Nanofluids are tailored or engineered suspensions of nanoparticles in a suitable base fluid. Nanofluids gained importance as next generation heat transfer fluids due to high thermal conductivity. The nanofluids are also proved as a potential candidate for direct absorption solar collectors
(DASC). The present work investigates the optical absorption of TiO2 and carbon doped TiO2 (C-TiO2) nanofluids which is necessary for DASC and tunable optical filters. TiO2 and C-TiO2 are prepared by sol gel and characterized by XRD. Nanoparticles
of TiO2 and C-TiO2 with weight fractions of 0.04 are dispersed in water and ethylene glycol to obtain TiO2 and C-TiO2 nanofluids. The nanofluids are investigated for their sedimentation time by gravity sedimentation method. Stability of TiO2
nanofluid is nine times more than C-TiO2 nanofluid with water as base fluid but C-TiO2 nanofluid are found to be efficient absorbers than TiO2 nanofluid in certain wavelength regime as shown by the UV results. We suggest that implementing a low volume fraction
of C-TiO2 nanofluid can give high stability and good absorption which is a prerequest for DASC and tunable optical filters.
