Studies On The Nonlinear Characteristics In A Vapor-Liquid-Solid Flow Boiling System

The previous studies on the flow and heat transfer behavior for the system of vapor-liquid-solid flow boiling are basically based on the steady-state and linear analysis methods, and the nonlinear features existing in this complex system are often neglected. It is not favorable for the study and application of this technique. In this paper, deterministic chaos theory is applied to study the nonlinear characteristics of this flow boiling system, so as to supply more solid theory foundation for the vapor-liquid-solid flow technique.On the base of the evaporation installation of TCM, an apparatus and parameter automatic measuring system of vapor-liquid-solid flow boiling was established. Many time-series data of key parameter that could reflect system evolution information of vapor-liquid and vapor-liquid-solid systems are measured for chaotic analysis. The analysis method of deterministic chaos theory and traditional methods are used to analyze the time-series of different parameters.The investigation results show that vapor-liquid two-phase and vapor-liquid-solid three-phase flow boiling systems exhibit chaotic behavior at certain operating conditions. The values of nonlinear characteristic parameters such as correlation dimension and K entropy are different for different steam pressure and solid holdup and multi-values are obtained for the same operation condition. According to the value of D2 for middle-scale, a degree of freedom of 2 is determined, namely, two independent variables are demanded to describe the whole motion of the boiling system. Affected by the flow state in the tube and the position of the inlet of steam, the qualitative and quantitative characteristics of every tube and different axial position of every tube are distinct. The analysis results of time-series of pressure difference and heat-transfer coefficient at the upper part of every tube are basically consistent with those of the signals of wall temperature. The relationship between the nonlinear characteristics and heat transfer characteristics is close.