Effect of the baffle's type on thermal performance of solar air heaters

To determine the optimal baffle's type (longitudinal and transverse baffles) and the number of baffles, two computational fluid dynamics (CFD) models for solar air heaters (SAHs) were developed by using "ANSYS Fluent" software. The computational results closely aligned with the experimental data. As the width of the air channel in SAHs with transverse baffles was narrower than in those with longitudinal baffles under the same number of baffles, the heat transfer coefficient of SAHs with transverse baffles was greater than those with longitudinal baffles. Thus, for the airflow rate () range of 0.013 kg·s-1 to 0.078 kg·s-1, SAHs with transverse baffles exhibited 2.34% to 6.97% higher collection efficiency compared to those with longitudinal baffles. An analysis of the impact of the number of transverse baffles (N) on the flow and heat transfer characteristics in SAHs revealed that both the size and intensity of the vortex zones increased with an increase in N, thereby influencing the heat transfer between the air and the absorber plate. Specifically, among the studied values of N (2, 4, 6, and 8), at = 0.026 kg·s-1, N = 4 achieved the peak effective efficiency at 54.32%. Conversely, for = 0.039 kg·s-1, 0.052 kg·s-1, 0.065 kg·s-1, and 0.078 kg·s-1, the highest effective efficiency was observed at N = 6, with values of 60.03%, 63.78%, 64.39%, and 64.38%, respectively.