Numerical Simulation Of Flow,Heat Transfer And Water Losses In A Natural Draft Counter-flow Wet Cooling Tower

As one of effective cooling equipment, the natural draft counter-flow wet cooling tower is broadly used in industry, especially in cooling water for power plant thermal system. Cooling tower is one of the important equipment for maintaining the vacuum of condenser. The cooling towers, however, consume a huge amount of water which not only bring great economic loss to power plants, but also pollute the environment by forming white smoke on the top of cooling tower. Therefore, the research on fluid flow, heat transfer, and mass transfer has realistic theoretical significance and practical engineering values.The three-dimensional numerical computation model for natural draft counter-flow wet cooling tower is established to study the characteristics of flow field, heat and mass transfer. The changes of operation parameters, water distribution and arrangements of water collector affecting the flow field, water loss and cooling effect are simulated and analyzed. These works provide reference basis for energy conservation and water saving for cooling tower. The major research works are as follows:(1) The three-dimensional numerical computation model was established for the natural draft counter-flow wet cooling tower. The influences of the resistances of fill and water collector and the heat and mass transfer of fill are considered in the model. By adding the body force, the heat transfer and mass transfer of fill were simulated. The field experiment and empirical formulae were used to improve the three-dimensional numerical computation model and the results are reasonable and accurate.(2)The influence of the equivalent diameter of raindrops, inlet water temperature, spray water rate and water distribution to the thermal performance and water losses were analyzed. The results show that the cooling effect is enhanced and the outlet temperature is dropped when the equivalent diameter of raindrops reduces. With the increase of circulating water or the rise of inlet water temperature, the evaporation loss increases. Therefore, reducing the heat of the circulating water entering the tower is an effective way to reduce the evaporation loss. The results indicate the direction for the reduction of the evaporation loss. The non-uniform water distribution methods make full use of cooling capacity and reduce the outlet water temperature, and therefore the inlet water temperature is reduced. But, the improvement of heat exchange efficiency leads to more evaporation loss. Therefore, the influence of non-uniform water distribution to reduce evaporation loss is not obvious. (3) The influence of inlet air velocity and water droplet diameter to the resistance characteristic and water separation efficiency were analyzed. The results show that uniform flow field is an effective way to reduce the wind loss. By providing four layout schemes of water collector and after comparing the flow field and cooling performance, recommendations of layout of water collector are provided for engineering practice reference.