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 (ε = 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.

中文翻译：

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填充床太阳能蓄热器的实验研究

填充床是太阳能热电厂最常用的存储系统。在该领域中进行的大多数实验研究都使用空气作为传热流体（HTF）。因此，本文进行了以水和油为HTF的填充床存储系统的实验研究，以观察具有不同HTF的储罐的性能。直径为6 cm的混凝土球体被用作菱形面体（ε = 0.28）。对于水和油作为HTF以及在三种不同的体积流量下，都观察到了存储材料表面温度的变化。已经观察到，与作为油的HTF相比，当水用作HTF时，温度的升高更快。还发现由于HTF与存储材料的接触时间增加，在较低体积流量下的增量较高。发现温度首先沿轴下降，但由于HTF在储罐下部气室中的存储，在底部又开始升高。