Browsing by Author "Sheremet M.A."

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    Forced convection of Fe 3 O 4 -water nanofluid in a bifurcating channel under the effect of variable magnetic field
    (MDPI AG, 2019) Selimefendigil F.; Oztop H.F.; Sheremet M.A.; Abu-Hamdeh N.
    In this study, forced convection of Fe 3 O 4 –water nanofluid in a bifurcating channel was numerically studied under the influence of variable magnetic. Galerkin residual finite element method was used for numerical simulations. Effects of various values of Reynolds number (between 100 and 500), Hartmann number (between 0 and 3), and solid nanoparticle volume fraction (between 0% and 4%) on the convective heat transfer characteristics were analyzed. It was observed that location and size of the re-circulation zones established in the walls of the bifurcating channel strongly influenced by the variable magnetic field and Reynolds number. Average Nusselt number versus Hartmann number showed different characteristics for hot walls of the vertical and horizontal branching channels. The average Nusselt number enhancements were in the range of 12–15% and 9–12% for hot walls of the branching channel in the absence and presence of magnetic field (at Hartmann number of 3). © 2019 by the authors.
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    Thermoelectric generation with impinging nano-jets
    (MDPI AG, 2021) Selimefendigil F.; Oztop H.F.; Sheremet M.A.
    In this study, thermoelectric generation with impinging hot and cold nanofluid jets is considered with computational fluid dynamics by using the finite element method. Highly conductive CNT particles are used in the water jets. Impacts of the Reynolds number of nanojet stream combinations (between (Re1, Re2 ) = (250, 250) to (1000, 1000)), horizontal distance of the jet inlet from the thermoelectric device (between (r1, r2 ) = (−0.25, −0.25) to (1.5, 1.5)), impinging jet inlet to target surfaces (between w2 and 4w2 ) and solid nanoparticle volume fraction (between 0 and 2%) on the interface temperature variations, thermoelectric output power generation and conversion efficiencies are numerically assessed. Higher powers and efficiencies are achieved when the jet stream Reynolds numbers and nanoparticle volume fractions are increased. Generated power and efficiency enhance-ments 81.5% and 23.8% when lowest and highest Reynolds number combinations are compared. However, the power enhancement with nanojets using highly conductive CNT particles is 14% at the highest solid volume fractions as compared to pure water jet. Impacts of horizontal location of jet inlets affect the power generation and conversion efficiency and 43% variation in the generated power is achieved. Lower values of distances between the jet inlets to the target surface resulted in higher power generation while an optimum value for the highest efficiency is obtained at location zh = 2.5ws . There is 18% enhancement in the conversion efficiency when distances at zh = ws and zh = 2.5ws are compared. Finally, polynomial type regression models are obtained for estimation of generated power and conversion efficiencies for water-jets and nanojets considering various values of jet Reynolds numbers. Accurate predictions are obtained with this modeling approach and it is helpful in assisting the high fidelity computational fluid dynamics simulations results. © 2021 by the authors. Li-censee MDPI, Basel, Switzerland.
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    Entropy Analysis of the Thermal Convection of Nanosuspension within a Chamber with a Heat-Conducting Solid Fin
    (MDPI, 2022) Le X.H.K.; Oztop H.F.; Selimefendigil F.; Sheremet M.A.
    Heat transport augmentation in closed chambers can be achieved using nanofluids and extended heat transfer surfaces. This research is devoted to the computational analysis of natural convection energy transport and entropy emission within a closed region, with isothermal vertical borders and a heat-conducting solid fin placed on the hot border. Horizontal walls were assumed to be adiabatic. Control relations written using non-primitive variables with experimentally based correlations for nanofluid properties were computed by the finite difference technique. The impacts of the fin size, fin position, and nanoadditive concentration on energy transfer performance and entropy production were studied. It was found that location of the long fin near the bottom wall allowed for the intensification of convective heat transfer within the chamber. Moreover, this position was characterized by high entropy generation. Therefore, the minimization of the entropy generation can define the optimal location of the heat-conducting fin using the obtained results. An addition of nanoparticles reduced the heat transfer strength and minimized the entropy generation. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
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    CONTROL OF NANOLIQUID THERMAL CONVECTION WITH COMBINED EFFECTS OF ROTATION,MAGNETIC FIELD, AND POROUS OBJECT IN A CYLINDRICAL CAVITY
    (Begell House Inc., 2022) Selimefendigil F.; Öztop H.F.; Sheremet M.A.
    In this study, convective heat transfer performance under the coupled effects of magnetic field, rotations, and natural convection are analyzed by using a porous object in a cylindrical cavity. Finite element method analysis is considered for the range of parameters: permeability of the object (Darcy number: 10-4 ≤ Da ≤ 10-1), Rayleigh number (Ra: 105 ≤ Ra ≤ 8 × 105), rotational Reynolds number (Rew: 0 ≤ Rew ≤ 2000), strength of magnetic field (Hartmann number: 0 ≤ Ha ≤ 25) and aspect ratio of the porous object (AR: 0.5 ≤ AR ≤ 2. Water-Ag/MgO hybrid nanofluid is used. It is observed that thermal performance is improved when rotations become active. For an object with lower permeability at the highest speed, the amount of increment becomes 137%. The average Nu rises with higher permeability while increasing the aspect ratio of the object reduces the heat transfer at lowest permeability. When rotations become active, the impacts of magnetic field on the heat transfer reduction becomes less while 48.5% reduction of average Nusselt number is obtained without rotations. Proper orthogonal decomposition method is used for thermal field and performance estimations by using 12 modes for the fluid domain and 4 modes for porous regions. © 2022 by Begell House, Inc.