Comparative performance evaluation of fly ash-based hybrid nanofluids in microchannel-based direct absorption solar collector

In this study, the performance of the hybrid nanofluid of alumina/fly ash-based nanofluid and silica/fly ash-based nanofluid in the direct absorption solar collector is compared. SiO2, Fe2O3, Al(2)O(3)and CaO are main components of the fly ash. The effect of different proportions of major components in fly ash and flow rate on the thermal and exergy efficiency is studied. Microchannel-based flat plate solar collector is used for the experimentation with a channel height of 800 microns. Experiments are conducted to evaluate the thermal efficiency, pumping power, performance evaluation criteria, entropy generation rate and exergy efficiency of fly ash-based nanofluids in direct absorption solar collector. The experimental results revealed that the thermal efficiency of the alumina/fly ash (80:20)-based nanofluid for direct absorption solar collector is 72.82% while silica/fly ash (80:20) nanofluids showed 59.23% thermal efficiency. Exergy efficiency achieved by the alumina/fly ash (80:20)-based nanofluids is 73%. This is significantly more than the silica/fly ash-based nanofluids. Silica/fly ash (80:20)-based nanofluids achieved an exergy efficiency of 68.09%. The study revealed that an increase in the concentration of alumina in the fly-ash nanofluid will increase the thermophysical property and efficiency of the nanofluid and an increase in the silica concentration will lead to decrease in the thermophysical property and efficiency of the fly ash-based nanofluid.