| The indirect air cooling units with its good performance of water saving,which is only 15%-25% of water consumption compared with water-cooled units,are widely used in power plants of above areas for solving the contradiction effectively between coal and water.Air cooling tower,which is an important part,directly affects the safety and economic operation of indirect air cooling units.In order to solve the increase of backpressure in summer windy days and the frost crack of air cooling raditor tubes in winter windy days,we investigated numerically the flow and heat transfer characteristics of interrupted finned tube bundles and air cooling tower of a 200 MW Heller-type indirect air cooling unit,based on the CFD platform,using the porous medium model,the ?-? turbulence model and incompressible ideal gas model.Under different ambient wind speed,we calculated the flow resistance of interrupted finned tube bundles,velocity and temperature distribution inside and outside the tower,and the ventilation rate of the air cooling tower.Ambient wind will reduce the ventilation volume of air cooling tower,thereby reducing the cooling efficiency of the cooling tower.On this basis,we consider adjusting the louver opening of each sector in order to improve the air side flow field inside and outside the air cooling tower and reduce the influence of ambient wind.The simulation results show that under different wind speeds,closing windward side and leeward side sector louver opening can effectively increase inlet air volume of the side sector,and balance the tower circumferential air inflow and heat transfer,but it will also proportionally decrease the inlet air volume of windward side and leeward side sector according to the resistance characteristic of the louver,which probably rise the water temperature outlet the tower.Therefore both two factors should be considered in the regulation of louver opening.As rising back pressure causes load drop of air cooling units in summer,the calculation results show that all the louver should be kept open when the wind speed is less than 7.5m/s,and the opening of windward and leeward louver should be kept close gradually when the wind speed is larger than 7.5m/s.In addition,the winter average ambient temperature can reach minus 10 degrees,often accompanied by strong northwest wind.By comparing the results obtained from several different louver regulation schemes,it was found that a relatively safe and economic condition existed by adjusting the sector louver opening degree when the wind speed varies from 2m/s to 8m/s.In the condition,the outlet water temperature of each sector is higher and as close as possible to the limit,which will ensure the unit operates more safely and economically in winter. |
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