Towards the improvement of the global efficiency of concentrating solar power plants by using Pt-based nanofluids: The internal molecular structure effect

Nanofluids are a promising alternative to the typical heat transfer fluid (HTF) used in concentrating solar power (CSP) plants, possibly improving their global efficiency and leading to the increase the use of renewable clean energy. This study analyses nanofluids based on a typical HTF used in CSP and Pt nanoparticles. Pt nanoparticles were synthesized and dispersed in the base fluid. Dodecylamine (DDA) was used as a phase transfer and as a surfactant. Also, 1-octadecanethiol (ODT) was added as a surfactant and pulsed ultrasonication was used to disperse the nanoparticles. As the base fluid, the eutectic mixture of diphenyl oxide (73.5%) and biphenyl (26.5%) was used. This fluid is typically used in CSP plants based on parabolic through collectors. The stability of the nanofluids was analysed according to the kind of surfactant and ultrasonication process. Furthermore, to analyse the efficiency of the nanofluids, several properties were measured, including density, dynamic viscosity, isobaric specific heat and thermal conductivity. We found an increase in thermal conductivity of up to 37%, and the heat transfer coefficient also improved by up to 20%. Molecular dynamics calculations were performed to determine how the inclusion of ODT affected the system. ODT competes with DDA to interact with the Pt, forming a lattice around the Pt. The base fluid molecules, and in particular the diphenyl oxide molecules, take advantage of this competition to move closer to the Pt. This movement of molecules as the temperature rise must be Brownian in nature and enhances the heat transfer processes, improving the thermal properties of the nanofluids with both ODT and DDA compared with those prepared only with DDA. Thus, nanofluids with ODT and DDA would appear to be of interest for use in CSP.