Malvern MPT-2 Autotitrator Stability and Thermophysical properties of Aluminium Oxide nanofluids Sanjeeva Witharana, Mohammed Rehan, Haisheng Chen, and Yulong Ding* Institute of Particle Science and Engineering, School of Process, Environmental and Materials Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom *y.ding@leeds.ac.uk 1. INTRODUCTION Aluminium oxide is a material widely used in industrial applications. Moreover water based and ethylene glycol based Aluminium oxide nanofluids have often been examined for thermal and rheological behaviour. Due to its high reactivity with H+ and OH- ions in liquid environments, the properties of such nanofluids are expected to be time-dependant. This has eventually led to controversies while interpreting experimental data. One part of this study is aimed at investigating the stability of Alumina nanofluids. The other part is dedicated to demonstrate their thermal conductivity and rheological properties. 3. EXPERIMENTS Stability Rheology Malvern MPT-2 Autotitrator Shear viscosity of ethylene glycol based nanofluids at 40°C measuring temperature. Alumina nanofluids 20hrs, 7days and 6 weeks after formulation. All nanofluids were formulated by adding the dry nanopowder into the liquid, followed by magnetic stirring and ultrasonification for few hours. No dispersants were introduced. Bohlin CVO rotational rheometer 2. NANOPARTICLES Spherical shape ϒ-Aluminum Oxide nanoparticles; Nanophase Technologies Inc, USA Primary particle diameter 46nm Acicular shape ϒ-Aluminum Oxide nanoparticles; Sasol North America Inc, USA Primary particle diameter:length ratio ~1:15 4. DISCUSSION Thermal conductivity Alumina nanofluids are initially more stable in acidic region. However, they too tend to collapse with time. Alumina-water nanofluids exhibit two IEPs depending on the direction of titration. Similar behaviour had earlier been reported for α-Alumina particles. Thermal conductivity of Alumina-EG nanofluids is fairly stable with temperature, falling inline with our previous experience at lower temperatures. The exception is acicular Alumina particles of 8wt%. Moreover, the enhancement shows clear dependence on particle concentration. Shear viscosity of acicular Alumina–EG nanofluid resembles spherical nanoparticles than nanotubes. This is possibly due to breakage of acicular particles as evident from SEM image. Lambda measuring system Lambda system is highly accurate. Each data point shown here was an average of five consecutive measurements. The precision was >99%.