Effects of multi walled carbon nanotubes shape and size on thermal conductivity and viscosity of nanofluids

In this study, effective thermal conductivity and viscosity of multi walled carbon nanotubes water based nanofluids containing multi walled carbon nanotubes with various geometrical characteristics were investigated, with volume fraction 0.05 vol%. The experimental results demonstrated that thermophysical properties of the nanofluids depend on the geometrical characteristics of carbon nanotubes. The results were compared with some well-known models for thermal conductivity enhancement and relative viscosity and good conformities were observed. In this research, maximum enhancements of 36% and 5.5% were achieved for nanofluids effective thermal conductivity and dynamic viscosity respectively; these improvements were established in comparison to the base fluid at 45 degrees C. In addition, the results indicate that applying processes based on the surface modification on the nanotubes and improvement in nanoparticles dispersion can lead to enhancement in thermophysical properties in the nanofluids. During the experiments, the effective procedure of nanofluids stabilization was obtained. These findings combined with obtaining a pH value near the neutral state result an improvement in heat transfer and flow characteristics of the nanofluids.