| Mine air coolers are important terminal equipment of mine cooling system.The overall energy efficiency of the mine cooling system is significantly affected by the heat transfer performance of the mine air cooler.The mining air cooler is affected by dust fouling,resulting in a reduction in the heat transfer efficiency of the air cooler.To enhance the performance of heat transfer,it is necessary to reduce the dust concentration in the inlet air stream of the air cooler and then carry out heat transfer optimization of the mine air cooler.The work in this thesis is based on the optimization of heat transfer in finned tube air coolers to conduct the investigation.A spray dust removal module was installed at the air cooler inlet,and the dust removal effect of the spray was studied.The performance of the fin and tube air cooler was tested experimentally.Then,the effects of fin parameters and heat exchanger tube parameters on the heat transfer and flow performance of the fin and tube air cooler under high air velocity(4～12 m/s)conditions were analyzed by numerical simulation.Finally,response surface method and orthogonal test were used to carry out the optimization studies of the structural parameters.And the correlations of heat transfer and friction factor were proposed.The main contents of this full text are as follows:(1)The performance test bench of the fin and tube air cooler with spray dust removal module was built.The influence of the number of nozzles and the spray angle on the dust removal efficiency was studied.Meanwhile,the heat transfer and flow characteristics of the fin and tube air cooler were tested.With a single nozzle,the reverse spray has the best spray and dust removal efficiency of 75.8%.With two single nozzles,the combination of forward spray and reverse spray has the best spray and dust removal efficiency of 84.2%.At a spray angle of 90°,the dust removal efficiency of the double nozzle is improved the most over the single nozzle,by 29.3%.With the increase in inlet air velocity,the heat transfer coefficient and pressure drop of the fin and tube air cooler increase,but the heat transfer and resistance factors decrease.And it also decreases the comprehensive performance evaluation index of the air cooler.(2)A numerical model of the fin and tube air cooler was established.The effect of fin parameters on heat transfer and flow performance of the fin and tube air cooler was analyzed.The heat transfer coefficient increases with the decrease in fin pitch and the increase in fin thickness.The pressure drop decreases with the increase in fin pitch and increases with the increase in fin thickness.Increasing fin pitch is beneficial to improving the comprehensive performance,while increasing fin thickness has the opposite effect.The vortex generator can greatly improve the heat transfer coefficient,and it can also increase the pressure drop slightly.Meanwhile,it can improve the comprehensive performance of the air cooler.(3)The effect of heat exchange tube parameters on heat transfer and flow performance of the fin and tube air cooler was analyzed.The transverse tube pitch has a greater impact on the heat transfer and flow performance of the air cooler than the longitudinal tube pitch.The heat transfer coefficient and pressure drop decrease with the increase in the transverse tube pitch.The transverse tube pitch has a best value at which it maximizes the comprehensive performance evaluation index.With the increase in the longitudinal tube pitch,the heat transfer coefficient and comprehensive performance evaluation index increase slowly at first and then tend to be gentle.Meanwhile,the pressure drop slightly increases with the increase in longitudinal tube pitch.The heat transfer coefficient and comprehensive performance decrease with the increase in the number of tube rows.However,with increase in the number of tube rows,the pressure drop increases.Increasing the air velocity reduces the effect of the number of tube rows on heat transfer performance.In addition,the influence of tube diameter on heat transfer coefficient is not obvious,but decreasing the tube diameter can significantly reduce the pressure drop and improve the comprehensive performance.Flat and elliptic tubes have better heat transfer performance and less flow resistance than round tubes.Meanwhile,the flat tube with the lower width to length ratio has the better heat transfer and comprehensive performance of the heat exchanger.The short to long axis ratio has the same effect on elliptic tubes.(4)By using response surface method,the impact of two structural parameters acting together on the air cooler’s heat transfer and flow performance was investigated.When the longitudinal tube pitch and other parameters are combined,there exists an optimal value that has the highest heat transfer coefficient and comprehensive performance evaluation index.However,the influence of longitudinal tube pitch on pressure drop is negligible.When the fin pitch,fin thickness and transverse tube pitch are combined,the best values of heat transfer coefficient,pressure drop and comprehensive performance evaluation indexes are obtained at extreme values.Meanwhile,the influence rankings of structural parameters on heat transfer coefficient,pressure drop and comprehensive performance evaluation index were determined by orthogonal test.The structural parameters affect the heat transfer coefficient and comprehensive performance evaluation index in the following descending order of impact: transverse tube pitch,fin thickness,fin pitch and longitudinal tube pitch.And these factors affect the pressure drop in the following descending order of impact: fin thickness,fin pitch,longitudinal tube pitch and transverse tube pitch.The best heat transfer performance is obtained by the combination of 2.6 mm fin pitch,0.4 mm fin thickness,15 mm transverse tube pitch and 24 mm longitudinal tube pitch.The best flow performance is obtained by the combination of 3.2 mm fin pitch,0.1 mm fin thickness,30 mm transverse tube pitch and 12 mm longitudinal tube pitch.The best comprehensive performance is obtained by the combination of 2.6 mm fin pitch,0.4mm fin thickness,20 mm transverse tube pitch and 24 mm longitudinal tube pitch.Besides,the correlations were developed based on the data obtained from the simulation,and 90% of the heat transfer and friction factors exhibited errors within±15% with the simulation data. |
