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天然气水合物是由水分子和气体分子在一定温压条件下形成的一种类冰状笼形化合物.天然气水合物主要存在于海底和大陆的永久冻土区和青藏高原等多年冻土区,是一种潜在的替代能源.在考虑对天然气水合物资源进行开采和考察地球温压变化对含水合物层的影响时,有必要掌握水合物的热物性和含水合物层的有效导热系数,但目前报道的水合物导热系数数据不一、差异很大.水合物是一种非化学计量的化合物,因此很难获得一个不含自由气、自由水的零孔隙率完美样品.利用多孔介质的理论模型对多孔水合物的导热系数进行预测是获得水合物本征导热系数的有效途径之一.我们在一个自行设计的实验台上使用HotDisk系统独特的单面测试技术,并利用瞬态平面热源法测定了含甲烷气的多孔甲烷水合物的有效导热系数,获得该样品的导热系数和温度以及所加压力的关系.为了研究含甲烷气的多孔甲烷水合物的有效导热系数与孔隙率的关系,我们利用自相似的Sierpinski地毯分形模型,先假设多孔介质体系由多孔介质和流体两部分组成,而多孔介质颗粒则由随机分布不相接触的颗粒和带有接触热阻的自相似分布颗粒组成,再通过一维热流假设和采用等价电阻网络(即通过电-热阻模拟分析得到系统的热导率)分别模拟了干砂(含空气)和多孔甲烷水合物样品(含自由甲烷气)导热系数与样品孔隙度的关系,推测了无孔隙水合物样品的导热系数.实验和模拟结果均显示样品的有效导热系数随着孔隙度的增大而降低,样品的有效导热系数在30%的孔隙度时降低了25%.通过分析实验结果和模拟结果发现,无孔隙甲烷水合物样品的导热系数约为0.7Wm-1K-1.
Natural gas hydrate is an ice-like clathrate compound formed by water molecules and gas molecules under a certain temperature and pressure.Gas hydrate mainly exists in permafrost regions such as seabed and continent and permafrost regions such as the Qinghai-Tibet Plateau A Potential Alternative Energy Considering the effects of changes in the temperature and pressure of the Earth on the hydrate layer, it is necessary to know the thermophysical properties of the hydrate and the effective thermal conductivity of the hydrate layer, in order to exploit the gas hydrate resources. Currently reported hydrate thermal conductivity data vary widely, and hydrate is a non-stoichiometric compound, so it is difficult to obtain a perfect sample of zero porosity free of free gas and free water.Using the theory of porous media Predicting the thermal conductivity of porous hydrate is one of the effective ways to obtain the intrinsic thermal conductivity of hydrate.Using HotDisk system’s unique single-side test technology in a self-designed experiment stage, we use the transient planar heat source method The effective thermal conductivity of methane-containing porous methane hydrate was determined, the thermal conductivity and temperature of the sample and the pressure In order to study the relationship between the effective thermal conductivity and the porosity of methane-rich porous methane hydrate, we use a self-similar Sierpinski carpet fractal model, first assuming that the porous media system consists of porous media and fluid two parts, and porous media particles It consists of particles that are not in contact with each other and self-similar particles with contact thermal resistance. The one-dimensional heat flux hypothesis and the equivalent resistance network (that is, the thermal conductivity of the system is obtained through the simulation of electric-thermal resistance) The relationship between the thermal conductivity of dry sand (including air) and porous methane hydrate samples (including free methane gas) and the porosity of the sample were simulated respectively, and the thermal conductivity of the sample without pore hydrate was estimated.The experimental and simulation results show that the sample is effective The thermal conductivity decreases with the increase of porosity, and the effective thermal conductivity decreases by 25% at 30% porosity.By analyzing the experimental results and simulation results, it is found that the thermal conductivity of non-porous methane hydrate samples is about 0.7 Wm-1K-1.