| Based on the theories of heat and mass transfer between air and water in the natural draft cooling tower,this paper built a solid model of the natural draft wet cooling tower of a 600 MW power unit with the software Gambit and corresponding numerical model with the CFD software FLUENT. The discrete 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 source terms into the control equations to simulate heat and mass transfer. With the methods mentioned, this paper calculated the flow heats transfer of the cooling tower in the conditions of various cross winds and without cross wind. The result shows that the heat transfer effect of the center of cooling tower is poor without cross wind, but when adding the cross wind, whirlpool is formed reducing the cooling efficiency of the cooling tower. So this paper proposed a solution by adding deflectors surrounding the rain regions which can lead the flow into the cooling tower, forming a stable rotating updraft that will not be influenced by the natural wind easily, thus reducing the uneven distribution of air flow, improving the heat transfer between air and cooling water and then the outlet water temperature will be decreased in advantage of the increase of cooling efficiency. This paper also optimized the numbers and installation angles of the deflectors. It is showed that the best cooling effect comes up when the number is 80 and the angle is 20°, and the outlet water temperature is decreased by1.2℃ compared with no deflector when it is without cross wind. When applying this technology to an actual power plant and making proper improvement, the author found a decrease of 1℃ at least compared to the original equipment, thus the correctness of the simulation and the practicability of this technology are verified. |
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