孔隙水相变在非饱和土传热传质中的作用机制

The accurate determination and quantitative analysis of temperature response of geo-materials under various thermal boundary conditions are crucial to numerous energy related geo-systems. As for unsaturated soils, the heat and mass transfer under elevated temperatures becomes significantly complicated due to the involvement of phase change where pore water evaporate and condense on the liquid-air interface. The mechanisms of this physical process are still not fully understood. This proposal will study the mechanisms of heat transfer and water migration in unsaturated soils at different temperatures by examining the variations of temperature profile in the soil domain under different thermal boundary conditions. Particularly, this research will investigate the water vapor evaporation-condensation mechanism at pore-scale; and develop the theoretical model of thermal conductivity function correlated with soil water retention and considering the effect of temperature for representative element of unsaturated soils; and finally verify the physical and numerical model for the temperature and water content evolution by the bulk-level soil box tests. This study will establish profound theoretical fundamentals and effective analytical methodologies for the heat and mass transfer problems in unsaturated soils, and provide practical implications on energy storage and management for energy geo-systems.

在许多与能源相关的岩土工程问题中，岩土介质材料在不同热边界条件下的温度响应通常需要准确计算和定量分析。但是在非饱和状态下温度梯度使得土中孔隙水在弯液面处蒸发和凝结。相变的参与使得非饱和土在不同温度下的传热传质变得尤为复杂，其中的物理过程尚未完全理解，试验测试和理论建模都缺乏系统和完整的研究。本项目针对非饱和土传热传质中的相变机制，将不同温度下非饱和土表观导热率的变化作为切入点，分别从孔隙、单元体和宏观不同尺度研究非饱和土在不同温度下的传热机理，重点考察孔隙水相变对土水特征以及土体温度场变化的影响机制。本项目将开展室内细观模型、试样和土箱试验研究，分析热传导、热对流以及相变等主要传热机制对热量传递、温度扩散和水气迁移的影响，建立物理过程清晰、考虑温度影响并与土水特征相关联的非饱和土导热率模型。本项目将对能源岩土工程中能量的存储和管理、环境条件的演化，提供有效的分析方法和坚实的理论基础。

岩土材料的导热特性是多孔介质热质运移行为的重要物性参数，岩土介质的传质传热过程也是能源环境岩土工程领域中诸多共性科学问题及工程难题中的基本物理行为。当前对孔隙介质中孔隙水相变引起的增强型热质运移的机理尚未完全掌握。本项目从水的蒸发速率着手，开展了自由水、毛细水、土水蒸发等一系列模型试验，测量了不同温度和湿度梯度条件下的表观和真实蒸发速率，并细致考察了毛细作用对孔隙水蒸发的影响规律。研究发现了真实蒸发速率与孔隙特征尺寸之间的双对数负线性相关性，并运用CT表征技术分析了孔隙水分布和几何形态对蒸发过程的影响。基于实验测试数据建立了自由水和孔隙水的蒸发速率维象模型。并通过玻璃珠、砂土、粉土的代表性介质的土水特征曲线与渗透率方程与表观蒸发曲线相关联，揭示了微细观土水蒸发的物理机理，为相变引起的孔隙介质传质传热数学模型建立了坚实的理论基础。