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Brownian Motion and Nanolayer Study on Thermal Conductivity of Al2O3-CO2 Nanofluid: a Molecular Dynamics Approach
Zeeshan Ahmed, Ajinkya Sarode, Pratik Basarkar, Atul Bhargav and Debjyoti Banerjee

The use of CO2 as a natural refrigerant in data center cooling, oil recovery and in CO2 capture and storage is gaining traction in recent years which 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 this study consists of alumina (Al2O3) nanoparticle and CO2 as a base fluid. The experimental data on thermal conductivity of CO2 based nanofluid is not available. 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 (k) and self-diffusion coefficient (D). In addition to this, diffusion coefficients are calculated for base fluid and nanofluid to investigate the Brownian motion effect. We found that it decreases with increase in particle size. Thickness of the dense semi-solid layer formed at the nanoparticle-gas interface is studied through radial distribution function (RDF) and distribution around nanoparticle. This thickness is found to increase with diameter. The thermal conductivity enhancement of the nanofluid was 20%, 46% and 62% for 1 nm, 2 nm and 3 nm diameter, respectively. 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.

Keywords: Al2O3-CO2 nanofluid, Molecular interfacial layer, Thermal conductivity, Molecular dynamics simulation

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