Enhanced optical properties and light-to-heat conversion performance of Ti3C2/[BMIM]BF4 nanofluids based direct absorption solar collector

A solar-thermal utilization heat transfer fluid with excellent light-to-heat conversion performance and good thermal reliability at high temperature is highly desirable for direct absorption solar collector (DASC). To obtain IL-based nanofluids as suitable HTFs for medium-high temperature DASCs, GO, MWCN and Ti ₃C ₂ were selected as nanoadditives, respectively. The result shows that the light-to-heat conversion efficiency of Ti ₃C ₂/[BMIM]BF ₄ nanofluid is 20% and 29% higher than that of GO/[BMIM]BF ₄ nanofluid and MWCN/[BMIM]BF ₄ nanofluid, respectively, after irradiation for 1000 s, due to the excellent optical absorption performance of Ti ₃C ₂. Furthermore, the effects of mass fractions of Ti ₃C ₂, solar concentrations and DASCs heights on the light-to-heat conversion performances of Ti ₃C ₂/[BMIM]BF ₄ nanofluids are investigated systematically. The light-to-heat conversion performances of Ti ₃C ₂/[BMIM]BF ₄ nanofluids rapidly increase with the increase of mass ratios of Ti ₃C ₂ owing to the outstanding broad-spectrum absorption properties (250–2100 nm) of Ti ₃C ₂. Moreover, the light-to-heat conversion performances of Ti ₃C ₂/[BMIM]BF ₄ nanofluids in DASCs increase with the increase of solar concentrations and DASCs heights. Additionally, the light-to-heat conversion efficiency of 0.04 wt% Ti ₃C ₂/[BMIM]BF ₄ nanofluid is 2.7 times that of the pure ionic liquid at solar concentration C = 2.5, DASCs height H = 2.5 cm and 6500 s of irradiation. The obtained high-performance Ti ₃C ₂/[BMIM]BF ₄ nanofluids show great potential application as advanced heat transfer fluids (HTFs) for DASCs.