Browsing by Author "Chamkha A.J."
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Item Magnetohydrodynamics mixed convection in a lid-driven cavity having a corrugated bottom wall and filled with a non-newtonian power-law fluid under the influence of an inclined magnetic field(American Society of Mechanical Engineers (ASME), 2016) Selimefendigil F.; Chamkha A.J.In this study, the problem of magnetohydrodynamics (MHD) mixed convection of lid-driven cavity with a triangular-wave shaped corrugated bottom wall filled with a non- Newtonian power-law fluid is numerically studied. The bottom corrugated wall of the cavity is heated and the top moving wall is kept at a constant lower temperature while the vertical walls of the enclosure are considered to be adiabatic. The governing equations are solved by the Galerkin weighted residual finite element formulation. The influence of the Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of the magnetic field (between 0 deg and 90 deg), and the power-law index (between 0.6 and 1.4) on the fluid flow and heat transfer characteristics are numerically investigated. It is observed that the effects of free convection are more pronounced for a shear-thinning fluid and the buoyancy force is weaker for the dilatant fluid flow compared to that of the Newtonian fluid. The averaged heat transfer decreases with increasing values of the Richardson number and enhancement is more effective for a shearthickening fluid. At the highest value of the Hartmann number, the averaged heat transfer is the lowest for a pseudoplastic fluid. As the inclination angle of the magnetic field increases, the averaged Nusselt number generally enhances. © 2016 by ASME.Item Mixed convection in a partially layered porous cavity with an inner rotating cylinder(Taylor and Francis Ltd., 2016) Chamkha A.J.; Selimefendigil F.; Ismael M.A.In this study, mixed convection in a cavity that has a fluid and superposed porous medium with an adiabatic rotating cylinder is numerically investigated. The bottom horizontal wall is heated and the top horizontal wall is cooled while the remaining walls are assumed to be adiabatic. An adiabatic rotating cylinder is inserted inside the cavity. The governing equations are solved by the Galerkin weighted residual finite element method. The effects of Rayleigh number (between 103 and 106), angular rotational speed of the cylinder (between 0 and 6,000), Darcy number (between 10-5 and 10-2), cylinder sizes (between R = 0.1 and R = 0.3) and three different vertical locations of the cylinder on the fluid flow and heat transfers characteristics are numerically investigated. It is observed that the cylinder size has a profound effect on the local and averaged heat transfer. The local and averaged heat transfers generally increase and the convection is more effective in the upper half of the cavity as the Rayleigh number and Darcy number enhance. The averaged heat transfers increases with the cylinder size until Ra = 105. The averaged heat transfer increases almost linearly with the angular rotational velocity of the cylinder and the increase rate becomes higher as the cylinder size increases. The local and averaged heat transfers enhances/deteriorate as the cylinder approaches the upper/lower wall of the cavity. Copyright © Taylor & Francis Group, LLC.Item MHD mixed convection and entropy generation of nanofluid filled lid driven cavity under the influence of inclined magnetic fields imposed to its upper and lower diagonal triangular domains(Elsevier, 2016) Selimefendigil F.; Öztop H.F.; Chamkha A.J.In this study, mixed convection of CuO-water nanofluid filled lid driven cavity having its upper and lower triangular domains under the influence of inclined magnetic fields is numerically investigated. The top horizontal wall of the cavity is moving with constant speed of uw with +x direction while no-slip boundary conditions are imposed on the other walls of the cavity. The top wall of the cavity is maintained at constant cold temperature of Tc while the bottom wall is at hot temperature of Th and on the other walls of the cavity are assumed to be adiabatic. The governing equations are solved by using Galerkin weighted residual finite element formulation. Entropy generation is produced by using formulation and integrated with calculated velocities and temperatures. The numerical investigation is performed for a range of parameters: Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of magnetic field (between 0° and 90°) and solid volume fraction of the nanofluid (between 0 and 0.05). Different combinations of Hartmann numbers and inclination angles of the magnetic fields are imposed in the upper and lower triangular domains of the square cavity. It is observed that the local and averaged heat transfer deteriorates when