Experimental studies on heat transfer and friction factor characteristics in a square duct for laminar flow fitted with swirl flow generators

Abstract

newline The present experimental work conducted on heat transfer augmentation using full length twisted tapes increasing and decreasing order of twist ratio sets and full length screw tapes The test liquid flows in laminar flow through an inner square duct and hot water at very high flow rate in counter current fashion through an annular channel to attain nearly uniform wall temperature conditions, using water and ethylene glycol as test liquids The inserts when placed in flow path of test liquid reduces flow passage area and creates a high degree of turbulence resulting in an increased heat transfer rate and pressure drop The work also presents the variation of friction factor, heat transfer coefficient and thermohydraulic performance ratios R1 and R3 with Reynolds number for twisted tapes and screw tapes with different twist ratios The results of a square duct fitted with twisted tapes and screw tapes with different twist ratios have been compared with a plain duct data Effects of insertion of full length twisted tapes of different twist ratio, increasing and decreasing twist ratio sets on heat transfer and pressure drop characteristics in a concentric double pipe heat exchanger square duct inner and circular tube outer were experimentally investigated The data were taken for Reynolds number well in the laminar region Re 100 to 2100 with full length twisted tapes of different twist ratios and increasing and decreasing order of twisted tapes The water flows through inner square duct and hot water at very high flow rate though an annular channel formed between a square duct and circular tube to ensure nearly a uniform wall temperature conditions The results demonstrate that as twist ratio decreases the twisted tape gives higher friction factor and better heat transfer enhancement The heat transfer coefficient hi increases and friction factor f newlinedecreases with increasing Reynolds number Re The increasing and decreasing order of newlinetwist ratio sets gives almost same heat transfer enhancement, as the intensi