This study investigates the effects of graphene nanoplatelet-based nanofluids

modified with various surfactant types and concentrations

on the thermal performance of solar thermal systems. The nanofluids were synthesized and characterized in terms of structural

thermophysical

rheological

and dispersion properties. These data were integrated into computational simulations of a photovoltaic-thermal heat exchanger. Among all formulations

the nanofluid containing 0.1 wt% polyvinylpyrrolidone exhibited the highest thermal efficiency

increasing from 40.21% (water) to 45.26%. This enhancement is attributed to its superior thermal conductivity

higher specific heat capacity

low viscosity at elevated shear rates

and stable dispersion. Rheological testing confirmed shear-thinning

non-Newtonian behavior that facilitates convective heat transfer. In contrast

nanofluids without surfactants or with anionic surfactants showed higher viscosity and reduced stability

resulting in lower thermal efficiency. The integrated experimental computational approach offers a comprehensive understanding of the mechanisms governing nanofluid-enhanced heat transfer in photovoltaic-thermal systems. Enhancing the heat exchanger directly improves overall system performance. The proposed nanofluid formulation presents a viable pathway toward scalable

efficient solar thermal applications. Future work should focus on long-term stability and techno-economic validation under real-world operating conditions.