Browsing by Author "Akgül M.B."
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Item Analytical and numerical solutions of electro-osmotically driven flow of a third grade fluid between micro-parallel plates(2008) Akgül M.B.; Pakdemirli M.Electro-osmotic flow of a third grade fluid between micro-parallel plates is considered. The equations of motion are derived and made dimensionless. Approximate analytical solutions are obtained by perturbation techniques. Constant viscosity and temperature dependent viscosity (Reynolds model) cases are treated separately. Numerical solutions of the equations are also obtained. Influences of non-Newtonian parameter, Joule heating effect, viscosity index and electro-kinetic effect on the velocity and temperature profiles are shown. Approximate and numerical solutions are contrasted. © 2008 Elsevier Ltd. All rights reserved.Item Lie group analysis of a non-Newtonian fluid flow over a porous surface(Sharif University of Technology, 2012) Akgül M.B.; Pakdemirli M.Two-dimensional, unsteady squeezed flow over a porous surface for a power-law non-Newtonian fluid is considered. Continuity, momentum and energy equations are written and cast into a non-dimensional form. Boundary conditions are selected in a general form. Lie Group theory is applied to the equations. Then, a partial differential system with three independent variables is converted into an ordinary differential system, via application of two successive symmetry generators. The ordinary differential equations are solved numerically. Effects of flow behavior index, Prandtl number, squeezing parameter, surface velocity parameter and suction/injection parameter on the flow are outlined in the figures. © 2012 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.Item Cooling intensification of a continuously moving stretching surface using different types of nanofluids(2012) Akgül M.B.; Pakdemirli M.The effect of different types of nanoparticles on the heat transfer from a continuously moving stretching surface in a concurrent, parallel free stream has been studied. The stretching surface is assumed to have power-law velocity and temperature. The governing equations are converted into a dimensionless system of equations using nonsimilarity variables. Resulting equations are solved numerically for various values of flow parameters. The effect of physical quantities on the temperature profiles is discussed in detail. © 2012 M. B. Akgül and M. Pakdemirli.Item Lie group analysis of unsteady flow and heat transfer over a porous surface for a viscous fluid(2012) Akgül M.B.; Sari G.; Pakdemirli M.The problem of a two-dimensional, unsteady flow and a heat transfer of a viscous fluid past a surface in the presence of variable suction/injection is analyzed. The unsteadiness is due to the time dependent free stream flow. The governing equations are derived with the usual boundary layer approximation. Using Lie group theory, a group classification of the equations with respect to the variable free stream flow and suction/injection velocity is performed. Restrictions imposed by the boundary conditions on the symmetries are discussed. Adopting the obtained symmetry groups, governing partial differential equations are converted into ordinary differential equations and then solved numerically. Effects of the dimensionless problem parameters on the velocity and temperature profiles are outlined in the figures. © 2012 M. B. Akgül et al.Item Non-Newtonian fluid effects on surface reactions in a microfluidic flow cell(2012) Akgül M.B.; Sari G.; Pakdemirli M.Mass transfer over a reactive surface in microfluidic flow cells plays a key role in understanding biomoleculer interactions and diagnosis of small molecules for biomedical and environmental applications. The effects of Non-Newtonian power law fluid on the binding reaction kinetic of immunoglobulin G in a flow cell are analyzed in this study. Governing equations for the fluid flow, mass transport and surface reaction are derived. The finite element method is employed to solve resulting equations. In addition, the effects of volumetric flow rate, fluid behavior index and reaction constants on the surface reaction are analyzed and presented graphically. © 2012 American Institute of Physics.Item Magnetohydrodynamic and slip effects on the flow and mass transfer over a microcantilever-based sensor(2012) Akgül M.B.; Pakdemirli M.Hydromagnetic flow and mass transfer of a viscous incompressible fluid over a microcantilever sensor surface are studied in the presence of slip flow. In addition, chemical reaction at the sensor surface is taken into account. The governing equations for the flow are reduced to a local nonsimilarity form. Resulting equations are solved numerically for various values of flow parameters. Effects of physical quantities on the velocity and concentration profiles are discussed in detail. © 2012 M. B. Akgül and M. Pakdemirli.Item Thermal analyses for induction sintering of powder metal compacts up to sintering temperature(Palladin Institute of Biochemistry of the NASU, 2014) Çavdar U.; Atik E.; Akgül M.B.; Karaca H.Induction sintering is developed as an alternative method to conventional sintering in order to sinter iron-based powder metal (PM) compacts. In this study, the 12 kW power and 30 kHz frequency induction-sintering machine is used for 3 wt.% copper-mixed iron. The effects of different shapes and sizes of the induction coil, and temperature differences on the PM compacts up to sintering temperature are investigated; these parameters are determined both theoretically and experimentally during induction sintering. Iron-based PM compacts are sintered at 1120°C. Induction sintering of iron-based PM compacts are simulated using a program to examine the effects of magnetic flux and temperature distribution in the sample over time. The results are compared with the experimental studies.Item Experimental Study on Thermal Performance of a Novel Solar Air Collector Having Conical Springs on Absorber Plate(Springer Verlag, 2016) Abuşka M.; Akgül M.B.This study presents a thermal analysis for a novel type of solar air heater. The thermal performance of a solar air collector having conical springs on the absorber plate is determined experimentally. A flat absorber plate (Type I) and the absorber plate with mounted conical springs (Type II) are designed and constructed, and their thermal performance is tested in the collectors. Experiments