Optimum rib-to-rib spacing to enhance forced convection in the triangular duct with ribbed inner surfaces

An experimental investigation had been conducted on the forced convection of a fully developed turbulent flow in an air-cooled horizontal equilateral triangular duct. Uniformly spaced square ribs of the same size of 7.9mm were fixed on the triangular duct's inner surfaces, orthogonal to the mean airflow. Effects of rib-to-rib spacing on the thermal performance of the duct had been studied and an optimum spacing was found corresponding to the maximum convection heat transfer. In the current study, the considered experimental triangular ducts of the same length and hydraulic diameter were fabricated with duralumin. The entire wall of the ducts was heated uniformly, while the outer wall was thermally insulated. The investigation had been conducted over a wide range of hydraulic diameter based Reynolds numbers (i.e. from 4,000 to 23,000). Non-dimensional correlations for the determination of the heat transfer coefficients for such a thermal system had been developed from the experimental results.