基于Lee模型与VOF方法的ACC基管内凝结性能的比较与数值模拟

Numerical Comparison and Investigation of Condensation Heat-transfer Performance in ACC Base Tubes with Lee Model and VOF Method

为了比较电厂不同ACC基管内的凝结换热性能,基于600MW空冷机组上实际运行的工程基管,建立1∶4缩小比例的大扁管、椭圆管和圆管3种样管,利用Lee模型和VOF方法,对基管内两相流的流动与凝结换热进行数值模拟,得到了3种管型的管内凝结传热系数、Nu与两相流体积分数。结果表明:30°倾角下的圆管管内凝结性能最好;ACC基管内凝结性能受蒸汽入口饱和温度与入口轴向流速的影响较大,基管管壁过冷度会轻微影响管内换热性能;3种管型内的两相流都可归类为降落膜状流,凝结液膜厚度受到基管管型、蒸汽入口轴向流速和管壁过冷度的影响。

To compare the condensation heat-transfer performance in flat,oval and round base tubes of aircooled condensers (ACCs)widely used in power plants,a 1:4 scale model was set up based on actual base tubes of a 600 MW air-cooling unit to simulate the two-phase flow and condensation heat-transfer performance in the tubes with Lee model and VOF method,thus obtaining the condensation heat-transfer coefficient,Nusselt number and volume fraction of the two phase fluids.Results show that the round tube with an inclined angle of 30° has the optimal in-tube condensation performance;the condensation heat-transfer performance in ACC base tubes is considerably influenced by both the temperature of saturated steam and the axial velocity at the tube inlet,which is slightly affected by the subcooling degree of the tube wall.The two-phase flows in above three tubes are all of the falling film kind,and the thickness of condensate film over the tube wall depends on the tube type,the inlet velocity of steam and the subcooling degree of the tube wall.