Study On The Flow And Heat Transfer Characteristics And Optimization Of Large-scale Air Cooling System

Air cooling technology is preferable under certain conditions,especially for the insufficient water supplies in Three-North Area of China.Air cooling technology makes use of ambient air as cooling medium,then it is sensible of the change of ambient conditions,the performance drops sharply with ambient wind especially.The traditional direct draft dry cooling system has a lower investment costs but a higher operation cost and produces more noise pollution compared with the natural draft dry cooling.Based on the characteristics,the natural draft direct dry cooling systems with heat exchangers horizontal and vertical arrangement are developed in this paper.Results show the tower of the new system can introduce more air and have an effect similar as deflectors,the temperature and velocity field show a more uniform trend,a better heat transfer is obtained.And natural draft direct dry cooling systems with.heat exchangers vertical arrangement have a better temperature and velocity field than the horizontal one.The performance of the bundles with 150 degrees shows more advantage than others.In the view of indirect dry cooling system,deflectors and two new arrangement methods of heat exchangers are proposed.Results show when wind speed is small or zero,compared with the cooling tower without deflectors,the cooling tower with arc or spiral deflectors has a worse thermal performance.However,when wind speed is big,the flow and heat transfer characteristics of the cooling tower could be improved by installing deflectors in it.For the new proposed system,the heat flux increase with the velocity when the wind flow from 0 degree,which will aggravate the heat transfer performance of air condenser,and decrease in 90 degree.For the system with parts of heat exchangers arranged inside tower and parts surrounded tower,the performance improves under low velocity of ambient wind and deceases under the high one.It is need to be pointed the height of tower inlet greatly affected the system with parts of heat exchangers arranged inside tower and parts surrounded tower,then the height of tower inlet and wind speed have an optimum point for the best performance.Multi-towers are studied in the final section.Measures applied in single tower are studied in multi-towers.A comparison is conducted with deflectors added into single tower and all towers among the multi-towers,results show a similar improvement and the promotion is more obvious while deflectors added into all towers.The simulation results show the performance of downsteam tower is improved when deflectors is added into a single tower,while having nearly no effect on the upsteam tower.The airflow field is more uniform when deflectors is added into all towers,and such an improvement is more obvious with a higher speed.