Heat And Mass Transfer Of Surrounding Rock And Airflow For Deep Thermal Environment

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.