6f027614-c479-4f23-ba76-db3a9d051afd.doc Investigation of flow characteristics of nanofluids containing carbon nanotubes H. Alias, Y. Ding, and R.A. Williams Institute of Particle Science and Engineering, University of Leeds, Leeds LS2 9JT, UK. firstname.lastname@example.org ABSTRACT Advanced heat transfer fluids are required in many industrial applications. Fluid with high thermal conductivity is needed in energy-efficient heat transfer equipment. Due to this fact, the research in advanced fluid has rapidly increased in the last decade. Suspending nanoparticles in conventional fluid has significantly increased the fluid thermal conductivity. Since then the term ‘nanofluid’ was introduced in the research world. Nanofluid is defined as suspension of nanoparticles which are significantly smaller than 100nm. Nanofluids have thermal conductivity remarkably higher than the base liquid. Various nanoparticles have been used in production of nanofluids such as metal, metal oxide and also carbon nanotubes. Carbon nanotubes are a new form of material formed by elemental carbon, and possess different properties than other forms of carbon materials. Carbon nanotubes exhibit excellent properties due to their structure and size. Because of these properties, carbon nanotubes may be ideal for thermal management. The thermal conductivity of carbon nanotubes have been reported in many literatures. The value ranges from 2 to 4 orders of magnitude higher than that of conventional fluid. Thus suspending carbon nanotubes in fluids would therefore enhance the fluids thermal conductivity. Recent publications have revealed a significant enhancement of heat transfer in nanofluids, but no report has been seen on relating the thermal behaviour to the rheological behaviour. Dispersing the nanotubes into aqueous medium has been a serious challenge. The nanotubes tend to aggregate, form agglomerates and separate from the dispersion (Zhang et. al., 2004). In this present study, multiwalled carbon nanotubes are suspended in distilled water using gum arabic as the dispersing agent. Prior to the production of nanofluids, the critical micelle concentration (CMC) of gum arabic in water was determined. Applying a constant concentration of gum arabic which is below the CMC, a range of concentration of carbon nanotubes was applied in preparing the suspensions. In addition to that, pH factor was also considered in the investigations. The suspensions were treated with acid and base to adjust the pH. Rheological analysis was also performed on the samples. The mooney geometry was selected as the measuring system. The suspensions showed flow behaviour of pseudo plastic profile. The observation had been reported in other studies but different methods of production and surfactant were used (Kinloch et. al., 2002). The viscosity-temperature dependence of the suspensions was also studied. The thermal and rheological behaviour of the suspensions were then investigated to see how they are related. Keywords Nanofluids, Rheology, Carbon nanotubes, Thermal behaviour. REFERENCES Kinloch, I.A., Roberts, S.A., Windle, A.H. 2002. A rheological study of concentrated aqueous nanotube dispersions, Polymer, 43, 7483-7491 Z. Zhang, Lockwood, F.E. (2004). Preparation of stable nanotube dispersions in liquids, US Patent 6,783,746 B1.