【作者】 王义江；

【导师】 周国庆；

【作者基本信息】 中国矿业大学 ， 供热、供燃气、通风及空调工程， 2010， 博士

【摘要】 随着矿产资源的大规模开发,埋藏于浅部的矿产资源日益枯竭,大批矿山过渡到深部开采,深部开采与浅部开采最大的区别在于深部围岩体所处的特殊环境。对深部热害矿井来说,包括煤体在内的围岩体散热是矿井热环境最重要的影响因素。本文采用物理试验、数值模拟和理论分析相结合的方法对热害矿井围岩传热传质机理进行了研究,重点对巷道围岩体的热物理性质、巷道围岩非稳态传热传质以及风流对流换热特性进行了分析。对于破碎围岩体,通过微观试验发现其结构符合分形模型,利用图像分形维数计算方法获得了无压力下破碎煤体计盒维数。根据有效导热系数的定义和热阻模拟方法,计算了干燥破碎煤体的导热系数,与实测值吻合;对于孔隙岩体,采用ANASYS模拟了不同孔隙率条件下孔隙规则分布与随机分布两类模型的稳态热传导。结果表明,等效导热系数与固体基质率之间呈双对数线性关系,拟合公式指数与Archie定律一致;含小孔隙且未集中分布岩体的导热系数是各向同性的。采用分离变量法求解了进风流参数恒定条件下巷道围岩体非稳态热传导方程,获得了温度场理论解的显式形式,分析发现,壁面无量纲温度与无量纲传热系数均随Fo增加而不断减小,Bi数越大两者变化幅度越大。提出了适合判断巷道非稳态传热正规状况的公式,计算发现巷道型非稳态传热也存在正规状况阶段,此时围岩过余温度变化率由边界条件和相对位置决定,与初始条件无关;理论计算发现,当Fo=2-12时采用无穷级数第一项代替完整级数误差大,当项数增加到5项时可近似代替完整级数,当Fo>12后才可用第一项代替完整级数。通过自行设计、研制的试验系统对巷道非稳态传热传质规律进行了研究,试验结果表明,均质围岩温度与Fo数可用多项式拟合,当阶数为4时有很高精度,且在正规状况阶段的拟合优度明显高于初始阶段;围岩温度与无量纲半径可用对数关系拟合,在正规状况阶段拟合优度高;巷道壁面温度与进风流温度、风速均为线性关系,对预测某种进风流参数下壁面温度提供了简洁计算公式。试验发现,裂隙对温度场有很大影响,宽度为总长度4%左右的裂隙,其两端温度梯度约占总温度梯度51%;含湿岩体温度场与干燥围岩温度场分布类似,在通风初期含湿岩体近壁端温度变化速率大,是受水分蒸发产生的潜热引起。对围岩体含水率实测可知,相比温度场来说,风流对湿度场的影响明显偏低。在影响区域内,围岩含水率为对数分布,与温度场分布类似,可用Fick第二定律进行分析。计算发现实际巷道中风流流动状态均为紊流,根据实测数据获得了巷道风流的阻力系数公式;采用光滑圆管紊流模型,计算了巷道风流速度分布,并推导了巷道风流温度分布;根据温度分布与速度分布类比定律,采用恒热流模型计算了巷道风流对流换热的准则方程。实测数据表明,沿巷道延伸方向的风流温度为线性分布,验证了恒热流模型分析风流对流换热特性正确;回归了紊流条件下巷道风流对流传热的经验准则关联式,可用于工程计算。对含湿巷道风流温度和绝对含湿量变化进行了实测分析,结果表明风流温度在短时间内趋于恒定,绝对含湿量变化与温度变化相同,说明质量传递与非稳态传热规律类似。更多还原

【Abstract】 With the long-term and large-scale exploiting of mineral resources, high-grade mineral resources buried in the shallow seam are being gradually exhausted, so more and more coal mines have been being faced with the challenge of deep mining. However, the most significant difference between deep mining and shallow mining is the special circumstances of rock mass. For heat harmful coal mine, heat transfer of or rock mass is the most important factor of the thermal environment. Therefore, the research on heat transfer mechanism of rock mass or coal mass is extremely necessary for thermal disaster control. Laboratory test, numerical simulation and theory analysis have been used to study the mechanism of heat and mass transfer of surrounding rock for heat harmful mine. Major issues including characteristic of thermo-physical, characteristic of unsteady heat and mass transfer of airway and heat convection were analyzed thoroughly.For cracked surrounding rock, the structure belongs to fractal model through micro-test. According to the calculation method of fractal dimension for image, the box-counting dimension of cracked coal mass without pressure was calculated, which is about 1.76. Based on the definition of affective conductivity, the heat conductivity of loose coal mass was calculated through the method of thermal resistance, which was equal to test results. For pore rock mass, steady heat transfer of models with different porosity which the distribution of pore was regular and random was simulated by ANASYS. The results show that the effective heat conductivity was isotropic for rock mass without connected cranny. The fitting formula for effective heat conductivity and solid matrix ratio was linear double logarithmic expression, and the index accords with Archie laws.By using the method of separation of variables, the explicit form of analytical solution for temperature field of airway surrounding rock was accepted. The wall surface temperature and unsteady heat transfer coefficient diminish, both of which are concerned with Bi number. The judgment formula of normal status stage of unsteady heat transfer for airway was proposed. Both the calculating and test results show that there is normal status stage for unsteady heat transfer of airway, and change ratio of excess temperature of surrounding rock depends on boundary conditions and is independent of initial conditions. When Fo=2-12, the error was big by using the first item instead of complete series. When the number of terms was 5, the values of first five items and complete series are approximately equal. The first item could replace the complete series only when Fo>12.The laws of unsteady heat transfer of dry airway were studied through self designed experimental system. The results show that the relation between surrounding rock temperature and Fo is polynomial sums, with high precision when the order is 4, and the fitting precision of normal status stage is higher than that of initial stage. The relation between surrounding rock temperature and radius is logarithmic expression, and the fitting precision of normal status stage is also higher than that of initial stage. The relation between wall surface temperature and airflow temperature is linear expression, and the relation between wall surface temperature and wind speed is also linear expression. The simple formula was accepted for calculating wall temperature under some parameters of airflow. Through analysis on concrete masonry test, cranny plays important role on temperature distribution. The ratio of temperature gradient of cranny is about 51% while the ratio of length is only 4%. The laws of unsteady heat and mass transfer for wet airway were also studied. The temperature field of wet surrounding rock is similar to that of dry surrounding rock. The change ratio of wall temperature is much bigger than that of dry surrounding rock on the initial stage because of the latent heat transfer due to water evaporation. The distributing of moisture content was also analyzed. Compared with temperature field, the influence on moisture content was much less. On the disturbance range, the moisture distributing accords with parabola formula, which is similar to temperature field and can be analyzed by the second Fick laws.The flow state of airflow in real airway is turbulent flow. The regression formula of resistance coefficient of airflow was obtained based on the test results. The distributing of velocity and temperature of airflow was analyzed by using the model of smooth pipe with turbulent flow. Based on the model of constant heat flux, the criterion correlation of convective heat transfer was calculated, by using the analogical laws of velocity and temperature. The test results show that the distributing of airflow temperature accords with linear expression, which verifies that the calculated model is correct. The regression expression of experience criterion correlation for turbulent flow was accepted. The parameters of airflow in wet airway were also analyzed. The airflow temperature tends to fixed value in a short time. The law of mass transfer is similar to that of heat transfer.更多还原