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Nanotechnology. 2009 Jul 29;20(30):305706. doi: 10.1088/0957-4484/20/30/305706. Epub 2009 Jul 8.

Frequency dependent enhancement of heat transport in a nanofluid with ZnO nanoparticles.

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1
Unit for Nanosciences, Department of Material Sciences, S N Bose National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata-700 098, India. neogy@bose.res.in

Abstract

In this paper we report an observation of an unusual frequency dependent enhancement of the heat transport parameter (C(p)kappa, C(p) = heat capacity and kappa = thermal conductivity) of a nanofluid containing ZnO nanoparticles of an average size of 10 nm (volume fraction<or=1.5%) in ethanol. The enhancement of C(p)kappa at low frequency is substantial. C(p)kappa becomes frequency independent at low frequency but it shows a strong dependence on the measuring frequency where it decreases as the frequency is increased. The enhancement also depends on the temperature and also scales with the concentration of ZnO. This frequency dependent thermal conductivity of nanofluids cannot be explained by the classical effective medium theory. A new model has to be developed to explain the above phenomenon. We have suggested local aggregation as the likely cause that may give rise to the observed frequency dependence.

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