A review on the application of hybrid nanofluids for parabolic trough collector: Recent progress and outlook

By far, the Parabolic trough collector (PTC) is the most established solar concentrating technology worldwide. This paper draws a comparison among various studies done earlier in the domain to bring forth different models and mediums used to evaluate the effect of nanofluids on thermal parameters for PTC providing an optimum output, resultantly. The study also reveals that by using nanofluid and hybrid nanofluids as heat transfer fluid (HTF) inside the absorber tube of solar collector, the thermal and optical characteristics can be enhanced. Reported papers in literature mention stability, effect on PTC's performance by implementing various novel designs, collector efficiency enhancement by using various inserts, and selecting proper hybrid nanomaterial into the base fluid. Varied experimental studies report that using hybrid nanofluid results in a more significant enhancement in thermal properties viz-a-viz than the mono fluids. A close look at the results of some of the notable works of the domain explicitly implies that for enhancing the thermal conductivity of nanofluid, metal oxide hybrid nanofluids are more promising than the oxide ones in a rather ‘pecking order’. The study also verges on the proposition that the thermal properties of nanofluid can be accelerated by the usage of hybrid nanofluid instead of mono nanofluid, as a medium, into a more efficient hybrid structure. Conclusively, this review advances the understanding of optimizing alteration parameters for obtaining maximum increase in outcomes and offers substantially adequate understanding for choosing specific techniques to enhance the overall efficiency of PTC, which can be used as a guideline for future trends.