竖直管束外含空气蒸汽冷凝传热特性数值分析

Numerical Analysis on the Characteristics of Steam Condensation in Presence of Air under Vertical Tube Bundle Conditions

采用STAR-CCM+软件对管束条件下含空气蒸汽冷凝开展了数值模拟研究。主要考察了3×3管束、管间距为2倍管径条件下不同传热管的局部场分布和流动传热特性。结果表明,在管束条件下,各传热管附近的空气层发生了重叠,形成了高空气浓度区。这一方面促进了气体的自然对流,提高了对流传热能力;另一方面增加了空气层厚度,抑制了冷凝传热。在管束结构的影响下,管束区域的浓度、温度和速度梯度均较单管有明显的差异,导致各传热管的局部传热系数沿轴向降低了50%以上,周向传热系数最大相差1.88倍。其中,轴向传热性能主要受浓度边界层发展的影响,周向传热性能主要受相邻传热管的影响。通过分析表面平均传热系数发现,各传热管较单管最大降低了9.06%。

Numerical simulations on steam condensation in the presence of air under tube bundle conditions were performed based on the software STAR-CCM+.Calculations were carried out based on a the 3 by 3 tube bundle which has a tube pitch of double diameter,aiming at recognizing local field distributions and thermal-hydraulic characteristics of various tubes.Results indicate that the air layers of various tubes interfere in the tube bundle region,forming a larger high concentration air layer region.On the one hand,this enlarges local velocity and facilitates convective heat transfer;and on the other hand increases the air layer thickness and inhibits condensation heat transfer.On the effect of bundle structure,the concentration,temperature and velocity in the tube bundle region are obviously different from those of the single tube one,sharply decreasing the local heat transfer coefficient by 50%and has a maximum variation of 1.88 times circumferentially.The axial heat transfer property mainly is affected by the development of concentration boundary layer,and circumferential heat transfer property by the adjacent tubes.By analyzing the average heat transfer coefficient,it indicates that compared to the single tube,the maximum reduction of the bundle tube average heat transfer coefficient is 9.06%.