Study On Assessment And Theory Of Heat And Moisture Energy Extracted From Mine Exhaust Airflow

Due to the heat dissipation and humidity dissipation of surrounding rock and various facilities,mine roadway airflow’s heat and humidity parameters are kept constant in four seasons.The dry-bulb temperature and relative humidity are kept at 25 ℃ and about 90 %,so there is a lot of low-grade heat and humidity energy in the exhaust airflow.For a long time,this heat and moisture energy is directly discharged,fails to get effective utilization,resulting in a significant waste of heat energy.The heat pump technology to improve the grade of this heat and moisture energy can be used in winter preheating air intake,centralized heating,and four seasons heating water,obtain considerable economic and environmental benefits,energy-saving,and emission reduction in mining areas of great significance.The premise of utilizing the heat and humidity energy of mine exhaust air is low-grade energy extraction.The spray droplets are directly in contact with airflow,extract the low-grade heat from the exhaust air,and turn it into high-grade energy,which can be directly used to realize the transfer of low-grade heat energy to high-grade heat energy.Due to the complexity of the heat and mass transfer between droplets and airflow,the research is still qualitative,and the research on the heat transfer process between droplets and exhaust airflow is not sufficient,especially in confined space.There is little research on spray form,droplet atomization mechanism,characteristics,transport law,heat and moisture transfer control model,and transfer efficiency.Based on the National Natural Science Foundation of China(Grant No.51774134),this study aimed to efficiently extract heat and moisture energy from mine exhaust air.It decomposed into droplet atomization,spatial topology structure,kinematics,dynamics,thermodynamic,potential partition,and other aspects.On this basis,Using theoretical analysis,mathematical derivation,numerical simulation,and model experiment,the characteristics of heat and moisture energy extraction from mine exhaust with upper injection are systematically studied.(1)Based on the theoretical basis of two-phase fluid dynamics,an experimental device for confined space atomization was designed and optimized.It includes variable frequency regulation and control of the fan,optimization design of streamline diffuser,selection of spray mode of the droplet,design of constant pressure atomizing device,selection of nozzle type,etc.The atomization mechanism of droplets by the hollow conical nozzle and the variation of dispersed phase fraction under different injection pressure and air velocity were studied by experimental measurement.There were two stages of droplet fragmentation,the atomization process and the atomization process.Combined with the experimental data,the effects of spray pressure,gas velocity,and liquid physical parameters on the droplet atomization process were quantified,and the secondary droplet crushing process under different spray pressure and airflow disturbance was determined.(2)The fractal theory is introduced to form a method to characterize droplet size distribution by fractal dimension,and the atomization effect of the nozzle is optimized according to this method.Then,the droplet transport control equation was established according to the kinematic and dynamic characteristics of the droplet in the mine exhaust thermal and wet energy extraction device.The droplet limit migration distance was predicted.Finally,the vertical droplet transport is measured experimentally to achieve the inversion of droplet group migration.(3)Theoretically derive the control equation of heat and moisture transfer between the droplets and exhaust airflow,establish the evaluation method of thermal efficiency and exergy efficiency of the gas-liquid two-phase heat transfer process.Then,numerical simulation method is utilized to optimize the heat transfer parameters with the help of theoretical analysis results.An experimental platform of spray mine exhaust energy recovery was set up,carry out experimental measurement research.It is quantifed that the change rules of the droplet and air state parameters,heat transfer efficiency,and exergy efficiency at the device’s outlet under different spray volumes,airflow,water-air ratio,and spray length.(4)Entransy theory was introduced given the shortcomings of heat exchange efficiency and exergy efficiency in analyzing heat and moisture exchange.Based on this theory,the relationship between atmospheric parameters in the cold temperate zone of China and Entransy efficiency was specifically analyzed,and the influence rule of environmental dry bulb temperature and moisture content on Entransy efficiency was quantified.Furthermore,according to the characteristics of other climate zones in China,the Entransy efficiency of annual hourly exhaust was calculated for typical cities in climate zones.According to the annual hourly frequency,three extraction regions of mine exhaust air heat and moisture energy are divided into low-frequency,middle,and high-frequency regions.According to the characteristics of each area,it provides ideas for practical engineering application.