Performance study on a new solar air heater with integrated phase change materials and external recycle: A numerical and experimental study

This study represents a numerical and experimental analysis to assess how the recycling technique affects the performance of solar air heaters (SAHs) integrated with phase change materials (PCMs). Hence, an experimental setup was constructed and tested in Bam, Iran, in autumn 2022; then, a three-dimensional numerical model was developed and validated with acquired experimental data using ANSYS FLUENT software. This model was uti-lized in different recycle ratios, r, including r = 0, 1, 2, 3. External recycle raises the maximum exhaust tem-perature in r = 1 and r = 2, nearly 21.9% and 26.8%, compared to r = 0 (without recycling). Furthermore, the SAH with external recycle has higher efficiency, nearly 111.4% and 135.9% in r = 1 and 2, than the SAH with r = 0. Surprisingly, increasing the r-value to 3 does not affect the exhaust temperature. Enhancing the recycle ratio improves the convective exchange rate but reduces the air residence time. These two conflicting factors lead the exhaust temperature and efficiency to approach an asymptote of nearly 52 degrees C and 54%. It can be concluded that utilizing the recycling with the appropriate recycle ratio, r = 2, considerably affects thermal efficiency and in-creases exhaust temperature.