Computational fluid dynamics investigation of heat transfer, pressure loss, and exergy efficiency in serpentine solar air heaters with variable turn numbers

Abstract Solar air heaters have been widely used for space and industrial process heating. However, serpentine Solar Air Heaters (SAHs) exhibit limited thermohydraulic efficiency due to high pressure losses caused by the bends. To address this, the present study numerically investigated different configurations of serpentine SAH. Four configurations of SAH with varying numbers of turns were analyzed: 4 turns (SAH‐4T), 3 turns (SAH‐3T), 2 turns (SAH‐2T), and 1 turn (SAH‐1T). The shear stress transport (SST) k‐ω turbulence model was used to describe the flow behavior. In addition, the Discrete Ordinates (DO) radiation model was applied to capture radiative heat transfer accurately. Different meshes were tested using various criteria to select an adequate mesh. To ensure accuracy, the numerical model was compared with both established correlations and experimental data. The comparison showed excellent agreement, with an average deviation in outlet air temperature of 3.3%. The results indicated that a maximum temperature of 85.1°C and a thermal efficiency of 62.6% were achieved in SAH‐4T at 0.005 kg/s. In addition, a pressure loss of 858.7 Pa was observed in the reference configuration (SAH‐4T). In contrast, SAH‐3T demonstrated the best thermohydraulic efficiency at a higher flow rate. It achieved 53.3%, compared to 52.1% for SAH‐4T, 51.1% for SAH‐2T, and 44.7% for SAH‐1T at 0.03 kg/s. Furthermore, a maximum exergy efficiency of 3.92% was achieved with SAH‐3T at 0.02 kg/s. Overall, for flow rates above 0.02 kg/s, SAH‐3T was recommended for optimal thermohydraulic efficiency among serpentine SAHs.