热能转化降低混凝土箱体结构表面温度机理研究

Concrete case structures have been used widely in civil engineering，including but not limited to girders of continuous rigid frame bridge，cable towers and piers. Because of solar radiation, the temperature in their external surfaces is not the same as that in their internal surfaces. Hence, concrete cases are prone to temperature cracks. In this study,based on thermal insulation and proactive cooling, we propose a new mechanism and technology to drop concrete surface temperature by using the solar and thermal energy. Research methodolgy is based on computational thermal dynamics and fluid dynamics and labortory studies. The study has three objectives:1) To establish a general formula to calculate the temperature difference between internal and external surface of the concrete cases based on environmental factors such as solar intensity, Reynolds number of air stream and latitude,longitude,suface azimuth and the representative thickness of the concrete case; 2) To study the mechanism of the concrete sleeve and the solar energy powered chiller in reducing concrete case surface temperature and how thermal conductivity of the concrete sleeve, air Reynolds number,and the representative thickness of the concrete case may affect the heat flow and the temperature field of the concrete case; and develop a multi-agent based control methdology for the solar concrete sleeve chiller; 3) To develop a mult-factor based model for computing the temperature field of the solar sleeve-concrete case structure. This study can make a significant contribution,both in theory and in practice, in solving concrete case temperature cracks in bridges.

混凝土箱体结构在土木工程中应用广泛，如主梁、索塔和高桥墩等。但是，由于箱内外温差太大导致其表面开裂现象普遍。本项目拟从隔热和制冷两大机理出发，提出太阳能套筒热能转化降低混凝土箱体结构表面温度的新理论和新技术。项目采用理论分析和实验验证相结合的研究方法，首先构建基于混凝土箱体方位角、结构特征及辐射参数和空气Reynolds number的混凝土箱体内外表面温差计算模式。其次，揭示基于材料物性、空气Reynolds number以及箱体结构参数的太阳能套筒隔热降温机理，提供箱体- - 太阳能套筒扁平制冷机的工作机制和Multi-agent智能控制计算理论与方法，并剖析出热能转化降低混凝土箱体结构内外温差的机理。最后，提供基于多因子分析的太阳能套筒-混凝土箱体复合结构温度场计算模式。项目对于解决桥梁混凝土箱体结构由于内外温差过大引起应力偏大导致开裂的问题具有重要的科学意义和实用价值。

混凝土箱体结构表面开裂现象普遍，严重时会对结构造成重大安全隐患，影响其使用寿命。本项目通过研究混凝土箱体结构内外温差分布规律及其降温途径与机理，从“源头”解决箱体结构开裂问题，具有重要科学意义与广阔应用前景。课题组采用广泛调研、深查资料、理论与数值分析、试验研究、实桥验证等相结合的研究方法和技术路线，较系统、深入地研究了混凝土箱体结构温度场计算模式、太阳能套筒（膜板）与转化制冷机降温机理、复合箱体结构温度场分布、相变储能材料降温机理与试验研究等系列问题，取得了诸多进展：针对箱体温度场分布问题，提出了根据实测数据反演热力学参数并结合瞬态平面传热数值分析获取箱体温度场的计算模式，并运用该模式获取了箱体结构最不利情况下的温差应力裂缝控制的温度阈值；针对太阳能套筒（膜板）及转化制冷机降温机理深入剖析，研发了一种新型高效发电降温膜板及大型混凝土箱体结构新型制冷系统；同时，通过研究相变储能材料降温机理，提出了相变储能材料——混凝土复合箱体结构温度场计算模式，研发了可显著调节混凝土温度场分布的相变储能稻壳灰-混凝土及基于R113相变储能材料的自调温装置，并借助相变储能材料试验研究得以验证。