Theoretical study on enhancement of heat transfer of nanofluids with functionalized graphene flakes in confined nanopipe system

Abstract

In order to find a suitable type of nanoparticles to improve the heat transfer of nanofluids, the role of nanoparticles should be elucidated. The nanoparticles are known to affect the heat transfer, and here we investigated the role of nanoparticles using a nanopipe model system. Specifically, the heat transfer phenomena of nanofluids containing hydrophobic (i.e., hydrogenated) and hydrophilic (i.e., carboxylated) functionalized graphene flakes (GFs) were compared. Confined nanopipe (i.e., 325 K) with a diameter of 400 Å system were adopted for the heat transfer and coarse-grained molecular dynamics (CGMD) simulations were performed. In the nanofluids, GF-concentrated layer was formed near the pipe wall, which induced the high HTC value of nanofluids. We found that after the thermal change of fluid became constant (i.e., thermally fully developed region), the thermal boundary layer was maintained for 100 Å due the GF-concentrated layer. The thermal boundary layer and HTC was thicker and higher when using carboxylated GF, which was more soluble in the coolant.