【作者】 陈彦泽；

【导师】 丁信伟；

【作者基本信息】 大连理工大学 ， 化工过程机械， 2006， 博士

【摘要】 在对能源和环保高度重视的今天,和许多发达国家相比,我国能源利用的现状还存在许多问题。例如,能源的利用水平低,可再生能源的利用比例低,对能源的投入和产出比远远低于国际先进水平。具体主要表现为,大量的热工设备热效率相对较低,许多价值极高的各种工业余热被白白浪费。因此,对能源高效回收技术和强化传热技术的研究,以及各种高效传热元件的开发研究一直是科技人员致力的重要领域。 热管及热虹吸传热是同时存在蒸发和冷凝、流动和传热的复杂过程,表现出显著的非线性动力系统不稳定性,具有混沌的特征。由于对其机理和特征研究的欠缺,使得热虹吸传热在实际应用中,如控制、预测和设计放大等仍存在一定困难。 非线性科学是当今世界科学发展的前沿和热点,其研究和应用几乎涉及自然科学和社会科学的所有领域,是目前倍受关注的交叉学科和重要的理论方法。特别是随着非线性科学和计算机技术的发展,在各学科研究中,混沌理论的观点越来越被人们所接受,并得到了越来越广泛的应用。 本文的主要目标是以热虹吸传热过程的振荡现象为切入点,以温度波动信号的频谱分析为基础,以人工神经网络模型预测和非线性理论等为研究工具,以热虹吸传热过程的不稳定特征—混沌现象为基本研究对象,在前人研究工作的基础上,探讨热虹吸传热过程不稳定现象和基本机理,利用非线性的理论和方法描述热虹吸传热过程的混沌特征,揭示其振荡传热的本质。 本文研究工作主要分为两部分内容。第一部分通过传热实验,研究热管的不稳定传热过程及其温度波动信号的基本特征,描述实验条件下热管传热波动现象和不稳定现象,研究了热虹吸管内部强化传热的方法和机理以及对传热波动的影响。在实验研究内容中,重点对热虹吸管传热性能具有较大影响的参数进行了分析。完成了对充装率、倾角、热流密度、传热极限等因素的研究,得到了实验条件下的相关准则方程。采用螺旋内置物、添加第三相等方法进行强化传热和抑制气泡的实验研究,给出实验条件下相关传热性能和强化传热准则方程。 第二部分以热虹吸传热过程的非线性特征分析为主线,采用频谱分析,人工神经网络,ARIMA模型等工具,对热虹吸传热振荡过程进行预测和动态建模。进一步采用不变变换的相似约化方法等数学工具,将表述热虹吸传热过程的偏微分方程组演化为具有和Lorenz方程组形式一致的常微分方程组。通过在Maple(V9.0)平台上建立符号运算过程,从数学的角度严格证明了热虹吸传热过程是具有和Lorenz方程完全相同混沌特征的系统。在此基础上,分析了热虹吸传热的稳定性、分岔特征、稳定临界值等问题。应用G-P算法更多还原

【Abstract】 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.更多还原