Stability and Thermal Property Optimization of Propylene Glycol-Based MWCNT Nanofluids

Propylene glycol-based MWCNT (multi-walled carbon nanotubes) nanofluids were prepared in the framework of a two-step method and by using a suitable PVP (polyvinyl pyrrolidone) dispersant. The BBD (Box-Behnken design) model was exploited to analyze 17 sets of experiments and examine the sensitivity of the absorbance to three parameters, namely the concentration of MWCNT, the SN ratio (mass ratio of carbon nanotubes to surfactants) and the sonication time. The results have revealed that, while the SN ratio and concentration of MWCNT have a strong effect on the absorbance, the influence of the sonication time is less important. The statistical method of analysis of variance (ANOVA) was further used to determine the F- and p-values of the model. Five experiments were run to validate this approach. Since sample 2 was found to display the greatest absorbance, it was selected for stability monitoring as well as thermal conductivity and viscosity measurements. This sample has been found to be stable; the viscosity decreased with increasing temperature; the addition of MWCNT nanoparticles was more effective in improving the thermal conductivity of propylene glycol than other methods in the literature. Moreover, the MWCNT nanofluid based on propylene glycol exhibited higher thermal conductivity at low temperatures.