Investigating the effect of volume fraction on Brownian displacement, thermophoresis, and thermal behavior of graphene/water nanofluid by molecular dynamics simulation

Abstract

Nanotechnology focuses on materials at the nanoscale, including nanoparticles and nanofluids are created by dispersing nanoparticles in a base fluid. This study examined the impact of volume fraction on thermophoresis, thermal conductivity, and Brownian motion in graphene/water nanofluid through molecular dynamics simulations. Simulations were performed at a constant temperature of 300 K, representative of room temperature conditions for thermal applications. This research aimed to understand how the amount of graphene in the water-based nanofluid affected these properties, which were crucial for heat transfer and thermal management systems. The study examined the effects of various nanoparticle volume fractions (1 %, 3 %, 6 %, and 10 %), ranging from dilute to semi-concentrated nanofluids, on thermal conductivity, Brownian motion, and thermophoresis. Results indicate an increase in average Brownian displacement and thermophoresis displacement from 3.06 and 23.88 Å to 4.14 and 26.88 Å, respectively, as the volume fraction increases from 1 % to 6 %. However, as the volume fraction increased from 6 % to 10 %, these values decreased to 3.35 Å and 23.99 Å. This decrease may be attributed to increased interparticle interactions and clustering at higher volume fractions. After 10 ns, increasing the nanoparticle volume fraction to 6 % raised heat flux and thermal conductivity from 39.54 W/m2 and 0.36 W/m·K to 45.05 W/m2 and 0.46 W/m·K. However, at a 10 % volume fraction, both parameters decreased to 39.56 W/m2 and 0.37 W/m·K, respectively. The temperature profile shows that increasing the graphene volume fraction to 6 % raised the maximum temperature from 1415 K to 1879 K; further increasing the volume fraction to 10 % decreased it to 1572 K. These findings indicate that the volume percentage of graphene nanoparticles significantly affected Brownian displacement, thermophoresis displacement, heat flux, thermal conductivity, and maximum temperature in the nanofluid. An optimal volume fraction of approximately 6 % is identified for enhancing thermal performance. Overall, the volume fraction, along with nanoparticle size, shape, and dispersion stability, was crucial in determining the atomic and thermal behavior of nanofluids, highlighting the need to identify the optimal concentration for superior performance.