Research On Heat Transfer Characteristics Of Coal Pile Spontaneous Combustion Based On Capillary Core Heat Pipe Heat Transfer

Spontaneous combustion often occurs in openair coal storage during storage and transportation.The harmful gases and elements produced by the oxidative decomposition pose a great threat to the ecological environment and safe production of storage sites.The treatment effect of grouting,nitrogen injection,mulching on the thermal storage of coal piles is lack of significance,and the internal high temperature area cannot be eliminated,there are still hidden dangers of spontaneous combustion.Based on the heat conduction of the heat pipe and the fast heat transfer properties of the working medium phase change,the heat at the high temperature end can be quickly transferred to the outside of the heat source.This study applied experiments and numerical simulation research to explore the influence of capillary core heat pipes on the thermal migration behavior of coal piles through the coal pileheat pipe heat transfer performance test experimental system.Through statistical analysis of the experimental data,the conclusions are summarized as following:Using the heat pipe performance test platform,the heat transfer experiment of capillary core heat pipe in the coal pile is carried out,and the temperature change characteristics during the cooling process of the coal pile are obtained.The findings elucidate that:the coal body near the heat source has high temperature sensitivity;the cooling rate of the coal pile under the intervention of the heat pipe is as upper layer>middle layer>bottom layer.The enhanced heat dissipation effect of the capillary core heat pipe reduces the maximum temperature of the coal pile to 130.6℃,and the cooling rate reaches 46.93%;Through the curve trend,the heat transfer process of the heat pipe can be divided into three ranges:the sensitive area(5～25 cm),the transition area(25～35 cm)and the steady state area(>35 cm).A numerical heat transfer model between coal pile and heat pipe is established to simulate the heat flow characteristics of the coal pile,and the heat transfer behavior of the coal pile under different heat pipe parameters is quantitatively compared.The heat transfer rate,temperature field and distribution law of high temperature danger zone(SCDZ)in the coal pile are obtained.During the interaction between the heat pipe and the loose coal body,the temperature contour of the coal pile shifts to the hot end,and the migration rate v is inversely proportional to △x,and finally presents a "saddle" shape.The heating and cooling trends of the marked measuring points are in common with the experimental results.The built model and input parameters are suitable for verification results with high accuracy.The high temperature area of the coal pile is highly concentrated and tends to the middle and lower parts of the windward and leeward sides.The study found that significant differences in the inhibitory effect of heat pipe inclination on the heat transfer behavior of coal piles.The cooling effect reaches the best when θ is set to 60°,the integrity of the natural danger zone of the coal pile is destroyed to 10.5589 m2,and the reduction rate is about 0.176 m2/day,the maximum temperature of the coal pile drops by 10.5 K,the cooling efficiency is about 0.18 K/d.In the scheme of this study,when the heat pipe insertion distance is not greater than 1.5 m,the overall temperature of the coal pile is below 60℃,and the maximum cooling rate is 0.46 K/d.These demonstrate that the heat stored in the coal pile is dissipated to the outside through the cyclic phase change of the heat pipe.Taking into account the prevention and control effect and economic benefits,the inclination angle of the heat pipes should be 60°,and the spacing should be set between 1.0～1.5 m.The results provide a theoretical basis for the popularization and application of capillary core heat pipe in coal pile fire-fighting engineering.