基于CFD-DEM相变微胶囊液固两相流时空分布及对流传热特性

The flow and heat transfer of microencapsulated phase change material(MEPCM)liquid-solid two phase fluid in heat and mass transfer device is a complex convective heat transfer process with a heterogeneous multiscale structure. And the issues such as solid-liquid phase change mechanism in limited micro space and microscale agglomerate structure of particle and interaction between particles and fluid are concerned. In this project, coupling of computational fluid dynamics (CFD) and discrete element method (DEM) methods are employed to study the movement and heterogeneity distribution of MEPCM particles and MEPCM slurry structure near wall region and the interaction between particle and fluid and wall and heat transfer process. The visualization experiment system is also designed to study the flow pattern and convective heat transfer characteristics of MEPCM slurry in tube. Through the above research work, the time-space distribution characteristics, the movement and phase change process of MEPCM particles and the coupling relationship with fluid flow and heat transfer will be obtained. The energy transfer mechanism and interaction between particle and particle, particle and fluid, particle and wall will be explicated. This project not only has great scientific significance for integrity of solid-liquid two phase flow theory considering phase change, but also has important directive function for large scale engineering application using MEPCM slurry.

相变微胶囊液固两相功能流体在传热装置中的流动与传热是一个多相多尺度结构的复杂运动与传热过程，涉及微小受限空间固-液相变机理、颗粒微观聚团性结构、颗粒间及颗粒与流体间相互作用及传热等诸多问题。本项目拟采用CFD-DEM耦合方法研究相变微胶囊颗粒的运动及不均匀性分布、近壁区微胶囊化相变材料功能流体结构、颗粒与流体及壁面相互作用和对流传热过程；搭建可视化实验测试平台，观测通道内相变微胶囊液固两相功能流体的流动形态以及对流传热特性。通过上述研究获得通道内相变微胶囊液固两相功能流体的时空分布特性；相变微胶囊颗粒运动及相变过程与流体流动与传热的耦合关系；揭示颗粒-颗粒之间、颗粒-流体之间、颗粒-壁面之间的相互作用及能量传递机制。本项目不仅对于完善含有相的转变但没有物质传递的固液两相流基础理论具有重要的科学意义，同时对微胶囊化相变材料功能流体的工程化大规模应用也具有重要的指导意义。

相变微胶囊液固两相流体是由微胶囊化的相变材料和单相液体按一定比例制备而成。因微胶囊颗粒运动效应及相变潜热存在，增加了有效导热系数和有效比热容，使其在热控制和热能输运领域具有广阔的应用前景。但该两相流体在传热装置中的流动与传热是一个多相多尺度结构的复杂运动与传热过程，涉及微小受限空间固-液相变机理，颗粒微观聚团性结构，颗粒之间、颗粒流体之间相互作用及传热等诸多问题。项目基于CFD-DPM及CFD-DEM耦合模型系统研究了单个细小槽道内相变微胶囊悬浮液流动与传热特性，分析讨论了微胶囊颗粒质量分数、微胶囊颗粒粒径、壁面加热热流密度等因素的影响。研究结果进一步明确了相变微胶囊悬浮液强化传热机制，掌握了通道内相变微胶囊颗粒的空间浓度分布规律；得到了不同质量分数、不同粒径、不同加热热流密度时通道内相变微胶囊悬浮液的阻力特性、温度分布规律及强化传热特性。此外，为将相变微胶囊功能流体更好的应用工程实际，项目还开展了多个细小通道集成的热交换器的流体分配均匀性的研究工作，设计出一种热交换器，使其具有较低功耗和较好的传热性能，为相变微胶囊悬浮液的应用奠定基础。通过上述研究，掌握了液固两相流领域内只有热传递、无质传递的强化传热机制，并明确了颗粒效应和相变潜热各自的强化传热能力，为相变微胶囊功能流体的工程实际应用提供了数据支撑。本项目的研究成果不仅对于完善含有相的转变但没有物质传递的固液两相流基础理论具有重要的科学意义，同时对微胶囊化相变材料功能流体的工程实际应用也具有一定的指导意义。