Experimental study of free convective heat transfer around a spherical electronic component cooled by means of porous media saturated by nanofluid

Abstract

This experimental work deals with quantification of free convective heat transfer around a spherical electronic device. This so-called active sphere generates during its operation a heat flux leading to Rayleigh number ranging from 6.84 × 106 to 9.79 × 108. Its cooling is done through porous media saturated by Water-ZnO nanofluid contained in a spherical closed cavity maintained isothermal. Steady state measurements were carried out on an industrial prototype at scale 1:1 using various porous media whose thermal conductivity, relative to that of the base heat transfer fluid (water), varies between 0 (without porous medium) and about 40. These porous media are saturated with a water-based ZnO nanoparticles nanofluid with a volume fraction ranging from 0 (pure water) to 10%. The average Nusselt number determined for different combinations of the three influencing parameters confirms that saturated porous media enhances natural convective heat transfer. Influences of Rayleigh number, volume fraction and thermal conductivity ratio have been quantified. Results are in agreement with those of recent numerical approaches done by means of the control volume method in the 6.51 × 106 - 1.32 × 109 Rayleigh number range. Measurement-calculation deviations are of about 5% on average. They confirm the validity of the model implemented in the numerical approach. The new results of the present work can be applied to various engineering fields such as electronics to optimize thermal design of electronic assemblies and improve their reliability.