This paper aims to investigate and analyze the thermal performance of a double-pass solar air heater using multiple rectangular capsules filled with paraffin wax-based on a phase change material PCM. An indoor projector simulator was used to test a new system during the charge/discharge process. In order to verify the accuracy of these readings, a mathematical model based on finite-volume scheme SIMPLE algorithm was applied to solve the three-dimensional forced convection turbulent flow in the double-pass solar heater. The computational results were in reasonable agreement with the experimental readings. The investigations were carried out at various airflow speed of (0.6, 0.9,1.2, 1.5, and 1.8) kg/min and three solar irradiance intensities of 625, 725, and 825 W/m(2). The results showed that the increased airflow rate leads to delay in the melting period and decrease melting temperature of the paraffin during the melting period. Furthermore, it can be detected that the optimal discharging period and the air temperature rise of the heater were reached of: 3hr with (17.95-3) degrees C, 2 h with (14-3) degrees C, and 1.25 h with (11-2.5) degrees C, for various solar intensity of 825, 725, and 625 W/m(2) at the same airflow speed of 0.6 kg/min, respectively. (C) 2019 Elsevier Ltd. All rights reserved.