Effects of ZnO-H2O nanofluid saturated porous medium on the thermal behavior of cubical electronics contained in a tilted hemispherical cavity. An experimental and numerical study

Abstract

A porous medium saturated with a ZnO-H2O nanofluid is used for cooling purposes of a cubic electronic assembly contained in a hemispherical enclosure. The significant power generated by the active assembly leads to Rayleigh numbers ranging from 5.21 × 107 to 7.29 × 1010. The cavity base could be tilted with respect to the horizontal plane at an angle varying between 0 and 180° (horizontal disc with dome facing upwards and downwards respectively). A monophasic model is used for the nanofluid whose volume fraction varies between 0 (pure water) and 10%. The porosity of the considered porous media is of 95% and the thermal conductivity of its solid matrix varies in a large range reaching 70 times that of the fluid-base. The solution of the considered 3D problem achieved through the volume control method using the SIMPLE algorithm allowed to determine the surface average temperature of the active cube for any combination of tilt angle, volume fraction, Rayleigh number and ratio between solid matrix and fluid base thermal conductivities. The results of this work, which were experimentally confirmed, show that this temperature evolves with a conventional power type law versus the Rayleigh number. The fraction volume has little influence, whereas thermal conductivities ratio has a significant effect on the average temperature. The proposed correlation allows determination of this average temperature for any combination of the four influence parameters discussed in this study. It allows correct thermal sizing of the considered assembly and enhances its reliability.