Evaluation and effect of mixture ratio on heat transfer performance of Al2O3/water nanofluids

A two-step method was used to prepare Al2O3/water of nanofluids at mass fraction of 0.5% and 1.0%. This work focuses on the effect of mixture ratio of 20nm and 50nm Al2O3 nanoparticles on the thermal conductivity and viscosity. Moreover, the comprehensive heat transfer of Al2O3/water of nanofluids was estimated by cμ/cλ and Mo in the real heat transfer process. The experimental results showed that the effect of the cluster size on effective thermal conductivity and viscosity is obvious. Al2O3/water of nanofluids with mass fraction of 1.0% and mixture ratio of 50:50 exhibited the largest enhancement of effective thermal conductivity while the relative viscosity was the lowest with mixture ratio from 40:60 to 60:40. The reason is that the smaller clustering size of order enables nanofluids to reduce sedimentation rate indicating the dispersion of nanofluids. Thus, the formation of a localized particle-rich zone creates high-conductive percolation path of lesser thermal resistance compared to a particle-free zone, which forms 50nm-20nm-liquid layered structure and results in enhancing thermal conductivity. Lastly, the suitable areas for nanofluids applied in laminar flow were the temperature range from 25℃ to 50℃ and mixture ratio of 40:60 and 50:50 at mass fraction of 0.5 % and 1.0%. Moreover, the suitable areas for nanofluids applied in turbulent flow were the mixture ratio range from 40:60 to 60:40 and temperature higher than 40℃ at mass fraction of 0.5 %. © 2019, Chemical Industry Press. All right reserved.