Performance Evaluation And Model Test On Influence Of Wind Of Natural Draft Counter-Flow Wet Cooling Towers

In power plant, the performance of cooling tower is related to the safety, economical and steady running of power plant. Therefore the analysis on the performance of cooling tower is of great importance.Based on the research of heat and mass transfer in cooling towers, the natural draught wet cooling tower (NDWCT) is analyzed. The mathematical model is established, and the one-dimension calculation of cooling tower is realized through program, which could be used to evaluate the performance of cooling towers.Some NDWCT is calculated as an example to analyze the effect of water temperature, water flow rate and environmental parameters on the performance of cooling tower. The results show that the influence of water temperature on outlet temperature is little. And the outlet temperature increases as the water flow rate, or air temperature, or relative humidity increases, which means the performance of cooling tower is poor.The model test of cooling tower is also carried out. And the result without crosswinds shows that the inlet speeds are almost the same around the air inlet of cooling tower. The effect of water temperature and water flow rate is also analyzed, and the conclusion is the same as the calculation.The test under crosswinds is also done, and the proportion between test wind speed and real wind speed is about 1:10. When the wind speed is low, the inlet speeds around the air inlet of cooling tower are about the same, and both the temperature difference and efficiency factor change a little. When the wind speed increases, the inlet speed of windward increases, the inlet speed of the side and lee side decrease, and both the temperature difference and efficiency factor decrease. When the crosswind speed is about 0.5m/s, both the value of temperature difference and efficiency factor is the least. When crosswind is quite strong, both the temperature difference and efficiency factor begin to increase, and the value is larger than that without wind when the cross wind speed is more than 0.7m/s, and then the crosswind is in favor of the performance of cooling tower.Air deflectors are placed around the air inlet of cooling tower so as to reduce the adverse effects of crosswind on cooling tower. The test result shows that the inlet speed around air inlet of cooling tower is almost the same, and as the air deflectors will induce transverse eddy which could enhance the heat and mass transfer in rain zone, so the temperature difference and efficiency factor are larger than these without air deflectors when there is no crosswind. The effect of air deflectors will be more evident with crosswind. The transverse eddy that induced by air deflectors can balance the inlet flow around the cooling tower, and the flow field in cooling tower under crosswind can be improved, which could be in favor of the heat and mass transfer in cooling tower, so the temperature difference and efficiency factor are quite larger than these without air deflectors. It is discovered that, when the crosswind is not so strong, that is when the effect of crosswind on the performance of cooling tower is unfavorable, the amplification of temperature difference and efficiency factor is the largest, which means that the air deflector is an efficiency wind proof method.In north China, water in cooling towers would freeze, which would threaten the safety and economic running of cooling towers. So the causes of freezing are analyzed here, and then some anti-freezing methods are discussed.