| With the increase of coal mining depth,the degree of heat damage in mining face is increasing,and mine cooling method and cooling mode need further development to meet the needs of cooling requirements.Based on heat and mass transfer,fluid mechanics,engineering thermodynamics theory and other basic theories,methods combined theoretical analysis,numerical simulation,field measurement method,experimental study and industrial test are used to finish the study task.This dissertation studys on heat and humidity transfer law between surrounding rock and airflow in roadway,which provide a basis for discussing the mechanism of active heat insulation and cooling in tunnel.Combined with the space features,technique characteristic and thermal environment distribution characteristics of mining and heading face,a liquid CO2 refrigeration and cooling technology for high temperature mines is proposed and developed.In view of large energy consumption disadvantages of the traditional cooling mode by cooling full airflow of roadway,a new energy saving cooling mode for coalface is proposed and studied.Specific main achievements of the study include the following aspects.(1)Heat and humidity transfer law between surrounding rock and airflow in roadway.The implicit finite difference method is used to separately construct numerical solutions for the one-dimensional dimensionless heat conduction control equation of dry roadway surrounding rock and the control equation of heat and moisture coupled transfer between surrounding rock and airflow in three-dimensional axisymmetric roadway.The simulation results show that the greater the Fourier number Fo and the number of Bi,the larger the surrounding rock is disturbed,the dimensionless heat transfer coefficient decreases with the increase of Fourier number Fo and increases with the increase of Bi.The wet exchange increases the disturbance intensity of airflow on the temperature field of surrounding rock.The airflow temperature in roadway is inversely proportional to the moisture rate of the roadway wall surface,and the temperature and moisture content of the airflow decrease with the increase of wind speed.The effect of increasing wind for cooling is limited,which has the optimal wind speed range with reasonable economy.(2)Study on thermal physical parameters experiment of coal and rock and active heat insulation for cooling.The relationship between thermal diffusion coefficient,thermal conductivity and specific heat capacity of coal and rock is experimentally obtained.Through simulation analysis,it shows that the radius of the heat transfer ring and the excess temperature of the surrounding rock are linearly related to the square root of thermal diffusivity and the heat storage coefficient respectively.The heat insulation layer reduces the heat dissipation of surrounding rock by changing the temperature gradient inside the surrounding rock.The greater the thickness of heat insulation layer is,the smaller the thermal conductivity is,the more obvious the heat insulation effect is,it is a power function relationship between the heat dissipation of surrounding rock decreased by insulation layer and its thickness and thermal conductivity.(3)The liquid CO2 refrigeration cooling method for mine is proposed,an experimental device for liquid CO2 refrigeration and cooling is designed to explore the feasibility and effectiveness of the cooling method.The experimental results show that with the increase of liquid CO2 flow,the greater the decrease of airflow temperature and moisture content,the more obvious the cooling effect of liquid CO2 is.The effective utilization rate of liquid CO2 cooling capacity is over 90%,and the average cold loss rate of 100 meters in the transport process is about 5.5%.The humidification coefficient of the heat exchanger is proportional to the relative humidity of the inlet flow,and is inversely proportional to the temperature of the inlet flow.The air pressure drop of the heat exchanger increases with the increase of the heat transfer coefficient.The heat transfer coefficient of the heat exchanger decreases with the increase of the dry degree of the liquid CO2,and increases with the increase of the mass flow of the liquid CO2.(4)Industrial test of liquid CO2 refrigeration cooling and fire prevention and extinguishing integration technology.The thermal environment distribution characteristics and heat source composition of 52305 heading face are obtained through the field measurement.Liquid CO2 refrigeration cooling and fire prevention and extinguishing integration system of 52305 heading face are designed.The results show that the temperature of heading face drops down 6.9℃ and the humidity ratio is reduced by 4.94g/kg.The utilization rate of cooling capacity released by liquid CO2 phase-change is 77.36%.The width of the oxidation zone in the goaf of No.52303 mining face decreases obviously.Liquid CO2 refrigeration cooling system can effectively reduce the temperature of the cooling place and prevent the spontaneous combustion in the goaf.(5)A new energy saving cooling mode of local air volume cooling and positioning air supply in mining face is put forward.The thermal environment distribution characteristics of mining face are obtained through the field measurement analysis.Using numerical simulation method,the cooling effect of the new cooling mode is studied.The results show that the cooling mode can create enough thermal comfort area for the mining face,and the comfort area is related to the air supply volume,the air distribution mode,the flow state of airflow and the ambient temperature.The energy saving effect of the cooling mode is obvious. |
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