含相变的多孔介质中汽液两相流动与传热的LBM研究

Liquid-vapor flow and heat transfer including phase transition (evaporation, boiling and condensation) in porous media plays an important role in many technologies in engineering and science. In this work, we plan to apply the lattice Boltzmann method (LBM) to study these complex flows. Through LBM simulations, the micro flow and heat transfer mechanism in these flows will be explored. Specifically, the research involves following objectives. (1) Based on theoretical analysis, the thermal two-phase LBMs including phase-transition effect would be further developed. It is expected the developed method is able to improve the accuracy and the stability for simulations of such complex flows. (2) Through an extensive series of 3D parallel computational studies, the effect of the porous structure, the wetability, gravity and the temperature on the evaporation in the porous media would be identified. (3) Water management inside the gas diffusion layer (GDL), which is made with hydrophobic porous carbon fibre,is key to the performance of the fuel cell. At high current densities, the wettability of the GDL and the temperature field may change. As a result, liquid water might lead to blocked pathways in the GDL and the catalyst layers which in turn limit the maximum achievable power density. Hence, the effect of the wettability, temperature, and porous structure on liquid water distribution will be investigated intensively.(4) For geothermal systems, the porous structure and thermal conductivity of the rock may affect the boiling and the movement of the liquid-vapor interface, we would try to explore the relevant mechanism. Micro-cavity in a structured superheated surface may significantly enhance the pool boiling. The mechanism about how different shapes of pores in mm scale enhance boiling heat transfer would be investigated.This proposed research is of great academic interest. It also shed some light on the management and control of the water in soil, the performance enhancement of the fuel cell, improvement of the geothermal system and the boiling heat transfer enhancement. It may provide theoretical bases for the energy, chemical and algriculture departments.

本项目拟开展含相变（蒸发、沸腾、凝结）的多孔介质中汽液两相流动和传热的格子玻尔兹曼方法(LBM)数值模拟研究，探讨此类复杂流动与传热问题的微观机理。研究内容主要包括：基于理论分析，进一步发展含相变的热LBM两相模型，提高其模拟多孔介质中两相流的精度及稳定性；通过三维LBM大规模并行计算，研究多孔介质中孔隙结构、润湿性、重力和温度对蒸发的影响；针对燃料电池大电流工况下，气体扩散层(GDL)疏水性质（润湿性）及温度发生改变的情况，研究GDL中水分动态分布规律；对于多孔介质中的沸腾问题，考察孔隙结构及导热系数的影响；研究毫米级不同孔隙结构的多孔介质加热面上容积沸腾时强化传热的机理。通过以上微观模拟建立相应宏观预测模型。本项应用基础研究具有重要学术价值，研究成果对土壤水分管理、提高燃料电池效率及寿命、提高地热利用率及提高沸腾强化传热效率等具有技术价值，可为能源化工及农业部门提供重要的理论依据。

含相变（蒸发、沸腾、凝结）的多孔介质中汽液两相流动广泛存在于土壤水分管理、燃料电池、沸腾强化传热等自然界及工业生产中。本研究旨在探讨此类复杂流动与传热问题的微观机理。首先基于理论分析，我们进一步发展了含相变的热LBM两相模型，开发了三组分Shan-Chen多相流模型；发展了曲面无滑移边界处理方法；成果发表在Chem. Eng. Sci.，POF上，我们还改进了多种LBM两相流模型，出版英文学术著作一本。通过LBM及分子动力学方法并行计算，我们研究了二维及三维多孔介质中孔隙结构、润湿性、重力和温度对蒸发的影响，相关成果已发表在Appl. Sci.上及已投稿 Langmuir。针对多孔介质中的沸腾问题，我们研究了气泡的生长规律（发表在Comput. Fluids）以及毫米级不同孔隙结构的多孔介质加热面上容积沸腾时强化传热的机理（已投稿POF）。 针对燃料电池中气体扩散层(GDL)，我们研究了润湿性、温度等对多孔介质中两相流的影响，探讨了其中水分动态分布规律（已发表Comput. Fluids或投稿POF）。这些研究成果可为能源化工及农业部门提供一些的理论依据。