Enhancing solar thermal energy harvesting efficiency and temperature uniformity of Fe₃O₄ nanofluid in receiver of direct solar thermal collector using dynamic magnetic field

To improve the solar thermal energy harvesting performance (STEHP) according to the receiver depth of a direct absorption solar collector (DASC), the Fe3O4 nanofluid (NF) was used as a working fluid. Besides, an external dynamic magnetic field (MF) was applied to the working fluid, and the effect of the dynamic MF on the heat transfer performance and temperature uniformity of the working fluid was investigated. As a result, with the increase in receiver depth, the STEHP decreased due to the temperature non-uniformity of working fluid and the increase in heat loss at the top part. When the receiver depth was 6 cm, the highest solar thermal energy har-vesting efficiency (STEHE) was observed at the concentration of 0.075 wt%. When an external dynamic MF was applied to the 0.075 wt% Fe3O4 NF, the temperature non-uniformity was reduced; therefore, solar energy ab-sorption and storage performance improved significantly. The STEHE using an external dynamic MF increased by 119.6 % compared to DI-water. It was confirmed that applying a dynamic MF to the Fe3O4 NF could significantly improve the STEHP of DASC by enhancing the temperature uniformity within the working fluid and the solar energy absorption performance.