An Investigation On The Models For The Effective Thermal Conductivity Of Nanofluids

In this paper, the effective thermal conductivity of naofluids is derived by taking into account for the several factors respectively.A fractal model, which takes account for the heat convection due to Brownian movement of nanoparticles, for the effective thermal conductivities of nanofluids is derived. The proposed model is expressed as a function of average size of nanoparticles, fractal dimension, minimum and maximum diameters of nanoparticles, volume fraction and temperature. No new empirical constant is introduced in the proposed model and every parameter in the model has clear physical meaning. The model predictions are compared with the experimental data, and good agreement between the model predictions and experimental data is found. It is found that the parameter c introduced in thermal boundary later is related to fluids, but independent of nanoparticles added in the fluids. It is also found that the thermal conductivity contributed by heat convection due to Brownian movement of nanoparticles increases as the volume fraction of nanoparticles is less than the critical concentration, at which the contribution from heat convection reaches the maximum value, and decreases as the volume fraction of nanoparticles is higher than the critical concentration.Moreover, Based on the fact that nanoparticles and clusters coexist in the fluids, another model for the effective thermal conductivity of nanofluids is derived. The effect of the contact between nanoparticles in clusters on the effective thermal conductivity of nanofluids is analyzed. The model predictions are compared with the available experimental data, and good agreement between the model predictions and experimental data is found.The validity of the proposed models is thus verified...