Investigation On Air-Side Flow Property And Characterization Methods Of Direct Air-Cooling System Based On Time-Series Analysis

The primary advantages for direct air cooling system are water-saving and simple structure, which can promote the electric power development of the areas in shortage of water but rich in coal. Because of this, in the recent years direct air cooling system is used extensively in the northern of china. However, due to the array-fans platform and A-type frame are adopt in direct air cooling system and the ambient air is used as cooling medium, some problems such as low operating efficiency of fan cluster, uneven distribution of airflow and being vulnerable to environmental impact will be occurred during the fans operation in cluster. These problems will directly affect the heat exchange performance of air condenser. Therefore, how to reveal and grasp the flowing property of air-side flow in direct air cooling system and its effect mechanism on heat transfer performance of air condensers have became the troublesome problems in the design and development stage of direct air cooling system.The studies about the flowing property and characterization method of air-side flow in direct air cooling system presented in the paper are originates from the problems of environment-sensitive of air cooling unit and low operating efficiency of fan cluster. The experimental study is carried out by collecting the pulsation timing signals of air cooling fan and its around air flows. In this study, the difference between environmental wind and mechanical wind are investigated, the interference effects of fan inlet and the mechanism of fan cluster pumping are revealed, the distribution property of flow field in air cooling unit is explored, and then the study is extended to the optimization of typical year in air cooling system design on the basis of meteorological timing series data of air cooling plant.Firstly, on the basis of the combined effects of environmental wind and mechanical wind on air cooling system, the method of power spectral analysis is used in the study of dynamic property of airflows around air cooling fans. The experiment plan is determined by collecting the pulsation timing signals of turbulent flows using hot-wire anemometer. The representative parameters (such as power spectral index and energy accumulation factor) which characterize the dynamic property of air flows are used to distinguish the dynamic property in frequency domain of environmental wind and mechanical wind.Secondly, the paper applies the conclusion which is the ability of power spectral analysis method to distinguish the environmental wind and mechanical wind to the flowing performance experiment of fan inlet so as to analyze the air velocity, turbulence intensity, power spectral index and the energy distribution in frequency domain quantitatively, and then obtain the quantitative effective range of mechanical wind in fan inlet.Thirdly, increasing the number of fans around the measured fan slowly, the cluster operating performances of fans are studied, the major conclusions are obtained as follows:1) the flow rate of measured fan is not decreased monotonously as the increase of the number of ambient fans;2) whether the fan inlet is symmetry is one of the major factors affecting the flow rate of fan;3) when the fan is running in cluster, the air flow rate and velocity of the mainstream region of measured fan is lower than that in single fan, the air flow rate and velocity of the wall-closed region of measured fan is larger than that in single fan;4) the turbulence intensity in fan inlet is increased as increasing the fans number.Fourthly, the experimental study about the flow field of A-type frame in air cooling unit is conducted so as to investigate the feature of velocity distribution in the interior of unit and the outlet of A-type frame, and reveal the reason why the distribution of flow rate of air cooling unit is not uniform. The experiment results show that the flow field far from the center cross section of fan is not symmetry, the bottom-corner of air cooling unit exists flowing dead-zone, the center region of air cooling unit exists low-velocity zone, the velocity distribution and turbulence intensity of A-type frame outlet are not take center cross plane as symmetry plane.Fifthly, according to the meteorology timing data of local power plants, a characterization method about FS statistics meteorology typical year with multiple environmental factors introduced is proposed. This method can take into account all meteorological parameters (such as environment temperature, wind velocity, solar radiation, etc.) affecting the air cooling system, and reflect the long-term meteorological law of winter and summer to which the air cooling system is most sensitive, which provide a more reasonable guidance for air-cooling system design and improvement.