Nanofluid is a new class of heat transfer fluids engineered by dispersing metallic or nano_ metallic nanoparticles with a typical size of less than 100 nm in the conventional heat transfer fluids.In order to study the heat transfer behavior of the nanofluids, precise values of thermal and physical properties such as thermal conductivity of the nanofluids is required . There are a few well_known correlations for predicting the thermal conductivity of nanofluids which are often cited by researchers to calculate the convective heat transfer behaviors of the nanofluids. Each researcher has used different models of the thermal conductivity in their works. This article aims to summarize the various models for predicting the thermal conductivity of nanofluids which have been commonly cited by a number of researchers and use them to calculate the experimental and theoretical convective heat transfer coefficient of nanofluid flowing in heat exchangers.Results show that difference between calculated thermal conductivity from models increases with increasing the volume concentrations and also slightly increases with thermal conductivity of nanoparticles. Experimental results show that aggregation of nanoparticles have significant effect on the predicted values of thermal conductivity of nanofluids.Keywords: Nano fluids; Thermal conductivity; Nanoparticles; Convective heat transfer coefficient; Aggregation
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