Sunlight absorbing potential of carbon nanoball water and ethylene glycol-based nanofluids

Solar thermal collectors are applicable in the water heating or space conditioning systems in which surface-based absorption of incident solar flux cause high heat losses. Therefore, an enhancement in the efficiency of solar harvesting devices is a basic challenge which requires great effort. Adding nanoparticles to the working fluid in direct absorption solar collector, which has been recently proposed, leads to improvement in the working fluid thermal and optical properties such as thermal conductivity and absorption coefficient. This results certainly in collector efficiency enhancement. In this paper, the characteristics of nanofluids consisting carbon nanoball in water- and ethylene glycol-based suspensions in consideration of their use as sunlight absorber fluid in a DASC are investigated. It was found that by using of 300 ppm carbon nanoballs, the extinction coefficient of pure water and ethylene glycol is increased by about 3.9 cm(-1) and 3.4 cm(-1) in average, respectively. With these significantly promising optical properties, a direct absorption solar collector using carbon nanoball-based nanofluids can achieve relatively higher efficiencies, compared with a conventional solar collector.