| With the development of economy,the mining intensity of coal resources is increasing,the depth of mine mining is deepening,the environmental temperature of deep mine workplace is gradually increasing,and the number of mines affected by heat damage is also increasing.The high temperature environment will not only endanger the physical health of operators,but also reduce the work efficiency and lead to frequent industrial accidents,which will have a negative impact on mine safety production work.Therefore,it is of great significance to study mine heat damage for safe and efficient mining of coal resources.There are many kinds of heat sources in the coal mining face,which are usually divided into absolute heat source,relative heat source and hot air leaked from the goaf.The influence process of the relative heat source and the hot air leaked from the goaf on the temperature of the working face is complex.The mining position is advancing along the mining direction in the coal seam,the coal seam in front is gradually reduced,the goaf behind the fully mechanized mining machine is increasing,and the surrounding rock boundary and goaf boundary of the coal mining face are constantly changing.The heat dissipation of surrounding rock in coal face belongs to relative heat source,and it depends on the temperature of surrounding rock surface and air flow,which.The premise of air temperature prediction in coal face is to study the law of surrounding rock heat dissipation and the law of air leakage in goaf.First of all,the numerical simulation research on the heat dissipation of the coal face surrounding rock is carried out when the shearer is cutting coal,and the data support is provided for improving the calculation results of the surrounding rock heat dissipation program of coal face through the air inlet roadway surrounding rock temperature field similar simulation experiment.Secondly,the law of air leakage in goaf under different ventilation modes is studied by numerical simulation.On this basis,the prediction model of the temperature of the air flow in the working face is established under multi-factor coupling effect of the heat dissipation of surrounding rock,falling coal,hot air in the goaf,other heat sources and the air flow in the working face.In this paper,theoretical analysis,numerical simulation and similar simulation experiments are used.The heat dissipation of surrounding rock in coal face is simulated.The change of the air temperature and the surrounding rock temperature field of the air inlet have an important influence on the heat dissipation of the surrounding rock in coal face.Using the similar simulation experiment,this paper analyzes the law of the thermal inertia index and the attenuation of temperature wave amplitude of the surrounding rock medium in the air inlet roadway under the influence of the periodic variable temperature air flow.The difference of temperature field distribution in different directions of the air inlet roadway surrounding rock is analyzed,which provides the data support for the supplement and improvement of the calculation results of the surrounding rock temperature field in the coal face.After that,being as another main heat source,the hot air leaked from the goaf of is simulated.Based on the numerical simulation on and the hot air leaked from the goaf,a prediction model of air flow temperature in the working face is established under multi-factor coupling effect of the heat dissipation of surrounding rock,the heat dissipation of falling coal,the hot air in the goaf and the air flow in the working face.The change of air temperature and surrounding rock temperature field of the air inlet roadway has an important influence on the prediction of the air temperature in coal face.Considering the influence of periodic variable temperature air flow,this paper analyzes the law of thermal inertia index and temperature wave amplitude attenuation in surrounding rock medium of the air inlet roadway of coal face by similar simulation experiment.The difference of temperature field distribution in the surrounding rock of the air inlet roadway is studied from the perspective of heat storage.It provides data support for optimizing and improving the wind temperature prediction program of coal face.Heat dissipation of surrounding rock is one of the main heat sources in coal face.In order to study the law of heat dissipation of surrounding rock in coal face,this paper deduces the non steady dimensionless heat balance equation under the condition of coal face advancing.By introducing Fourier number,Bivor number,dimensionless temperature,dimensionless equivalent radius and so on,the dimensionless temperature field equation of propulsive coal mining face is carried out,and the excess temperature is calculated to determine the unstable heat transfer criterion of surrounding rock wall of coal mining face.The dimensionless heat balance equation of unsteady temperature field in propulsive coal mining face is discretized by using finite volume method.The numerical simulation program of surrounding rock temperature field in working face is compiled by VB language,and the cloud map of surrounding rock temperature field distribution in propulsive coal mining face is simulated.The variation of dimensionless temperature on the working face and the coal wall is studied.By changing the key parameters of temperature field control in coal mining face,such as cutting Fourier number,the number of times the shearer cuts the coal wall and the cutting depth of the shearer,the distribution law of unsteady surrounding rock temperature field and and the periodic change law of the unsteady heat transfer criterion of the wall in propulsion coal mining face under different key parameters is analyzed,and the average temperature of the mined coal is calculated by numerical simulation,which provides theoretical support for heat dissipation prediction of surrounding rock of coal mining face.In the numerical simulation of heat dissipation of surrounding rock in coal face,the law of temperature field of surrounding rock under constant temperature ventilation is studied.In fact,the temperature of the air entering the mine should change periodically because of the seasonal influence of the air on the surface,and the air flow temperature in the air inlet roadway of coal face is also affected by the surface air,its temperature also changes periodically.The