Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7051601 | Experimental Thermal and Fluid Science | 2018 | 35 Pages |
Abstract
Thermal performance improvements for tubular flows using spirally coiled spring (SCS) inserts to disturb boundary layers by tripping near-wall separated vortices are proposed. Combined with the segmental solid cords to induce axial swirls, a new convenient passive heat transfer enhancement (HTE) method is formulated. The interval of segmental solid cords is fixed at one tube diameter (d); while the pitch ratios (P/d) of the SCSs are 0, 1, 1.5, 2, 2.5 and â. The axial Nusselt numbers (Nu), mean Fanning friction coefficients (f) and thermal performance factors (TPF) at Reynolds numbers (Re) between 750 and 70,000 are measured for each test tube. Acting by the interactive near-wall vortices and the axial swirls in the tubes with the SCSs and segmental solid cords, both HTE effectiveness and f augmentation are boosted from those developed in the tubes with SCSs alone. Relative to the plain tube heat transfer references over the developing (Nuâ¾0DE) and developed (Nuâ¾0FD) flow regions, the ratios of Nuâ¾DE/Nuâ¾0DE and Nuâ¾FD/Nuâ¾0FD are elevated to 1.81-9.04 and 1.01-8.21 at 750â¯â¤â¯Reâ¯â¤â¯2000; and 1.11-2.41 and 1.02-2.33 at 10,000â¯â¤â¯Reâ¯â¤â¯70,000 by the SCSs of 0â¯â¤â¯P/dâ¯â¤â¯â without cord. For present SCSs of 0â¯â¤â¯P/dâ¯â¤â¯â with segmental cords, the ratios of Nuâ¾DE/Nuâ¾0DE and Nuâ¾FD/Nuâ¾0FD are raised to 1.81-10.74 and 1.01-9.07 at 750â¯â¤â¯Reâ¯â¤â¯2000, and 1.11-3.15 and 1.02-2.66 at 10,000â¯â¤â¯Reâ¯â¤â¯70,000, respectively. With present geometrical and flow conditions tested, the TPF values for the tubes enhanced by the SCSs without and with segmental solid cords are in the respective ranges of 5.07-0.61 and 3.75-0.64. For each type of enhanced tubular flows, the Nu and f correlations are devised to assist the relevant applications.
Keywords
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Fluid Flow and Transfer Processes
Authors
Shyy Woei Chang, Kuo-Ching Yu,