红粘土传热特性及其渗流-传热耦合作用机制研究

Red clay is a kind of special soil, which extensively distributed in the southwest region of China. As its unique mineral compositions and micro-pore structures, red clay has a complex heat transfer characteristics and flow-heat coupling mechanism which have not been systematically investigated in home and abroad at present. Therefore, it has hindered the effective utilization of geothermal energy and disaster prevention of related engineering. The project starts from binding forms of pore water and soil particles and its interaction mechanism to study the relationship of the thermal parameters and water content in red clay. Combined with composite medium theory, the calculation models of thermal conductivity with water-soil interaction mechanism have been determined. With the modern testing techniques such as mercury intrusion porosimetry(MIP) and nuclear magnetic resonance(NMR), the microscopic pore structure characteristics and the binding forms of pore water and soil particles can be obtained to investigate the evolution laws of soil-water binding forms and its microscopic distribution during the heat transfer process of red clay and establish the quantitative relationships of the micro-structure characteristics quantities and water content, thermal parameters. Based on small-size model test, the heat transfer mechanism of red clay with the conditions such as flow and water content changing is analyzed to establish the flow-heat coupling theoretical model of red clay and make test verifications. The research not only provides reliable theoretical models and analysis methods for exploiting geothermal energy in red clay region, but also plays an important theoretical guiding role in solving engineering disasters related to red clay.

红粘土是我国西南地区广泛分布的一类特殊土，因其特殊的矿物组成和“二级”微孔隙结构，红粘土具有复杂的传热特性及渗流-传热耦合作用机制。目前国内外对此缺乏系统的认识，阻碍了该地区地热资源的有效利用及相关工程灾害的防治。本项目从孔隙水与土颗粒的结合形态及相互作用机理入手，研究红粘土热特性参数随含水量的变化规律，结合复合介质理论确定水-土相互作用下热导率计算模型；利用核磁共振、压汞试验等技术手段，获取红粘土内部的微孔隙结构分布特征及确定孔隙水与土颗粒的结合形态，探讨红粘土传热过程中土-水结合形态及其微观分布的演化规律，建立红粘土微结构特征量和含水量与热特性参数的定量关系；基于小模型实验，研究在渗流和含水量变化条件下红粘土的传热机制；建立红粘土渗流-热传导耦合的理论模型，并对其进行试验验证。本研究不仅为红粘土地区地热能的合理利用提供可靠的理论模型与分析方法，同时为解决有关红粘土灾害问题提供理论依据。

红粘土是我国西南地区广泛分布的一类特殊土，具有复杂的传热特性及渗流-传热耦合作用机制。目前国内外对此缺乏系统的认识，阻碍了该地区地热资源的有效利用及相关工程灾害的防治。项目组围绕这一课题，在大量试验的基础上，进行了红粘土传热特性及渗流-传热耦合作用机制的理论分析和数值模拟，取得以下主要成果：（1）综合运用X射线衍射、全化学元素分析、鲍格法、K值法等方法计算和确定了所取红粘土试样的矿物成分，桂林、柳州、来宾和武鸣4地红粘土的矿物成分主要为高岭石、三水铝石、针铁矿、石英，其含量各有不同。（2）采用热探针法对红粘土的热物理特性及变化规律进行了研究，发现红粘土的热导率、比热容随体积含水率的增加而线性递增，热导率变化曲线存在临界含水率点；红粘土的热导率、比热容、热扩散率均随干密度的增加而线性递增；采用有效介质理论模型（EMT模型）和并联模型可分段计算广西红粘土的热导率；红粘土的热导率对体积含水率的敏感程度与温度有密切关系，且热导率均随温度的升高而增大；红粘土的热导率变化均随盐浓度的增加而增加。（3）通过容量瓶法、等温吸附法、热分析法等方法综合测定了红粘土中结合水形态演化及数量，发现红粘土在含水量逐渐增加的饱和过程中，土中结合水依次经历了在粒团内孔隙和粒团间孔隙里面形成强结合水、弱结合水和自由水的形态演化过程，由于各形态结合水熵值和水膜“液桥”两者影响的差异，红粘土热导率依次经历了“迅速增长”——“趋于稳定”的两个阶段；在此基础上，通过核磁共振技术和压汞试验对红粘土的微观结构进行了合理分析，系统阐释了红粘土热特性演化的微细观机理。（4）通过改进水通量方程，建立了土壤一维热湿传递理论模型；在此基础上，搭建了土壤一维热湿传递试验平台，进行了3种土壤的一维热湿传递试验；改进水通量方程后的一维热湿传递模型计算值能较好的吻合室内模型试验结果，验证了所建理论模型的正确性。