固液相变储热的传热机理及其拓扑优化研究

Heat transfer enhancement in latent heat storage is of great significance to increase the heat charging/discharging rate, enhance the power adjustability and improve the applicability. Among the methods to enhance heat transfer, heat transfer tubes and fins have obvious advantages in terms of performance stability, manufacturing feasibility, technical maturity and economy, etc. However, their structure optimization mostly relies on experience and lacks theoretical guidance, which makes it difficult to achieve the optimal heat transfer effect..The project aims at realizing high degree of freedom optimization of heat transfer tubes, fins and other heat transfer structures of latent heat storage unit with specific optimization objectives based on topology optimization theory. However, the heat storage and transfer characteristics of the phase change materials are affected by the interface of the heat transfer structure and show a strong coupling relationship with microscopic mechanisms such as supercooling (superheating) and contact thermal resistance, thus affecting the topology optimization of the heat transfer structure at the macroscopic scale. Therefore, the macroscopic topology optimization model of solid-liquid phase change must be modified based on the micro-scale solid-liquid phase change heat transfer mechanism..Due to the complexity of the problem, the project will study the mechanisms of solid-liquid phase change heat transfer and the topology optimization of heat transfer structures in latent heat storage, following the gradual principle of "from micro to macro, from theory to experiment" and combining with theoretical analysis, numerical simulation and experimental verification method. The project will realize the high degree of freedom optimization of latent heat storage unit based on specific optimization objectives and enhance the technological innovation ability of China in the field of heat storage.

固液相变储热的强化传热问题对提升储放热功率、加强功率可调性和提高适用性具有重要意义。在强化传热方式中，传热管与肋片在性能稳定性、制造可行性、技术成熟性和经济性等方面具有明显优势，但其结构优化多依靠经验，缺乏理论指导，难以达到最优传热效果。.本项目旨在基于拓扑优化理论实现明确优化目标下相变储热单元传热管、肋片等传热结构的高自由度优化。但是，相变材料的储热与传热特性受传热结构界面影响而表现出与过冷（过热）和接触热阻等微观机理的强耦合关系，进而影响宏观尺度的传热结构拓扑优化。所以，宏观尺度固液相变拓扑优化模型必须基于微尺度固液相变传热机理进行修正。.基于问题的复杂性，本项目将遵循由微观到宏观、由理论到实验的循序渐进原则，结合理论分析、数值模拟和实验验证对相变储热的固液相变传热机理及其传热结构的拓扑优化开展研究，实现基于明确优化目标的相变储热单元高自由度优化，提升我国在储热领域的技术创新能力。

本项目以固液相变储热的传热机理及其拓扑优化研究为切入点，从材料机理、装置优化和系统集成三个层面对相变储热开展了研究。.材料机理层面，基于分子动力学研究了纳米颗粒对无机盐相变材料比热容的影响，阐明了纳米颗粒表面变化在增强无机盐相变材料比热容中的基本作用，揭示了在液态和固态下纳米颗粒对无机盐相变材料比热容的不同影响机制。研究发现，比热容的增强只发生在压缩离子层内部，HCl处理的亲水纳米颗粒对无机盐相变材料比热容的增强作用更明显。.装置优化层面，基于拓扑优化理论对储热单元内的肋片与流道开展了优化，研究了数值参数对最佳肋片构型的影响机制，得到了熔化过程自然对流对最佳肋片构型的影响，讨论了传热与流动权重系数与流道结构的关联机制，探究了优化流道结构的传热与流动特性。研究发现，优化肋片呈树枝状分布，自然对流会影响肋片分布；传热效果好的优化流道更加弯曲。建立了小直径比堆积床的三维随机堆积模型，得到了小直径比堆积床孔隙率在径向上的统计变化规律，研究了堆积床内部流动、传热及储热性能与径向孔隙率的耦合关系，探究了不同进口温度、流量下堆积床流动、传热与储热特性。研究发现，堆积床相变储热单元的流动、传热与储热特性沿径向呈现波动性变化。建立了梯级相变单元的数学模型，讨论了设计参数对相变单元纯储电模式和热电联供模式下热力学性能的影响意义。研究发现，梯级相变单元的热电联供模式往返效率可达62-100%。.系统集成层面，对比了卡诺电池采用显热材料时的热力学与经济性指标，研究了相变材料对布雷顿循环卡诺电池储能密度和热力学损失的影响，探讨了有机朗肯循环卡诺电池在热电厂调峰的适用性。研究发现，采用跨临界CO2循环和Therminol VP-1导热油的卡诺电池往返效率达68%，并有最优的热经济指标；相变材料将系统储能密度提升了5.5%；配备卡诺电池的热电厂可满足94%峰值负荷。