Browsing by Author "Selimefendigil F."
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Item Numerical investigation and pod-based interpolation of natural convection cooling of two heating blocks in a square cavity(Springer Verlag, 2012) Selimefendigil F.In this study, natural convection cooling of two heating blocks placed in a square cavity is numerically investigated. The cavity is cooled from vertical walls and the surface of the heating blocks are kept at constant temperature. The effect of placing the heating blocks at top, middle and bottom of the cavity, and the distance between the blocks on the heat transfer characteristic is numerically analyzed for the range of Grashof numbers between 103 and 106. The results are presented in terms of streamlines, isotherm plots and averaged Nusselt number plots. A POD-based interpolation method is also employed to predict the flow field and heat transfer characteristic for the case where the heating blocks are placed in the middle of the cavity. Nusselt number variation with respect to Grashof number is captured well with this approach of POD-based interpolation compared to the CFD calculations. © King Fahd University of Petroleum and Minerals 2013Item Numerical analysis of mixed convection heat transfer in pulsating flow for a horizontal channel with a cavity heated from vertical side and below(2012) Selimefendigil F.; Yurddas A.In this study, a channel with a cavity heated from below and a left vertical side is numerically investigated for the mixed convection case in pulsating flow for a range of Richardson numbers (Ri = 0.1, 1, 10, 100) and Reynolds numbers of 300, 500, and 800 in the laminar flow regime. At the inlet of the channel, pulsating velocity is imposed for Strouhal numbers of 0.25, 0.5, 0.75 and 1 and velocity amplitude ratios of 0.7, 0.8, and 0.9. The effect of the pulsation frequency, amplitude, Reynolds number, and Richardson number on heat transfer enhancement is analyzed numerically. The results are presented in terms of streamlines, isotherm plots, and averaged Nusselt number plots. Transfer function plots for the Nusselt number response to single sinusoidal velocity forcing at the inlet and nonlinearity in the response is also provided. © 2012 by Begell House, Inc.Item Fuzzy-based estimation of mixed convection heat transfer in a square cavity in the presence of an adiabatic inclined fin(2012) Selimefendigil F.; Öztop H.F.In this study, heat transfer from a square cavity in the presence of a thin inclined adiabatic fin is estimated using inputs-outputs generated from a CFD code with a fuzzy based identification procedure. The Reynolds number based on cavity length is 300 and the Richardson number is varied between 1 and 30. The top and bottom walls of the cavity are kept at constant temperature while the vertical walls are assumed to be adiabatic. The fin height, fin inclination angle, and Richardson number are considered as the input and the spatial averaged Nusselt number is taken as the output for the fuzzy model. Two data sets are used. One data set which contains 45 cases is used for estimation and another data set which contains 10 cases (not used in estimation) is used for validation purposes. The predictions using fuzzy model compare well with the CFD computations. © 2012 Elsevier Ltd.Item Numerical analysis of laminar pulsating flow at a backward facing step with an upper wall mounted adiabatic thin fin(2013) Selimefendigil F.; Öztop H.F.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 Lf=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. © 2013 Elsevier Ltd.Item Numerical analysis and pod based interpolation of mixed convection heat transfer in horizontal channel with cavity heated from below(2013) Selimefendigil F.In this study, a channel with a cavity heated from below is numerically investigated for the mixed convection case for a range of Richardson numbers (Ri=0.1, 1, 5, 10, 15 and 20) and Reynolds numbers (Re=400, 500, 600, 700 and 800) in the laminar flow regime. The results are presented in terms of streamlines, isotherm plots, local Nusselt number distribution along the bottom wall of the cavity and averaged Nusselt number plots. A POD-based interpolation method is also employed to predict the flow field and heat transfer characteristic for the mixed convection case at Re=400 for a range of Richardson numbers. Excellent agreement between the field variables is obtained for the considered range (Ri=0.1, 1, 2, 5, 10, 15 and 20) and targeted (Ri=3, 7 and 12) Richardson numbers. Nusselt number variation with respect to Richardson number is also captured well with this approach of POD-based interpolation compared to the CFD calculations. © 2013 Taylor and Francis Group LLC.Item Numerical investigation of impinging jets with nanofluids on a moving plate(Association for Scientific Research, 2013) Ersayin E.; Selimefendigil F.In this study a numerical investigation of an impinging jet flow, on a heated moving plate, is presented. The purpose of this study is to numerically investigate the effects of various parameters such as nanoparticle volume fraction, pulsating frequency, plate velocity, Reynolds number on the heat transfer characteristics. Navier-Stokes equations and energy equations are solved with a commercial finite volume based code. It is observed that adding nanoparticles increases the peak value of Nusselt number. It is also observed that