Impact of artificial roughness variation on heat transfer and friction characteristics of solar air heating system

Abstract

The present study describes the optimization of the spacer length parameter of perforated delta-shaped winglets (PDWs) imposed on the absorber plate of the solar air heater (SAH). An experimental set up is designed to analyze the influence of artificial roughness (AR) variation on the thermo-hydraulic performance of SAH. The variable parameter of the PDWs is the spacer length (Spdw) which varies from0 mm to 300 mm in steps of 100 mm. The impact of variation of Spdw on Nusselt number (Nupdw), friction factor (frpdw) and thermo-hydraulic performance (ηpdw) is investigated. The fixed parameters of the PDWs are relative roughness height of perforated delta-shaped winglets = 0.8, relative longitudinal length of the perforated delta-shaped winglet = 2, relative transversal length of the perforated delta-shaped winglet = 0.66 and angle of incidence = 90°. The Nupdw and frpdwof SAH provided with artificial roughened in the form of PDWs were improved by 5.17 and 4.52 times in comparison to SAH having smooth absorber plate. At the optimum value of spacer lengthSpdw = 0 mm and Re of 12000, ηpdw attains a maximum value of 3.14 (>1). The study reveals the effectiveness of perforated delta winglets in the heat transfer augmentation of SAH.

Keywords

• Solar air heater
• Spacer length
• Friction factor
• Delta winglets