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

Abstract

In this paper we report an observation of an unusual frequency dependent enhancement of the heat transport parameter (C_pκ, C_p=heat capacity and κ= thermal conductivity) of a nanofluid containing ZnO nanoparticles of an average size of 10 nm (volume fraction=1.5%) in ethanol. The enhancement of C_pκ at low frequency is substantial. C_pκ 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.