the value of Nusselt number at the stagnation point is higher at the low velocities of impingement surface. In the unsteady case, heat transfer enhancement is seen at low frequencies.Item Numerical study of heat transfer due to twinjets impingement onto an isothermal moving plate(Association for Scientific Research, 2013) Başaran A.; Selimefendigil F.In this study, heat transfer from a moving isothermal hot plate due to double impinging vertical slot jets was investigated for a laminar flow. The rectangular geometry consists of a confining adiabatic wall placed parallel to the moving impingement. The jets are located symmetrically at mid point of upper wall. Water and Al2O3 nanoparticles mixture with different volumetric fraction was used as working medium. In considered jet impingement problem, the effects of the jet exit Reynolds numbers, ranging from 50 to 200, the normalized plate velocity, ranging from 0 to 2, and volumetric fractions of nanofluid, ranging from 0% to 6% were investigated. The commercial software package based on finite volume method FLUENT (version 6.3.26) is used in this study for the computations. It has been observed that increasing normalized plate velocity increases the heat transfer from bottom surface. Similarly, increasing Reynolds number of slot jets leads to enhancement of heat transfer. Besides, increasing volumetric fraction of nanofluid conributes to heat transfer enhancement.Item Numerical analysis and identification of mixed convection in pulsating flow in a square cavity with two ventilation ports in the presence of a heating block(Springer Verlag, 2013) Selimefendigil F.In this study, a square cavity with two ventilation ports in the presence of a isothermal heating block placed in the middle of the cavity is numerically analyzed for the mixed convection case in pulsating flow for a range of Richardson numbers (Ri = 1, 10, 100) and at Reynolds number of 300. At the inlet of the ventilation port, pulsating velocity is imposed for Strouhal numbers of 0.1, 0.5, 1, 2.5, 5 and velocity amplitude ratio of 0.3, 0.6 and 0.9. The effect of the pulsation frequency, amplitude and Richardson number on the heat transfer and fluid flow characteristics is numerically analyzed. The results are presented in terms of streamlines, isotherm plots and averaged Nusselt number plots. A neural network-based identification approach is utilized for the low amplitude of pulsating velocity to obtain an input-output model for the heat transfer for a range of pulsating frequencies. © The Brazilian Society of Mechanical Sciences and Engineering 2013.Item Identification of forced convection in pulsating flow at a backward facing step with a stationary cylinder subjected to nanofluid(2013) Selimefendigil F.; Öztop H.F.In the present study, the application of the system identification method for forecasting the thermal performance of forced pulsating flow at a backward facing step with a stationary cylinder subjected to nanofluid is presented. The governing equations are solved with a finite volume based code. The effects of various parameter frequencies (0.25. Hz-8. Hz), Reynolds number (50-200), nanoparticle volume fraction (0.00-0.06) on the fluid flow and heat transfer characteristics are numerically studied. Nonlinear system identification toolbox of Matlab is utilized to obtain nonlinear dynamic models of data sets corresponding to different nanoparticle volume fractions at frequencies of 1, 4 and 8. Hz. It is observed that heat transfer is enhanced with increasing the frequency of the oscillation, nanoparticle volume fraction and Reynolds number. The level of the nonlinearity (distortion from a pure sinusoid) decreases with increasing φ and with decreasing Reynolds number. It is also shown that nonlinear dynamic models obtained from system identification toolbox could produce thermal output (length averaged Nusselt number) as close to as output from a high fidelity CFD simulation. © 2013 Elsevier Ltd.Item Effect of rectangular and triangular thin adiabatic fins on mixed convection in a square cavity with two ventilation ports(2013) Selimefendigil F.In the present work, a square enclosure with two ventilation ports in the presence of adiabatic differently shaped fins placed on the bottom wall of the cavity are numerically analyzed for the mixed convection case in the range of Richardson numbers from 1 to 120 at the Reynolds number equal to 300. The walls of the cavity are kept at a constant temperature, and two different fin shapes (a rectangular and a triangular one) are considered. The effect of the fin height and Richardson number on the heat transfer and fluid flow characteristics is analyzed numerically. The results are presented in terms of streamlines, isotherm plots and averaged Nusselt number plots. It is observed that the length of a fin has a considerable effect on the thermal performance of the system. The shape of a fin affects the flow field and heat transfer characteristics only at a short fin length. © 2013 by Begell House, Inc.Item Numerical investigation and dynamical analysis of mixed convection in a vented cavity with pulsating flow(2014) Selimefendigil F.; Öztop H.F.In the present study, numerical investigation of pulsating mixed convection in a multiple vented cavity is carried out for the range of parameters; Reynolds number (500≤Re≤2000), Grashof number (104≤Gr≤106), Strouhal number (0≤St≤2). The governing