过热型太阳能腔式吸热器光热转换与吸收机理及多原子气体填充下热流均匀化规律

Solar cavity receiver is a key component in solar power tower system. It plays a dominant role in the solar-thermal conversion. Hence, the thermal performance of solar cavity receiver can directly affect the efficiency of power generation. Most of previous studies only focused on the radiation and convection of simple cavity or cavity with boiling tubes, without considering the influence of the layout of both boiling and superheated tubes. The receiver geometry will become more complex after the superheated tubes are added. It causes the solar-thermal conversion and absorption mechanism of cavity receiver become more complicated. Meanwhile, there are also some problems about energy balancing and optimizing between the boiling tubes and the superheated tubes. With the development of large-scale solar thermal power, high efficiency heat absorption and heat flux homogenization become the two key performance goals of cavity receiver. Therefore, it is necessary to conduct researches on the thermal performance of solar cavity receiver with both the boiling tubes and the superheated tubes. Results from more realistic cavity receiver can more effectively solve the key problems. The present project aims to develop a calculation model for evaluating the thermal performance of solar superheated steam cavity receiver. Based on the Monte-Carlo method and genetic algorithm, this calculation model can be used to explore the solar-thermal conversion and absorption mechanism and to establish the optimization theory of tube layout and the optimum design method of radiant energy flux. Besides, the mathematical model of non-gray gas radiation will also be added to the whole thermal calculation model. Thus the radiative heat transfer and the heat flux homogenization mechanism of cavity receiver filled by polyatomic gases can be studied. The optimal gas composition and working pressure will be raised as well. In addition, combining the polyatomic gases homogenizing method with the multi-aiming point strategy and the zonal absorptivity distribution strategy, the synergistic effect of different heat flux homogenization ways will also be studied. Thus, the homogenization theory on the heat flux of cavity receiver can be enriched. This research will promote the development of the solar thermal power technology in our country.

腔式吸热器是塔式太阳能热发电系统中光热转换的核心部件，其热性能直接影响到光热发电整体效率。以往的吸热器热性能研究局限于腔体或腔体带有沸腾管，而加入过热管后的吸热器内部光热转换与吸收特性将更为复杂，并存在沸腾管和过热管之间的供能平衡与最优化问题。随着太阳能热发电向规模化发展，高效吸热和热流均匀化成为吸热器热性能的两个关键问题，而只有对更切合实际的吸热器进行研究，才能有效地解决关键问题，因此对带过热器的水工质腔式吸热器进行热性能研究很有必要。本项目欲发展太阳能过热水工质腔式吸热器热性能计算模型，基于蒙特卡罗光线追迹法，引入遗传算法，探索其内部辐射传递规律及光热转换与吸收机理，提出沸腾管和过热管的最优化布置理论以及辐射能流分布优化设计方法。在此基础上引入气体非灰辐射模型，探索多原子气体填充下吸热器内部辐射热传递规律与热流均匀化机理，获得最佳填充气体成分和工作压力，并结合多点聚焦、表面吸收特性分区分布等策略，探索不同热流均匀化方式协同作用规律，丰富吸热器热流均匀化理论，促进我国太阳能热发电技术发展。

塔式太阳能热发电系统中，腔式吸热器是光热转换的核心部件，其热性能直接影响到光热发电整体效率。本项目围绕高效吸热和热流均匀化的两个关键问题，通过对已有的计算模型上进行改进，引入了两波段半灰模型和参与性介质散射模型，建立了含参与性介质两波段半灰辐射-对流耦合的过热型腔式吸热器传热数值模型，采取辐射特性改性、吸热面结构优化、吸热器周围风环境改进等手段，开展了基于辐射特性改性的辐射传输机理及热流均匀化技术研究，基于结构改进的光热吸收优化技术研究和基于气幕结构的对流抑制机理研究等。考虑材料对阳光和红外的吸收率不同，研究了表面辐射特性对腔体内部辐射传输的影响机制，揭示了吸热器温度分布及辐射传输方向随吸热面对阳光的吸收率和自身的发射率的变化规律。为解决吸热器内部热流密度分布高度不均匀的问题，采用在腔内填充参与性介质，克服了其它热流均匀化方式时空适应性差等缺点，并大幅降低了热流密度和温度分布的不均匀度约90%。为解决腔体非直接照射面高温所致的热损失严重问题，优化了吸热面结构，大幅降低了非直接照射面的温度约230-300℃，有效提升吸热器光热吸收效率达5%。为解决过热器换热系数低而导致壁温高热应力大的问题，对过热器位置进行优化，发现过热器位置并不影响系统热效率，置与低热流密度区可显著降低部件温度达270℃，减少热应力50-80%，且过热器出口温度不受入射阳光的影响。为减少吸热器对流热损失，采用向下喷射气流，发展了基于气幕结构的对流抑制技术，有效减小腔内对流区域，使自然对流热损失减少28.6%。研究工作实现了吸热器光热转化吸收过程高效和热流密度分布均匀化，为高效太阳能吸热器的科学设计提供理论指导。