Mechanism of enhanced thermal conductivity of hybrid nanofluids by adjusting mixing ratio of nanoparticles

At certain mixing ratios, hybrid nanofluids exhibit superior thermal conductivity performance compared with mono nanofluids, without significant enhancements in viscosity. Studying the microstructures formed by nanoparticles in the base fluid is key to revealing the mechanism of enhanced heat transfer in nanofluidic systems. Here, effects of varying the nanoparticle volume fraction (0.5–2.0 vol%) and Cu:Al volume mixing ratio (20:80, 40:60, 50:50, 60:40, and 80:20) of Cu-Al/Ar hybrid nanofluids were investigated using non-equilibrium molecular dynamics (NEMD) simulations at a temperature of 85 K. The mechanism of thermal conductivity enhancement was elucidated through quantitative analysis of the nanolayer structure and atom trajectory. The results showed that the thermal conductivities of Cu-Al/Ar hybrid nanofluids with a mixing ratio of 20:80 were lower than those of the corresponding Cu/Ar mono nanofluids with volume fraction below 1.3 vol% due to the low quantity of Cu nanoparticles. However, when the quantity of Cu nanoparticles was increased by using mixing ratios from 40:60 to 80:20, the thermal conductivities were higher at all volume fractions. Compared to Cu/Ar nanofluids, the thermal conductivity of Cu-Al/Ar hybrid nanofluids improved from 0.149 to 0.166 W/(m·K) which was higher 2.76 % to 14.48 % as the mixing ratio increased from 20:80 to 80:20 at 2.0 vol%. Radial distribution function (g(r)), the number density and diffusion rate calculations indicated that the density and velocity of Ar atoms around Cu atoms were higher than those of Al atoms due to stronger interactions between Cu-Ar atoms. The main reason for the enhanced thermal conductivity of hybrid nanofluids with increasing mixing ratio was the higher unit nanolayer density and Brownian motion velocity.