A Model for Calculating Turbulent Friction and Heat Transfer Coefficients of a Rectangular Duct With Angled Ribs on Two Opposite Walls Free

A new model is presented in this paper to calculate the pressure drop and the heat transfer coefficient for a rectangular duct with two smooth walls and two rough walls. Ribs on the rough walls may be at an angle with the main flow and are distributed in a repeated pattern. The model is based on the law-of-the-wall theory, which is known to give satisfactory results for turbulent flows in a circular duct or a channel, and for two-dimensional boundary layer flows. When the theory is applied to a rectangular duct, it gives simplified relationships between the friction, heat transfer coefficients, the flow Reynolds number, and geometry parameters, which include the rib angle, rib height, the rib pitch, and the duct aspect ratio. Comparisons with experimental data show that the present model gives satisfactory results for a wide range of Reynolds numbers and geometry parameters. A Prandtl number dependence is retained for applications involving fluids other than air.