Discrete Element Numerical Simulation Of Coal And Rock Mass Heat Transfer Performance

In recent years,the increasing consumption of coal has caused the mining depth to be deeper and deeper,and the mining difficulty has also increased,among them,the problem of high temperature heat damage has become one of the inevitable hazards in the mining process.Coal rock mass is an important part of coal seam in mines,the lithological combination of coal rock mass in the coal seam and the thickness of the interface between the rock and coal are often varied,the change of the two will cause the heat transfer in the coal rock mass to change,which directly affects the surface temperature of the coal rock mass,it is easy to cause hidden dangers such as coal seam spontaneous combustion,mine heat damage,gas accidents,etc,therefore,it is of great significance to carry out the thermal conduction study of coal and rock mass with different lithology and different contact surface thicknesses.Based on the above engineering background,this paper uses the method of numerical simulation to analyze the influence of lithology and thickness of the contact surface on the heat transfer performance of coal and rock mass,the main research contents are as follows:(1)For coal and rock masses of different lithology(siltstone,mudstone,sandstone and fine sandstone),conduct two-dimensional numerical simulation research on heat conduction,focusing on the analysis of changes in the temperature field cloud map and the curve comparison map of each measurement point.The research results show: the thermal conductivity of coal rock mass will be affected by its internal coefficient of thermal conductivity distribution,the greater the coefficient of thermal conductivity area,the better the thermal conductivity and the faster the thermal conduction velocity;Among the four types of coal and rock mass with different lithologies,the one with the largest coefficient of thermal conductivity in the rock area,has the strongest thermal conductivity,and the one with fine sandstone in the rock area has the best thermal conductivity.(2)For coal and rock masses with different contact surface thicknesses(2mm,3mm,4mm and 5mm),conduct two-dimensional numerical simulation research on heat conduction,focusing on the analysis of changes in the temperature field cloud map and the curve comparison map of each measurement point.The research results show: the change of the thickness of the contact surface will also affect the distribution of the strength of heat conduction inside the coal and rock mass.Whenthe thickness is 2mm,the heat conduction effect on the high temperature side of the coal rock mass is the strongest,and the overall thermal conductivity is the best;when the thickness is 3mm,4mm,and 5mm,the heat conduction effect on the low temperature side of the coal rock mass is the strongest.(3)Carry out three-dimensional numerical simulation research of coal and rock mass heat conduction under different lithology(siltstone,mudstone,sandstone and fine sandstone)and contact surface thickness(2mm,3mm,4mm and 5mm),focusing on the analysis of the temperature field and the changes in the curve comparison chart of each measuring point,and compare the two-dimensional numerical simulation analysis results with the three-dimensional numerical simulation analysis results.The results show: the numerical simulation results of the heat conduction of coal and rock masses with different lithologies and different interface thicknesses in the state of the three-dimensional model are roughly the same as those of the coal and rock masses with different lithologies and different interface thicknesses in the state of the two-dimensional model,however,the time required for coal and rock mass heat conduction to reach steady state obtained by three-dimensional numerical simulation is more in line with the actual situation,so the three-dimensional model can better simulate the heat transfer performance of coal and rock mass.