the Richardson number, Hartmann number of the triangular domains increase. When the Hartmann number and magnetic angle of the upper triangle are increased, more deterioration of the averaged transfer is obtained when compared to lower triangular domain. Local and averaged heat transfer increase as the solid volume fraction of the nanoparticles increases and adding nanoparticles is more effective for the local enhancement of the heat transfer when the heat transfer rate is high and convection is not damped with lowering the Hartmann number. Second law analysis of the system for different combinations of flow parameters is also performed. © 2016 Elsevier B.V.Item Fluid–structure-magnetic field interaction in a nanofluid filled lid-driven cavity with flexible side wall(Elsevier Ltd, 2017) Selimefendigil F.; Öztop H.F.; Chamkha A.J.In this study MHD flow in a lid driven nanofluid filled square cavity with a flexible side wall is numerically investigated. The top wall of the cavity is colder than the bottom wall and it moves in the +x direction with constant speed. Other walls of the cavity are insulated. The finite element formulation is utilized to solve the governing equations. The Arbitrary-Lagrangian-Eulerian method is used to describe the fluid motion with the flexible wall of the cavity in the fluid–structure interaction model. The influence of the Young's modulus of the flexible wall on the flow and heat transfer characteristics are numerically investigated for the following parameters: (104N/m2≤E≤2.5×105N/m2), with a Richardson number of (0.01≤Ri≤5), a Hartmann number of (0≤Ha≤50) and a volume fraction of the solid particles given by (0≤ϕ≤0.04). The effect of Brownian motion on the effective thermal conductivity of the nanofluid is taken into account. Averaged heat transfer decreases with increasing Hartmann number and decreasing Richardson numbers. As the Young's modulus of the flexible wall decreases, the averaged heat transfer increases and 66.5% of the heat transfer enhancement is obtained for E=104N/m2 compared with E=2.5×105N/m2. An averaged heat transfer enhancement of 33.87% is obtained for a solid volume fraction of 4% compared to the base fluid for the fluid–structure model coupled with the magnetic field. © 2016 Elsevier Masson SASItem Mixed convection in a vertically layered fluid-porous medium enclosure with two inner rotating cylinders(Begell House Inc., 2017) Ismael M.A.; Selimefendigil F.; Chamkha A.J.In this study, mixed convection in a vertically half partitioned cavity with two rotating adiabatic cylinders is numerically investigated. The horizontal walls are thermally insulated. The left vertical wall is kept isothermally at high temperature while the right vertical wall is kept isothermally at lower temperature. The Galerkin weighted residual finite element method is used to solve the governing equations. The numerical study is performed for various values of Rayleigh numbers (between 103 and 106), angular rotational speed of the cylinders (between -5000 and 5000), Darcy numbers (between 10-5 and 10-2), horizontal positions of the cylinder centers (between 0.4 and 0.6) and cylinder sizes (between 0.1 and 0.4). It is observed that angular velocity of the cylinders and cylinder sizes have a profound effect on the heat transfer enhancement along the hot vertical wall. The averaged heat transfer enhancements are 354.65% and 45.24% at a Rayleigh number of 106 compared to the case at a Rayleigh number of 103 for cylinder sizes of R = 0.1 and R = 0.4. Large variations in the local heat transfer are seen for various angular velocities of the cylinder, and cylinder rotation brings averaged heat transfer enhancement for sizes of R = 0.3 and R = 0.4. The averaged heat transfer enhances by 235.10% for a Darcy number of 10-2 compared to a Darcy number of 10-5 using cylinder sizes of R = 0.1. The horizontal movement of the cylinder centers increases the averaged heat transfer by 34.08% for (D1 = D2 = 0.6) compared to configuration at (D1 = D2 = 0.4) for angular rotational speed of Ω = -5000. © 2017 by Begell House, Inc.Item Analysis of mixed convection of nanofluid in a 3D lid-driven trapezoidal cavity with flexible side surfaces and inner cylinder(Elsevier Ltd, 2017) Selimefendigil F.; Öztop H.F.; Chamkha A.J.Numerical study of mixed convection in a lid-driven 3D flexible walled trapezoidal cavity with nanofluids was performed by using Galerkin weighted residual finite element method. Effects of various pertinent parameters such as Richardson number (between 0.05 and 50), elastic modulus of the side surfaces (between 1000 and 105), side wall inclination angle (between 0° and 20°) and solid particle volume fraction (between 0 and 0.04) on the fluid flow and heat transfer characteristics in a 3D lid-driven-trapezoidal cavity were numerically