LAMINAR HEAT TRANSFER AUGMENTATION THROUGH A SQUARE DUCT AND CIRCULAR TUBE FITTED WITH TWISTED TAPES

Experimental studies on friction factor and heat transfer characteristics for the laminar flow of ethylene glycol in a square duct fitted with twisted tapes of different twist ratios under nearly uniform wall temperature conditions are reported in this article. The Nusselt numbers were found to be 5.44-7.49 and 2.46-4.87 times that of plain square duct forced convection values based on constant flow rate and constant pumping power criteria, respectively, for y=2.66. The augmented friction factor and Nusselt number for a square duct is about 1.9 and 2.10 times higher than that for an augmented circular tube.