Efficient nanofluids based on Ag nanoparticles and a linear silicone-based fluid for concentrating solar power

• Efficient nanofluids using an environmentally-friendly HTF and Ag NPs were prepared. • Enhancement of about 4.5 % in C P at 298–478 K was obtained for all Ag concentration. • Increase up to 24 % in thermal conductivity at 378 K for 0.03 wt% Ag was observed. • Heat transfer coefficient enhances up to 16 % at 378 K for 0.03 wt% Ag nanoparticles. • Weak VdW interactions between Ag and PDMS define C P and thermal conductivity values. Improving the efficiency of renewable energy sources can lead to obtaining electrical energy in an environmentally-friendly way. Therefore, the development of nanofluids for use in parabolic trough collectors in concentrated solar energy (CSP-PTC) is a research line of interest. Thus, in this work, nanofluids based on Ag nanoparticles and a polydimethylsiloxane (PDMS) type fluid used in CSP-PTC technology were prepared. The use of this fluid in this technology and the preparation of nanofluids based on it has not been studied widely, and the evaluation of the use of nanofluids from this type fluid is of great interest. Thus, the physical stability and the properties of interest measured, that are density, surface tension, viscosity, isobaric specific heat and thermal conductivity, were characterized. The nanofluids prepared presented interesting thermal properties. An increase of up to 4.5 % in the isobaric specific heat and up to 24 % in thermal conductivity were observed with respect to the base fluid, without a significant increase in viscosity. Thus, an increase in the heat transfer coefficient of up to 16 % was obtained. These results are really promising for the use of the nanofluids prepared in CSP-PTC technology. Finally, the moderate increase in isobaric specific heat and the significant increase in thermal conductivity is explained by the weak Van der Waals force interaction observed between the Ag surfaces and the PDMS molecules.