Improving a solar collector’s efficiency by selecting the composition of the working fluid used

The study’s purpose was to determine the efficiency, as well as the energy and exergy analysis of the vacuum tube solar collector when using a mixture of water with Fe3O4 nanoparticles and multiwall carbon nanotubes in the selected percentage ratio as the working fluid. By varying the concentration of Fe3O4 nanoparticles in the working fluid from 0.05 to 0.15 wt. %, it was found that the maximum efficiency is achieved at a Fe3O4 content equal to 0.1 wt. %. At this concentration, the ratio of Fe3O4 and multiwall carbon nanotubes in the mixture varied from 4:1 to 1:4. It was found that the Fe3O4/ multiwall carbon nanotubes ratio (1:4) can increase the efficiency of the solar collector up to 84%. Exergy analysis performed showed that water without the addition of nanoparticles Fe3O4 and multiwall carbon nanotubes was characterized by the maximum values of exergy destruction and entropy generation at any level of solar radiation, and water with the addition of nanoparticles Fe3O4/ multiwall carbon nanotubes in a ratio of 1:4 was characterized by the minimum values of exergy destruction and entropy generation.