ANALYSIS OF COMBINED NATURAL AND FORCED-CONVECTION IN VERTICAL SEMICIRCULAR DUCTS WITH RADIAL INTERNAL FINS

A numerical analysis of combined natural and forced convection is conducted for the fully developed laminar flow and heat transfer in a vertical semicircular duct with radial, internal longitudinal fins. Accurate solutions for heating upward flow are obtained by the finite difference method based on a fine grid, while the hydraulic and thermal conditions of the fills are ascertained. The results represent a range of Rayleigh numbers and various values of fin lengths and number of fins. The fully developed f Re and Nu values for pure forced convection in the finned semicircular duct are also documented. It is found that both the friction factor and the Nusselt number in the finned tube increase as the Rayleigh number increases. The effect of buoyancy is significant in semicircular ducts with short fins. By comparing the results of finless ducts with those of finned ducts, it was concluded that heat transfer in combined natural and forced convection in the semicircular duct is dramatically enhanced by using radial internal fins.