Comparison of Different Empirical Models for Analysing the Thermal Conductivities of Various Materials for Use in Nanofluid Preparation

For over the past ten years, various empirical models have been studied for analysing the thermal conductivity of different materials. In this analysis, different empirical correlations and models of thermal conductivity have been compared. The thermal conductivities of four types of oxide materials (SiO 2 , TiO 2 , CuO, Al 2 O 3 ) and MWCNTs with volume fractions from 0.5 to 5% in a temperature range of 273–373 K and various nanoparticle shapes were compared. The results illustrated that the thermal conductivity of nanofluids based upon various nanoparticles increased with increasing volume fraction. In comparison, the effective thermal conductivity of nanofluids based on MWCNTs was enhanced much more than that of other types of nanofluids. Furthermore, Maxwell’s model was considered the basis for predicting the effective thermal conductivity of nanofluids. According to the basic models, a new correlation was proposed for predicting the effective thermal conductivity as a function of temperature and nanoparticle volume concentration. The nanoparticle shape has a great impact on the thermal conductivity of nanofluids. Regarding the precise heat transfer enhancement, the analysed nanofluids are suggested to be heat carriers in thermal systems, particularly solar thermal collectors. Typically, the use of nanofluids in solar thermal collectors improves the thermal efficiency of collectors in terms of the precise heat transference of nanofluids.