Nanobubbles in graphene-based nanofluids: Unraveling the mechanisms behind nucleation, behaviour and thermophysical properties using a molecular approach

Abstract

Significant endeavors have been undertaken to substitute conventional thermal fluids with those possessing enhanced thermophysical properties, wherein nanoscale phenomena, particularly the integration of nanoparticles like graphene, play a crucial role. Graphene's exceptional properties and interactions with surrounding molecules make it an ideal candidate for nanoparticle integration, particularly in renewable energy applications such as solar energy. The introduction of dissolved gases, especially in industrial processes like electrochemical reactions, further influences fluid behavior and thermophysical properties, potentially leading to the formation of nanobubbles, with this alteration becoming even more pronounced. This study employs molecular dynamics simulations to investigate nanobubble formation, behavior, and their impact on the inherent properties of graphene-water and graphene-methanol nanofluids, featuring a 9.5 nm × 9.5 nm graphene sheet immersed in 98,000 water molecules and 48,000 methanol molecules, respectively. The findings reveal distinct behaviors depending on the host liquid, with two-atom gases forming graphene-nanobubbles in water-based nanofluid, while nitrogen and hydrogen predominantly form bulk nanobubbles in methanol. Moreover, the presence of formed nanobubbles and dispersed graphene increases water viscosity but decreases it in two-atom gas/graphene-methanol nanofluids. The lowest viscosity is recorded for the graphene/methanol sample with hydrogen nanobubbles at 0.00053 Pa.s, while the highest viscosity is observed for the oxygen methanol sample without nanobubbles at 0.00068 Pa.s. Conversely, the specific heat capacity of water-based nanofluids decreases due to nanobubbles and dispersed graphene, particularly pronounced in oxygen/graphene-nanofluid. While in methanol-based nanofluids, the specific heat capacity increases, notably in oxygen-graphene/methanol nanofluids.