Molecular Dynamic Study Of Some Critical Effects On Thermophysical Properties Of Nanofluid For Photovoltaic/Thermal System

The ever-increasing demand for energy globally is rising beside the depletion of fossil fuels.Moreover,global warming and pollution due to fossil fuel burning are other hot issues in today’s world.Therefore,researchers and engineers try to find new ways for sustainable,reliable,clean,and green energy.Among them,Solar energy harvesting is one solution to the above issue.Although,the conventional working fluid improvement is required to produce electricity and heat as much as possible.The specific heat capacity(cp)and thermal conductivity(λ)are essential thermophysical properties related to heat storage and transfer in energy systems.An accurate estimation of the aforementioned parameters is necessary to characterize nanofluids’ heat transfer performance as working fluids in the photovoltaic/thermal(PVT)system.In this research work,the molecular dynamic MD simulation is performed to study some critical properties of nanofluids such as cp and A used in PVT systems.Initially,the particle size,interface,and temperature effects on the cp of Cu-water nanofluid(NF)and Cu nanoparticles(NPs)are systematically studied.Also,the TIP4P rigid and the SPC/Fw flexible water models are compared to demonstrate their influence on the estimation of cp.Secondly,the present work investigates the effect of the shell-to-total-radius ratio(Φ)on the cp and λ of SiO2@Au-water nanofluids using the MD simulation method.The initial study results show that the cp increases with increasing nanoparticle size but increases with decreasing temperature.The increase is attributed to the interface effect demonstrated by the vibrational density of state(VDOS).The VDOS mismatch is close to zero with the increase in the cp of the Cu-water nanofluids.In contrast,there is a substantial divergence of the cp of the nanoparticles from the theoretical values.The reason can be due to particle size and the interaction with the surrounding water molecules.Compared to the TIP4P model,the SPC/Fw model shows an increase in the cp.The findings of the second investigation show that cp increases with the increase in Φ,while λ increases as the Φ decrease.The role of solid/liquid and solid/solid interfaces on cp and λ is identified by using the calculations of the vibrational density of state(VDOS)of SiO2@Au nanoparticle,core(SiO2 molecule),shell(Au atom),and the thin layer of water molecules next to the particle surface.The effects of core-shell NPs on the characteristics of the base fluid are further understood by using the VDOS mismatch between the thin water layer and the core-shell nanoparticle and the radial distribution function of water molecules.Latterly,the heat current contribution is discussed to view the λmechanism increase of NF.So,the two components of the heat current are a considerable contribution.This research also proposed New correlations for calculating the cp and λ of nanofluids containing core-shell nanoparticles,thus explicating the contributions of the components to the cp and λ of NFs.The study of the effect of Φ on the thermophysical characteristics of nanofluids provides molecular insight into the roles of the solid/liquid and solid/solid interfaces.These results help understand the thermophysical properties of core-shell nanofluids and their uses in,e.g.,solar thermal applications.