NUMERICAL INVESTIGATION OF LAMINAR FLOW AND HEAT TRANSFER IN HEXAGONAL DUCTS UNDER ISOTHERMAL AND CONSTANT HEAT FLUX BOUNDARY CONDITIONS

Three-dimensional laminar flow and heat transfer characteristics in smooth hexagonal
ducts with equal sides have been numerically investigated in the Reynolds number range from 300
to 2000. The numerical solutions are obtained for both axially and peripherally constant wall
temperature (T) and heat flux (H2) thermal boundary conditions for five different values of the
duct angle ( = 30, 45, 60, 75, and 90o). Local Fanning friction factor and Nusselt number are
obtained along the duct. Hydrodynamic and thermal entrance lengths have been determined. The
accuracy of the results obtained in this study is verified by comparing the results with those
available in the literature. Results show that duct geometry plays an important role on both flow
and heat transfer characteristics. It is seen that the thermal entrance length for H2 boundary
condition is greater than that for T boundary condition. Minimum hydrodynamic and thermal
entrance lengths are obtained for  = 60o, regular duct. New correlations, important for the design
of thermal equipment, are presented for the hydrodynamic and thermal entrance lengths, friction
factor, and Nusselt number for 30o    90o and 300  Re  2000.