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

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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).