Thermal Transport and Rheological Properties of Hybrid Nanofluids Based on Vegetable Lubricants

Nanofluids based on vegetal oil with different wt.% of carbon nanotubes (CNT), hexagonal boron nitride (h-BN), and its hybrid (h-BN@CNT) were produced to investigate the effects of these nano-additives on the thermal conductivity and rheological properties of nanofluids. Stable suspensions of these oil/nanostructures were produced without the use of stabilizing agents. The dispersed nanostructures were investigated by SEM, EDS, XRD, and XPS, while the thermal conductivity and rheological characteristics were studied by a transient hot-wire method and steady-state flow tests, respectively. Increases in thermal conductivity of up to 39% were observed for fluids produced with 0.5 wt.% of the hybrid nanomaterials. As for the rheological properties, it was verified that both the base fluid and the h-BN suspensions exhibited Newtonian behavior, while the presence of CNT modified this tendency. This change in behavior is attributed to the hydrophobic character of both CNT and the base oil, while h-BN nanostructures have lip-lip bonds, giving it a partial ionic character. However, the combination of these nanostructures was fundamental for the synergistic effect on the increase of thermal conductivity with respect to their counterparts.

Automated summary

In this study, nanofluids based on vegetal oil with different weight percentages of carbon nanotubes (CNT), hexagonal boron nitride (h-BN), and a hybrid of both (h-BN@CNT) were produced. The effects of these nano-additives on the thermal conductivity and rheological properties of the nanofluids were investigated. The results showed that the fluids produced with 0.5 wt.% of the hybrid nanomaterials exhibited an increase in thermal conductivity of up to 39%. Furthermore, it was found that the presence of CNT affected the rheological properties of the fluid, while h-BN changed the fluid's Newtonian behavior.