Stable aqueous suspensions of multi-walled carbon nanotubes (MWCNTs) with mass fractions ranging from 0.0015% to 0.1% were prepared via two-step method.The impacts of mass fraction

setting time

and heating times on the optical absorption property of MWCNT-H2O nanofluid were investigated according to the transmittance measured by UV-VIS-NIR spectrophotometer over the wavelength from 200 to 2000 nm.Furthermore

an insolation experiment was performed to investigate the effects of mass fraction and light irradiation times on the photo-thermal property of MWCNT-H2O nanofluids.Results show that the transmittance of MWCNT-H2O nanofluid was decreased evidently after the addition of MWCNTs in deionized (DI) water

and long setting time leads to smaller transmittance.Heating is beneficial to improve light-absorption property of nanofluids.An optimal mass fraction of 0.01% with respect to the best photo-thermal conversion was found.Compared to DI water

the temperature of MWCNT-H2O nanofluid at the optimal mass fraction was increased by about 15.1℃ (or 22.7%) after a lighting time of 45 min.Additionally

photo-thermal conversion performance is enhanced with increasing the lighting time at a low concentration of nanofluid

while it is just opposite at higher concentrations.The nanoparticle agglomeration may account for the above results.