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 Ti3C2 were selected as nanoadditives, respectively. The result shows that the light-to-heat conversion efficiency of Ti3C2/[BMIM]BF4 nanofluid is 20% and 29% higher than that of GO/[BMIM]BF4 nanofluid and MWCN/[BMIM]BF4 nanofluid, respectively, after irradiation for 1000 s, due to the excellent optical absorption performance of Ti3C2. Furthermore, the effects of mass fractions of Ti3C2, solar concentrations and DASCs heights on the light-to-heat conversion performances of Ti3C2/[BMIM]BF4 nanofluids are investigated systematically. The light-to-heat conversion performances of Ti3C2/[BMIM]BF4 nanofluids rapidly increase with the increase of mass ratios of Ti3C2 owing to the outstanding broad-spectrum absorption properties (250-2100 nm) of Ti3C2. Moreover, the light-to-heat conversion performances of Ti3C2/[BMIM]BF4 nanofluids in DASCs increase with the increase of solar concentrations and DASCs heights. Additionally, the light-to-heat conversion efficiency of 0.04 wt% Ti3C2/[BMIM]BF4 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 Ti3C2/[BMIM]BF4 nanofluids show great potential application as advanced heat transfer fluids (HTFs) for DASCs.