Experimental study on developing and fully developed fluid flow and heat transfer in annular-sector ducts

Measurements are conducted for pressure drop and heat transfer in developing and developed regions of turbulent air flow in five annular-sector ducts. The experimental parameter ranges are as follows: Re = 5,000 to 50,000, apex angle = 18 similar to 40 degrees, and the ratio of outer and inner radius = 0.25. The outer surface of the large circular wall is healed uniformly, while the outer surfaces of the other walls are adiabatic. It is found that in the fully developed region, the variation of the friction factor with the Reynolds number can be expressed by the equation f Re-0.25 = C, where the constant C is less than 0.3164 and increases with the apex angle. The apex angle also has some effects on the thermal entrance length. The larger the apex angle, the shorter the thermal entrance length. The average Nusselt number in the fully developed region can be well correlated by a power-law equation, and the simplified Gnielinski equation can predict the data quite satisfactorily.