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This study explores the thermohydraulic performance of metallic-oxide and carbon-additives-based mono and hybrid nanofluids-cooled micro pin-fin heat sink by adopting the multiphase Eulerian model. The circular configuration is adopted for micro pin-fins, with the staggered arrangement and constant heat flux applied at the base of the heat sink. The mono and hybrid nanofluids are based on an aqueous solution of Ag, MgO, GNP, MWCNT, Ag-MgO, and GNP-MWCNT mono and hybrid nanoparticles, and a pressure drop (Δp) range is applied across the heat sink. The heat transfer and fluid flow performance are evaluated in terms of temperature difference (ΔT), thermal resistance (Rth) of the heat sink, average heat transfer coefficient (havg), average Nusselt number (Nuavg), pumping power (PP), overall performance (OP), and performance evaluation criteria (PEC), whereas the velocity, temperature, pressure coefficient, and flow streamline contours present the qualitative depiction of flow distributions across the heat sink. The results revealed that under certain Δpconditions, the GNP dispersed mono nanofluid showed the highest thermal performance of the micro pin-fin heat sink compared to the water as a coolant. The optimal nanoparticle loading (φ) is found between 0.50 % and 0.75 % of GNP nanoparticles. The maximum enhancement in PEC is achieved at 60 % for φ of 0.50 % and 0.75 % for both Δpof 1120 Pa and 1470 Pa, respectively. At an optimum Δp, the higher average havg, Nuavg, and lower Rthare achieved.

Microchannel heat sink is an effective method in compact and faster heat transfer applications. This paper numerically investigates thermal and hydraulic characteristics of a porous microchannel heat sink (PMHS) using various nanofluids. The effect of porosity (γ = 0.32–0.60), inlet velocity (win = 0.5–1.5 m/s), and nanoparticle concentration (ϕ=0.0025 – 0.05) on thermal-hydraulic performance is systematically examined. The result shows a significant temperature increase (40 °C) of the coolant in the porous zone. The pressure drop reduces by 35% for γ = 0.32 compared to the non-porous counterpart, and this reduction of pressure significantly continues when γ further increases. The pressure drop with win is linear for PMHS with nanofluids, and the change in pressure drop is steeper for nanofluids compared to their base fluids. The average heat transfer coefficient increases about 2.5 times for PMHS, and a further increase of 6% in h¯ is predicted with the addition of nanoparticles. The average Nusselt number Nu¯ increases nonlinearly with Re for PMHS. The friction factor reduces by 50% when γ increases from 0.32 to 0.60, and the effect of nanofluid on friction factor is insignificant beyond the mass flowrate of 0.0004 kg/s. Whilst Cu and CuO nanoparticles help to dissipate the larger amount of heat from the microchannel, Al2O3 nanoparticle appears to have a detrimental effect on heat transfer. The thermal-hydraulic performance factor strongly depends on the nanoparticles, and it slightly decreases with the mass flowrate. The increase of nanoparticle concentration, in general, enhances both h¯ and ΔP linearly for the range considered.

According to recent trends in the field of miniature electronics, the need for compact cooling solutions compatible with very thin profiles and small footprint areas is inevitable. Impinging synthetic jets are recognized as a promising technique for cooling miniature surfaces like laptops, tablets, smart phones and slim TV systems. Effect of jet to cooled surface spacing is crucial in cooling performance as well as predicting Nusselt number for such spacing. An experimental study has been performed to investigate the cooling performance of two different synthetic jets actuated with piezoelectric actuators cooling over a vertical surface. Results showed that a major degradation of heat transfer when jets are close to the surface is occurred. Slot synthetic jets showed a better performance in terms of coefficient of performance (COP) than semi-confined circular jets for small jet to surface spacing. Later, a correlation is proposed for predicting Nu number for a semi-confined circular synthetic jet accounting the effects of Re number (500≤Rej≤1150), jet-to-surface spacing (H∕D=2and H∕D=4) and the stroke length (1.75≤L0∕D≤4.75and L0∕H<2.5). It is found that correlation can provide predictions with an R2value of over 98%.