液氮冷浸作用下煤体热-流-固多场演化机制研究

This research mainly focuses on thermal-fluid-solid coupling evolution mechanism of coal under the condition of liquid nitrogen soaking, It is of great significance for China to effectively develop coal seam gas, ensure the safety of deep mining, readjust energy consumption structure and solve current social problems such as smog. In order to solve key scientific problems of frost heave damage of coal under the condition of heat transfer, Based on CT scanning technology, seepage law of liquid nitrogen in coal and the action of phase change imbibition will be studied, and the research on frozen area evolution in coal with different water saturation is also included, these studies are intended to uncover the effect of frozen area evolution on distribution of temperature field. With an assumption of local thermodynamic equilibrium, thermal-fluid coupling control equation and thermo-fluid-solid coupled dynamic constitutive model will be built considering the effects of fracture expansion, latent heat of phase change, and heat of vaporization on temperature distribution, to demonstrate the influence of heat conduction, latent heat of phase change, and osmotic pressure on the distribution of temperature field. After three-dimensional reconstruction of CT images of coal before and after liquid nitrogen soaking, numerical simulation of temperature field of liquid nitrogen cold-soaking coal was realized by digital image analysis, and then a numerical solution method will be proposed. These studies have a more comprehensive research on the failure mechanism and strength attenuation mechanism of coal under liquid nitrogen soaking, and provide a theoretical basis for the method of using liquid nitrogen to increase coal permeability.

研究液氮冷浸作用下煤体热-流-固多场演化机制对我国高效开发煤层瓦斯、确保煤层安全开采、调整能源消费结构、解决当前“雾霾”等社会难题具有重要意义。为解决温度演化的冷浸煤体冻胀损伤破坏关键科学问题，本课题以原煤试样为研究对象；基于CT扫描技术，分析煤体液氮渗透规律及相变渗吸行为，探究随冻结深入不同含水率煤体内部已冻区扩展演化范围，揭示冷浸过程中已冻区的移动演化规律对温度场分布的控制作用；基于局部热力学平衡假设，建立考虑裂隙扩展、相变潜热及气化热对温度分布影响的热-流耦合控制方程和冷浸过程中煤体热-流-固动态耦合本构模型，揭示热传导、相变潜热和渗透压力对温度场分布的影响规律，在液氮冷浸前后煤体CT图像的三维重建基础上，采用数字图像数值分析方法，实现液氮冷浸煤体温度场的数值模拟，提出煤体冷浸损伤破坏过程的数值解算方法，揭示冷浸作用下煤体破坏机制和强度衰减机理，为液氮冷浸致裂增透方法提供理论基础。

本课题以研究液氮冷浸作用下煤体热-流-固多场演化机制为研究目标，涉及液氮冷浸作用下煤体的孔隙损伤特征及增透作用、含孔隙-裂隙煤体内部煤体骨架、未冻水含量之间的导热特征、液氮冷浸过程中已冻区的移动演化规律对温度场分布的控制作用、及冻结煤体在冷浸载荷作用下的变形性质和强度特征等研究内容。依据项目申请书内容，经过系统的研究，总体上达到了预期目标。研究取得代表性成果如下：（1）开展了不同液氮注入压力条件下液氮冷浸煤体测试实验，探讨了液氮冷浸作用下煤体的孔隙损伤特征及增透作用；（2）进行了干燥、不同含水率条件下不同变质程度煤体的液氮冷浸温度测试实验，探究了含孔隙-裂隙煤体内部煤体骨架、未冻水含量之间的导热特征，计算了不同冻结温度条件下的煤体内部未冻水含量，研究了不同直径的孔隙水冻结临界温度，探究不同含水率煤体内部已冻区扩展演化行为，得到了冻区的扩展演化对煤体温度场分布的控制作用；（3）构建了考虑裂隙扩展、相变潜热及气化热对温度分布影响的热-流耦合控制方程，采用Comsol Muitiphysics有限元计算平台建立考虑冰水相变作用下的煤体温度场模型，揭示了煤体试样在冷浸过程的内部非等温传递机理；（4）开展了液氮循环致裂后饱水煤样的力学实验研究，构建了冻胀应力计算方程；基于温度应力和冻胀应力作用下的煤岩基质应变行为，建立了煤体孔隙度模型和液氮作用下煤体“三区域”（塑性区、弹性区、原始应力区）数学模型；（5）综合考虑了热-流-固耦合（THM耦合）效应，建立了冷浸过程中煤体热-流-固动态耦合本构模型并进行了解算，为揭示液氮冷浸作用下煤体的破坏机制和强度衰减机理提供理论支撑。以上研究成果为液氮冷浸致裂增透方法提供理论基础。