equations are solved with a general purpose finite volume based solver. The effects of various parameters on the fluid flow and heat transfer characteristics are numerically studied. It is observed that the flow field and heat transfer rate are influenced by the variations of Reynolds, Grashof and Strouhal numbers. Furthermore, recurrence plot analysis is applied for the analysis of the time series (spatial averaged Nusselt number along the vertical wall of the cavity) and for a combination of different parameters, the systems are identified using recurrence quantification analysis parameters including recurrence rate, laminarity, determinism, trapping time and entropy. © 2013 Elsevier Ltd.Item Numerical study and identification of cooling of heated blocks in pulsating channel flow with a rotating cylinder(2014) Selimefendigil F.; Öztop H.F.A numerical study of pulsating channel flow with heated blocks in the presence of an adiabatic rotating cylinder is performed. The governing equations are solved with a finite volume based commercial solver. The effects of pulsating frequency, Reynolds number and cylinder rotation angle on the fluid flow and heat transfer characteristics from the surface of the heated blocks are numerically studied. It is observed that the flow field and heat transfer rate are influenced by the variations of these parameters. Furthermore, nonlinear models are created to identify the dynamics of the heat transfer for each of the surface of the blocks using system identification. © 2014 Elsevier Masson SAS. All rights reserved.Item Effect of a rotating cylinder in forced convection of ferrofluid over a backward facing step(2014) Selimefendigil F.; Öztop H.F.In this study, numerical analysis of the heat transfer enhancement and fluid flow characteristics of a rotating cylinder under the influence of magnetic dipole in the backward facing step geometry is conducted. The governing equations are solved with a finite element based commercial solver. The effects of Reynolds number (10≤Re≤200), cylinder rotation angle (-75≤Ω≤75) and strength of the magnetic dipole (0≤γ≤16) on the heat transfer characteristics are studied for backward facing step flow. It is observed that the length and size of the recirculation zones can be controlled with magnetic dipole strength and cylinder rotation angles. As the Reynolds number increases, local Nusselt number increases and number of peaks in the presence of the magnetic field decreases. The effect of cylinder rotation on the local Nusselt number distribution is more pronounced at low Reynolds number. © 2013 Elsevier Ltd. All rights reserved.Item Soft computing methods for thermo-acoustic simulation(Taylor and Francis Inc., 2014) Selimefendigil F.; Öztop H.F.In the present study, soft computing methods are employed for thermoacoustic simulation. A ducted Burke-Schumann diffusion flame is used as the heat source for a horizontal duct. First, a dynamic model is constructed from the input-output data sets (velocity forcing - heat release) generated from the Burke-Schumann flame using Comsol. An efficient and cheap model of heat source is obtained using dynamic fuzzy identification. The full thermoacoustic system is simulated in a time domain with the Galerkin method using the identified heat source model. Finally, dynamic neural networks are utilized for obtaining a dynamic fit for a set of operating conditions for the acoustic velocity at the heater location. The overall agreement between the outputs of the soft computing tools (fuzzy and neural network tools) with the Comsol and Galerkin solver is found to be satisfactory. © 2014 Taylor & Francis Group, LLC.Item Estimation of the mixed convection heat transfer of a rotating cylinder in a vented cavity subjected to nanofluid by using generalized neural networks(2014) Selimefendigil F.; Oztop H.F.In this study, numerical investigation of mixed convection in a square cavity with ventilation ports filled with nanofluids in the presence of an adiabatic rotating cylinder is conducted. The governing equations are solved with a commercial finite element code (COMSOL). The effects of Grashof number (Gr103 to Gr105), Reynolds number (Re50 to Re300), nanoparticle volume fraction (/0 to /0.05), and cylinder rotation angle (X 5 to X5) on the flow and thermal fields are numerically studied for a range of different parameter sets. The generalized neural network (GRNN) is used to predict the thermal performance of the system. It is observed that the heat transfer increases almost linearly with increasing the nanoparticle volume fraction. The increasing rotation angle in the clockwise direction generally enhances the heat transfer. Moreover, the validation results with artificial neural networks show that generalized neural nets show better performance compared to radial basis and feed-forward networks. Copyright © Taylor & Francis Group, LLC.Item MHD mixed convection of nanofluid filled partially heated triangular enclosure with a rotating adiabatic cylinder(Taiwan Institute of Chemical Engineers, 2014) Selimefendigil F.; Öztop H.F.MHD mixed convection of Cu-water nanofluid filled triangular enclosure with a rotating cylinder is investigated numerically. A partial heater is added on the left vertical wall of the cavity and the right inclined wall is kept at constant temperature. Other walls of the triangular cavity and cylinder surface are assumed to be adiabatic. The governing equations are solved using the finite element method. The effects of the Grashof number, Hartmann number, angular rotational speed of the cylinder and volume fraction of the nanoparticle on fluid flow and heat transfer are investigated numerically. The second law of thermodynamics is also applied to the flow and heat transfer corresponding to different combinations of parameters. It is observed that with increasing the Hartmann number the total entropy generation, local and averaged heat transfer decrease. Averaged Nusselt number increases with the Grashof number. Averaged heat transfer and total entropy generation increase with increase in the angular rotational speed of the cylinder. 