Heat transfer and air flow friction in solar air heaters: A comprehensive computational and experimental investigation with wire-roughened absorber plate

Abstract

This research focuses on the purpose and importance of studying the impact of physical factors on heat transfer and air flow patterns in a solar air heater (SAH) with wire-shaped roughness on the absorbers rectangle conduit. By understanding these factors, we can enhance the radiation absorption effectiveness of solar collectors. To investigate the effects of artificial roughness arrangement on SAH efficiency, we developed an experimental apparatus. The experiments involved determining the allowable ranges of dimensionless factors such as relative wire roughness height (h/D), relative roughness wire pitch (p/h), and the angle of approach of flow (α). Additionally, we considered the Reynolds number (Re) and the duct width to height ratio (W/H) during the development of computer program code for optimization. By comparing experimental findings with those obtained from a smooth duct under similar flow circumstances, we evaluated the improved heat transfer and friction factor. Notably, for specific parameters such as W/H = 5, h/D = 0.01, p/h = 40, and α = 50◦, the average Stanton number (Stav) was found to be 1.196 times higher than that of a smooth SAH duct. Similarly, the average friction factor (fav) was observed to be 1.044 times higher than that of a smooth SAH duct. At p/h = 40 and h/D = 0.01, the average air friction factor and average Stanton number are the lowest for Reynolds number 3000. These numbers have the best efficiency index, which is 1.148. The research findings have implications for optimizing solar air heaters by incorporating wire-shaped roughness on the absorbers conduit. This enhances heat transfer and overall performance, leading to more efficient solar collectors with positive environmental and economic impacts through increased energy efficiency and reduced reliance on non-renewable energy sources.

Keywords

• Solar air heater
• V-symmetry wire roughness
• Average stanton number
• Average friction factor
• Efficiency index