Optimization Of Natural Draft Wet Cooling Tower Based On Three Dimensional Numerical Model

Natural draft wet cooling tower (NDWCT) has been widely used in electric power industry of China, and its performance is influenced by a number of factors such as fill distribution, environmental parameters and tower structure. As an important structure of energy conservation and emissions reduction of electric power industry, the optimization of NDWCT’s performance has always been the research focus at home and abroad. To study the NDWCT, model test cannot satisfy all the similar conditions in case of the large size of the tower structure, and its cost is always high. On the other hand, conventional one-dimensional and two-dimensional model cannot calculate and evaluate the effects of crosswind on NDWCT. Thus, it’s necessary to develop an accurate three dimensional numerical model to study and optimize the NDWCT’s performance.A three dimensional numerical model of NDWCT was established in this paper based on heat and mass transfer theory and Computational Fluid Dynamics (CFD) software FLUENT. After the validation using measured data, the model was used to investigate the different NDWCT’s performance under different spacing fills and different fill distribution. Furthermore, the improvement of NDWCT’s performance under windbreak wall was also discussed in this paper. These research results provide support to optimize the NDWCT’s performance and design parameters. The major research works are as follow:(1 Establishment of the three-dimensional numerical model of NDWCT. According to the actual fill distribution and the fill property, this study built the three-dimensional numerical model, which uses a unique dispersed solution to treat the temperature of cooling water in fill. The accuracy and reliability of the model are verified by comparing the data from the model and the measured data of the cooling tower under actual working conditions.(2) The research of different spacing fills. In this paper, through the qualitative analysis and the three-dimensional model of substitution analysis of the thermal and resistance performance of the same waveform but different spacing fills, conclusions can be summarized that the small spacing fill has the higher thermal performance and resistance. Only the thermal performance advantage outweighs the resistance disadvantages, using the small spacing fill can enhance the NDWCT’s performance.(3)The research of the fill distribution. Different fill distribution is corresponding to different packing volume. Through the studies of 17 fill arrangement type, results show that air flow rate and water temperature of fill down both decrease with the increasing of packing volume. To improve the performance of cooling tower, increasing the outer fill height is more effective than increasing the overall fill height. Fill non-uniform layout can reduces the packing volume, through rain and spray zone heat and mass transfer enhancement to improve the performance of the cooling tower and reduce cooling tower construction costs.(4)The validation of windbreak wall to improve the NDWCT’s performance. According to the average weather conditions and 3.3m/s crosswind, this paper studied the effect of windbreak wall to improve the NDWCT’s performance. Results show that the mechanism of windbreak wall is mainly by improving the windward air dynamic field to enhance the tower performance. However, installing windbreak wall also has a small amount of adverse effects to the heat exchange of leeward side of the cooling tower.