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Terra Joule Journal

Abstract

To enhance the heat transfer rate and the thermal performance of solar air heaters, specific methodologies such as artificial roughness, barriers, and obstructions should be employed to augment the heat exchange between the working fluid and the absorber surface. In this study, perforated V-shaped obstructions were utilized, featuring circular, hexagonal, square, rectangular, and triangular geometries. These obstructions were securely affixed to the absorber plate within a channel measuring 150 × 50 × 5 cm, increasing the exit temperature of the air traversing through the channel. The experimental investigation comprises six distinct cases conducted in November in Baghdad, Iraq, aimed at achieving optimal results. The investigated cases encompassed baffles featuring diverse geometric arrangements in conjunction with those devoid of any impediments. A comparative analysis was performed among these cases under uniform conditions and constraints, to identify the optimal configuration. The investigated mass flow rates ranged from 0.0098 to 0.049 kg/s, and the Reynolds number (Re) varied between 2000 and 10000. Furthermore, one of the aims of this comparison was to maximize the Nusselt number (Nu) while minimizing the friction factor. The results indicated an improvement in Nu by a factor of 153% and a decrease in the friction factor by 176% for the hexagonal perforated barriers, demonstrating the most favorable performance. In contrast, the triangular perforated barriers yielded a Nu improvement of 148.6% and a friction factor reduction was be 300%. The thermal efficiency was assessed by analyzing heat losses due to convection with the ambient air and long-wave radiation exchanges with the atmosphere. The results of the experiments revealed that employing barriers with hexagonal perforations yielded the best performance, due to their distinctive edges.

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