50.4% and 37.4% of heat transfer enhancements are obtained for ω= 20 and ω= -20 compared to motionless cylinder ω= 0. Heat transfer and total entropy generation increase as the solid volume fraction of nanoparticle increases. © 2014 Taiwan Institute of Chemical Engineers.Item Effects of an adiabatic fin on the mixed convection heat transfer in a square cavity with two ventilation ports(Serbian Society of Heat Transfer Engineers, 2014) Selimefendigil F.; Oztop H.F.In this study, a square cavity with two ventilation ports in the presence of an adiabatic fin of different lengths placed on the walls of the cavity is numerically analyzed for the mixed convection case for a range of Richardson numbers (Ri = 0.1, 1, 10, 100) and at Reynolds number of 300. The effect of the fin height, placement of the fin on each of the four walls of the cavity and Richardson number on the heat transfer and fluid flow characteristics is numerically analyzed. The results are presented in terms of streamlines, isotherm plots, and averaged Nusselt number plots. It is observed that for the convection dominated case, fin length and its position on the one of the four walls of the cavity do not alter the thermal performance whereas when the buoyancy effects become important thermal performance increases for high fin length.Item POD-based reduced order model of a thermoacoustic heat engine(Elsevier Ltd, 2014) Selimefendigil F.; Öztop H.F.In this study, numerical simulation of a thermo-acoustic heat engine is performed and a reduced order model of the system based on the Proper Orthogonal Decomposition method is obtained. The governing equations are solved with a finite volume-based solver. The reduced order model is constructed using the snapshots when the system reaches the limit cycle. A quadratic polynomial type ODE system with 11-modes is constructed from the Galerkin projection for the high fidelity CFD computations of the coupled thermo-acoustic system. © 2014 Elsevier Masson SAS. All rights reserved.Item Control of laminar pulsating flow and heat transfer in backward-facing step by using a square obstacle(American Society of Mechanical Engineers, 2014) Selimefendigil F.; Oztop H.F.In the present study, laminar pulsating flow over a backward-facing step in the presence of a square obstacle placed behind the step is numerically studied to control the heat transfer and fluid flow. The working fluid is air with a Prandtl number of 0.71 and the Reynolds number is varied from 10 and 200. The study is performed for three different vertical positions of the square obstacle and different forcing frequencies at the inlet position. Navier-Stokes and energy equation for a 2D laminar flow are solved using a finite-volume-based commercial code. It is observed that by properly locating the square obstacle the length and intensity of the recirculation zone behind the step are considerably affected, and hence, it can be used as a passive control element for heat transfer augmentation. Enhancements in the maximum values of the Nusselt number of 228% and 197% are obtained for two different vertical locations of the obstacle. On the other hand, in the pulsating flow case at Reynolds number of 200, two locations of the square obstacle are effective for heat transfer enhancement with pulsation compared to the case without obstacle. Copyright © 2014 by ASME.Item Nonlinear, proper-orthogonal-decomposition-based model of forced convection heat transfer in pulsating flow(2014) Selimefendigil F.; Polifke W.A nonlinear, low-order physics-based model for the dynamics of forced convection wall heat transfer in pulsating flow is formulated, based on the proper orthogonal decomposition technique. In a multivariate approach, proper orthogonal decomposition modes are constructed from computational fluid dynamics data for laminar flow and heat transfer over a flat plate in pulsating flow, spanning a range of pulsation frequencies and amplitudes. Then, the conservation equations for mass, momentum, and energy are projected onto the proper orthogonal decomposition modes, such that a system of ordinary differential equations for the modal amplitudes is obtained. The forcing at the inlet is written explicitly in the ordinary differential equations of the low-order model. The contribution of the nonvanishing pressure term resulting from the incompressible Navier-Stokes equation is included with a calibration method. The accuracy and stability of the low-order model are evaluated by comparison with computational fluid dynamics data. Possible applications of this heat source model to the computation of a describing function or the prediction of limit cycle amplitudes of thermoacoustic instabilities are discussed.