Effect of centred hole angular ribs roughness on the solar collector performance in a square tube

Abstract

The numerical study assessed the heat transfer and pressure drop in an evenly heated square duct with plane and perforated ribs. Working fluid is air with Reynolds number (Re) 10,000-80,000. The pitch ratio (y), the dimensionless spacing between ribs relative to hydraulic diameter, is 0.5, 1.0, and 1.5. Rib inclination angles (θ) from the downstream duct wall range from 30° to 60°. The hole ratio (h) is 0.1 to 0.2, depending on perforation size and hydraulic diameter. In all configurations, the heat transfer improvement is maximum at Re = 10,000 and gradually decreases with rising Re. The thermal performance factors (η) for Re = 10,000 vary between 1.4 and 2.2, depending on configuration. The highest η is found at θ = 60°, y = 0.5, h = 0.2. At Re = 40,000, all configurations have η values over 1. The thermal performance for Re = 80,000 is moderate (η ≈ 1.03) for θ = 60°, y = 0.5, h = 0.2. Other configurations provide lower values that are barely over unity.