Browsing by Author "Sehmefendigil, F"

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    Role of magnetic field and surface corrugation on natural convection in a nanofluid filled 3D trapezoidal cavity
    (PERGAMON-ELSEVIER SCIENCE LTD) Sehmefendigil, F; Öztop, HF
    In this study, the role of magnetic field and surface corrugation on the natural convective transfer characteristics in a three dimensional, CuO-water nanofluid filled trapezoidal cavity was numerically investigated with finite element method. Influence of various pertinent parameters such as Rayleigh number (between 10(4) and 10(6)), Hartmann number (between 0 and 40), number (between 0 and 16) and height (between 0 and 0.5H) of triangular wave form and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were analyzed. It was observed that when corrugation height and number of corrugation waves enhance, local and average heat transfer reduce. The use of CuO nanoparticles is advantageous when heat transfer is effective and for the configurations without magnetic field. 26.86% increase in the average Nusselt number is obtained when magnetic field is imposed at Hartmann number of 30 whereas 40.72% of increment in the average heat transfer is attained in the absence of magnetic field when 4% of CuO nanoparticles are added to the water. A mathematical model based on proper orthogonal decomposition and polynomial interpolation among modal coefficients is developed that could be used to reconstruct the whole flow and thermal field and perform thermal predictions for the 3D corrugated cavity.
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    Numerical analysis of laminar pulsating flow at a backward facing step with an upper wall mounted adiabatic thin fin
    (PERGAMON-ELSEVIER SCIENCE LTD) Sehmefendigil, F; Öztop, HF
    The effect of an upper wall mounted adiabatic thin fin on laminar pulsating flow in a backward facing step has been investigated numerically. Study is performed for different Reynolds numbers (based on the step height) in the range of 10 and 200 and for the expansion ratio of 2. The working fluid is air with the Prandtl number of 0.71. The governing equations are solved with a general purpose finite volume based solver, FLUENT. The effects of various pertinent parameters, Reynolds number, fin length and pulsating frequency on the fluid flow and heat transfer characteristics are numerically studied. It is observed that fin alters the flow field and thermal characteristics. In the steady flow case, heat transfer enhancement is obtained with the installation of the fin on the upper wall and increases with increasing fin length and increasing Reynolds number. Heat transfer enhancement of 188% is obtained for fin length of L-f = 1.5H at Reynolds number of 200. In the pulsating flow case, time-spatial averaged Nusselt number along the bottom wall downstream of the step normalized with spatial averaged Nusselt number in the steady flow case versus excitation Strouhal number shows a resonant type behavior; first an increase in the value is seen up to St = 0.05, then a decrease is seen with the increasing values of the frequency of the pulsation for the case without fin. Adding a fin shifts the maximum value of the normalized Nusselt number from St = 0.05 to St = 0.1. Compared to steady flow with no-fin case, adding a fin is not advantageous for heat transfer enhancement in pulsating flow. (C) 2013 Elsevier Ltd. All rights reserved.