Forced convection and pressure drop in a horizontal triangular-sectional duct with V-grooved (i.e. orthogonal to the mean flow) inner surfaces

An experimental investigation has been performed to study the forced convec tion and pressure-drop characteristics fully-developed steady turbulent flo ws in air-cooled, horizontal, equilateral-triangular ducts. These ducts wer e constructed of duralumin, each of the same axial length and hydraulic dia meter. The inner surfaces of each duct were either plane or machined with u niformly-spaced parallel, identical V-grooves. For each tested duct, these grooves had a depth of 1 mm, but were all of the same apex angle, theta, wh ere 0 less than or equal to theta < 150 degrees. The uniform separation bet ween the centre lines of two adjacent V-grooves was kept constant at 34 mm. The measurements were performed with the hydraulic diameter-based Reynolds number for the steady-state air flow, ranging from 2800 to 9500. The entir e inner wall of the duct was heated uniformly, while its outer surface was thermally insulated. The forced convection was enhanced by the presence of the V-grooves; the greatest forced-convection augmentation being achieved w ith V-grooves of apex angle theta approximate to 17.5 degrees. Non-dimensio nal expressions for the determination of the steady-state heat transfer coe fficient and the Darcy friction-factor for the equilateral triangular ducts , which were fabricated with uniformly-spaced identical V-grooves in their inner surfaces, have been deduced. (C) 2000 Elsevier Science Ltd. All right s reserved.