Nanolayer and nano-convection based enhanced thermal conductivity of Copper-CO2 nanofluid: A molecular dynamics approach

TL;DR

This study uses molecular dynamics simulations to show that adding copper nanoparticles to CO2 enhances its thermal conductivity through nanolayer formation, with nanoparticle size influencing heat transfer and diffusion.

Contribution

It introduces a molecular dynamics approach to quantify how copper nanoparticles improve CO2 thermal conductivity via nanolayer effects, a novel investigation for this nanofluid system.

Findings

Thermal conductivity increases with nanoparticle diameter.

Nanolayer thickness correlates with nanoparticle size.

Enhanced diffusion coefficients observed with larger nanoparticles.

Abstract

The use of CO2 as a natural refrigerant in data center cooling, oil recovery and in CO2 capture and storage which is gaining traction in recent years involves heat transfer between CO2 and the base fluid. A need arises to improve the thermal conductivity of CO2 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 in this study consists of copper (Cu) nanoparticle and CO2 as a base fluid. No experimental data are available on the thermal conductivity of CO2 based nanofluid. 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 molecular dynamics (EMD) simulations. This study also investigates the diameter effect of nanoparticle on the nanolayer, thermal conductivity and self-diffusion coefficient. In addition to this, diffusion coefficients are calculated for base fluid and nanofluid. The thickness of the dense semi-solid layer formed at the nanoparticle-gas interface is studied through radial distribution function (RDF) and density distribution around the nanoparticle. This thickness is found to increase with nanoparticle diameter. Enhancement in thermal conductivity and diffusion coefficient with nanoparticle diameter are strongly correlated, indicating that the dominant modes of heat and mass transfer are the same. The output of the current work demonstrates the enhancement in thermal conductivity due to nanoparticles addition which may improve data center cooling efficiency and CO2 capture and storing.