examined. It was observed that these characteristics are influenced when the pertinent parameters change. Flexible side surface can be used as control element for heat transfer rate. Increment and reduction in the space which are provided by the flexible side walls result in heat transfer enhancement and deterioration for side wall inclination angle of 0° and 10°. Average Nusselt number enhances by about 9.80% when the value of the elastic modulus is increased from 1000 to 105 for side wall inclination angles of θ = 0°. Adding nanoparticles to the base fluid results in linear increment of heat transfer and at the highest volume fraction, 25.30% of heat transfer enhancement is obtained. A polynomial type correlation for the average Nusselt number along the hot wall was proposed and it has a fourth order polynomial dependence upon the Richardson number and first order dependence upon the solid particle volume fraction. © 2017 Elsevier LtdItem Mixed convection in superposed nanofluid and porous layers in square enclosure with inner rotating cylinder(Elsevier Ltd, 2017) Selimefendigil F.; Ismael M.A.; Chamkha A.J.In this study, numerical simulation of mixed convection in a partitioned square cavity having CuO-Water nanofluid and superposed porous medium with an adiabatic rotating cylinder is performed. The bottom horizontal wall of the cavity is heated and the top horizontal wall is cooled while the remaining vertical walls are insulated. An adiabatic rotating cylinder is located at the center of the square cavity. Galerkin weighted residual finite element method is utilized to solve the governing equations of the system. The influence of Rayleigh number (between 103 and 106), angular rotational velocity of the cylinder (between 0 and 6000), solid volume fraction of the nanoparticle (between 0 % and 0.05 %), Darcy number (between 10−5 and 10−2) and three different vertical locations of the cylinder on the fluid flow and heat transfer characteristics are numerically investigated in detail for three different cylinder sizes. It is observed that the averaged heat transfer enhances as the value of Rayleigh number, angular rotational speed of the cylinder, nanoparticle volume fraction and Darcy number increase. The effect of the angular rotational speed of the cylinder on the averaged heat transfer enhancement is more pronounced for large cylinder size and 432.55% of averaged enhancement is achieved for Ω=6000 compared to motionless cylinder case at Ω=0 using cylinder sizes of R=0.3. The averaged heat transfer enhances almost linearly with nanoparticle volume fraction for different cylinder sizes and adding solid nanoparticles to the base fluid is favorable for the locations when high values of local Nusselt number is observed. Local and averaged Nusselt number enhance as the cylinder approaches to the upper wall of the cavity. © 2017 Elsevier LtdItem MHD free convection and entropy generation in a corrugated cavity filled with a porous medium saturated with nanofluids(MDPI AG, 2018) Chamkha A.J.; Selimefendigil F.MHD free convection inside a triangular-wave-shaped corrugated porous cavity with Cu-water nanofluid is numerically studied with the finite element method. The influences of the Grashof number (104 ≤ Gr ≤ 106), Hartmann number (0 ≤ Ha ≤ 50), Darcy number (10-4 ≤ Da ≤ 10-1) and solid volume fraction of the nanoparticle (0 ≤ ϕ ≤ 0.05) on the convective flow features are examined. It is observed that increasing the Grashof number and Darcy number enhances the heat transfer, while the effect is opposite for the Hartmann number. As the corrugation frequency of the triangular wave increases, the local and averaged heat transfer rates decrease, which is more effective for higher values of Grashof and Darcy numbers. Normalized total entropy generation increases as the Darcy number and solid volume fraction of the nanoparticles increase and decreases as the Hartmann number increases both for flat and corrugated wall configurations. © 2018 by the authors.Item Forced convection of pulsating nanofluid flow over a backward facing step with various particle shapes(MDPI AG, 2018) Chamkha A.J.; Selimefendigil F.In this study, numerical analysis of forced convective pulsating nanofluid flow over a backward-facing step with different nanoparticle shapes was performed by the finite volume method. The effects of the Strouhal number (between 0.1 and 2), solid nanoparticle volume fraction (between 0 and 0.04) and nanoparticle shapes (spherical, blade and cylindrical) on the heat transfer and fluid flow were examined with the aid of numerical simulation. It was observed that the average Nusselt number is a decreasing function of the Strouhal number for the considered range, and it enhances for higher solid particle fractions. Using nanofluids with spherical particles