Numerical Study Of Structural Improvement Of Natural Draft Wet Cooling Tower

Based on the theories of heat and mass transfer between air and water in the natural draft cooling tower,this paper built the three-dimension numerical model of the natural draft wet cooling tower of a 1000 MW power unit with the CFD software FLUENT.Thediscrete phase model(DPM)is used to simulate the heat and mass transfer between the water droplets and the air in the spray and rain zoon.While in the fill zone,based on the Poppe model,the user defined function(UDF)is used to add suorce terms into the control equations to simulate heat and mass transfer.In order to improve the heat transfer in the central region of the cooling tower and lower the outlet water temperature,a new plan which is called divided air inlet method with water collecting plate had been put forward.Acoording to the simulation of several design plans,the outlet water temperature dropped by 0.91℃ which is the best result when thewater collecting plate is 3.5m high from the bottom of cooling tower and itsinner diameter is 40 m.To increase the velocity component of the vertical direction,the inclined water collecting plate is adopted.After the simulation,the result is best when the angle of inclination is 5°.In consideration of divided air inlet method,the height of air inlet is optimized.According to the simulation,the result is best when the hight increment is 0.7m.What’s more,another plan is presented which can make a part of air flow into the central region of cooling tower directly by several air conduits so that the heat exchange is improved.After the simulation, the outlet water temperature can be decreased by 0.36℃.