熔融盐纳米复合材料混合蓄放热机理及调控机制

Thermal energy storage is a key process for the continuous operation of high temperature solar thermal power and for the large-scale grid-connection of renewable energy power. Molten salt, as a heat transfer and energy storage media, has become a key research area. Hybrid thermal charging and discharging mechanism and its regulation by high temperature molten salt is very important for the design of single thermal energy storage tank. In order to decrease the cost of thermal energy storage, some researchers added nanoparticles into molten salt to increase its thermal conductivity and specific heat capacity, so that the heat transfer and thermal energy storage performance can be enhanced. However, the most published research mainly focused on thermal properties enhancement of molten salt. Few studies were concentrated on the effect of nanoparticles on the heat transfer and energy storage performance, especially on the hybrid thermal charging and discharging mechanism. In this study, a quaternary nitrated salt with low melting point, developed by our group, has been selected as base materials to prepare molten salt nanocomposites. The study mainly focuses on the optimal preparation method of molten salt nanocomposites, on the thermal properties enhancement mechanism of molten salt nanocomposites, and on the phase change and natural convection heat transfer performance of molten salt nanocomposites. Based on the above researches, the hybrid thermal charging and discharging mechanism and its regulation can be got, which can provide a principle and basis data for the design of single thermal energy storage tank.

蓄能是太阳能高温热发电连续运行及风电、光伏发电规模接入的关键环节，熔融盐作为传热蓄热介质是人们的研究热点。高温熔融盐混合蓄放热机理及其调控机制对于高温单罐蓄热系统设计具有十分重要意义。为了降低蓄热成本，人们向熔融盐中添加纳米粒子，提高熔融盐导热系数和比热容，提高熔融盐传热蓄热特性。但现有的研究多集中在纳米粒子对熔融盐热物性影响研究，对于添加纳米粒子后熔融盐传热蓄热特性，尤其是单罐混合蓄放热机理影响报道较少。本研究以自主研发的低熔点四元混合硝酸盐为基体材料，探求稳定的高性能混合熔融盐纳米复合材料制备方法，探析纳米颗粒对混合熔融盐热物性提升机理，探究混合熔融盐纳米复合材料相变与自然对流传热规律及强化机理，获得混合熔融盐纳米复合材料混合蓄放热机理及调控机制，为熔融盐单罐蓄热系统设计提供理论设计依据及基础数据。

蓄热是太阳能高温热发电连续运行、风电/光伏发电规模接入及清洁能源供暖的关键环节，熔融盐作为传热蓄热介质是人们的研究热点。本项目在筛选出熔盐纳米复合材料批量制备方法的基础上，实验获得了熔盐纳米复合材料最佳制备条件及其热物性与温度的试验关联式，通过熔盐纳米复合材料的微观结构，揭示了熔盐纳米复合材料热物性提升机理；基于熔盐纳米复合材料的热物性，通过实验和数值模拟相结合的方法研究了熔盐纳米复合材料的相变传热规律，分析了导热系数和比热容变化条件下的相变传热影响机制；搭建了熔盐自然对流传热实验系统，分析了不同工况下熔融盐纳米流体在圆柱腔内的自然对流传热变化规律，获得熔融盐自然对流Nu数与瑞利数（Ra）的试验关联式。数值模拟研究了竖直排列两根圆柱、交错排列两根圆柱和多根管排圆柱表面的自然对流传热规律，优选出了最佳的管排间距。基于熔盐自然对流传热规律，设计和搭建了熔盐单罐蓄放热实验系统，通过实验对内置浸没式换热器与圆柱形隔板的熔盐单罐蓄热系统蓄放热性能进行了分析，通过数值模拟对盘管换器和圆柱形隔板进行了优化，研究了盘管换热器布置位置、取热方式和圆柱形隔板尺寸对单罐内熔盐流场的影响，获得了熔盐单罐蓄放热系统内部最佳设计参数。探究了低熔点混合熔融盐纳米复合材料混合蓄放热强化机制，提出调节换热器入口参数、设置混水器和混合熔盐蓄放热PID调控机制，可实现熔盐单罐蓄放热系统释热功率的稳定。本项目研究结果可为低成本熔盐单罐蓄放热系统用于清洁供暖提供思路。项目共发表期刊论文24篇，其中SCI收录期刊论文10篇，EI论文14篇，申请专利10项，授权6项，培养博士生2人，硕士生9人。