Table 2 Summary of articles that carried out studies of the effect of nanofluids on the performance of SWHs

Sokhansefat et al. (2014)

Numerical

Heat transfer coefficient enhanced with the presence of nanoparticles but decreased with an increased operating temperature of the absorber tube hence, the application of nanoparticles achieves reduced heat transfer areas in PTC systems

Mwesigye et al. (2015)

Numerical

The thermal efficiency of the receiver improved by nanofluids up to 7.6%

Conclusively, beyond certain Reynolds numbers application of nanofluids becomes thermodynamically undesirable

Bellos et al. (2016a, b)

Numerical

Thermal oil with nanoparticles showed the best working fluid performance compared to pressurized water as a result of high-pressure level demand

The study further revealed that the wavy collector design improved the average efficiency by 4.55%, but increased the pressure losses

Mirzaei (2017)

Experimental

Efficiency decreases as HTF decreases

CuO nanofluid provides better improvement than the Al₂O₃

Mwesigye and Meyer (2017)

Numerical

The optimal flow rate of about 22.5 m³ h⁻¹ was achieved for all the considered nanofluids and parameters

Huge potential for energetic and exergetic performance improvement with high concentration ratios was also observed

Genc et al. (2018)

Numerical

Nanoparticles were more effective at flow rates below 0.016 kg/s on the exit temperature of FPCs. The method of analysis was recommended for PV/T systems

Mohammed et al. (2021)

Numerical

Hybrid nanofluids showed superior thermal performance and boosted the thermal efficiency of the PTSC by 11.5%. The results were recommended for PTSC industry further development

Thulasi et al. (2021)

Numerical

The thermal performance of a SWH was enhanced with Epsom salt. The study indicated that 92% thermal efficiency higher than the 82% common SWH efficiency was observed