Vbrtcx gcncrator can produce a 加 rbulcncc and longitudinal vorticcs and control the separation point on the tubc surfacc , and thcn augmcnt an impinging arca ofthe now Qn thc fin surfacc . 【 n order to dct己rmin じ the best configuration ofvortcx gcncrator , it is noccssary to know the cff6cts of vortcx gcncrator on the flow and hcat transfbr characteristics ovcr thc tubc and fin surfacc . In this study , we uscd louvc ト typc vortex generator and tricd to find out thc ef 艶 ct of vQrtex gencrator on thc flow and hcat transfer charactcristics . Asarcsul 亡 , using a vortex generator , thc scparation point on し hc tubc moved tQ downstrcam up tQ l 30 °frorn thc f ヤ on 亡stagnation point and thc dcad watcr rcgion wa5 decreascd . Then . the hcat transfcr characteristics bchind the cylinder wcrc improved significantly 」 The m 巳 an ハ伽∬ 8 々 number on thc tubo wlth vortcx generator was increascd up to maximum 57% than the p匸 anc fin . κey 怖b 厂 ds: Fin − tube heat exchanger , F ' ow and heat transfer contrc ) 1, Vortex genera め 燗 e ∂t transfer e 肋 a ηceme η'
: Mixing and spreading characteristics of an orifice free jet are investigated changing the orifice plate thickness t/do, where do is the nozzle exit diameter, ranged from 0.01 to 1.5. Schlieren images show high mixing and spreading performances at t/do = 0.5 and Reynolds number Re = 1.5 × 10 4 because at the t/do = 0.5 the jet fluctuates by the separated flow from the inner edge of orifice alternates attachment and detachment to the outer edge. Hot-wire anemometry measurements are also performed to investigate the mean and fluctuating velocity profiles. It is found that the jet potential core length is insensitive to Re at Re > 7.0 × 10 3 , but significantly influenced by the orifice plate thickness.
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