Optical and Transport Properties of Metal-Oil Nanofluids for Thermal Solar Industry: Experimental Characterization, Performance Assessment, and Molecular Dynamics Insights

Concentrating solar power (CSP) technology can become a very valuable contributor to the transformation and decarbonization of our energy landscape, but for this technology to overcome the barrier toward market deployment, significant enhancements in the solar-to-thermal-to-electric energy conversion efficiency are needed. Here, an in-depth experimental analysis of the optical and transport properties of Pd-containing aromatic oil-based nanofluids is presented, with promising results for their prospective use as volumetric absorbers and heat transfer fluids in next-generation parabolic-trough CSP plants. A 0.030 wt % concentration of Pd nanoplates increases sunlight extinction by 90% after 20 mm propagation length and thermal conductivity by 23.5% at 373 K, which is enough to increase the overall system efficiency up to 45.3% and to reduce pumping requirements by 20%, with minimum increases in the collector length. In addition to that, molecular dynamics simulations are used to gain atomistic-level insights about the heat and momentum transfer in these nanofluids, with a focus on the role played by the solid-liquid interface in these phenomena. Molecules chemisorbed at the interface behave as a shelter-like boundary that hinders heat conduction, as a high thermal resistance path, and minimizes the impact of the solid on dynamic viscosity, as it weakens the interactions between the nanoplate and the surrounding nonadsorbed fluid molecules.