is advantageous in pulsating flow, whereas cylindrically-shaped particles are preferred in steady flow configurations. Average Nusselt number enhancements up to 30.24% and 27.95% are achieved with cylindrical- and spherical-shaped particles at the highest volume fraction. © 2018 by the authors.Item Numerical analysis for thermal performance of a photovoltaic thermal solar collector with SiO2-water nanofluid(MDPI AG, 2018) Chamkha A.J.; Selimefendigil F.Numerical analysis of a photovoltaic-thermal (PV/T) unit with SiO2-water nanofluid was performed. The coupled heat conduction equations within the layers and convective heat transfer equations within the channel of the module were solved by using the finite volume method. Effects of various particle shapes, solid volume fractions, water inlet temperature, solar irradiation and wind speed on the thermal and PV efficiency of the unit were analyzed. Correlation for the efficiencies were obtained by using radial basis function neural networks. Cylindrical shape particles were found to give best performance in terms of efficiency enhancements. Total efficiency enhances by about 7.39% at the highest volume fraction with cylindrical shape particles. Cylindrical shape particle gives 3.95% more enhancement as compared to spherical ones for the highest value of solid particle volume fraction. Thermal and total efficiency enhance for higher values of solid particle volume fraction, solar irradiation and lower values of convective heat transfer coefficient and inlet temperature. The performance characteristics of solar PV-thermal unit with radial basis function artificial neural network are found to be in excellent agreement with the results obtained from computational fluid dynamics modeling. © 2018 by the authors.Item MHD mixed convection and entropy generation in a lid-driven triangular cavity for various electrical conductivity models(MDPI AG, 2018) Chamkha A.J.; Selimefendigil F.; Oztop H.F.In this study, effects of different electrical conductivity models for magneto- hydrodynamic mixed convection of nanofluids in a lid-driven triangular cavity was numerically investigated with a finite element method. Effects of Richardson number and Hartmann number on the convective heat transfer characteristics were analyzed for various electrical conductivity models of nanofluids. Average Nusselt number decreases for higher Hartmann and Richardson numbers. Discrepancies in the local and average heat transfer exist between different electrical conductivity models, which is higher for higher values of Richardson number and Hartmann number. The total entropy generation rate was found reduced with higher values of Richardson number and Hartmann number while discrepancies exist between various electrical conductivity models. When the magnetic field is imposed, different behaviors of entropy generation rate versus solid particle volume fraction curve is obtained and it is dependent upon the range of solid particle volume fraction. © 2018 by the authors.Item Ferrofluid convection in a lid-driven cavity(Trans Tech Publications Ltd, 2018) Selimefendigil F.; Chamkha A.J.This study numerically investigates the mixed convection of ferrofluids in a partially heated lid driven square enclosure. The heater is located to the left vertical wall and the right vertical wall is kept at constant lower temperature while other walls of the cavity are assumed to be adiabatic. The governing equations are solved with Galerkin weighted residual finite element method. The influence of the Richardson number (between 0.01 and 100), heater location (between 0.25 H and 0.75H), strength of the magnetic dipole (between 0 and 4), and horizontal location of the magnetic dipole source (between -2H and -0.5H) on the fluid flow and heat transfer are numerically investigated. It is found that local and averaged heat transfer deteriorates with increasing values of Richardson number and magnetic dipole strength. The flow field and thermal characteristics are sensitive to the magnetic dipole source strength and its position and heater location. © 2018 Trans Tech Publications, Switzerland.Item Natural convection in a CuO–water nanofluid filled cavity under the effect of an inclined magnetic field and phase change material (PCM) attached to its vertical wall(Springer Science and Business Media B.V., 2019) Selimefendigil F.; Oztop H.F.; Chamkha A.J.In this study, natural convection of CuO–water nanofluid in a square cavity with a conductive partition and a phase change material (PCM) attached to its vertical wall is numerically analyzed under the effect of an uniform inclined magnetic field by using finite element method. Effects of various pertinent parameters such as Rayleigh number (between 10 5 and 10 6), Hartmann number (between 0 and 100), magnetic