Influence Of Head Wind Velocity On Flow And Heat Transfer Performance Of Direct Air-cooled Condenser

Because of its property of water-saving, direct air-cooled technology has beenwidely used in recent years, especially in the northwest of China where it is rich incoal but less in water resources. The direct air-cooled condensers (DACC) use air ascooling medium. The finned tube is the core element of DACC and the key offurther improving the performance of flow and heat transfer in DACC. Therefore,the research on the heat transfer performance of cooling air outside the signalfinned tube widely used in DACC is of great importance in the design and operationof DACC.Three-dimensional physical and mathematical models are established for thesignal finned tube used in Lingwu1000MW unit. The flow and heat transferperformances of signal finned tube are calculated by using CFD software on thebase of data obtained from the field experiment. Influence of head wind velocityand its distribution on air side heat transfer coefficient of the signal finned tube isstudied, and a better flow rate distribution of cooling air in front of signal finnedtubes is found in the end.Take signal finned tubes as research objects, physical and mathematicalmodels of flow in the interspace among fins are established. The flow and heattransfer performances of signal finned tube in the operating mode of autumn aresimulated numerically under different head wind velocity. The synergy degreebetween velocity and temperature gradient field is analyzed based on field synergyprinciple, and the influence of field synergy on heat transfer enhancement isresearched.The results show that under uniform head wind velocity distribution, the heattransfer coefficient of the finned tube increases with the head wind velocity value.Under the same cooling air mass flux, the head wind velocity decreasing alongvapor flow direction can enhance the heat transfer coefficient of finned tube and isin favor of heat transfer. Different head wind velocity distribution enhances the heattransfer performance of the finned tube in different degree. The parabolicdistribution is more beneficial than linear distribution for heat transfer enhancementof finned tubes. With the head wind velocity value increasing, the average fieldsynergy angle of the flow in the interspace between fins grows up, so that thecoordination of the velocity and the temperature gradient fields worsens. This goesagainst further enhancement of the heat transfer performance in finned tubes.