Effect of nanoparticle shape on cooling performance of boehmite-alumina nanofluid in a helical heat sink for laminar and turbulent flow regimes

Abstract

This study is motivated by the impacts of nanoparticle shapes on flow and heat transfer characteristics in a microchannel helical heat sink for cooling of electronics in both laminar and turbulent flow regimes. Therefore, effects of five different nanoparticle shapes (platelet, cylindrical, blade, brick and spherical) at five different volume fractions (ϕ = 0, 0.5, 1.0, 1.5, 2.0%) and at eight different Reynolds numbers corresponding to laminar and turbulent flow regimes (Re = 500–20,000) are investigated using finite volume method with two-phase mixture approach for nanofluids. Various performance parameters related with the first law of thermodynamics are considered. It was found that nanofluid utilization remarkably improves heat transfer along with causing an increment in pumping power. Furthermore, it was revealed that these variations in the parameters strongly depend on the utilized nanoparticle shape, and the platelet shaped particles were the most advantageous. They improved convective heat transfer coefficient up to 25% in laminar and up to 22.5% in turbulent flow regimes compared to base fluid. However, they increased pumping power up to 6.3-folds both in laminar and turbulent flow regimes. On the other hand, spherical particles yielded the least enhancement in convective heat transfer coefficient, which can reach up to 3.7% in laminar, and 1.8% in turbulent flow. Nevertheless, they slightly increase pumping power, which maximally reaches up to around 8%. Yet, the performance evaluation criteria showed that the heat transfer improvement effect of platelet shaped particles is more dominant over the increment effect in pumping power, which makes them favourable for applications.