基于场协同理论的混凝土温度场与水管冷却场换热机理研究

Recently, crack of concrete structure occurs frequently. Pipe cooling technology, which is an important crack control measure, is short of special theory study. Especially, the heat transfer mechanism is not fully recognized, which restricts the effects of temperature control. At present, numerical algorithm of concrete pipe cooling has three problems: (1) can't reflect heat transfer efficiency; (2) existing flaw of heat transfer coefficient model which is built base on traditional thermal resistance theory (3) neglecting the influence of contacting heat transfer between concrete and tube wall. In order to clarify the physical mechanism of heat transfer between concrete and pipe, this subject survey its heat transfer process and divide it into three cohesion and independent process which are contacting heat transfer between concrete and tube wall, heat transfer through tube wall and convective heat transfer in pipe flow. And then, the three heat transfer process is separately studied by thermal elastic contact model, Newton's law of cooling and field synergy theory. Based on the studying, a mechanical coupling analysis program of cooling field, concrete temperature field and creep stress field is developed to realize the numerical analysis of dynamic process of pipe cooling. The key cooling parameters and threshold value are identified by sensitivity analysis and numerical inversion method, and quantitative relationship between cooling effect with cooling mode, arrangement form of pipe, pipe material are determined, and so on. And then the index system and comprehensive evaluation method, which can reflect heat exchanger efficiency, are put forward. The results can provide new theoretical basis and model algorithm for optimization and control of concrete pipe cooling.

近年来混凝土结构开裂现象频繁发生，水管冷却技术作为防裂重要措施，尚缺乏专门的理论研究，对其换热机理认识不足是制约其充分发挥温控效益的瓶颈。目前混凝土水管冷却数值算法还不能体现换热效率，采用的换热系数模型所基于的传统热阻理论尚存在缺陷，以及忽略混凝土与管壁接触传热的影响。为了阐明混凝土与水管换热的物理机制，通过审视其换热过程，将其分立为壁面接触传热、管壁传热和管内对流传热三个既衔接又独立的过程，并利用热弹性接触模型、牛顿冷却定律和场协同理论等方法，分别研究后整合开发出机理性的水管冷却场、混凝土温度场与应力场的耦合分析程序，实现模拟水管冷却动态过程的数值分析，并运用敏感性分析和数值反演等手段，识别冷却关键参数及其界限值，确定冷却效率与冷却方式、布置型式、水管材质等多种因素的量化关系，从而提出能反映换热效率的指标体系及综合评价方法，研究成果可为混凝土水管冷却优化与控制提供新的理论基础和模型算法。

近年来，混凝土结构开裂现象频繁发生，水管冷却技术是温控防裂的重要措施，在诸多大体积混凝土中得到应用。在传统的有限元仿真分析时，一般把水管冷却的作用进行等效或按边界条件处理，难以反映出水管冷却的换热效率。本项目依据对流换热场的协同理论，将大体积混凝土内的水管冷却视为矢量场，即水管冷却场，并结合牛顿冷却定律，建立了水管冷却场的有限元控制方程，并在课题组前期研究成果基础，编制形成水管冷却场、混凝土温度场与应力场的耦合分析程序，实现模拟水管冷却动态过程的数值分析。该程序的边界耦合条件取决于换热系数，为此开展了纯导热条件下混凝土与水管冷却的换热试验，得到了不同加热面、加热温度以及不同水管材质、尺寸下的换热试验数据，其中加热温度设计为40℃、50℃、60℃，水管材质包括铁管和HDPE管，HDPE管包括20mm、25mm及32mm三中尺寸。然后根据试验结果，结合成熟的Dittus-Boelter方程，建立了换热系数关系式。为验证该关系式的合理性，项目开展了混凝土的通水试验，并采用耦合分析程序进行反演计算与分析，结果表明两者结果基本一致，可用于今后的仿真研究中。此外，根据项目的研究需要，还开展了不同初始温度的混凝土绝热温升试验，并进行算例仿真分析，提出了反映换热效率的温度峰值、峰值龄期、降温速率及停水温度等指标体系及评价方法。研究成果可为混凝土水管冷却优化与控制提供了理论基础和模型算法。