Temperature Distribution Of Porous Media Including Coal And Rocks With Internal Heat Source Under The Effect Of The Coupled Radiative And Convective Heat Transfer

Fires in coal mines mainly occur in the goaf,and high temperature points are the precursors of spontaneous fire in the goaf or the key information sent by the fire area.Since the goaf or fire area is mostly porous media including coal and rocks,based on the inversion technology to identify and locate the high temperature points in the porous media,it can effectively reduce the risk of spontaneous combustion in coal mines.The premise of this technology is to fully grasp the interior and boundary temperature distribution of the porous media including coal and rocks.Due to the complex and changeable internal pore structure of porous media,it is difficult to obtain the internal and boundary temperature distribution of the fire zone with the experimental method under the complex fire zone field conditions and limited test conditions,and numerical simulation methods can make up for this deficiency.Therefore,based on the premise that numerical simulation methods are needed to obtain the temperature distribution of porous media with internal heat sources,this paper deals with the method for solving the radiation transmission of porous media,the numerical simulation method for coupled radiative and convective heat transfer in porous media including coal and rocks,and the temperature distribution of porous media including coal and rocks with internal heat sources is studied.Firstly,compare and analyze the existing porous media convection heat transfer model and heat radiation transfer solution method.It is found that when the radiative properties of air are not considered,for the energy exchange between the fluid and solid phases,a more accurate solid phase temperature can be obtained by using a local non-thermal equilibrium heat transfer model that considers the temperature difference between the fluid and solid phases.The distribution can meet the requirement of obtaining accurate solid phase temperature when solving heat radiation transfer in porous media.In addition,by comparing the thermal radiation transfer solution methods,it is found that for the porous media including coal and rocks,which has a large optical thickness and complex internal geometric shapes,the Monte Carlo method can be used to solve the thermal radiation transfer inside the porous media to obtain more accurate calculation results.Therefore,the coupled radiation and convection heat transfer simulation method based on the local non-thermal equilibrium heat transfer model and the Monte Carlo radiative transfer solution method can more accurately simulate the convective heat transfer and radiative heat transfer in porous media coal and rocks.Secondly,the radiative transfer process of the solid phase of the porous medium is solved based on the Monte Carlo method,the corresponding program of radiation transfer solving module is compiled.Then,partition the model,and multi-partition parallel computing is realized.Based on the optimization program,the influence of the photon number and mesh number on the precision of Monte Carlo radiant transfer solution module is analyzed,and the results showed that with the increase of photon number or grid number,the distribution of radiative transfer factor value more and more smooth,the distribution of symmetry for the center with launch unit is higher,but the accompanying cost of time is also higher.In addition,the reliability of the radiation-convection coupled heat transfer simulation method based on the local non-thermal equilibrium heat transfer model and the Monte Carlo radiative transfer solution method established in this paper was verified,and it was found that the calculation results of this method are in good agreement with the experimental results of the literature.Then,the critical heat source temperature that porous media including coal and rocks needs to consider the thermal radiation effect is analyzed.The results show that: When the heat source temperature is 325 K,the temperature distribution of pure convection heat transfer is very close to that of coupled radiation and convection heat transfer,so this temperature is the critical heat source temperature to consider the thermal radiation effect in porous media including coal and rocks.Finally,the coupled heat transfer numerical simulation method based on the Monte Carlo radiative transfer solution method and the local non-thermal equilibrium heat transfer model is applied to analys the effects of porosity,particle diameter,heat source intensity and heat source depth on the surface and internal temperature distribution in the stacked porous media model with internal heat source.The results show that with the increase of porosity or particle size,the final heat source temperature at the heat source position decreases gradually,and the influence range of the heat source in the horizontal and vertical directions also tends to shrink.The temperature rise range shown on the upper surface of the model gradually decreases to a small extent,while the maximum temperature value of the upper surface does not change much.And with the increase of heat source intensity,the temperature and influence range of heat source increase,and the range of temperature rise and the maximum temperature on the upper surface of the model also show an upward trend.Then,with the increase of depth of the heat source,the temperature at heat source position gradually increased and the temperature rise scope expanding gradually.In addition,it also shows that the temperature rise scope of the upper surface of the model gradually with the increase of depth of the heat source,but its highest temperature of the upper surface gradually decreases.The coupled radiation and convection heat transfer simulation method of porous media including coal and rocks with inner heat source was verified by this research,and through the analysis of the simulation results under various influence factors,provide an exploratory for grasp the internal and surface temperature distribution of porous media including coal and rocks with inner heat source.However,due to the complexity of heat transfer in porous media including coal and rocks,some influencing factors have not been fully considered,which makes the understanding and exploration have certain limitations.Therefore,further in-depth studies should be carried out on this basis in the future,and then provide more powerful support for the realization of safe and green mining in mines.