Experimental studies on heat transfer augmentation and friction factor characteristics for laminar flow of water in a square duct induced by full-length helical tapes

Experimental studies on heat transfer enhancement and friction factor characteristics of water flowing in Laminar flow regime through a square duct, fitted with full-length helical inserts of varying twist ratio have been reported in the present paper. The test liquid flows in the laminar flow through a square duct and in counter current manner a hot water at very high flow rate is directed though the annulus to ensure a constant wall temperature conditions. A plain duct fitted with helical inserts provides higher friction factor and Nusselt number than that of empty duct. The heat transfer and pressure loss were observed to be higher at minimum twist ratio. The thermo hydraulic performance ratio on constant pumping power of the duct induced by helical inserts at different twist of 1.44, 2.55, 3.66, 4.66 were found to be 5.20, 4.44, 4.01, and 3.50 times higher than the plain duct.