An experimental and numerical study of flow field and heat transfer for square duct with slot-rib twisted tape

Abstract

In the literature the heat transfer enhancements (HTE) and pressure drop augmentations are simultaneously incurred by using the modified twist-tapes with ribs By using the regularly spaced or perforated twist-tapes the pressure drop penalties are moderated with the HTE effectiveness weakened As an attempt to moderate the considerable pressure-drop augmentations caused by a ribbed twist-tape the present study proposed the twist-tape with the inclined ribs and slots as a new type of twisted tape insert with the associated heat-transfer and pressure-drop performances investigated With a conventional twisted tape in a tube to separate the flow stream along two spiral pathways the newly slot-rib twisted tape permits the mass momentum and energy exchanges through the tape and provides the perforation effect to reduce the flow resistances owing to large pressure gradients The aerothermal performances of the rib-slot twist tape at the Reynolds number of 10000 20000 30000 40000 50000 with air as the coolant are numerically and experimentally studied The results show that with the Reynolds numbers in the range of 10000 to 50000 the Nusselt numbers are elevated to 3 8 to 4 2 times of the Dittus-Boelter correlation (plain tube) values with the friction factors raised to 32 5 to 40 2 times of the Blasius equation (plain tube) levels With the inclined ribs and slots the friction factor augmented by the present rib-slot twist-tape is reduced from that caused by the ribbed twist-tape whereas the heat transfer enhancements generated by the ribbed and the present rib-slot twist-tapes are similar With the reduced pressure-drop penalties and the raised HTE effectiveness the aerothermal performance factors attributed to the present rib-slot twist-tape are improved from many types of twisted tapes Based on the experimental data generated the empirical correlations for calculating the Nusselt number Fanning friction factor and heat transfer power ratio for the square duct fitted with the present rib-slot twist-tape are proposed for relevant applications

Date of Award	2021
Original language	English
Supervisor	Shyy-Woei Chang (Supervisor)