Hydrothermal behavior of nanofluid flow in a microscale backward-facing step equipped with dimples and ribs; Lattice Boltzmann method approach

Due to rapid development in the technology of electronic devices and improved performance of thermoelectric materials, thermal management is one of the significant issues to be dealt with. Hence, the conventional heat transfer methods are not responsive anymore, especially in micro-electric applications. In this work, the application of nanofluid, instead of pure fluids, in the microchannel heat sink with sudden explanation and insertion of ribs and dimples inside the backward-facing step microchannel is studied numerically. Lattice Boltzmann method is applied to study the heat transfer and laminar flow behaviour of 4% concentration of Al2O3-water nanofluids in Reynolds numbers ranging 40-100 through the backward-facing step microchannel. Microchannel size is 60 & mu;m (H) x 60 & mu;m (W) x 336 & mu;m (L), and the height of the microchannel's step is 27 & mu;m, and located 108 & mu;m from the entrance. The bottom wall of the microchannel, downstream of the step is exposed to constant heat flux. Ribs and hemispherical dimples are located on this wall section as vortex generators. A few studies focus on curved boundaries in Lattice Boltzmann Method due to some complexities in curved boundaries, especially spherical ones. So, the main novelty of this work is inserting hemispherical dimples in backward-facing step microchannel and combining them with ribs as proposed turbulators. The results showed that increasing the number of ribs from 4 to 8 (100% growth) leads to a 63.64 and 64.65% augmentation in the average Nusselt number at Re = 40 and 100, respectively. Also, increasing the ribs heights from 0.5H to 2H (300% growth) caused average Nusselt number augmentation of about 54.54 and 40.91% at Re = 40 and 100, respectively. In some cases, with lower numbers or shorter ribs, the effects of adding ribs on the Nusselt number are either minor or undesirable.