Numerical Simulation Of Flow And Heat Transfer Of Direct Air-cooled Condenser Under Crosswinds

In order to ease the tension of power supply and water scarcity, the direct air-cooled system with its excellent water conservation characteristics, has been widely used all over the world, especially in coal-rich but water-short areas. The direct air-cooled system uses ambient air as the cooling medium, and the condensers are exposed outdoor with axial-flow fans forcing ventilation, so the air flow field around the system is bound to influence the heat capacity and normal running of the whole direct air-cooled system. The flow characteristics directly impact the heat transfer characteristics and the efficiency of the condenser. Therefore, the study of flow and heat transfer performance of air-cooled condensers is essential to the design and optimization of the direct air-cooled system.The heat transfer performance of air-cooled condenser is greatly affected by environmental conditions, especially the crosswinds which may induce hot air recirculation. The condenser vacuum will decreased significantly as well as the efficiency, and the safety and economy of units will be greatly affected. In north China, the weather is always windy and the wind force is changeable, so it is necessary to know the impact rules of crosswinds on heat transfer performance of air-cooled condensers. It will be beneficial to technical staff to know and predict the operating efficiency under crosswinds and then take effective countermeasures. At present, the researches about air-cooled condensers focus mostly on the ventilation of fans and heat transfer coefficient of air-cooled hear exchangers or the whole platform but seldom involve the quantitative analysis of pressure field, therefore lack of the fundamental analysis about the influence mechanism of crosswinds. It is found that many researchers study on the reason and effects of hot air recirculation qualitatively, but none on the key areas that are sensitive to crosswinds or the performance differences between the heat exchanger bundles in one air-cooled unit.Hence, based on direct air-cooled power plant, the computational models of air-cooled unit and the whole platform are set. According to the infrastructure of air-cooled condenser and the characteristics of environmental wind field, the influence on the flow and heat transfer performance caused by crosswinds is investigated by means of numerical simulation. The influence laws of directions and speeds of crosswinds on the resistance characteristics of the plenum, ventilation of fans and heat transfer efficiency of heat exchangers are obtained. The analysis on mechanism of hot air recirculation is conducted and the exact areas of heat transfer deterioration are found, then more effective preventive measures are proposed.The study results show that the flow and heat transfer performance of direct air-cooled condensers will encounter varying degrees of influence under crosswinds with different directions and speeds. The influence mechanisms of environmental crosswinds and the exact location of heat transfer deterioration areas point out the direction for the precautions. The accuracy of the numerical models has been verified by the actual operation data. The work offers theoretical support and numerical reference to the optimizing design, safety and economy of the direct air-cooled power plant.