Molecular dynamics simulation of the effect of the solid gas interface nanolayer on enhanced thermal conductivity of copper-CO2 nanofluid

The use of CO<inf>2</inf> as a natural refrigerant in data center cooling, in oil recovery and in CO<inf>2</inf> capture and storage is gaining traction in recent years. These applications involve heat transfer between CO<inf>2</inf> and the base fluid, and hence, there arises a need to improve the thermal conductivity of CO<inf>2</inf> to increase the process efficiency and reduce cost. One way to improve the thermal conductivity is through nanoparticle addition in the base fluid. The nanofluid model in this study consisted of copper (Cu) nanoparticles in varying concentrations with CO<inf>2</inf> as a base fluid. No experimental data is available on thermal conductivity of CO<inf>2</inf> based nanofluid. Molecular dynamics (MD) simulations are being increasingly adopted as a tool to perform preliminary assessments of nanoparticle (NP) fluid interactions. In this study, the effect of the formation of a nanolayer (or molecular layering) at the gas-solid interface on thermal conductivity is investigated using equilibrium MD simulations by varying nanoparticle diameter and keeping the volume fraction (1.413%) of nanofluid constant to check the diameter effect of nanoparticle on the nanolayer and thermal conductivity. A dense semi-solid fluid layer was seen to be formed at the nanoparticle-gas interface, and the thickness increases with increase in particle diameter, which also moves with the nanoparticle Brownian motion. Density distribution has been done to see the effect of nanolayer, and its thickness around the nanoparticle.