土壤源热泵条件下非饱和/饱和带水热迁移规律研究

Ground-coupled heat pump systems (GCHP) have become the effective technology to develop renewable shallow-layer geothermal resources due to its good energy saving property and environmental protection. In view of the phenomenon of the heat accumulation and cool accumulation during the actual operation of GCHP, the project will conduct a moisture and heat transfer experiment under both summer and winter conditions with various moisture contents in unsaturated zones and different seepage velocities in saturated zones, through various porous media such as gravel sand, coarse sand, medium sand, fine sand, silt and clay. Based on the physical modeling experiments, and combining with numerical simulation methods, the objectives of this project are to (1) study heat and mass transfer mechanisms during the interaction of the soil water potential gradient with the temperature gradient by analyzing the variation characteristics of the temperature and hydrodynamic fields in unsaturated zones, and (2) to explore the rules of heat transfer and the spatio-temporal variation characteristics of the temperature field in saturated zones, and then (3) to establish coupled moisture and heat transfer models for both saturated and unsaturated zones. The study of this project is not only helpful to broaden the research field of hydrogeology, promote the basic theory of coupled moisture and heat transfer in both saturated and unsaturated zones, but also provides parameters and technical supports for the practical applications of GCHP.

土壤源热泵系统因其良好的节能性和环保性，目前已成为开发可再生浅层地热资源的有效技术。本项目针对土壤源热泵运行中产生"热堆积"和"冷堆积"的现象，以非饱和/饱和带砾砂、粗砂、中砂、细砂、粉砂、粘土等多孔介质为载体，进行土壤源热泵冬、夏运行工况的非饱和带不同含水率与饱和带不同渗流速度下的水热迁移实验。以室内物理模型实验为基础，结合数值模拟技术，分析非饱和带温度场和水动力场的变化特征，研究土水势梯度与温度梯度相互作用下热、质传输机理；探索饱和带热量传输规律及温度场的时空变化特征；建立非饱和/饱和带的水热耦合迁移模型，模拟预测不同工况下多孔介质中的水热耦合迁移规律。该项目的研究不仅有助于拓宽水文地质学的研究领域，促进非饱和/饱和带水热耦合迁移基础理论的发展，而且为土壤源热泵的实际应用提供参数和技术支持。

本项目从系统分析的角度出发，通过控制性实验，探索了非饱和/饱和条件下不同砂土的水热迁移规律。首先研究了砾砂、粗砂、中砂、细砂、粉砂、粘土等砂土在不同含水率条件下的导热系数、比热容、介电常数和基质势的变化规律，并建立了土壤的物性和热物性数据库。基于非饱和一维土柱实验，研究了不同土样类型、不同热/冷源温度和不同初始含水率条件下的土壤热湿迁移规律，建立了非饱和热湿耦合迁移数学模型，并进行了数值计算；基于饱和渗流砂箱实验，研究了不同热/冷源温度、不同渗流速度的水热迁移规律，建立了考虑非均匀渐变渗流、浸润曲线的饱和带水热迁移数学模型。研究发现：在非饱和/饱和带交界区域，存在温度分布异常区，特别是位于浸润曲线下方的饱和渗流区热量堆积现象明显。项目研究成果拓展和深化了对非饱和/饱和区域水热耦合迁移机理的认识，可为地源热泵的实际应用提供参数和技术支持。