Session: 17-01-01: Research Posters

Paper Number: 150966

150966 - Enhancing Convective Heat Transfer on Graphene Nanochannels Using Functional Groups 

The exploration of heat transfer and fluid flow within nanochannels has attracted significant attention due to its practical applications. Graphene, well known for its exceptional thermal conductivity, has been extensively utilized as a heat absorber, particularly in solar-thermal applications. This study aims to enhance thermal transport between nanochannel walls and flowing fluids by incorporating graphene and graphene oxide into the nanochannel walls. The objective is to elucidate the effects of graphene and graphene oxide on heat transfer and fluid flow in nanochannels and to investigate the key parameters influencing the thermal and hydrodynamic performance.

We employed non-equilibrium molecular dynamics simulations using LAMMPS software and multiple potentials, including a deep learning potential, to accurately model atomic interactions. Water was selected as the flowing fluid due to its practical relevance. The nanochannel walls comprised a 2D graphene (or graphene oxide) layer in contact with the fluid and a solid 3D silicon slab on the outer side to stabilize the graphene layer and prevent movement and distortion during fluid flow.

Our analysis identified two primary heat transfer mechanisms (axial conduction and advection) in nanochannels with graphene or graphene oxide walls, dependent on the Peclet number (Pe). Additionally, we examined the effects of the driving force at the nanochannel inlet and the nanochannel width on heat transfer and fluid flow. The applied driving force influences fluid velocity, a crucial parameter for Pe. Another key parameter investigated was the percentage of functional groups attached to the graphene walls or the degree of graphene oxidation.

Results indicated that increasing the oxidation percentage typically enhances wall roughness, decreases water flow velocity, and increases wall hydrophilicity. Consequently, thermal transport between channel walls and flowing water is improved due to higher surface area from increased roughness and lower velocity, with axial conduction being the dominant heat transfer mechanism. However, when the oxidation percentage is below 2%, the walls remain relatively smooth and hydrophobic, resulting in a slip condition, higher water velocity, and advection as the dominant heat transfer mechanism. Pristine graphene, known for its hydrophobicity, further supports these observations.

Higher driving forces at the nanochannel inlet were found to have varied effects based on oxidation levels. For graphene oxide walls with more than 2% oxidation, increasing the driving force or velocity minimally impacts the heat current, which can be attributed to the dominance of axial conduction. Conversely, for walls with 2% or less oxidation, increased driving force significantly boosts water velocity and heat current due to the dominance of advection.

Furthermore, increasing the channel width while maintaining the same driving force resulted in higher fluid velocities for all cases, likely due to reduced wall roughness influence. This velocity increase affects the Peclet number and heat transfer mechanisms, leading to lower water temperatures along the channel. These findings underscore the substantial impact of graphene oxidation on the thermal transport and fluid flow of water, demonstrating how it can enhance the efficiency of nanochannels in dissipating heat.

Presenting Author: Milad Nasiri University of Nevada, Reno

Presenting Author Biography: Mr Nasiri has joined the University of Nevada, Reno as a Mechanical Engineering PhD student in fall 2021, and has been working on heat transfer in micro/nano scale. Now he is a PhD candidate and is trying to expand his knowledge in heat transfer world. He also did his master in Mechanical engineering with a thesis on solar-thermal devices.

Authors:

Milad Nasiri University of Nevada, Reno
Haoran Cui University of Nevada, Reno
Yan Wang University of Nevada, Reno