Nonlinear Attribute And Heat Transfer Oscillating Characteristics In Two Phase Closed Thermosyphon

The 21st century is the epoch when people attach importance to the energy and environmental protection. Compared with many other developed countries, there are still large number of problems of energy actuality in our country, for example, low energy utilization level and renewable energy proportion, and the ratio of investment to output falls far behind international advanced level. The main specific performance is the massive hot working device thermal efficiency is comparatively low, much industry valuable afterheat wasted. Therefore, the research on both highly effective energy recycling and heat transfer enhancement technologies, as well as the research and development on all kinds of highly effective heat transfer elements, is always the important domain to which researchers devote themselves.Evaporation, condensation, flow and heat transfers co-exist in the complicated work process, which presents marked non-linear dynamic system instability and chaos characteristics, of heal pipes and thermosyphons. The lack of research on its mechanism and characteristics leads to difficulty in the practical application of heat pipe or thermosyphon, for instance, in the application of control, prediction and design enlargement.Nowadays, the non-linear science has developed rapidly into foreland and hot spot, the research and application of which involve nearly all domains of both natural and social sciences. So far it has become a highly concerned interdisciplinary and important theoretical method. Moreover, with the development of non-linear science and computer technology, more and more people are ready to accept chaos theory and apply it in various research areas.Taking the oscillatory occurrences in thermosyphon process as breakthrough point, the frequency spectrum analysis of temperature fluctuation signal as base, the artificial neural network (ANN) forecast model and non-linear theory as study tool and the unstable phenomenon of heat transfer process, identified as chaos phenomenon, in thermosyphon as basic research objective, this dissertation focuses on the instability and basic mechanism in heat transfer process and disclosing its essence of oscillatory heat transfer with non-linear theory and method describing the chaos phenomenon in the thermosyphon heat transfer.The research work is mainly divided into two parts.The first research part is on unsteady thermosyphon heat transfer process and its temperature fluctuation signal via heat-transfer performance experiment, describing the thermosyphon heat transfer oscillatory and unstable phenomena and studying method and mechanism of ther-mosyphon heat transfer intrinsic enhancement and the influence on heat transfer oscillation. The experimental research contents present the analysis of parameter, which greatly influences thermosyphon heat transfer properties. On completion of the research on filling factor, inclination angle, heat flux density and heat transfer limit, it acquired dependent dimensionless criterion equations under experimental condition. The heat transfer enhancement and bubble suppress experiment are conducted by means of adding third phase to work fluid and helical inserts, drawing the correlation heat-transfer property and the heat transfer criterion equation under experimental condition.Having non-linear characteristic analysis of thermosyphon heat transfer process as a master line, the second part adopts frequency spectrum analysis, artificial neural network, and ARIMA model as tools to try thermosyphon heat transfer vibration process forecast and the dynamic modeling prediction. Furthermore, it adopts mathematical method named invariant transformation similar reduce to change the Partial Differential Equation (PDE), which presents thermosyphon heat transfer process, into the Ordinary Differential Equation (ODE) identical to the Lorenz system in form. By means of symbolic operation process on the platform of Maple (V9.0), it strictly proves by mathematics that thermosyphon process is identical to the Lorenz equation with the same chaos characteristic. Thermosyphon stability, bifurcation, stable critical value and so on are analyzed based on it. The G-P algorithm and the Wolf method are adopted for computer program writing to process the time series data obtained from thermosyphon heat transfer experiment. Obtained by experimental data extraction, the correlation dimension (D2) and the maximum Lyapuonv exponent (λ1) concerning essential chaos characteristics may be used for quantitative description of complexity and the non-linear characteristics in thermosyphon process. They are also the essential criterion to identify thermosyphon heat transfer in chaos and the necessary index to predict and control over the thermosyphon heat transfer chaos. Taking the heat pipe with obvious characteristic of temperature fluctuation, the quantitative research, which is on the relationship between chaos characteristic and operating condition in thermosyphon heat transfer process, compares the inherent conformance in the maximum Lyapuonv exponent distribution and frequency and spectral analysis. As an important index that presents a quantitative description of chaos in thermosyphon heat process, the maximum Lyapuonv exponent may demonstrate more objectively the internal systematic non-linear attributes. The research result indicates that thermosyphon process is characteristic of chaos essence and of intrinsic difference from the stochastic process.Moreover, as an important complement to the non-linear research, the dissertation, based on irreversible thermodynamics theory, analyzes thermodynamics properties of thermosyphon heattransfer process and; trying minimum entropy production theory analysis and optimization from second law of thermodynamics; puts forward a new reasoning of heat pipe operating conditions and design optimization.