Optimization of thermal performance of multi-nozzle trapezoidal microchannel heat sinks by using nanofluids of Al2O3 and TiO2

In this study, a new multi-nozzle trapezoidal microchannel heat sink (MNT-MCHS) was proposed. Five substrate materials, two nanofluids with nanoparticle volume fractions, 0.1% ≤ φ ≤ 1%, and channel hydraulic diameters, 157.7 µm ≤ Dh ≤ 248.2 µm, were numerically examined in detail. In addition, heat fluxes in the range of 100-1450 W/cm2 subject to inlet coolant temperature from 15 °C to 75 °C were examined in detail. A locally optimal MNT-MCHS was defined, and a novel equation was proposed for predicting the maximum temperature on the locally optimal MNT-MCHS depending on the heat flux, coolant inlet temperature, and the Reynolds number. It was found that at a Reynolds number of 900, the overall thermal resistance of a MNT-MCHS using copper as a substrate material is improved up to 76% as compared to that using stainless steel 304. The locally optimal MNT-MCHS, using TiO2-water nanofluid with φ=1%, could dissipate a heat flux up to 1450 W/cm2 at a Re of 900. A minimum thermal resistance in the present study is improved up to 11.6% and 36.6% in association with those of a multi-nozzle MCHS and a double-layer MCHS, respectively.