✍ Scribed by Juin Chen; Hans Müller-Steinhagen; Geoffrey G Duffy
No coin nor oath required. For personal study only.
Heat transfer enhancement was investigated in a coaxial-pipe heat exchanger using dimples as the heat transfer modi®cation on the inner tube. Tube-side Reynolds numbers were in the range of 7X5 Â 10 3 ± 5X2 Â 10 4 for water ¯ow. A constant annular mass ¯ow rate was chosen to obtain the highest possible Reynolds number of 1X1 Â 10 4 . Typically, the heating water inlet temperature was 68X1 AE 0X1 C.
All six variants with inward-facing, raised dimples on the inner tube increased the values of heat transfer coecient signi®cantly above those for the smooth tube. Heat transfer enhancement ranged from 25% to 137% at constant Reynolds number, and from 15% to 84% at constant pumping power. At a constant Reynolds number, the relative J factor (ratio of heat transfer coecient to friction factor, relative to smooth tube values), had values from 0.93 to 1.16, with four dimpled tube con®gurations having values larger than unity. Despite the extremely simple design, this outperforms almost all heat transfer enhancements recommended in the literature. A correlation based on the results of the present work appears to be suciently accurate for predicting heat transfer coecients and friction factors for the design of dimpled-tube heat exchangers.
📜 SIMILAR VOLUMES
Friction and compound heat transfer behaviors in a dimpled tube fitted with a twisted tape swirl generator are investigated experimentally using air as working fluid. The effects of the pitch and twist ratio on the average heat transfer coefficient and the pressure loss are determined in a circular