Article ID Journal Published Year Pages File Type
656765 International Journal of Heat and Mass Transfer 2015 22 Pages PDF
Abstract
The objective of the experimental study is to investigate heat transfer of co/counter-dual swirling impinging jets (Co-DSIJs/C-DSIJs) on the impingement surfaces under uniform wall heat flux boundary condition. Two twisted-tapes were inserted into pipe nozzles with different arrangements: (1) each tape was twisted in the same direction as the co-dual tapes for producing co dual swirls and (2) each tape was twisted in the different directions as the counter-dual tapes for inducing counter dual swirls. The effect of the Co-DSIJs/C-DSIJs with baffles placed between the tapes for jet confinement on heat transfer was also investigated. The effects of jet Reynolds number (5000 ⩽ Re ⩽ 20,000), jet-to-plate spacing (1 < L/D < 8) and tape twist ratio (y/W = 3, 4, 5 and 6) were examined. In addition, the experiments using a single swirling impinging jet (SIJ) and a conventional impinging jet (CIJ) were also carried out, for comparison. The temperature distributions on impinged surfaces were recorded via a thermochromic liquid crystal (TLC) sheet and then Nusselt number distributions were obtained by a liquid crystal thermography technique. The experimental results revealed that for all Co-DSIJs and C-DSIJs, heat transfer increased with decreasing nozzle-to-plate spacing (L/D) and increasing Reynolds number. For the Co-DSIJs and C-DSIJs without baffle, heat transfer increased with increasing twist ratio (decreasing swirl number) while the opposite trend was found for the Co-DSIJs and C-DSIJs with baffle. At similar conditions, the Co-DSIJs and C-DSIJs with baffles offered higher heat transfer than the ones without baffle, owing to the combined effect of swirling flow and jet confinement. For small jet-to-plate spacings (L/D = 1 and 2), all swirling jets possessed considerably higher average Nusselt numbers than the conventional jets, at similar conditions. At large jet-to-plate spacings (L/D = 4, 6 and 8), the average Nusselt numbers of the conventional and swirling jets became comparable. For the studied range, the maximum average Nusselt number of 110 was achieved by using C-DSIJs with baffle at L/D = 1, y/W = 3 and Re = 20,000.
Related Topics
Physical Sciences and Engineering Chemical Engineering Fluid Flow and Transfer Processes
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