A Review on the Use of Hybrid Nanofluid in a Solar Flat Plate and Parabolic Trough Collectors and Its Enhanced Collector Thermal Efficiency

Energy demand is high in all parts of the world, mostly in all industrial sectors. To meet the energy demand the fossil fuel is the only way. Due to rapid industrial growth and use of fossil fuel result in global warming and environmental pollution. Moreover, the limited availability of the fossil fuels, it is necessary to depend on the renewable energy sources. Promising renewable energy in the world is solar energy, which is available largely on the earth surface. The solar energy can be converted into thermal energy in the solar flat plate collector. The collector thermal efficiency is purely depends on the working fluid used in it. Most of the studies revealed that replacing the working fluid with high thermal conductivity fluids called as nanofluids and hybrid nanofluids can improve the collector thermal efficiency. Few decades back studies have been conducted with nanofluids in solar collectors. Currently the researchers are working on solar collectors for further improvement of its efficiency using hybrid nanofluids. In this review paper, we will discuss about the synthesis of hybrid nanoparticles, hybrid nanofluids, characterization, thermophysical properties, and application of hybrid nanofluids in solar flat plate collector under natural and forced circulation of fluid. The research gap in the solar collector is also discussed in this article. This paper also explains about the heat transfer capabilities of hybrid nanofluids especially used solar collectors.