Abstract

Packed-bed solar air heaters have attracted considerable interest due to their ability to improve heat transfer efficiency. This study numerically investigates the influence of channel aspect ratio on the thermo-hydraulic performance of a packed-bed solar air heater filled with mixed-size aluminium spherical elements. Three-dimensional computational fluid dynamics simulations were performed in ANSYS 2023 R1 under steady-state turbulent flow conditions using the standard k–ε model. Four channel heights (8, 10, 12, and 14 cm) were evaluated while maintaining identical operating conditions. The results show that channel height significantly affects both heat transfer and pressure loss. The 12 cm channel height provided the best overall performance, achieving the highest outlet air temperature and thermal efficiency with a relatively low pressure drop. Compared with the lowest aspect ratio, the optimum configuration increased thermal efficiency by approximately 85% and the thermo-hydraulic performance factor by about 76%. These findings provide practical guidance for the design and optimization of high-performance packed-bed solar air heaters.