UKHTC2013/92 92-1 13 th UK Heat Transfer Conference, UKHTC2013 2 - 3 September 2013 Imperial College London Investigation into Effective Viscosity and Electrical Conductivity of -Al 2 O 3 -Glycerol Nanofluids in Einstein Concentration Regime SA ADIO, M SHARIFPUR and JP MEYER Nanofluids Research Laboratory, Thermofluids Research Group, Department of Mechanical and Aeronautical Engineering, University of Pretoria, Private Box 0002, Pretoria, South Africa. Abstract Energy sustainability is very crucial for any viable engineering solution to be achieved. In recent times, nanofluids have shown a great promise of bringing about sustainable energy development in the field of heat transfer and regarding the design of heat transfer equipment. In this study, the viscosity of -Al 2 O 3 – glycerol nanofluids; a prime factor in the design of heat tranfer equipment such as heat exchanger has been investigated in the Einstein’s volume concentration regime (  ≤ 2%). This was accomplished by studying the effect of the two most basic parameters, namely temperature and volume concentration at constant shear rate on 20–30 nm -Al 2 O 3 in glycerol. Stable -Al 2 O 3 –glycerol nanofluids samples were prepared using the famous two-step method, followed by ultrasonication at two different time period of 3 h and 6 h in a controlled temperature bath. The effect of volume concentration on the effective viscosity, electrical conductivity and pH were all monitored between the temperature range of 20–70 o C. In the case of 3 h samples, the study shows no appreciable increase in the relative viscosity up to 0.5% nanoparticles volume concentration and it was observed to reach a critical vlaue (beyond which the relative viscosity starts reducing with temperature) at 55 o C for 2%, 60 o C for 1% and 65 o C for both 0.5% and 0.1% volume concentrations respectively. However, 6 h sonication effect was only felt at the reduction of the relative viscosity of 2% volume concentration, with the critical temeprature observed at 55 o C for all volume fractions. Comparing the experimental data with the available low volume concentration classical models and emipiral model revealed that the classical models under predicted our experimental data, while, the empirical model anormalously over predicted the experimental data reported in this work. A critical volume concentration of 0.5% and 1% were observed with respect to the electrical conductivity increase with volume concentration for 3 h and 6 h samples respectively, after which a reduction to plateu was prominent which signifies counter-ion condenstation. Keywords: glycerol, nanofluids, viscosity, alumina, electrical conductivity, counter-ion condensation 1 Introduction Energy sustainability is an essential part of world’s developmental drive in this century and in order to achieve a sustainable development, the demand for energy efficient systems is on the increase, the likes of which has never been recorded before. This has led to more compact devices and systems being designed and built daily. However, conventional heat transfer fluids such as water, ethylene glycol, engine oil, glycerol etc. cannot deliver an efficient thermal management required in these devices due to their poor thermal properties [1] compared to the high density heat flux energy