Enhanced Heat Transfer in Square Duct Fitted Diagonally with Double-Sided V-Ribbed Tapes

Abstract

An experimental study on heat transfer enhancement in a heat exchanger square-duct fitted diagonally with 45° V-ribbed tapes has been conducted. The tested duct has a square section and uniform heat-fluxed walls and the flow rate of air used as the test fluid is presented in terms of Reynolds number from 4000 to 25,000. The insertion of the V-ribbed tape is performed with a rib-pitch to duct-height ratio, (P/H=PR=0.75 and 2) at the rib attack angle of 45° with respect to the main flow direction. The V-ribbed tape inserted diagonally in the duct is expected to generate a longitudinal vortex flow pair in each tape side through the heated duct. Influences of four rib-to-duct height ratios (e/H=BR=0.1, 0.15, 0.2 and 0.25) on the heat transfer and pressure drop in terms of respective Nusselt number and friction factor are investigated. The experimental result indicates that the BR and PR of the V-ribs provide a significant effect on the thermal performance of the test duct. The results reveal that at smaller PR, the V-rib with BR=0.25 provides the highest heat transfer and friction factor but the one with BR=0.2, PR=0.75 yields the best thermal performance.