An experimental study on the thermal performance of a packed-bed glass tube operated in the direct absorption solar heating

Improving the thermal efficiency of solar collectors is one of the most significant advancements in the field of harvesting and converting solar energy. In this study, a packed-bed strategy was employed in a direct absorption solar collector to enhance thermal performance. The heating system consisted of a transparent glass tube filled with the stainless-steel scrubbers (coated black) as packing materials. The working fluid was circulated through the packed-bed under forced flow conditions while being exposed directly to solar radiation. Pure water and an optical nanofluid (Fe 2 O 3 (0.05%)/water nanofluid) were used as the working fluids. A 57% improvement in the maximum efficiency of water flow was achieved with the packed-bed collector compared to the empty collector. The packed-bed design increased the surface area exposed to sunlight, enabling more efficient trapping and absorption of solar radiation. Additionally, the heat loss parameter for the nanofluid flow in the packed-bed collector decreased by 28% relative to the empty collector, demonstrating improved thermal management and energy storage. The packed-bed collector exhibited only a 24% higher pressure drop than the empty collector. Overall, the packed-bed strategy proved to be an efficient, eco-friendly, and straightforward technique for scaling up the operational efficiency of DASCs.