| The mining faces in coal mines are the places with severe heat harm and the focuses of heat harm investigation. This feature of the mining face is mainly caused by three reasons: the comparative concentration of mechanical and electrical equipment and personnel, the higher temperature and larger heat radiating area of surrounding rock, and the goaf air leakage of high temperature. The heat harm management of coal mine mainly includes two aspects, that is, the scientific prediction of coalface air temperature and formulating the reasonable cooling technical measurements. In addition, the air temperature prediction is the basis of the heat harm governance, and the precondition of formulating reasonable cooling technical measurements.The research on the air temperature prediction of coalface mainly includes the following six topics:(1) The effect of the temperature field of surrounding rock and its heat dissipation on airflow in coalface.(2) The effect of the goaf air leakage with high temperature on airflow in coalface.(3) The effect of the heat dissipation of outward transport drop coal on the scraper conveyor.(4) The air temperature prediction and the calculation of chilling requirement of working face under the coupling action of the heat dissipation of surrounding rock and the outward transport drop coal, the goaf air with high temperature and the airflow of working face together.(5) The airflow temperature prediction of intake air roadway of working face during the arrangement of air cooler as well as the calculation of chilling capacity.(6) The air temperature prediction of ventilation shaft and main ventilation roadway, and so on.This dissertation is completed by using theoretical analysis, numerical simulation, laboratory measurement, and field test. By using theoretical analysis, the mathematical model of surrounding rock temperature field, the theoretical model of goaf air leakage with high temperature, the air temperature prediction model under the coupling action of the coalface airflow temperature field and the temperature field of drop coal on scraper conveyor were established. By using the finite volume method, the temperature field calculation software modules and the numerical software module of goaf air with high temperature were developed and combined into the software of the air temperature calculation and chilling requirement of coalface with high temperature. Meanwhile, the mathematical prediction model of air temperature in intake air roadway of working face especially during the arrangement of air cooler was established by using the theoretical analysis and numerically calculated by the computer program, which is programmed by the finite difference method. In addition, the chilling mode and capacity that can meet the chilling requirements of working face were determined. Field sampling and laboratory testing the thermal physical parameters of coal and rock thermal conductivity can provide the basis of the numerical calculation for air temperature prediction. In-situ observation of face ventilation resistance and the changes of air flow and air temperature can validate the results of numerical simulation and optimize the calculation software, finally obtain the scientific and accurate software, which is used to forecast the air temperature of the mining face with high temperature and calculate the chilling requirement. In addition, all of these can provide the basis for chilling design of working face.At the same time of the heat dissipation of coalface surrounding rock to airflow, the temperature decline of surrounding rock can induce the unsteady surrounding temperature field. Specifically, the heat dissipation of surrounding rock is not only related to the original rock temperature, but also mainly depends on the wall temperature induced by the temperature field distribution. In addition, the temperature field and wall temperature of surrounding rock are also directly affected by the air temperature of working face. In other words, the coupling of the surrounding rock temperature field and working face airflow temperature makes the heat dissipation of surrounding rock and the prediction of air flow temperature much harder. As to the continuous advance of working face, the temperature field boundary of coalface surrounding rock is also advanced forward. Thus, the calculation is more complicated.In this dissertation, by introducing a moving coordinate, the unsteady heat conduction problem can be converted to the steady state heat conduction problem, which greatly simplifies to solve the complex problems of the heat dissipation for surrounding rock in the coalface moving boundary. The dimensionless analysis on the different coalfaces of a certain commonality improved the versatility of the calculative results, making it have a universal significance. Moreover, the unified calculation formula of the surrounding rock temperature field in the different locations of working face, which is an important way to solve the coupling of surrounding rock temperature field and the working face air flow. Based on the finite volume method, the surrounding rock temperature field of the coalface was numerically calculated, the dimensionless temperature distribution of surrounding rock was obtained, and the change law was revealed that under the condition of different Biot coefficient and Peclet coefficient, along the direction of face width and coal wall height, the dimensionless temperature of coal wall increased with the increase of Peclet coefficient at the certain Biot coefficient and decreased with the increase of Biot coefficient at the certain Peclet coefficient. The unstable heat transfer criterion and geometry size of mining face, the relationship chart of Biot coefficient and Peclet coefficient were induced, revealing the rule that the unstable heat transfer criterion increases with the increase of Biot coefficient and Peclet coefficient.Due to the existence of working face ventilation pressure difference, the goaf air leakage is inevitable. Both the source and collection of goaf air leakage are not a point but each of them is a face, and along overall length of the face, the leakage air flow, either in or out, exists with different leakage amount. In this dissertation, according to the law of mass conservation and Darcy’s law, the goaf air flow differential equations were established. According to the theory of heat transfer and the law of energy conservation, the goaf gas-solid dual medium temperature field equation was established. According to the law of mass conservation and the Fick’s law, the differential equation of oxygen concentration was established. Based on the multi-coupling goaf air flow field, air temperature field, solid temperature field and oxygen concentration field, the program for analyzing the emission law of goaf air with high temperature was organized. The migration law of goaf air with high temperature was calculated under the conditions of different ventilation resistance, original rock temperature, and air flow temperature. The