| Natural draft wet countercurrent cooling tower is the most widely used in power plants.The value of outlet water temperature affects the efficiency of the whole thermal power unit,and lowering the outlet water temperature of cooling tower has a direct impact on the economy of power plants.In this paper,the FLUENT numerical simulation method is used to study the cooling tower flow field as well as the way to lower the outlet water temperature of cooling tower.The factors affecting the outlet water temperature of cooling tower are divided into the factors outside the tower and the factors inside the tower according to priority.The factors outside the tower include: ambient temperature,wind speed,humidity,and the installed inclined upward guide plate outside the tower.The factors in the tower include:water distribution spray diameter,water distribution mode,height of filler body.Regarding the influence of factors outside the tower on the thermal characteristics of the internal flow field inside the cooling tower,the calculation results are as follows: 1)When there is no transverse wind,the entire flow field conforms to the central symmetry;in the central area the temperature is the highest,the heat exchange is the worst,and the wind speed is the lowest.2)When there is transverse wind,as the wind speed increases,the flow field distribution in the entire tower loses its central symmetry,vortices are generated in the tower,and heat transfer in some areas becomes worse.When the ambient wind speed is 4 m/s,the outlet water temperature of the cooling tower is relatively high.3)When the ambient temperature and humidity decrease,the outlet water temperature of cooling tower will decrease accordingly.The calculation result reveal that when the ambient temperature decreases from 32 ℃ to 2 ℃,the outlet water temperature of cooling tower decreases from 305.8 K to 295.75 K.When the atmospheric humidity decreases from 80% to 20%,the outlet water temperature of cooling tower decreases from 303.54 K to 302.24 K.4)The tower is equipped with an air intake regulating device,which rotates horizontally into an oblique upward flow guiding structure can reduce the vortex on both sides of the cooling tower and improve the heat exchange.Regarding the influence of the installed inclined upward guide plate on the tower under different wind speeds and different temperature conditions,the calculation results are as follows: when the ambient wind speed is 4 m/s,the outlet water temperature of cooling tower reduces the most,with the value being 0.82 K.When the ambient temperature is 12 ℃,the outlet water temperature of cooling tower reduces the most,with the value being 0.8 K.From the results above,it can be concluded that the conditions for reducing the outlet water temperature of cooling tower are as follows: 1)Reduce the wind speed of the tower inlet.2)Reduce the ambient temperature of the tower inlet.3)Reduce the environmental humidity.4)Install a guide plate device outside the tower.Regarding the influence of factors inside the tower on the outlet water temperature of cooling tower,based on the working conditions above,the calculation conditions are as follows: 1)When the spray diameter is reduced,the outlet water temperature of cooling tower also decreases.When the spray diameter is 0.003 m,the outlet water temperature of cooling tower is lowered by 2.59 K than that when the drop diameter is0.007 m.2)When the area ratio of the inner ring,the middle ring and the outer ring is1:1:1,and the spray ratio is adjusted to 27%,35.5%,37.5% accordingly,the cooling is the best,and the highest outlet water temperature of cooling tower is reduced by 0.57 K compared with that before the water distribution.3)When the height of filler body increases,the outlet water temperature of cooling tower reduces accordingly;when the height of filler body is increased from 1.1 m to 1.5 m,the outlet water temperature of cooling tower is reduced by 1.31 K.From the results above,the ways to reduce the outlet water temperature of cooling tower are as follows: 1)Reduce the diameter of the spray water.2)Optimize the water distribution mode.3)Increase the height of filler body. |
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