Research On Optimizing Aerodynamic Field In Natural Draft Counter-flow Wet Cooling Tower

Thermal power generation is the main body of the electricity production of our country. As the cold end of thermal power plant, the performance of cooling tower has a direct effect on the safe, economical and steady running of thermal power plants. Therefore research on how to improve the cooling tower performance is of great importance.It has been over one hundred years since the first cooling tower was built up. Domestic and foreign scholars have done a great deal of research work on heat and mass transfer process in cooling tower, and have established various types of mathematical models. In order to improve cooling tower performance, many researchers have put forward lots of effective measures and schemes, such as proper arrangement of fill and water distribution system. So far most optimizing modifications have been conducted in the water distribution zone and fill zone, but little attention has been paid to the rain zone which is also named wind distribution zone.After numerical simulation and model test of temperature and humidity field in cooling tower, the author has had some discovery. When cold and dry ambient air enters the rain zone through tower inlet, there will be heat and mass transfer between the air and spraying water in the course of air flowing, therefore circulating water is cooled. But there is mismatch between water mass velocity and air mass velocity in cooling tower, so cooling efficiency of some zone in cooling tower is rather low.Based on this, the author proposes the thought of optimizing aerodynamic field in cooling tower, and adopts the method of proper wind distribution. By this mean, water mass velocity and air mass velocity are properly matched, and the air temperature and humidity field and the cooling water temperature field are properly coupled and optimally arranged. Therefore cooling performance in the central are is improved, hence cooling efficiency of the whole tower is increased.After this energy-saving optimization scheme is established, predictive numerical simulation is performed using CFD software by the author. Structured grid is meshed, boundary conditions are defined according to actual working conditions, and ambient air induced into the tower is transformed into additional source terms of mass, energy, momentum and fraction. A series of working conditions are simulated and the results are as follows. When other boundary conditions such as inlet water temperature, water mass velocity and environmental parameters are all given the same, the outlet water temperature after optimization is about 0.3℃lower than that before optimization, and relative performance parameters of cooling tower such as temperature difference, efficiency factor, cooling number, heat transfer coefficient and mass transfer coefficient are improved by different degree.Finally comparative thermal state tests are performed on the available cooling tower model test bed. And the tests are composed of variable circulating water flow, inlet water temperature, crosswind velocity and air-inducing pipes. Comparisons between test data show that under same condition, the temperature difference after optimization is commonly 0.1-0.4℃larger than that before optimization. It proves that the optimization scheme proposed in this paper is feasible and effective, and it has certain engineering application value. This can be further proved by field test of cooling tower.