Utilization of the magnetogranulometric analysis to estimate the thermal conductivity of magnetic fluids

In this study, the semi-empirical equation for the effective thermal conductivity of the Holotescu–Stoian model was applied to a set of four dilutions of a transformer oil based magnetic fluid with magnetite nanoparticles as magnetic phase, using the results obtained for the size distributions from the magnetogranulometry analysis, followed by a comparison with the measured values of the effective thermal conductivity obtained by the hot ball method. The link between the size distribution by number and by volume used in the magnetogranulometry analysis and the Holotescu–Stoian model adaptation to the lognormal distribution were presented. The comparison between the results given by the model and the corresponding experimental data showed that by using the approximated size distribution to calculate the effective thermal conductivity the analytical results much closer to the experimental ones are obtained, compared to those given by the Maxwell classical model.

Research Highlights
► Utilization of the approximate particle size distribution obtained by magnetogranulometric analysis to evaluate the effective thermal conductivity of a ferrofluid.
► Presentation of the relationship between the magnetogranulometric method based on the lognormal particle size distribution by volume (Chantrell) and the method based on the lognormal distribution by number (Rasa), highlighting that they give different results.
► Presentation of a generalized form of the model for evaluating the effective thermal conductivity that includes the particles size distribution.