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

本文采用实验和数值模拟相结合的方法研究了涡流发生器对翅片管换热器强化传热和降低压力损失的同时作用。对实验室的传热试验装置进行了改进，采用单吹法测量了三种不同结构（即：螺旋管、螺旋管仅带翅片、带翅片加两排管和带翅片、两排管加单排涡流发生器）的换热器表面。雷诺数为150-800。结果表明：（1）涡流发生器的安装使压力损失增加了10%，且对雷诺数的依赖性较小;（2）它们的安装可使传热系数提高10- 35随着雷诺数的增加，局部换热系数的增加率。上述三种结构的翅片表面上的局部换热系数的定量的瞬态方法使用IR成像仪。雷诺数为200-600。在水流实验装置上，用粒子图像测速仪（ParticleImageVelocimetry）（Re=200-300）测量了翅片间距为9mm的管后三维流场。壁面剪应力分布的测量速度场进行评估。此外，利用商用CFD软件对换热器内的传热和流体流动进行了研究，比较了实验和计算的总传热系数和局部传热分布。结果表明，涡流发生器的安装确实有效地改善了换热的净增强效果，其增强幅度随雷诺数的增加而增大，但在低雷诺数（小于300）时，这种改善效果可以忽略不计。

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).