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             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.


         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.


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.