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    Effect of natural convection hybrid nanofluid flow on the migration and deposition of MWCNT-Fe3O4 in a square enclosure
    (Elsevier France-Editions Scientifiques Medicales Elsevier, 2023) Cicek, Oktay; Sheremet, Mikhail A.; Baytas, A. Cihat
    In the present study, the migration and deposition of multi-walled carbon nanotube (MWCNT)-Fe3O4 nanocom-posite particles in a square enclosure for natural convection hybrid nanofluid flow are analysed numerically using the Eulerian-Lagrangian model with one-way coupling. The governing equations are solved by the finite volume method and Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. The location and velocity of 3000 selected composite particles in the host nanofluid are obtained by employing the Lagrangian approach. The influences of Rayleigh number and nanoparticle volume fraction on the thermal and flow behaviours of the system are presented. It is observed that the increasing volume fraction leads to a rise in the average Nusselt number at low Rayleigh numbers, while the case of 0=0.1% is the optimum volume fraction of nanoparticle in terms of heat transfer enhancement and strength of flow structure at Ra >= 104. The simulations of Lagrangian particle tracking demonstrate that the minimum deposition rate of composite particles with dp=0.5 mu m is obtained for a given Rayleigh number. The number of deposited large composite particles for the case of 0=0.1% is slightly more than for 0=0.3%, while the deposition rate of ultra-fine composite particles gets a higher value in the case of 0=0.3%. Moreover, the thermophoresis force plays a more significant role in small particle deposition than the Brownian random force.
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    Entropy generation minimization of hybrid nanofluid mixed convection flow in lid-driven square enclosure with heat-generating porous layer on inner walls
    (Emerald Group Publishing Ltd, 2024) Cicek, Oktay; Baytas, A. Filiz; Baytas, A. Cihat
    PurposeThis study aims to numerically scrutinize the entropy generation minimization and mixed convective heat transfer of multi-walled carbon nanotubes-Fe3O4/water hybrid nanofluid flow in a lid-driven square enclosure with heat generation in the presence of a porous layer on inner surfaces, considering local thermal non-equilibrium (LTNE) approach and the non-Darcy flow model.Design/methodology/approachThe dimensionless governing equations for hybrid nanofluid and solid phases are solved by applying the finite volume method and semi-implicit method for pressure-linked equations algorithm.FindingsThe roles of the internal heat generation in the porous layer, LTNE model and nanoparticles volume fraction on mixed convection phenomenon and entropy generation are introduced for lid-driven cavity hybrid nanofluid flow. Based on the investigation of entropy generation and heat transfer, the minimum total entropy generation and average Nusselt numbers are found at 1 <= Ri <= 10 where the effect of the forced and free convection flow directions being opposite each other is very significant. When considering various nanoparticle volume fractions, it becomes evident that the minimum entropy generation occurs in the case of phi = 0.1%. The outcomes of LTNE number reveal the operating parameters in which thermal equilibrium occurs between hybrid nanofluid and solid phases.Originality/valueThe analysis of entropy generation under various shear and buoyancy forces plays a significant role in the suitable thermal design and optimization of mixed convective heat transfer applications. This research significantly contributes to the optimization of design and the advancement of innovative solutions across diverse engineering disciplines, such as packed-bed thermal energy storage and thermal insulation.