distribution of the quantity and the temperature of air leakage with high temperature from goaf to working face were deduced.As the continuation of heat dissipation of surrounding rock, the coal with high temperature under the scraper conveyor due to the cutting, mutually exchanged the heat with the face air flow in the process of coal transportation, increasing the difficulty of the coalface air temperature prediction. Because of the influence of the heat source with greater strength and hot air, the change of air flow temperature turned an s-shaped curve along the length of face, which made the air temperature prediction more complicated. According the related knowledge of the heat transfer, each heat source of the working face was analyzed and calculated, and the distribution law of its heat dissipating capacity was obtained. According to the law of mass conservation and energy conservation, based on the coupling action of the heat dissipation of surrounding rock, the heat dissipation of drop coal on scraper conveyor, the goaf air with high temperature and the air flow of working face, together with the effects of other heat sources, the differential equations of air temperature prediction of intake air section and outlet air section for the working face were respectively established. By the finite difference method, the differential equation of coalface air temperature prediction could be transformed into the difference equation, which was used to program the coalface air temperature prediction. According to the former mathematical model of the air temperature prediction, the mathematical calculative model of the coalface chilling requirement was established. The numerical simulation calculation of surrounding rock temperature field in the coalface with high temperature, the numerical simulation of goaf air with high temperature, the coalface air temperature prediction and the chilling requirement were combined into complete software, which was verified and improved by the field test. And the new method of the heat harm degree prediction of the coalface with high temperature and the chilling requirement was established.At present, the chilling of the coalface mainly depends on the cool energy transferred from the cooler layout in the intake air roadway to realize. In addition, the chilling supplement code of the air cooler and its supplement can determine the intake air flow temperature of the coalface, thus affecting the chilling effect of working face. The thermodynamic state of air flow in the intake air roadway is determined by the changes in the thermodynamic state parameters of the intake ventilation shaft and the main intake air roadway, so as to be researched. In addition, in this dissertation, through the numerical calculation, the forward and reverse ventilation modes of the coalface were compared and analyzed. In addition, in the respect of the mine chilling, the forward ventilation mode should be used in the coalface with high temperature as far as possible. Regarding the forward ventilation of the coalface as the presupposition, the mathematical air temperature prediction models were established respectively in the arrangement of single and two air coolers in the intake air roadway, which were difference dispersed. Combined with the engineering background, the corresponding calculation was completed. And the air flow temperature were predicted in the different air temperature with the layout of three, four sets of air cooler or other combinations in the roadway. According to the heat and wet exchange characteristics of ventilation shaft and roadway in the high temperature mine, their simple and convenient method for predicting the air temperature were respectively established.Finally, the chilling requirement of the coalface with the number of 2302 S in Xinjulong mine was calculated by using the software for the air temperature prediction and the chilling requirement of the coalface programmed in this dissertation. In addition, through the comparative analysis, the feasible coalface chilling aims was determined. Under the former chilling aims, the related content was predicted through the air temperature in the intake air roadway of the coalface, the chilling supplement of air cooler and the heat exchange amount of intake air in the coalface were calculated and compared, while four air cooler were ranged in different locations. In addition, the optional layout range of the air cooler for making sure certain chilling effects was determined. The chilling supplement mode and the chilling supplement of air cooler to meet the chilling needs for the coalface were also determined. Through the application of this chilling scheme in the 2302 S coalface, the overall climate of the working face was dramatically improved, which proved that the design was scientific and reasonable. The air temperature prediction theory researched in this dissertation could provide reliable basis for the chilling design of coalface with high temperature.Innovations of this dissertation are mainly in the following three terms:(1) Using the principle mechanism and method of finite volume method, researching and calculating the mathematical model of the surrounding rock temperature field of two-dimensional semi-infinite body moving boundary in the coalface with high temperature, is the new development in the numerical simulation research on the heat dissipation of surrounding rock. In the advancing process of the coalface with high temperature, the mathematical model of surrounding rock temperature field was dimensionless analysed, the general dimensionless redundant temperature and numeral calculation empirical formula of unstable heat transfer were obtained, which is the most important way to solve the coupling action between temperature field of surrounding rock and the temperature field of air flow in the coalface.(2) Utilizing the numerical simulation method, the surrounding rock temperature field of coalface with high temperature, the temperature field of outward drop coal on the scraper conveyor, the goaf air leakage fluid field and the temperature field of air flow in the coalface were coupled and calculated. Especially, fully considering the influence of hot goaf air leakage into the working face, is a new breakthrough of the coalface air temperature prediction method, the new idea and method of the establishment of comprehensive and scientific prediction of the chilling requirement in the coalface with high temperature.(3) Through the numerical simulation method, the temperature of air flow in or out of the air duct with different arrangement of air cooler in the intake air roadway of the coalface were coupled and calculated. And based on the certain calculative results, the chilling supplement mode and capacity meeting the needs of coalface chilling were determined, filling into the blank of air temperature prediction during the arrangement of air cooler in the intake air roadway and the chilling supplement capacity. |
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