Diversion Structure Optimization Of The Ventilation Of Natural Draft Wet Cooling Tower

Based on the relative theories of cooling tower of coal-fired power plants, this paper built the three-dimension heat and mass transfer numerical model of the natural draft wet cooling tower of a1000MW power unit. The simulation adopted Poppe model in the fill zoon where the circulating water flows with membrane form and exchanges heat and mass with the upward flowing cold air. and discrete phase model is used in the spray and rain zoon to describe the heat and mass transfer between the water droplets and the air, the mass and energy source terms in the control equations are interpreted by the user define function tool UDF. On these bases, the model simulated and analyzed the thermal performance and the influence factors of the tower in the design condition and off-design condition. The scheme of installing catheter pipes in the rain zoon was presented to solve the problem of low efficiency in the central area of the tower. The thermal performance of the tower with different specifications of the pipes at variant cross wind velocities was simulated, and the results show that the cooling tower’s work efficiency is the highest when the tower is equipped with pipes of thirty-five and forty-five meters whose porosity are0.2,which make the outlet water temperature reduced by0.67degree. In response to the uneven heat and mass transfer inside the tower and the eddy current which appears in the leeward side of the tower that has cross windbreak walls in the rain zoon, a method of installing tilted windbreak walls was proposed, in this way the air distribution was improved and the thermal characteristics is optimized. By comparing the outlet water’s temperatures of the towers which are equipped with tilted windbreak walls of various angles, the outlet water temperature of the tower with tilted windbreak walls of thirty degree is the lowest, which make the temperature reduced by0.52degree. Besides, the cooling towers’thermal characteristics in various wind speeds and wind directions is analyzed, the results show that the effect gets much bigger when the wind speed get higher, and the tower works best when the direction of the tilt windbreak walls is the same with the local annual wind direction. It provided the theoretical principle for further optimization of the cooling tower’s design and operation.