Abstract
In this research study, the development of a theoretical model to estimate the efficiency of a double pass solar air heater (DPSAH) was the main objective. The mathematical model was compared to experimental results and found to be in agreement, both qualitatively and quantitatively. The model used energy balance equations to determine the outlet temperature and could solve the temperature equations of each component of the heater simultaneously. A matrix inversion method was used for this purpose. The study found that increasing the Nusselt number led to an increase in energy efficiency, but also caused a drop in outlet temperature at any solar radiation. The mass flow rate (MFR), with larger flow rates resulting in better efficiencies, had a significant impact on the double pass air heater's efficiency. Thus, increasing of DPSAH’s length increases its thermal performances and reach its maximum values for L=9m. These findings could be beneficial in selecting the most efficient design parameters for DPSAH.