Towards a multiscale simulation approach of nanofluids for volumetric solar receivers: Assessing inter-particle potential energy

A modern concept for solar thermal collectors is based on volumetric absorption of sunlight, where nanoparticles suspended in liquids directly receive the incident radiation. Suspending nanoparticles in traditional fluids can drastically enhance their optical properties and improve thermo-physical performances, thus leading to highly efficient volumetric solar receivers. Several studies have been addressed on the physical understanding of such nanosuspensions; however, the relation between nanoscale effects and macroscopic properties is far from being fully understood. The present work represents a first step towards a multiscale modeling approach for relating nanoscale properties to macroscopic behaviour of nanofluids. In particular, a suitable Coarse-Grained (CG) method for nanofluids is described. By means of Molecular Dynamics (MD) simulations, the pair Potential of Mean Forces (pPMF) between CG beads of nanofluid is evaluated. A complete CG force field can be then defined by including the effects of water adsorbed at solid-liquid interface, nanoparticle surface charge and solution pH. Our multiscale model is intended to permit a future study of the complex mechanisms of nanoparticle clustering, which is known to affect nanofluids stability and properties. We hope that this multiscale approach may start the process of rational design of nanofluids thus facilitating technology transfer from lab experiments to large-scale industrial production.