3D numerical analysis of thermal-hydraulic behaviors of turbulent flow inside twisted square ducts
P. Promthaisong1, V. Chuwattanakul2, S. Eiamsaard1
1Mahanakorn University of Technology, Bangkok, Thailand
2King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand
Keywords: heat transfer, passive heat transfer, swirl, turbulent periodic flow, twisted square duct
Abstract
Heat transfer, local distributions of Nusselt number, flow structure, and friction characteristics of twisted square ducts are presented. Numerical analysis was carried out to investigate the influence of the twist ratio ( TR = p / D = 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0) on the thermal-hydraulic performance of twisted square ducts under constant wall heat flux condition for Reynolds numbers based on the hydraulic diameter of the twisted square duct ranging from 3000 to 20 000. The straight square duct was also analyzed for comparison. The numerical results showed that the twisted square ducts were more efficient in heat transfer than the straight square ducts because the swirl flow helped to increase fluid mixing and reduce thermal layer boundary thickness. The decrease of the twist ratio led to the increase in the Nusselt number and friction factor due to the higher frequency of swirl flow. As compared to the straight square duct, the twisted square ducts with TR = 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0 improved heat transfer by 52, 49.82, 45.85, 42.22, 39.54, 35.41, and 31.77 %, respectively. Among the studied twisted ducts, the ones with twist ratio TR = 3.5 offered the maximum thermal enhancement factor of 1.42 at Re = 3000. In addition, the results also revealed that the twisted square ducts are thermo-hydraulically superior to the straight square ducts.
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