Abstract
The study investigates the influence of free surface by jet impingement of aqueous nanodispersion dominant with hybridized nanoparticles. Hybrid nanofluid (HNF) was prepared by a two-step approach using 7 nm Alumina (γ-Al2O3) and a dominant portion of 3–5 nm Multi-Walled Carbon Nano-Tubes (MWCNT) in the ratio of 10:90 dispersed within deionized (DI) water base fluid. The nanofluid viscosity and thermal conductivity measurements were at varying temperatures (10–60 °C) and volume concentrations (0.025, 0.05, 0.1, and 0.15%). A jet nozzle (1.65 mm inner diameter) impinged the HNFs onto a targeted round surface (42 mm diameter) at an H/Dj ratio of 4. The Nusselt number (Nu) evaluations were at varying fully-developed turbulent regimes: Reynolds number (Re) between 6000 and 16,500, Weber number (We) between 1000 and 7000, and Peclet number (Pe) between 80,000 and 205,000. Besides, we investigated a transient cooling rate for varying volume concentrations (vol%) and the numerical aspect of the work by employing the Eulerian-Eulerian approach to model jet impingement. The maximum augmentation in Nu number is at 0.05 vol% HNF, with a 17% increase compared to DI water. Based on the numerical investigation using Computational Fluid Dynamics (CFD), a maximum improvement of 19.7% in Nu number was with the 0.15 vol% HNF, whereas the improvement in the 0.05 vol% particle concentration fluid was 13.7%. The ambiguity of the results between the experiment and CFD analysis could be connected to the size and shape of nanoparticles, mixing or swirling parameters, surfactant type, or a combination of all the above. In terms of the transient cooling rate investigated, the best-performing fluid is the 0.15 vol% particle concentration fluid with a relaxation time of 1 s in CFD and 1.75 s in the experiment. Besides, the steady time is 23 s in CFD and 33 s in the experiments. A correlation for the Nusselt number is proposed based on the obtained data.
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