inclination angle (between 0 ∘ and 90 ∘), PCM height (between 0.2H and 0.8H), PCM length (between 0.1H and 0.8H), thermal conductivity ratio (between 0.1 and 100) and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were numerically analyzed. It was observed that when magnetic field is imposed, more reduction in average Nusselt number for water is obtained as compared to nanofluid which is 31.81 % for the nanofluid at the highest particle volume fraction. The average heat transfer augments with magnetic inclination angle, but it is less than 5 %. When the height of the PCM is increased which is from 0.2H to 0.8H, local and average Nusselt number reduced which is 42.14 % . However, the length of the PCM is not significant on the heat transfer enhancement. When the conductivity ratio of the PCM to the base fluid within the cavity is increased from 0.1 to 10, 29.5 % of the average Nusselt number enhancement is achieved. © 2018, Akadémiai Kiadó, Budapest, Hungary.Item Magnetohydrodynamics mixed convection in a power law nanofluid-filled triangular cavity with an opening using Tiwari and Das’ nanofluid model(Springer Science and Business Media B.V., 2019) Selimefendigil F.; Chamkha A.J.Numerical simulation of mixed convection heat transfer in a lid-driven triangular cavity filled with power law nanofluid and with an opening was performed under the effect of an inclined magnetic field. The left vertical wall of the cavity moves in + y-direction, and the bottom wall of the cavity is partially heated. Galerkin weighted residual finite element method was used to solve the governing equations. Influence of Richardson number, Hartmann number, inclination angle, opening ratio and nanoparticle volume fraction on the fluid flow and heat transfer is examined for various power law indices. It was observed that average heat transfer deteriorates as the value of Richardson number and Hartmann number enhances. At the lowest value of Richardson number, the discrepancy between the average heat transfer corresponding to different power law indices is higher. The inclination angle of the magnetic field where the minimum of the average Nusselt number is seen depends on the fluid type. Average heat transfer number is the highest for the highest value of the opening ratio. The average Nusselt number enhances with solid particle volume fraction, and there are slight variations in the reduction in the average Nusselt number when base fluid and nanofluid are considered for various power law indices. © 2018, Akadémiai Kiadó, Budapest, Hungary.Item MHD mixed convection in a nanofluid filled vertical lid-driven cavity having a flexible fin attached to its upper wall(Springer Science and Business Media B.V., 2019) Selimefendigil F.; Oztop H.F.; Chamkha A.J.In this study, fluid flow and heat transfer in a vertical lid-driven CuO–water nanofluid filled square cavity with a flexible fin attached to its upper wall under the influence of an inclined magnetic field are numerically investigated. The left vertical wall of the cavity is colder than right vertical wall, and it moves in + y direction with constant speed. Horizontal walls of the cavity are insulated. The governing equations are solved with finite element method. The arbitrary Lagrangian–Eulerian method is used to describe the fluid motion within the cavity for the flexible fin in the fluid-structure interaction model. The influence of Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of the magnetic field (between 0 and 90%), nanoparticle volume fraction (between 0 and 0.05) and Young’s modulus of flexible fin (between 250 and 5000) on the flow and heat transfer were numerically studied. It is observed that the presence of the elastic fin affects the flow field and thermal characteristics of the cavity. The local and average heat transfer enhance as the Richardson number, solid volume fraction of the nanoparticle increase whereas deteriorate as the value of the Hartmann number and inclination angle of the magnetic field increases due to the dampening of the fluid motion with Lorentz forces. The addition of the nanoparticles is more effective along the lower part of the right vertical wall where the heat transfer process is effective. The average heat transfer increases by 28.96% for solid volume fraction of 0.05% compared to base fluid when the flexible fin is attached to the upper wall. The average heat transfer deteriorates by 10.10% for cavity with and without fin at Hartmann number of 50 compared to the case without magnetic field. The average heat transfer enhances as the Young’s modulus of the flexible fin decreases and the average Nusselt number increases by 13.24% for Young’s modulus of 250 compared to configuration for the cavity having the Young’s modulus of 5000. © 2018, Akadémiai Kiadó, Budapest, Hungary.Item