Investigation on thermal performance of nanofluids in a microchannel with fan-shaped cavities and oval pin fins

In this paper, a combined structure of fan-shaped cavities and oval pin fins is designed for the rectangular microchannel heat sink with an aspect ratio of 2. Four structural parameters are investigated, including cavity height (h_r), chord length (I_r), rib offset distance (S₀) and rib height (H_f). Overall performance factor and total thermal resistance are used to reflect the microchannel performance. In the Reynolds number range of 132–531, the microchannel shows the best hydrothermal performance under h_r of 0.05 mm, I_r of 0.2 mm, S₀ of 0, and H_f of 0.1 mm. When the Reynolds number is 398, the overall performance factor of the microchannel with optimal parameter combination is 33% higher than that of a rectangular microchannel. Field synergy angle in the microchannel is calculated based on the field synergy principle. According to the KKL (Koo-Kleinstreuer-Li) model, the local thermal conductivity distribution of Al₂O₃ nanofluids is studied at different nanoparticle diameters. Moreover, the overall performance factors of the heat sink are investigated at several volume fractions of Al₂O₃ nanofluids. Under the Reynolds number of 132, the Nusselt number of 0.04 vol% nanofluid is 9.5% higher than the deionised water. Based on optimal structural parameters, compared with deionised water, Al₂O₃ nanofluid with a diameter of 10 nm and volume fraction of 0.04 further improve the overall performance factor of micro-channels by 5.8% and reduce the total thermal resistance by 2.9%.