| Dry cooling tower is widely used due to its remarkable water saving characteristics,but the cooling medium of dry cooling tower is air;its working performance is easily affected by ambient air temperature.Especially during the hot period in summer,the cooling capacity of dry cooling tower is greatly limited,thenreducing the power generation efficiency of the power plant.But the period is the peak time of the electricity consumption,so a lot of economic losses are caused.Under the hot time in summer,the dry cooling tower can be precooled by spray cooling to enhance its heat transfer capacity.Spray cooling has many advantages,such as convenience,low cost,easy operation and maintenance.It only use a small amount of water but can significantly improve the power generation efficiency and has been used in some dry cooling units.According to the ventilation type,dry cooling tower is diveided into direct air cooling condenser(ACC)and indirect dry cooling tower,the ventilation mode of direct dry cooling tower is forced ventilation by fan and indirect air cooling tower is natural draft caused by air density difference.At present,the technology of spray cooling is mainly used in the direct dry cooling unit,and the indirect dry cooling tower is seldom used.And the current application is just put the nozzle in front of the radiator,and do not optimize the arrangement of the nozzle.This will cause waste of water resources,and the cooling effect is not uniform,some of the most needed radiators are not cooled.The purpose of this study is to optimize the water quantity and layout of pre-cooled nozzles,and to use the minimum water consumption and the minimum number of nozzles to achieve the best cooling tower efficiency.This paper takes Harmon dry cooling tower as the research object,establishes its geometric model by ICEM software and uses Fluent to simulate its flow and heat transfer characteristics,the radiator was simulated by radiator model.The spray cooling system was then designed and optimized based on cooling tower temperature and flow field,where the nozzle was simulated by discrete phase model(DPM).The results show that the location and arrangement of nozzles have a great influence on the effect of spray evaporative cooling;the air flow at different locations affects the trajectory of droplet at the tower inlet.By comparing the cooling effect and evaporation of the nozzle at different positions,two evaluation indexes of nozzle cooling efficiency were put forward:surface average temperature T and relative standard deviation of temperature distribution σT According comparing these indexes,the best combination of temperature drop and uniformity is obtained,which can reduce the inlet air temperature of the dry cooling tower by 8℃,and realize the uniformity of temperature drop.At the same time,it ensures that the droplets evaporate completely before the radiator,saving water resources and at the same time avoiding the corrosion caused by unevaporated droplets reaching the radiator surface.The cooling towe heat transfer and flow characteristics under crosswind are calculated.It is found that when the wind speed is 6m/s,the heat transfer of the radiator on the windward side is worst due to poor flow.In order to improve this situation,the spray system is further optimized and improved.By designing different arrangements and comparing cooling effect,the nozzle combination that can improve the heat exchange on the windward side can be found out.It can ensure that the cooling area covered the worst heat sink and avoided extreme conditions. |
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