Enhanced thermal performance of copper-based polydimethylsiloxane nanofluids for parabolic trough solar collectors

Addressing global energy demand while reducing environmental impact remains a key challenge in the transition to sustainable energy systems. Concentrating solar power (CSP) stands out for its potential to meet large-scale needs although its economic competitiveness is still limited compared to fossil fuels. Improving the thermal efficiency of CSP technologies has become a key research objective, particularly through the use of nanofluids. Taking this a step further, attention is shifting not only to the nanoparticles used, but also to the environmental profile of the base fluid itself. In this context, the present study explores nanofluids based on Cu nanoparticles and polydimethylsiloxane (PDMS), a more environmentally friendly fluid compared to the conventional biphenyl/diphenyl oxide mixtures typically used in parabolic trough collectors (PTCs). The physical stability of the prepared nanofluids was confirmed over a 25-day period. Once stabilized, thermophysical properties such as density, surface tension, dynamic viscosity, isobaric specific heat and thermal conductivity were measured. The results revealed no significant changes in dynamic viscosity compared to the base fluid which is advantageous for maintaining the operational conditions. Notably, the nanofluids exhibited enhancements of up to 5% in isobaric specific heat and up to 16% in thermal conductivity. These improvements lead to an increase in heat transfer of 11% in the nanofluid of concentration 0.10 wt.% Cu calculated using the Dittus-Boelter equation. Therefore, the findings suggest that Cu-based nanofluids in PDMS offer considerable potential as efficient and comparatively environmentally favourable alternatives to conventional heat transfer fluids for CSP-PTC systems.