Analysis of mixed convection and entropy generation of nanofluid filled triangular enclosure with a flexible sidewall under the influence of a rotating cylinder(Springer Science and Business Media B.V., 2019) Selimefendigil F.; Oztop H.F.; Chamkha A.J.In this study, mixed convection and entropy generation in a nanofluid filled triangular cavity under the influence of rotating cylinder and flexible sidewall were numerically analyzed with finite element method. The inclined sidewall was cooled while the left vertical wall is partially heated. Heat transfer rate enhances as the values of Rayleigh number, angular rotational velocity of the cylinder, elastic modulus of the flexible sidewall and solid nanoparticles volume fraction increase. Nusselt number enhances more in the counter-clockwise direction of the cylinder as compared to clockwise directional rotation and 13.55% of average heat transfer enhancement was achieved for Ω= 3000 when compared to motionless cylinder. Average Nusselt number increases by about 30.50% when the elastic modulus of the flexible wall is changed from 500 to 10 5. The changes in the velocity profiles are significant for the lower part of the triangular enclosure with respect to changes in angular rotational velocity and elastic modulus as compared to upper part of the cavity. Adding nanoparticles increases heat transfer especially for the lower part of the cavity and 49.63% of heat transfer enhancement was achieved for the highest volume fraction when compared to base fluid. Normalized total entropy generation rates enhance for higher values of elastic modulus of the flexible wall, angular rotational speed of the circular cylinder and nanoparticle volume fractions. © 2018, Akadémiai Kiadó, Budapest, Hungary.Item MHD mixed convection of nanofluid due to an inner rotating cylinder in a 3D enclosure with a phase change material(Emerald Publishing, 2019) Chamkha A.J.; Selimefendigil F.Purpose: The purpose of this study is to numerically examine the mixed convection of CuO-water nanofluid due to a rotating inner hot circular cylinder in a 3D cubic enclosure with phase change material (PCM) attached to its vertical surface. Heat transfer and fluid flow characteristics were examined for various values of pertinent parameters. Design/methodology/approach: Finite element method was used in the numerical simulation. Influence of various pertinent parameters such as Rayleigh number (between 10$^5$ and 10$^6$), Hartmann number (between 0 and 100), angular rotational speed of the cylinder (between −50 and 50), solid nanoparticle volume fraction (between 0 and 0.04) and PCM parameters (height-between 0.2H and 0.8H, thermal conductivity ratio- between 0.1 and 10) on the convective heat transfer characteristics are numerically studied. Findings: It was observed that local heat transfer variations along the hot surface differ significantly for the cases with and without magnetic field where three distinct hot spots of peak Nusselt number are established when magnetic field is imposed. The average Nusselt number enhancement with the nanofluid at the highest particle volume fraction is 52.85 per cent at Hartmann number of 100, whereas its value is 39.76 per cent for the case in the absence of magnetic field. When the inner cylinder rotates, flow and thermal fields are affected within the cavity. The local heat transfer variations spread over the hot surface with cylinder rotation and 16.43 per cent of reduction in the average heat transfer is obtained with counter-clockwise rotation at 100 rad/sec. An enhancement in the PCM height and a reduction in the thermal conductivity of the PCM result in average heat transfer deterioration for the 3D cavity. The amount of the reduction is 43 per cent when the PCM height is increased from 0.2H to 0.8H, whereas 19.10 per cent enhancement in the heat transfer is achieved when thermal conductivity ratio (PCM) to the base fluid is increased from 0.1 to 10. Originality/value: Such configurations can be designed for convection control, and in our case, various methods are available. Some of the investigated methods can be used in applications where magnetic field already exists. Convection control study in 3D cavity gives more realistic results as compared to 2D configurations, and results of the current investigation may be used for the design, optimization and flow control of many thermal applications involving magnetic field effects. © 2018, Emerald Publishing Limited.Item Mixed Convection of Pulsating Ferrofluid Flow Over a Backward-Facing Step(Springer International Publishing, 2019) Selimefendigil F.; Öztop H.F.; Chamkha A.J.In this study, mixed convection of pulsating ferrofluid flow over a backward-facing step under the effect of a magnetic source is performed. Heat transfer and fluid flow characteristics