Investigation of thermal conductivity and viscosity of nanofluids containing carbon nanotube and surfactants

Conventional coolants such as water, oil and ethylene glycol are commonly used in thermal systems. However, they offered poor thermal characteristics such as low thermal conductivity. The developments in nanotechnology have introduced heat transfer fluids with improved thermal conductivity known as nanofluids. Addition of highly conductive particles like MWCNT can increase the thermal conductivity of heat-transfer fluids. Therefore, the objectives of this study are investigation on thermal conductivity and viscosity characteristics of MWCNT based water/ethylene glycol nanofluid. Apart from that the stability of nanoluids was measured via observation and zeta potential methods. KD2-Pro thermal analyser and Brookfield R/S rheometer were used to measure the thermal conductivity and viscosity of the samples, respectively. Based on observation method, the particle sedimentation and coagulation occurred at 0.01 wt. % and 0.05 wt. % of MWCNT. However, the nanofluids samples remained stable when added with surfactants namely GA, PVP, and CTAB. This experimental result concluded that sample added with 0.01 wt. % of MWCNT and CTAB exhibited highest zeta potential value compared to that of other type of surfactants. The thermal conductivity increases up to 18.4% for PVP, 25.67 % for GA and lastly 16.03% for CTAB for 0.05 wt. % of MWCNT based nanofluid compared to that of base fluid. The viscosity results indicated that for high particle content, the nanofluids behaved as shear-thinning. Finally, statistical mathematical equations were developed for thermal conductivity and viscosity of MWCNT based nanofluids in the present study.