The optimal design of airflow modes for double-layer solar air heater with perforated baffles

Abstract To further improve the thermal performance of SAH, two mathematical models of the double-layer solar air heater with perforated baffles (DSAH-PB) were established to analyze the optimal airflow modes. In Mode 1, the air flowed parallelly in the upper and lower channels; in Mode 2, the airflow in the upper channel was opposite to the airflow in the lower channel. Validation against reported data showed the models’ accuracy with a maximum relative deviation of less than 10%. Results indicated that Mode 2 achieved a collection efficiency 2.57∼4.28% higher than Mode 1, attributable to a thinner boundary layer and increased turbulence, enhancing the convective heat transfer coefficient. Comparative analysis revealed that the outlet temperatures in Mode 2’s upper and lower channels exceeded those in Mode 1 by 0.37∼ 3.67°C and 1.63∼7.48°C, respectively. Velocity distribution analysis confirmed the superior performance of Mode 2, with a more uniform velocity distribution and lower absorber plate temperature, contributing to improved thermal efficiency. The study underscored the importance of airflow distribution and channel design in optimizing SAH performance.