Permittivity of (40 nm and 80 nm) alumina nanofluids in ethylene glycol at different temperatures

Abstract

This article studies the effective permittivity of alumina nanofluids (aluminium oxide) in ethylene glycol. Two nanoparticle sizes (40 nm and 80 nm) were considered and the measurements were carried out at various concentrations (up to 2% in volume) and at six different temperatures (from 298.15 K to 348.15 K). An empirical equation is proposed that allows to obtain the permittivity value at any concentration or temperature in the studied ranges. The influence of the volume fraction, nanoparticle size and the temperature on relative permittivity is shown. When compared to the previous published values for alumina (40 nm) in water, current results show the influence of the base fluid. The enhancement of permittivity was calculated, and its behaviour was analysed. Smaller sized particles have the highest values of permittivity and enhancement. Theoretical models in the study of permittivity are applied. The poor predictions of classical models are attributed to the positive behaviour of the permittivity change on mixing for these nanofluids. The contributions to permittivity from ethylene glycol and nanoparticles are separated in two distinct terms in the variable index equation. The permittivity change on mixing calculated from this equation points out that the nanoparticles are the main responsible for the unusual permittivity increment in these colloids.