analysis of two-phase flow instability in boiling process is investigated and a simple and comprehensive model is modified to express pressure drop. The defined model and nondimensional numbers give a comprehensive sight of different parameters effect on the oscillations. By using Lyapunov stability analysis, conditions in which instability occurs are identified. The effect of parameters on diagram of pressure drop versus mass flow rate are investigated and the existence of extremum is discussed. The oscillation form varies according to the value of the basic oscillation damping parameter from an elliptical orbit to a quadrilateral, corresponding to the pressure drop curve. In addition, by nonlinear analysis, variation of the oscillation period and amplitude is examined and its relation to the parameter of systems is investigated.