Photothermal properties of a multilayer composite nanoparticle with random surface roughness for direct absorption solar collector

The photothermal utilization of solar energy is significant in promoting the transition towards more sustainable energy consumption patterns. Direct absorption solar collector (DASC) plays an important role as the main way of solar energy photothermal utilization. The application of nanofluids in DASC is critical. Previous studies commonly make the assumption that nanoparticles possess an ideal, smooth surface. However, in actuality, the surfaces of nanoparticles tend to exhibit random roughness. In this study, composite nanoparticles with randomly rough surfaces (CNRSs) are modeled, and their photothermal properties are investigated by numerical simulations. First, on the premise of verifying that CNRSs have good surface roughness randomness, it is found that the rough height (a) causes the "red shift" of the absorption peak. At the same time, the spectral absorption performance Qabs decreases by 14.79 % when a = 30. The mechanism affecting the absorption is analyzed through the electric field distribution, which is attributed to the local surface plasmon resonance (LSPR). Further, the increase in the number of rough spots (b) results in a slight decrease in the absorption performance of CNRSs. When the value of b is set to 4000, the spectral absorption performance of CNRSs exhibits a decrease of 3.97 % in comparison to that of smooth nanoparticles. Finally, it is found that the material and size of nanoparticles are very sensitive to the surface roughness.