三叶膨胀管换热器壳程强化传热的数值研究

三叶膨胀管是一种新型强化传热管,针对纵向流换热器特点,设计了三种不同管束结构参数的三叶膨胀管自支撑纵向流换热器。应用FLUENT软件及Realizable k-ε湍流模型,对三种不同结构参数的三叶膨胀管换热器壳程强化传热特性展开了数值模拟,并通过与实验数据的对比,验证了计算模型的可靠性。计算了不同壳程介质流速下,三叶膨胀管换热器壳程的换热系数与压降值,并获得了壳程流体流线以及相应的温度场、速度场和二次流分布图。结果发现,在壳程水流速一致的情况下,管束横向间距越大的三叶膨胀管换热器,壳程拥有更高的综合换热性能和更低的压降值,但相应地,换热系数也更低。流场分析显示,壳程流体流线呈现出三维纵向旋流形态,二次流的出现改变了速度场和温度场分布,二次流的强度随着管束横向间距的减小而增大。

Numerical Investigation on Shell-Side Heat Transfer Enhancement of Trefoil Expansion Tube Heat Exchanger

The trefoil expansion tube is a novel enhanced heat transfer element. Based on the fluid flow characteristics of the shell-side longitudinal flow heat exchanger, three trefoil expansion tube heat exchangers with different tube bundle structure parameters were designed. The shell-side performance of trefoil expansion tube heat exchangers was numerically investigated by FLUENT software using Realizable k-ε mode. Compared with the experimental data, the accuracy of the calculation model was verified. The heat transfer coefficient and pressure drop value were calculated at different shell-side velocity. The streamline, temperature field, velocity field and secondary flow distribution were also obtained. The results showed that under the same shell side velocity, the trefoil expansion tube heat exchanger with the larger transverse tube spacing possessed higher comprehensive performance and lower pressure drop, but correspondingly lower heat transfer coeffcient. The flow field analysis demonstrated that the flow pattern in shell side was presented as three-dimensional longitudinal helical flow. The appearance of secondary flow changed the distribution of velocity field and temperature field, and the intensity of the secondary flow increased with the decrease of the transverse tube spacing.