Optimization Of Flow Field And Heat Transfer In Cooling Unit Of Air Cooling Island Of Direct Air-Cooled Unit

Direct air-cooled units are often set up in areas where water resources are short,which can greatly reduce the consumption of water resources while ensuring normal power generation.However,the turbine of direct air-cooled unit has high back pressure and high coal consumption.Because its main cooling equipment is directly exposed to the air,it is easily affected by environmental factors,which leads to a wide range of cooling effects and affects the long-term safe and efficient operation of the unit.Hot air backflow and "backward flow" are common problems to be optimized in the operation of direct air-cooled condensers,especially the extreme high temperature and strong wind conditions will seriously affect the cooli ng performance of direct air-cooled condensers.Therefore,a multi-angle design optimization study is carried out to optimize the maximum heat excha nge capacity of air-cooled condenser of direct air-cooled unit.Firstly,this paper considers the optimization of heat transfer of air-cooled island under extreme wind conditions.The variable wind speed setting of wind speed profile is adopted instead of the conventional fixed wind speed setting,and the change of heat exchange capacity of air-cooled island under different wind speed settings of 12m/s,14m/s and 16m/s is considered.The calculation model of air-cooling island of direct air-cooling unit is established,and its heat transfer performance is studied.The influence law of hot air reflux and "backward flow" phenomenon on condenser heat transfer under constant wind speed and variable wind speed is analyzed.The results show that the variable wind speed setting can obtain the flow field information of the air-cooled island closer to the actual situation,and the actual condenser heat exchange capacity under the variable wind speed setting is higher than that under the usual prescribed wind speed setting,which provides practical data for reference for more economical and efficient design of the optimal wind-proof wall and wind-proof net.When the wind speed is set at 12m/s,14m/s and 16m/s,the heat exchange capacity of the variable wind speed setting is increased by 0.349 MJ,0.494 MJ and 0.222 MJ,which are 3.87%,5.56% and 2.4%,respectively.Secondly,the optimal design parameters of the wind-proof wall are optimized and analyzed,and the design parameters of the wind-proof wall with the highest heat exchange capacity are sought.Three factors,including the height,thickness and distance of wind shield,are designed by using ternary quadratic orthogonal test.The modeling and numerical simulation of 17 groups of air-cooled islands with additional lower wind shield are carried out,and the regression equation is obtained.Through quantitative analysis of the obtained regression equation,the law that the heat exchange rate varies with the height,thickness and distance of the wind-proof wall is obtained,and the optimal design parameters of the wind-proof wall under specific working conditions are obtained.For the modeled air-cooled island in this area,the final optimal distance of wind-proof wall is set to 3.75 m,the optimal thickness of wind-proof wall is set to 1.125 m,and the optimal height of wind-proof wall is between 10 and 15 m according to the actual factors.Finally,the nozzle layout optimization of the air-cooling unit with spray cooling device under high temperature conditions in summer is studied.A non-uniform nozzle layout scheme is proposed,and its model and numerical simulation are carried out under the layout scheme that the nozzle is 1m,2m and 3m away from the fin.The relationship between the droplet radius,droplet velocity,droplet temperature and other parameters and the heat exchange capacity is analyzed and studied.Based on the ternary quadratic orthogonal test,three factors including nozzle distance,nozzle pressure and nozzle angle are designed.The results show that the spray cooling device can obviously improve the heat dissipation efficiency of fins in high temperature condition in summer,and the non-uniform arrangement is more effective in this condition.The fitting regression equation is obtained,and the relationship between the nozzle distance,nozzle pressure,nozzle angle and heat exchange capacity is obtained by analyzing the obtained regression equation,and the optimal nozzle arrangement scheme is obtained.