Effect of sensible heat storage materials on the thermal performance of solar air heaters: State-of-the-art review

Solar air heaters are the most cost-effective method of converting solar energy into heat and are used for room heating, crop drying, and other industrial uses. However, they suffer from poor thermal efficiency. The leading cause behind the poor performance of solar air heaters is heat losses from its different parts. Researchers have used various innovative methods to improve solar air heaters thermal performance by reducing heat losses using energy storage material. The present work demonstrates the state-of-the-art review of different solar air heaters loaded with sensible heat storage materials. This investigation has found that integrating sensible heat storage systems such as pebbles, sand, metal chips, oil and gravels with solar air heaters effectively reduces heat losses and increases thermal efficiency. This study revealed that Therminol-55 gave better efficiency than engine oil. For blacked pebble stones, free convection solar air heater provided better efficiency than forced convection. The cement gave better thermal efficiency than concrete. Gravels integrated with iron chips showed more efficiency than used alone. Pure iron chips contributed maximum efficiency compared to other metal chips. The desert sand furnished better efficiency compared to different types of sand. The overall best performing sensible heat storage material is found as a mixture of desert sand and granular carbon having the highest thermal efficiency of 80.05%; however, the lowest performance is demonstrated by cement with 9.5% of thermal efficiency.