Experimental investigation of packed-bed solar thermal storage

Packed beds are the most commonly used storage systems in solar thermal power plant. Most of the experimental studies carried out in this field use air as heat-transfer fluid (HTF). Therefore, an experimental study on packed-bed storage system using water and oil as HTFs is conducted in this paper to observe the behaviour of storage tanks with different HTFs. Concrete spheres of 6 cm diameter were used as storage materials arranged in rhombohedral arrangement (epsilon =0.28). The variation in the surface temperature of storage materials was observed for both water and oil as HTF and at three different volume flow rates. It has been observed that the increment in temperature was faster when water was used as HTF as compared to oil as HTF. It was also found that the increment at lower volume flow rate was higher due to more contact time of HTF with the storage materials. The temperature was found to decrease first along the axis but at the bottom it again starts increasing due to storage of HTF in the lower plenum of the storage tank.