【作者】 刘燕；

【导师】 王延吉； 张少峰；

【作者基本信息】 河北工业大学 ， 化学工艺， 2010， 博士

【摘要】 管内流动沸腾过程是流动与沸腾两种基本物理过程的有机结合。而将固体颗粒加入到沸腾两相流动过程中形成汽液固三相流动,能够很好地解决换热管内的防除垢问题,且能达到强化传热目的。但其复杂的流动特性使人们采用已有的研究方法很难揭示系统内存在的非线性特征,从而影响对沸腾多相流系统的认识和该技术的推广应用。本文利用非线性研究方法中的混沌理论作为研究工具,通过自己编写有关计算混沌特征量的程序,考察汽(气)液固多相流动沸腾过程的流体动力学特性,为此类系统的应用提供更加坚实的理论依据。以蒸发器内的竖直换热管为对象,考察了气液固三相、汽液两相及汽液固三相自然循环流动、汽液两相及汽液固三相强制循环流动过程,通过对多相流动沸腾过程的压力波动信号的确定性混沌分析,首次对竖直管内汽(气)液固多相流动沸腾过程的压力波动信号进行了混沌识别,证明此类系统具有混沌特征。另外,对汽液两相自然循环流动过程的温度时间序列进行了较深入分析。理论和实验研究结果表明:大颗粒的气液固三相循环流化床的压力波动信号具有混沌信号的特征。热流密度的变化对多相沸腾系统的功率谱密度函数有一定的影响,且功率谱密度函数的主峰个数及第一主峰的起始频率能反映出流型的变化规律。汽液两相自然循环流动中,随着介质粘度的增加,加热段循环温度降低,循环过程更加稳定。不同表观液速下,随着热流密度的增加,汽液两相强制循环流压力波动信号的分维数有变大的趋势,说明汽液两相流动的复杂程度在加剧,流动接近随机运动。热流密度对汽液两相流压力波动信号的关联维数、Kolmogorov熵和Lyapunov指数均有较明显影响,且都为有限正值,可用这些非线性特征参数预测流型的变化。汽液固三相自然循环及强制循环流动过程中,颗粒体积分率对压力波动信号的关联维数、K熵及Lyapunov指数均有影响,且可从这些特征参数对流动状态进行粗略划分。在沸腾两相流中加入固体颗粒使流动过程更加稳定,且能较好地将流动状态控制在泡状流阶段,有利于系统的稳定操作。更多还原

【Abstract】 Solid particles fluidized by the two-phase boiling mixture may accomplish sufficient deposit removal to keep boiling surfaces clean. This results in a self-cleaning fluidized flow boiling heat exchanger. The particles additionally enhance the heat transfer. This hydrodynamics of a vapor liquid solid boiling flow is very complex. This complexity which results mainly from the strong nonlinearity and structural heterogeneity of particle-fluid flow system, makes simple methods not sufficient for elucidating their intrinsic characteristics. In this paper, deterministic chaos theory is applied to study the nonlinear characteristics of this flow boiling system. And a set of software which were verified and can used to describe actual system dynamic behavior qualitatively and quantitatively were developed and modified. Hydrodynamics of boiling multi-phase flow were studied, so as to supply more theory foundation for the vapor (gas) liquid solid flow technique.Experiments are carried out in the paper to study the feature of pressure fluctuation in vertical tube for boiling multi-phase flow. The gas-liquid-solid, natural circulation of vapor-liquid two phase and vapor-liquid-solid three phase, forced circulation of vapor-liquid two phase and vapor-liquid-solid three phase were studied. On the basis of detailed study on chaos theory of pressure fluctuation in boiling multi-phase flow, such as statistical analysis, quantitative analysis and qualitative analysis, it is evidence that boiling multi-phase flow system is a deterministic system. In addition to, the prime analysis of temperature signal on vapor-liquid two phase natural circulation flow was carried.The investigation results show that the pressure fluctuation signal in coarse circulation fluidized bed with big particles had chaos characterization. And the effects of heat flux on power spectrum density function of the pressure fluctuations are stressed study, and the flow regime transitions is correlation to number and frequency of the main peak value of power spectrum density function. The temperature of circulation liquid decreases with liquid viscosity increasing, and the circulation process becomes more steady in the vapor-liquid two-phase natural circulation. The effects of solid holdup on correlation dimension, K entropy and Lyapunov exponent of pressure fluctuation signal are studied in vapor-liquid-solid three phase natural circulation and forced circulation. And flow pattern can be identified by chaos characteristic parameter. By comparing vapor-liquid two-phase with vapor-liquid-solid three phase, the advantage of mixed solid particle in vapor-liquid two phase boiling is that flow process become more steady and flow regime can maintain bubble flow. In different velocity of flow, the fractal dimension of the pressure fluctuation time series in vapor-liquid two-phase forced circulation increased with increase of heat flux. The Kolmogorov entropy and correlation dimension have change with difference of heat flux. A positive, nonfinite estimate of correlation dimension and Kolmogorov entropy provides further evidence that pressure fluctuation signals behave chaotically. It can be concluded that the flow pattern transition on basis of characteristic parameters can be predicted.更多还原