| Spontaneous combustion of coal seams is one of the main disasters affecting mine production safety.Existing ventilation systems inevitably cause spontaneous combustion of coal in the goaf or spontaneous combustion in adjacent old ponds with air leakage channels.The empty space environment is inaccessible by manpower,so the specific location of the fire source is often difficult to find directly,and other indirect methods are needed.Such a hidden fire source location is not only difficult to find,but also delays the best time for fire fighting.The blindness of fire prevention work in engineering practice is very high,and the fire prevention measures cannot be effective,resulting in low efficiency or even ineffectiveness,resulting in more serious consequences.Therefore,accurate,reliable,and rapid identification of the specific location of the fire source in the goaf,the economics of investment in the fire prevention of the goaf,and the timeliness of fire prevention and suppression of disasters have important theoretical and practical significance.In this paper,through theoretical analysis,laboratory experiments,numerical simulation and neural network analysis methods,the use of the idea of presupposing high temperature heat sources is used to carry out numerical simulation research on the goaf,and the temperature distribution on the return air side,the location of the high temperature point and the maximum are established.The relationship between temperature.First of all,after studying a large number of relevant documents on the mathematical model of the goaf,this paper proposes a new mathematical model of the spontaneous combustion temperature field of the leftover coal in the goaf.The equivalent thermal conductivity term under ventilation conditions replaces the traditional thermal conductivity term and convection.The heat transfer coefficient term establishes a mathematical model of spontaneous combustion of coal in the goaf through theoretical analysis of heat and mass transfer in the goaf.Secondly,through the improvement of the TC3200 thermal conductivity tester,the ventilation function module was added,the laboratory tested the equivalent thermal conductivity of loose coal under controllable air flow,and the experiment took coal samples of different particle sizes from the coal seam of Lu Ning Coal Mine.Through repeated experiments,the functional relationship between different particle sizes,different temperatures,different wind speeds and equivalent thermal conductivity is obtained.Afterwards,according to the law of overburden caving,the continuous distribution function of broken expansion coefficient,porosity and permeability of nonuniform mined-out area is established.The above parameters are used as the basic parameters of numerical simulation analysis.Then,use Fluent to establish a two-dimensional model to simulate the wind flow field and temperature field.Obtained the heterogeneous goaf air leakage flow field distribution and superimposed "three zones" of spontaneous combustion,and preliminarily determined the potential high temperature area,using the method of presetting high temperature heat sources,set up 12 high temperature heat sources in this area,and passed Numerical simulation obtains the temperature distribution law of the goaf,and it is obtained that the temperature distribution on the return side of the goaf conforms to the cubic polynomial distribution along the strike.Finally,the Matlab was used to establish a BP neural network of the highest temperature,the location of the high temperature point and the temperature of the return air side,which contains 2 hidden layers,each with 10 neurons;1 input layer,contains20 neurons,1 output layer,including 3 neurons;the error of the result after training is small,indicating that it is feasible to predict the location of the high temperature point and the maximum temperature by obtaining the temperature distribution on the return air side.The paper has 68 pictures,11 tables,and 59 references. |
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