Numerical Simulation Study On The Collaborative Optimization For Non-equidistant Fillings And Partition Water Distribution In Large Wet Cooling Towers

With the rapid development of China's power industry,the Cooling Towers equipped with large-capacity generating units of power plants are developing in large and super large directions.The large natural wet cooling tower has a large base diameter resulting in uneven distribution of thermal and resistance characteristics in the radial direction,which further deteriorates the cooling capacity.As the "heart" of the heat and mass transfer in wet cooling tower,the fillings performance directly affects the cooling efficiency.Furthermore,the fillings arrangement and water distribution method have a great influence on the thermal and resistance characteristics.Therefore,it is necessary to conduct a comprehensive study for the fillings arrangement and water distribution methods on the thermal resistance characteristics.Based on the prototype of a large wet cooling tower equipped with a 600 MW unit in a power plant,this paper divides the cooling tower fillings into inner and outer zones,and arranges non-equidistant fillings in these two zones to formulate different fillings layout plans.In this paper,ICEM is used to perform 3D geometric modeling and meshing,Fluent is used to establish a three-dimensional numerical calculation model of a large wet cooling tower,and the user-defined-function(UDF)is embedded for numerical simulation.Using the above method,the distribution characteristics of the flow and temperature field under various fillings layout plans were studied,and the variable working conditions were analyzed.On this basis,combined with partition water distribution,a collaborative optimization study was conducted and the main conclusions obtained are as follows.The results under design conditions show that non-equidistant fillings can significantly improve the uniformity of the temperature and flow field in the tower,and optimize the thermal and resistance performance of the cooling tower.For the 600 MW cooling tower,under design conditions,when only non-equidistant fillings is used and the radius division point is 47.5m,the thermal performance of the whole tower is relatively excellent.The water temperature drop,cooling efficiency and Merkel number are reach to the highest points,which the values are 10.04?,62.3%and 1.40,respectively.Compared with the original conventional tower,the values are increased by 0.23?,1.4%and 0.01,respectively.And the relative growth rates are 0.7%,2.3%and 0.76%,respectively.After non-equidistant fillings is used,the wind speed in the z-direction(vertical direction)on the upper surface of the drift eliminator and the air mass flow rate are increased.When the radius division point increased from 0 m to 57 m,the air mass flow rate and the wind speed in the z direction on the upper surface of the drift eliminator increase by 751.32 kg/s and 0.05 m/s,and the relative growth ratio are 6.3%and 3.6%,respectively.The results of the variable working condition show that when the ambient temperature changes,the non-equidistant fillings enhance the thermal and resistance performance of the cooling tower.Under the typical environmental working conditions in winter,the outlet water temperature is reduced by 0.35? at most.When the inlet water temperature changes,the thermal performance of the cooling tower with non-equidistant fillings are more stable than the original tower.The simulation results for non-equidistant fillings and partition water distribution collaborative optimization show that as the proportion of water mass flow rate in the inner zones increases,the outlet water temperature decreases first and then increases,and the air mass flow rate increases first and then decreases.Compared with the uniform water distribution condition,the partition water distribution can effectively reduce the outlet water temperature and improve the thermal performance.When the radius division point is 45 m and the water distribution accounts for 70%of the total water distribution,the cooling performance of the cooling tower is relatively optimal.After using this optimized configuration,the outlet water temperature of the tower is 0.32?lower than that of the conventional tower.In this paper,the numerical simulation method is used to study the effect for non-equidistant fillings and partition water distribution on the cooling tower performance.The distribution characteristics of the flow and temperature field are analyzed.The performance improvement effect of the wet cooling tower in the optimized configuration mode is obtained.The research results can lay the foundation for the in-depth energy-saving and efficiency-enhancing research of the wet cooling tower and provide guidance for the three-dimensional thermal design of the cooling tower.