Thermal performance of solar collector based on volumetric absorption harvesting method using Fe3O4 nanofluid

In this study, the characteristics of volumetric absorption for solar harvesting using a Fe3O4@polyacrylic acid (PAA) nanofluid (NF) are investigated experimentally. The concentration of the Fe3O4@PAA NF was varied from 0 to 0.2wt%, and its mass flow rate was set to 0.0025 and 0.005 kg/s. As a result, the average efficiency of the solar collector at the Fe3O4@PAA NF of 0.05wt% was the highest at the mass flow rates of 0.0025 kg/s and 0.005 kg/s and the improvement ratio of average efficiency was 1.15 and 1.19, respectively, compared to water. The collector performance of the solar thermal harvesting improved owing to the improvement in the solar absorption and heat transfer, as well as the uniform temperature at the receiver tube as the concentration of the Fe3O4@PAA NF increased to a concentration of 0.05wt%. However, the collector performance of the solar thermal harvesting decreased for the 0.05wt% Fe3O4@PAA NF because of the increase in heat loss by the non-uniform temperature at the receiver tube and heat transfer. The increase in mass flow rate can reduce the heat loss by the decrease in temperature in the receiver tube; consequently, the efficiency of the solar collector using NFs is improved.