are performed for air mass flow rates of 0.06 and 0.07 kg/s. Thermal efficiency and collector outlet temperature are the main indicator for determining thermal performance. The efficiencies and energy distribution ratios are determined and compared for the collectors. The results of the experiments show that a substantial enhancement in the thermal efficiency is obtained with conical springs. Also, to this thermal efficiency increases with the rise of mass flow rate. © 2016, King Fahd University of Petroleum & Minerals.Item Numerical Analysis of Mixed Convection of Nanofluids Inside a Vertical Channel(World Scientific Publishing Co. Pte Ltd, 2016) Akgül M.B.; Pakdemirli M.Laminar mixed convection of an Al2O3/water nanofluid inside a vertical channel is investigated numerically. Single-phase and two-phase Eulerian models are employed to analyze flow and thermal fields of the nanofluid in conjunction with the suitable expressions for the particle viscosity and effective particle thermal conductivity. The results of two-phase Eulerian model are compared with the single-phase model and with the published experimental data. Effects of the solid volume fraction, Reynolds number and Grashof number on the heat transfer performance of the nanofluid are investigated and discussed in detail. © 2016 World Scientific Publishing Company.Item An experimental study of a piezoelectrically actuated touch screen(Institute of Electrical and Electronics Engineers Inc., 2017) Sari G.; Akgül M.B.; Kirişken B.; Ak A.F.; Akiş A.A.An audiovisual feedback is used on touch screens in portable electronic devices. When these devices are used in noisy and distracting environments, suitable available feedback methods is severely inadequate and the availability of the device severely reduced. For these reasons, touch screen technology has become a popular recently. These panels used in many sectors such as watches, cars, mobile devices, aerospace. Touch screens, which provide tactile feedback to the user, are activated using solenoid actuators, coil-type actuators or vibration motors. The use of evolving piezoelectric vibrators has attracted considerable attention in recent years to obtain high-resolution tactile feedback. Their higher bandwidth helps create more user-perceivable haptic effects. In this work, we experimented to observe the effect of the piezo vibrator on the screen. As a result, the various types of tactile feedback functions will be developed on the screen and compared. The best vibration functions depending on the settings are obtained through experiments. © 2017 IEEE.Item Numerical analysis of vibrating touch screen actuated by piezo elements(Institute of Electrical and Electronics Engineers Inc., 2017) Ak A.F.; Sari G.; Akgül M.B.; Kirişken B.; Akiş A.A.Audiovisual feedback generally is used on touch screens on portable electronic devices, which are frequently used in daily life. Tactile feedback is one of the issues that have recently gained importance in this technology. Tactile feedback occurs by stimulating the nerves at the fingertip by moving the touch screen. In this study, we have determined the vibration characteristics of touchscreens made from different materials used in the sector. The finite element method is employed to obtain the vibration modes of the screen. In addition to, the effects of the materials of piezo, applied voltage, the number of the piezo patches are investigated to produce the best vibration function and graphically are presented. © 2017 IEEE.Item Passive thermal management of an OLED TV display(National Institute of Optoelectronics, 2018) Nil M.; Öztürk Y.; Akgül M.B.; Çatalbaş M.C.; Nil M.In this study, passive thermal management of a 15’’ OLED TV display is studied. In addition to the OLED display, the effect of other heat generating electronic components on the device is taken into account. Experimental temperature measurements are conducted on the OLED display. The CFD model of the device is developed in order to be able to predict the temperatures and validated with experimental results. A good agreement is obtained between CFD simulation and experimental measurements. To eliminate hot spots and homogenize the tem perature distribution, heat spreaders like copper and graphite are used and the effects of them are discussed in detail. © 2018, National Institute of Optoelectronics. All rights reserved.Item Experimental and numerical studies on improvement of heat transfer of OLED TVs; [OLED TV’lerin ısı transferinin iyileştirilmesi üzerine deneysel ve nümerik çalışmalar](Gazi Universitesi Muhendislik-Mimarlik, 2019) Nil M.; Öztürk Y.; Akgül M.B.; Sarı G.In this study, the thermal behaviors of organic light emitting diodes (OLED) televisions are investigated experimentally and numerically. Organic light emitting diodes are very sensitive to temperature. For this reason, the heat emitted from the diodes must be removed quickly from the environment. The study consists of two parts. In the first part, the use of an effective heat spreader between the screen and the metal casing is proposed as a mechanism for improving the temperature distributions for heat transfer. Pyrolytic graphite plate and tempered pyrolytic graphite plate were used as heat spreader. The graphical heat transfer coefficients of the graphite plates are considerably higher than in the normal direction. The effectiveness of these proposed mechanisms is demonstrated by simulation. As an example model, OLED TV was selected in 15 "dimensions and both experimental and numerical thermal analyzes were performed. The temperature distributions of the OLED were obtained with the help of the ANSYS ICEPAK program, a commercial code that uses the finite volume method. Simulation and test results are obtained very close to each other. The thermal management contributions of OLED TVs using different thicknesses of pyrolytic and tempered pyrolytic graphite plates are presented experimentally and numerically. In the second part, a dual action piezo fan design is proposed. The design parameters of the piezo fan were determined and the numerical analyzes for these parameters were made with the Comsol Multiphysics program. Experimental measurements were made for design dimensions determined by numerical analysis. The result is that the use of a dual-acting piezo provides more efficient cooling than the existing synthetic jets. © 2019 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.