复合介质能量输运及蓄热性能的微尺度调控

It is the basis of high efficiency thermal design of energy storage and heat release for the high performance thermal storage material. The promising potentials of the enhancement of heat conduction and thermal energy storage (TES) have been proved valid, which employed nano size supplements to construct multi-scale phase interface configuration in TES material. However, the variations of its thermal physical properties, as well as the enhancement mechanism, still are not clear. Therefore, the guidance for optimal thermal design of TES material is far from enough. The molten salt, as the typical high temperature TES material, is selected as the object of the present proposal. Two key scientific problems, including that of the heat conduction mechanism controlled by temperature variation of composite by nano supplements and molten salt, phonon vibration density on the nano cross-scale interface and construction of interfacial thermal resistance network, are proposed. Based on the scientific problems, the microscale visualization experiments of interfacial transport characteristics for nano particles, as well as the direct measurements of heat conductivity and specific heat capacity of the objective composite will be conducted. By combining the experiments with theoretical analysis, the elastic continuum theory is employed to establish the thermal resistance network prediction model for the nano cross-scale near wall microstructure, in which either interfacial effect or temperature effect will be taken into consideration. The object of this proposal commits to reveal the relationship between the macroscopic transport phenomena, thermal energy storage performance and microscale physical mechanism for composite by nano supplements and molten salt. In further, the study may obtain the effective approach of structure construction and realize the characteristic control for high performance TES composites. The investigations will provide the scientific fundamental for the progress of TES material and technology.

高性能蓄热材料是能量高效存储与释放热设计的基础和前提；利用纳米添加物构建跨尺度相界面结构，在提高材料导热和储能性能方面表现出良好的发展前景，但对其热物理性能的演化规律和强化机理仍缺乏系统认识，尚不能为高性能蓄热材料热设计提供方向性指导。本项目以熔融盐类高温蓄热材料为对象，围绕“温度变化主控的纳米添加物-熔盐复合材料导热机理”，以及“纳米跨尺度界面上声子振动及相界面热阻网络构建”两个科学问题展开探索。以微观尺度下纳米颗粒相界面输运特性的精细观测，以及复合材料热导率和比热容的直接测量为基础，考虑界面效应和温度效应，采用连续介质弹性波理论，针对纳米跨尺度近壁区微结构，建立同时预测导热和蓄热性能的热阻网络模型。厘清不同条件下复合材料物性差异性变化的物理机理及其与微观传递特性之间的关联机制；为高性能复合熔融盐蓄热材料构建及性能调控探索可行技术途径。进而，为蓄热材料及蓄热技术的发展提供科学依据。

太阳能等可再生能源具有时域不稳定波动等特征；能源系统中也存在各类用能负荷的峰谷波动。蓄热可实现热能在时间尺度上的传输，是解决能量供给与需求失衡矛盾的重要途径。高性能蓄热材料是能量高效存储的基础和前提；利用纳米添加物构建跨尺度相界面结构，在提高材料导热和储能性能方面表现出良好的发展前景，但对其热物理机理仍缺乏系统认识，尚不能为高性能蓄热材料热设计提供方向性指导。本项目利用金属和非金属化合物纳米颗粒、碳纳米管等添加物与典型二元熔融盐构建复合蓄热材料，围绕“温度变化主控的纳米添加物-熔盐复合材料导热机理”，以及“纳米跨尺度界面上声子振动及相界面热阻网络构建”两个科学问题，考虑复合介质的固液相态转化过程，在宽广的温度范围内，从输运性质和蓄热性能的实验观测、纳米宏观跨尺度界面热质传输机理的理论建模，以及复合材料热物理性能的调控机制三个方面开展研究。完整揭示出纳米添加物熔融盐复合蓄热材料的热物理性能，获得热输运强化效果的基础数据；以微观尺度下界面输运及储能性能的精细观测和宏观热物性表征为基础，基于连续介质弹性波理论，同时考虑界面尺度效应和温度效应，建立了纳米复合材料输运性能和蓄热性能的预测模型。利用分子动力学方法，揭示出高温熔盐基纳米复合介质界面热质传输机制，发现复合介质性能提升的物理机理；在宽广的温度范围和不同相态条件下，建立了纳米复合材料宏观输运和蓄热性能与微观结构之间的关联机制，模拟蓄热介质实际运行条件设计，实验揭示出纳米高温融盐复合材料蓄放热过程对复合材料稳定性影响规律，探索纳米颗粒分散稳定性改性途径。研究成果为高性能复合熔融盐蓄热材料构建，以及性能的主动调控探索了可行技术途径，有望为蓄热材料及蓄热技术的发展提供科学依据。项目执行期间，发表国内外学术期刊论文28篇，授权发明专利1项，获河北省技术发明一等奖1项；培养博士后1名、研究生8名。按照任务书要求达到了预期研究目标。