Simultaneous Heat-Transfer Augmentation and Pressure-Loss Reduction of Fin-Tube Heat Exchanger by Means of Vortex Generators

对涡流发生器强化翅片管式换热器的同时强化换热和降低压力损失进行了实验和数值研究，对实验室内的换热试验台进行了改进，采用单吹法测量了3种不同结构的换热器表面的总换热系数和压力损失，分别为带翅片、带翅片加双排管和带翅片、双排管加单排涡流发生器。雷诺数是150-800。结果表明：(1)涡流发生器的安装增加了10%的压力损失，且对雷诺数的依赖性很小；(2)随着雷诺数的增大，涡流发生器的安装使换热系数增加了10%~35%，利用红外成像仪采用瞬态法对上述三种布置的翅片表面局部换热系数进行了定量。雷诺数是200-600。利用粒子图像测速仪(Re=200-300)，在水流实验装置上测量了相邻翅片间9 mm缝隙内管子的三维流场。根据测得的速度场估算了壁面剪应力分布。此外，还利用商用CFD软件对换热器内的换热和流体流动进行了研究，比较了实验和计算的总换热系数和局部换热分布。结果表明，旋涡发生器的安装对换热强化的净改善是非常有效的，并且随着雷诺数的增加而增大，但在低雷诺数(如小于300)时，这种改善可以忽略不计。

Simultaneous heat-transfer augmentation and pressure-loss reduction of fin-tube heat exchanger by means of vortex generators is studied experimentally and numerically.The heat-transfer test facility in the laboratory is modified single-blow method is used to measure the overall heat-transfer coefficient and the pressure loss for three different configurations (i.e., the ones with fin only, with fin plus two-row tubes, and with fin, two-row tubes plus single-row vortex generator) of the heat exchanger surface considered. The Reynolds number is 150-800. It is found that (1) the installation of the vortex generators increases the pressure loss by 10% and its Reynolds number dependency is small, and (2) their installation increases the heat transfer coefficient by 10-35% with increasing rate of augmentation with the Reynolds number.Local heat transfer coefficients on the fin surface for the three configurations above are quantified by the transient method using an IR imager. The Reynolds number is 200-600. Three-dimensional flow fields behind the tubes in the 9-mm gap between neighboring fins are measured in a water flow facility by means of particle image velocimetry (Re=200-300). The wall-shear stress distributions are evaluated from the measured velocity fields. In addition, the thermal and fluid flow in the heat exchanger considered is studied by using a commercially available CFD software to make comparison of overall heat transfer coefficient and local heat transfer distribution between experiment and computation. Good agreement between them is obtained together with similarly good agreement of flow field between the PIV measurement and he computation.It is concluded that the installation of the vortex generators is truly effective to the net improvement of heat transfer augmentation with its increasing magnitude with the Reynolds number and that such improvement, however, becomes negligible at low Reynolds numbers (say, less than 300).