振荡流通过内插螺旋翅片管传热特性的数值模拟

Numerical simulation of heat transfer of oscillatory flow in a tube fixed with spiral fins

振荡折流换热器广泛应用在包含传热传质过程的化工过程中,本文对管内插入螺旋翅片的振荡折流换热器进行了三维非稳态数值模拟,模拟在斯特劳哈尔数St=2,4,8和振荡雷诺数Reo=20,40,80范围内进行。通过作出瞬时三维流线,以观察流动状态随时间变化规律,发现其中有纵向涡和横向涡的周期性形成和脱落;得到了圆管周向局部传热系数随时间变化规律,以及不同振荡参数(St和Reo)下周向平均传热系数随时间的变化规律。结果表明:局部传热系数沿周向不均匀分布,并在翅片斜对面达最大;周向平均传热系数随时间周期性变化,时间平均传热系数随振幅增大而增大,但受频率影响却不明显;在本文讨论的参数范围内,平均传热系数最大可达圆管层流的4倍。

Oscillatory baffled heat exchangers（OBHEs） are widely used in chemical processes involving heat or mass transfer. OBHE with spiral fins inserted was simulated using the three dimensional unsteady method in the range of Strouhal number St=2,4,8 and oscillatory Reynolds number Reo=20,40,80. Instantaneous three dimensional stream lines were drawn to show the change of flow status with time,and periodic formation and shedding of spanwise and streamwise vortexes was observed. The changes with time of peripheral local heat transfer coefficients（HTCs）and peripherally averaged HTCs with different oscillatory parameters（St and Reo） were obtained. The local HTCs were not distributed uniformly peripherally and a maximum value was reached at the diagonally across position of fins. Peripherally averaged HTC varied with time periodically and time averaged HTC increased with increasing amplitude,but hardly changed with frequency. In the range covered by this work,averaged HTC could be four times higher than that of tube laminar flow.