Numerical investigation of hydrodynamically fully developed, thermally developing flow in hexagonal duct

In this study, hydrodynamically fully developed, thermally developing turbulent flow in hexagonal duct was numerically investigated under constant wall temperature and steady flow conditions. Air (Pr=0.7) is used as the working fluid and the study was carried out in the Reynolds number range of 10000 < Re < 50000. Hydrodynamically fully developed flow obtained in the first of two consecutive channels with the same cross-section and thermally developing flow were investigated in the second channel under constant wall temperature. Solutions were made for different lateral angle such as 90° (rectangular with aspect ratio ½), 75°, 60° (honeycomb hexagonal), 45° and 30°. Heat transfer and three-dimensional numerical analysis was carried out with standard k-? model. Three dimensional continuity, momentum and energy equations are numerically solved via Ansys Fluent 12.1 software using finite volume method and Simple algorithm. At the result of the study, average Nusselt number (Nu) and Darcy friction factor (f) are presented in term of Reynolds number (Re) in form of empirical Nu=aReb and f=cRed equations. The results were compared with the literature and shown compatible. As a result, it was shown that the Nusselt number is the highest in the equilateral hexagonal ducts. In addition, some of the formulas given in the literatur for circular channel can be used for hexagonal cross section ducts with the same hydraulic diameter considering a difference of 5%.Key Words : Turbulent flow, hexagonal cross-section duct, rectangular crosssection duct, hydrodynamically fully developed flow, thermally developing flow, fluent, heat transfer