管束效应对含空气蒸汽冷凝传热影响数值分析

Numerical Analysis of Bundle Effect on Steam Condensation in Presence of Air

采用数值模拟的方法分析管束效应对管外含空气蒸汽冷凝传热的影响。基于3×3管束,分析了管间距在1.5d^5d(d为管径)范围内的管束效应及管间距对局部和平均冷凝传热性能的影响。在管间距为1.5d条件下讨论了管束结构对冷凝传热性能的影响。结果表明,管束效应包括高浓度空气层的抑制传热作用和管束抽吸效应的强化传热作用。随着管间距的减小,第2类和第3类传热管主要受高浓度空气层的影响,第1类传热管主要受管束抽吸效应的影响。当管间距为1.5d时,第2类和第3类传热管的传热系数分别比单管恶化了6%和29%,而第1类传热管比单管增加了2.5%;在1.5d管间距条件下,管束抽吸效应随管列数的增加而明显增大,导致管束平均冷凝传热系数(hb)逐渐增大。当管列数达到20列时,hb高于单管。

This paper numerically investigated the tube bundle effect on steam condensation in the presence of air.Simulations were firstly performed based on the 3 by 3 tube bundles with various tube pitches.Via these cases,the tube bundle effect was defined and the effects of tube pitch on local and average condensation heat transfer were discussed.Then at a tube pitch of 1.5d,the effect of bundle structure on the condensation heat transfer was evaluated.Results indicate that the bundle effect includes the high concentration air layer inhibition effect and the bundle suction enhancement effect.With the decreasing of the tube pitch,the second and third type tubes are mainly influenced by the high concentration air layer effect,and the first type tubes mainly by bundle suction effect.At 1.5d tube pitch,the average heat transfer coefficient for the second and third type tubes decreased 6%and 29%compared to the single tube.In comparison,the first type tubes increased 2.5%.At the tube pitch of 1.5d,the bundle suction effect increases with the increasing of the tube column,resulting in an enhancement of bundle average condensation heat transfer coefficient.For the 3 by 20 bundle structure,the bundle average heat transfer coefficient exceeded that of the single tube.