periodic change of the air flow in air inlet roadway will lead to the formation of a periodically changing temperature field in the surrounding rock of the roadway.The periodic change of the air temperature and the surrounding rock temperature field has an important influence on heat dissipation of surrounding rock in coal face.Through the heterogeneous surrounding rock temperature field similar simulation experiment,the change rule of the temperature field in the anisotropic surrounding rock of the air inlet roadway in the coal face is analysed,and the difference phenomenon of the temperature fluctuation characteristics in different directions of the roadway surrounding rock caused by the different thermal inertia index of the medium is discussed,which provides the data support for optimizing and perfecting the calculation results of the coal face surrounding rock temperature program.The goaf is located behind the coal mining face,and the hot air leakage from goaf is another heat source in the mining face.Due to the existence of ventilation pressure difference in the working face,the air leakage phenomenon in the goaf is caused.The air flow temperature of the working face directly affects the air flow temperature of leaking into the goaf,the air flow into the goaf is related to the air flow in the goaf,which in turn directly affects the air flow temperature in the return air section of the working face.Therefore,the air leakage in the goaf has an important influence on the prediction of the air temperature in the coal face.The difference of ventilation mode in working face has an important influence on the flow field in goaf.This paper analyzes the boundary conditions of the mined-out area under the U-type and Z-type ventilation based on the numerical simulation module of the flow field in the goaf of U-shaped ventilation.According to the law of Darcy and the law of mass conservation,the equation of the flow field of the mined-out area under the Z-type and Z-type ventilation are established.According to the relevant theory and the first law of thermodynamics,the equation of gas and solid temperature field of the mined-out area under the Z-type ventilation is established,and the equation of oxygen concentration field of the mined-out area under the Z-type ventilation is established according to the Fick law and mass conservation.Under the coupling of the above-mentioned fields,the air leakage migration model of the Z-type ventilation of goaf is established.The distribution characteristics of pressure field,velocity field and temperature field in goaf under U-type and Z-type ventilation mode are analyzed,and the distribution velocity and temperature of air leakage in the goaf are studied,which provide theoretical support for the prediction of air temperature in the working face.The shearer cuts coal in the working face,and the coal falling out is transported out of the working face by scraper conveyor.The heat dissipation of the coal falling in the transportation process can be regarded as the continuation of the heat dissipation of the surrounding rock of the working face.The transportation distance of the coal falling changes with the coal cutting position of the shearer,and the heat dissipation of the coal falling in transportation process also changes.Based on the previous model of surrounding rock heat dissipation and air leakage in goaf,the differential equation of air temperature prediction in coal face considering heat dissipation of surrounding rock,heat dissipation of coal falling on scraper conveyor,hot air in goaf and air flow is established.The equation is discretized by the finite difference method,and the corresponding solution program is compiled.The influence of transportation distance on the air flow temperature and coal flow temperature of coal face is analyzed by numerical simulation.The innovations of this paper include the following three aspects:(1)Based on the triangle area method,the algorithm of searching the position of moving node is designed,which can simulate the advancing process of coal face in the fixed coordinate systemBased on the triangle area method,the position of the triangle element which contains the moved node can be determined.According to the interpolation function principle,the moved node temperature can be expressed by the vertex temperature of the triangle element.Before each cycle,the temperature of the moved node is assigned to the original node,and the unsteady surrounding rock heat dissipation in the process of advancing the coal face is simulated in the fixed coordinate system.(2)Through the numerical simulation of surrounding rock heat dissipation of working face,the analysis law of surrounding rock temperature field and the periodic change law of the unsteady heat transfer criterion of the wall under the key control parameters of propulsion coal mining face is revealed.The equation of unsteady dimensionless heat balance of working face is discretized by finite volume method,and the numerical simulation calculation program is compiled.The key parameters of driving condition control in coal mining face,such as mining time,cutting times of coal wall,single coal cutting by shearer,etc.,are selected,and the distribution law of unsteady surrounding rock temperature field and the periodic change law of the unsteady heat transfer criterion of the wall in propulsion coal mining face is studied.(3)The mathematical model of multi field coupling coal face air temperature prediction under the influence of coal falling transportation distance is established,and the corresponding calculation program is compiled to study the influence of coal falling transportation distance on the air flow and coal flow temperature in the coal face.The heat dissipation of falling coal in the process of transportation can be regarded as the continuation of the heat dissipation of the surrounding rock of the coal face.The differential equation of wind temperature prediction under the coupling effect of the heat dissipation of the surrounding rock,the heat dissipation of the falling coal on the scraper conveyor,the hot air in the goaf and the air flow in the working face is established.The influence of the different distance of mined coal transportation due to change of shearer position on the air flow temperature and the coal flow temperature in the working face is carried out by numerical simulation. |
PDF Full Text Request