Study on the influence of the agglomeration effect of composite nanoparticles on the photothermal properties of nanofluids

Direct absorption solar collectors (DASCs) that utilize nanofluids as working fluids are an important method for solar photothermal utilization. However, the instability caused by the agglomeration effect of nanoparticles significantly impacts the photothermal performance of nanofluids. The majority of previous research has primarily focused on reducing agglomeration phenomena in the preparation process of nanofluids, but the mechanism of the agglomeration effect on the photothermal properties of nanofluids remains unclear. In this study, finite element theory is used to numerically calculate the photothermal properties of composite nanoparticles in several different agglomeration modes, and to quantitatively analyze the influence of agglomeration effects on the photothermal properties of composite nanoparticles. The incidence angle at which sunlight strikes has a significant impact on the absorption efficiency of nanoparticle clusters. When roll = -90°, the spectral absorption efficiency of the four agglomerates decreases by 18.59 %, 22.79 %, 31.03 %, and 34.77 %, respectively. The photothermal properties of nanoparticle clusters are attributed to local surface plasmon resonance (LSPR). Furthermore, as the depth of agglomeration increases, the spectral absorption efficiency gradually decreases. Composite nanoparticles made of different materials exhibit varying resistance to the weakening of photothermal properties caused by the agglomeration effect. Non-metallic nanoparticles exhibit strong resistance to the reduction of photothermal properties due to agglomeration. Finally, by extending the planar agglomeration mode to space, it was observed that the spectral absorption efficiency sharply decreases with an increase in the number of spatially agglomerated nanoparticles. This study uncovers the mechanism behind the agglomeration effect of nanoparticles on the photothermal performance of nanofluids and systematically quantitatively analyzes its impact characteristics. This expands the theory of photothermal utilization of nanofluids, which is of great significance for improving the service life of nanofluids and guiding their applications.