The ability of the nanofluids in absorption the solar radiation and steam generation has attracted considerable attentions in recent years. The purpose of the present study is to examine the optical properties of carbon nanotubes for application in solar steam generation and distilled water production. Accordingly, three types of carbon nanotubes were selected including single-wall and functionalized multi-wall carbon nanotubes (by carboxyl and hydroxyl groups). The evaporation performances of all three carbon nanotubes are evaluated at light intensities up to 3.5 kW/m2 using a solar simulator. Furthermore, a distillation system was constructed to analyze the effects of nanoparticle type, concentration and light intensity on water production. The results indicated that the nanofluid containing the multi-wall carbon nanotube functionalized by hydroxyl group (MWCNT-OH) presents more promising optical and stability properties, with higher evaporation rates as compared to the other nanoparticles. Adding this nanoparticle cuts the beginning of water production in half and enhances the evaporation rate and water production efficiency about 3 times larger than pure water at 3.5 kW/m2 light intensity., The results for the mentioned nanofluid (MWCNT-OH) also revealed that the mass concentration increase from 0.0005% to 0.002%

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