Energy and exergy analysis of a thermosiphon and forced-circulation flat-plate solar collector using MWCNT/Water nanofluid

The scientific community has focused on the use of nanofluids to enhance solar collectors' thermal efficiency. Solar energy is considered an extensively available energy resource with a weak effect on the environment. The flat-plate solar collector is considered to be the most common collector used, but the efficiency of the collector has limitations, such as the low effectiveness of the absorber in terms of energy absorption and the transmission of that energy to the working fluid. The flat-plate solar collector can be enhanced by replacing the working fluid with a nanofluid. Nanofluids are considered new media that exhibit thermophysical properties superior to those of ordinary working fluids. In this study, the effect of using multi-walled carbon nanotubes in a thermosiphon and forced-circulation flat-plate solar collector was investigated experimentally. A set of different concentrations was tested (0.01 wt%, 0.05 wt% and 0.1 wt%) with distilled water. The experimental results show an enhancement of the system's exergy efficiency and energy efficiency when a nanofluid was used compared with those attained using distilled water in both forced and thermosiphon systems.