基于多场协同和火积耗散极值原理的盖板式渗透型集热器优化传热机理研究

Flow and heat transfer performance of glazed transpired collector in clean condition is superior. However, the influence of dust in air has not been studied and the mechanism of optimizing heat transfer is not yet clear. Trough obtaining absorber general equations respectively reflecting flow resistance and heat transfer performance, and studying dust particles force analysis and separation mechanism, the relationship between particle settling rate, structural parameters, operating parameters and relaxation time is got. The changes of field distribution characteristics in collector are investigated due to dust. Then, mathematical models of collectors with circular hole and slit-like perforation are perfected. From the point of the synergy of flow and heat transfer, flow and driving force, and reducing the momentum loss, multi-field synergy relationship is established and multiple field synergy angles are introduced. Using entransy dissipation extreme principle, optimized flow field is obtained. With contrast to actual flow field, the changes of field synergy angles and physical quantities are summarized. Thus, the optimal control approach of heat transfer process is found. The nature of changes of performance evaluation factors with geometry size, inlet air conditions and dust mass is revealed. The results will point out the direction for improving physical quantities distribution in flow field of glazed transpired collector, and provide theoretical guidance for finding new heat collecting technology.

盖板式渗透型集热器在清洁条件下的性能十分优越，但入口空气含尘对集热器性能的影响尚未有人报道，集热器优化传热的物理机制尚不明确。本项目通过获取表达圆孔和冲缝式吸热板流阻和传热特性的通用关系式、分析灰尘颗粒的受力情况以及研究尘粒的分离机理，明确尘粒沉降速率与结构、运行参数和粒子松弛时间之间的关系，掌握积尘前后集热器内各场分布特性的变化规律，完善这两种开孔形式的盖板式渗透型集热器流动和传热数学模型。从流动和传热相协同、流动与推动力相协同以及减小动量损失率的角度出发，建立多场协同关系，引入多个场协同角。利用火积耗散极值原理获取优化流场，与实际流场对比，研究各场协同角与物理量的变化情况，探明对流传热过程的最优控制途径，揭示集热器性能评价因子随几何结构尺寸、入口空气条件和积尘量变化的内因。研究成果为改善盖板式渗透型集热器流场内物理量分布指明了方向，为寻找新的集热技术提供了理论指导。

渗透型集热器因优越的集热性能成为研究热点，但其内部积尘带来的影响还未见报道，优化传热机理尚未完全明确。为此，本项目展开了对清洁和积尘条件下采用圆孔和冲缝式吸热板的盖板式渗透型集热器的特性研究和机理剖析，主要研究内容和结论如下：. （1）通过获取圆孔和冲缝式吸热板两侧与空气间努谢尔特和穿越吸热板处局部阻力系数的通用公式，建立描述盖板式渗透型集热器热传递过程的控制方程组及空气流阻表达式，完善了清洁条件下表达该装置性能的数学模型。. （2）总结了灰尘颗粒在盖板式渗透型集热器内部的沉降行为和部件表面颗粒沉积分布规律，分析了颗粒沉降随颗粒松弛时间、结构参数和运行参数的变化，研究了积尘对集热器换热特性的影响，拟合得到了吸热板吸收率和盖板透过率下降度与颗粒沉积密度的经验关联式，完善了积尘工况下表达该装置性能的数学模型。. （3）探讨了多场协同角随盖板式渗透型集热器结构、运行参数和积尘量变化的协同规律，结合总火积耗散数，指出了优化对流传热过程和流场的控制参数取值范围，揭示了该类集热器高效减阻强化传热的内在机理，同时阐明了多场协同和火积耗散极值原理应用在渗透型集热器上的可行性。. 本项目研究成果为集热器运行效果的准确预测和与建筑热物性的优化匹配提供了更全面的科学依据，通过掌握盖板式渗透型集热器优化传热的机理，从本质上更深入认识了现有渗透型集热技术的对流传热现象，为集热器流场内物理量分布的设计或改进指明了方向，为寻找新的太阳能集热技术提供了理论指导。