纵向涡强化换热的数值研究及场协同原理分析

Numerical Analysis to Vortex Heat Transfer Enhancement Based on Field Synergy Principle

用三维数值模拟的方法研究了纵向涡发生器用于管-翅表面的流动换热特征．计算了Re（为800～2000）、三角形小翼型涡发生器的冲角（分别为30°和45°）对管一翅表面平均Nu、压降的影响，并利用场协同原理进行了分析．结果发现纵向涡强化管一翅表面换热的内在机理可以用场协同原理进行解释，即纵向涡发生器使全场速度和温度梯度之间的平均夹角减小．另外计算还发现：三角形小翼对顺排换热器的强化换热效果好于对叉排换热器的强化；冲角为45°的三角形小翼强化换热效果好于冲角为30°的三角形小翼；冲角为45°的三角形小翼导致空气压降提高，而冲角为30°的三角形小翼则可使压降有所减小．无论传热管是叉排还是顺排，冲角为30°的三角形小翼比冲角为45°的三角形小翼在消耗单位泵功条件下带来的强化换热效果更大．

3-D numerical simulation results are presented for fin-and-tube heat transfer surface with vortex generators. The effects of Reynolds number（from 800 to 2 000）, the attack angle（30° and 45°）of delta winglet vortex generator are examinee The numerical results are analyzed based on the field synergy principle to explain the inherent mechanism of heat transfer enhancement by longitudinal vortex, namely second flow generated by the vortex generators causes the reduction of the intersection angle between the velocity and fluid temperature gradient. In addition, the computational evaluations indicate that the heat transfer enhancement of delta winglet for aligned tube bank heat exchanger is more significant than that for staggered tube bank heat exchanger, the heat transfer enhancement of delta winglet with the attack angle of 45° is more obvious than that of 30°; the delta winglet with the attack angle of 45° leads to an increase in pressure drop, while the delta winglet with the attack angle of 30° results in a slight decrease. The heat transfer enhancement per unit pumping power for attack angle of 30° is larger than that for attack angle of 45° either for staggered or for aligned tube bank arrangement.