| It is important to study the cooling tower in power plant. The process of cooling water is a very important part in the production of power plant. The low temperature of condenser is the result of circulating water. So the performance of cooling tower influence the economic and stability deeply. The fill is the "heart" of cooling tower and it is the most important part in the heat-mass transfer. The property of fill is the key factor that influence the efficiency of cooling tower.The thermal performance of natural draft wet cooling towers (NDWCT) has been investigated numerically. The governing equations are utilized to describe the air dynamic field of inside and outside of cooling tower, the movement of water in cooling tower, the heat-mass transfer between air and water, and the resistance of air and water in cooling tower. The three dimensional model has utilized the standard k-εturbulence model as the turbulence closure. At last, the "hot model" is established.The computational fluid dynamic (CFD) software is utilized for numerical calculation. The hexahedral mesh is used in the calculation region. The finite volume method is used to structure the difference scheme. The SIMPLE method is used in numerical simulation of flow fields and temperature field in cooling tower.The validation process of the current model has been conducted against the design conditions of the NDWCT and the result is well. As a consequence, the current code is utilized to investigate effect of different conditions on the thermal performance of natural draft wet cooling towers.The result of the model shows that the enthalpy and the humidity content of the fill-up face are lower than the value that relay on the water temperature. It is meaning that the capability of the fill can be used better. As a result, the concept of "optimization space" is proposed firstly in the paper. The reform of cooling tower that based on the concept contains tow schemes: 4#fill and 5#fill. The result of the reform is that, 4#fill and 5#fill make the temperature dropping of cooling tower increase 0.639K and 0.455K respectively, and the temperature dropping in the fill increased obviously. The crosswind of environment decreases the efficiency of cooling tower. There are tow main reasons. Firstly, the uniformity of the air that flow into the tower is destroyed by the crosswind, and the vortex is raised in the back of the tower which decreased the air input, on the other hand ,the cross ventilation will be generated when the velocity of crosswind is big enough. Secondly, the structure of the airflow under the fill is changed by the crosswind and several high temperature regions are generated which make the air temperature raise there. These two factors decrease the heat and mass transfer in the fill and raise the water temperature at last. The reformed fills have the same property in the crosswind with the previously in the crosswind.The model test of cooling tower is also carried out. And the result shows that the reformed fills work more effective than the previous which fit the calculation well.The result also shows that the temperature of outlet water will be raised when the spray water content increased. The reformed fills will not change the advantage in the crosswind.The result of this study provides a basis for the optimal design and performance improvement of cooling tower.
|
PDF Full Text Request