Turbulent heat transfer and pressure loss in a square-duct heat exchanger with inclined-baffle inserts

Thermal and friction loss characteristics in a square-duct heat exchanger fitted with inclined-baffles are experimentally examined. Air as the test fluid enters the test duct having a uniform surface heat-flux. The baffles are placed repeatedly on both sides of a rectangular centre-cleared tape/frame before diagonally inserting the baffled frame into the test duct to produce longitudinal vortex flows through the test section. Effects of five different relative baffle height or flow blockage ratios (b/H=BR=0.1, 0.2, 0.3, 0.4 and 0.5) on heat transfer, pressure loss and thermal performance in the square duct are investigated for Reynolds number ranging from 4100 to 25,600. The relative baffle pitch or pitch ratio (P/H=PR) and baffle attack angle (α) are fixed at 3.0 and 30°, respectively. The experimental results reveal that the heat transfer and pressure drop in the form of respective Nusselt number (Nu) and friction factor (f) from using the baffle tend to increase with the rise of Reynolds number (Re) and BR. The maximum enhancement in Nu and f has been found to be 4.61 and 63.67 times above the smooth duct, respectively. The thermal enhancement factor (η) is maximum at BR=0.3.