Turbulent Heat Transfer Enhancement and Surface Heating Effect in Square Channels with Wavy, and Twisted Tape Inserts with Interrupted Ribs

Abstract

Regionally averaged heat transfer distributions and friction factors in square channels with hemi-circular wavy tape, hemi-triangular wavy tape, twisted tape inserts, and twisted tape inserts plus interrupted ribs are investigated. The effect of surface heating condition on heat transfer enhancement is also investigated. Each wall of the square channel is composed of isolated copper sections. Regionally averaged Nusselt number ratio, channel averaged Nusselt number ratio, and friction factor ratio in turbulent air flows are presented for Reynolds numbers from 10,000 to 70,000. The results show that uneven surface heating enhances the heat transfer coefficient over uniform heating condition. Square channels with hemi-circular wavy tape (δ/D = 0.1) inserts produce a heat transfer coefficient three times higher than twisted tape inserts (H/D = 6) with almost 25 times the pressure drop penalty. Square channels with hemi-triangular or hemi-circular wavy tape (δ/D = 0.25) inserts produce almost a 2.5 times higher heat transfer coefficient than twisted tape inserts with 5 to 6 times pressure drop penalty. Square channels with twisted tape inserts plus interrupted ribs (e/D = 0.33) produce two times the heat transfer augmentation with four times pressure drop penalty over twisted tape inserts only. Square channels with twisted tape inserts plus interrupted ribs (e/D = 0.33) show the best overall heat transfer performance over other configurations.