for a range of flow parameters were identified in terms of streamlines, isotherms and local and averaged Nusselt number plots. Finite element method was used to solve the resulting governing equations. The effects of the Richardson number (0.05 ≤ Ri ≤ 50), strength of the magnetic dipole (0 ≤ γ≤ 6), horizontal and vertical locations of the magnetic dipole (H≤a≤5H,-5H≤b≤-0.75H), amplitude and non-dimensional frequency of flow pulsation (0.25 ≤ A≤ 1 , 0.01 ≤ St ≤ 5) on the fluid flow and heat transfer enhancement were numerically investigated in detail. It was observed that the magnetic dipole parameters effect is different in pulsating flow compared to steady flow simulation results. The flow pulsation was found to enhance the average heat transfer which is about 17.5% in the absence of magnetic dipole source. When magnetic dipole source was used, up to 32% in the average heat transfer was obtained with flow pulsation. The primary recirculation zone behind the step is deteriorated by the presence of the magnetic source, and an addition vortex which is restricted to a very small region near the step is formed. The magnetic dipole source can be combined with flow pulsation to control the mixed convective flow over the backward-facing step. © 2018, Shiraz University.Item MHD mixed convection of nanofluid in a cubic cavity with a conductive partition for various nanoparticle shapes(Emerald Publishing, 2019) Selimefendigil F.; Öztop H.F.; Chamkha A.J.Purpose: This paper aims to numerically examine the mixed convection of SiO2-water nanofluid flow in a three-dimensional (3D) cubic cavity with a conductive partition considering various shapes of the particles (spherical, cylindrical, blade, brick). The purpose is to analyze the effects of various pertinent parameters such as Richardson number (between 0.1 and 10), Hartmann number (between 0 and 10), solid nanoparticle volume fraction (between 0 and 0.04), particle shape (spherical, cylindrical, blade, brick) and different heights and lengths of the conductive partition on the fluid flow and heat transfer characteristics. Design/methodology/approach: The numerical simulation was performed by using Galerkin-weighted residual finite element method for various values of Richardson number, Hartmann number, solid nanoparticle volume fraction, particle shape (spherical, cylindrical, blade, brick) and different heights and lengths of the conductive partition. Two models for the average Nusselt number were proposed for nanofluids with spherical and cylindrical particle by using multi-layer feed-forward neural networks. Findings: It was observed that the average Nusselt number reduces for higher values of Richardson number and Hartmann number, while enhances for higher values of nanoparticle volume fraction. Among various types of particle shapes, blade ones perform the worst and cylindrical ones perform the best in terms of heat transfer enhancement, but this is not significant which is less than 3 per cent. The average Nusselt number deteriorates by about 6.53per cent for nanofluid at the highest volume fraction of spherical particle shapes, but it is 11.75per cent for the base fluid when Hartmann number is increased from 0 to 10. Conductive partition geometrical parameters (length and height) do not contribute to much to heat transfer process for the 3D cavity, except for the case when height of the partition reaches 0.8 times the height of the cubic cavity, the average Nusselt number value reduces by about 25per cent both for base fluid and for nanofluid when compared to case with cavity height which is 0.2 times the height of the cubic cavity. Originality/value: Based on the literature survey, a 3D configuration for MHD mixed convection of nanofluid flow in a cavity with a conductive partition considering the effects of various particle shapes has never been studied in the literature. This study is a first attempt to use a conductive partition with nanofluid of various particle shapes to affect the fluid flow and heat transfer characteristics in a 3D cubic cavity under the influence of magnetic field. Partial or all findings of this study could be used for the design and optimization of realistic 3D thermal configurations that are encountered in practice and some of the applications were already mentioned above. In this study, thermal performance of the system was obtained in terms of average heat transfer coefficient along the hot surface, and it is modeled with multi-layer feed-forward neural networks. © 2019, Emerald Publishing Limited.Item Fluid-structure interaction analysis of entropy generation and mixed convection inside a cavity with flexible right wall and heated rotating cylinder(Elsevier Ltd, 2019) Alsabery A.I.; Selimefendigil F.; Hashim I.; Chamkha A.J.; Ghalambaz M.The current work concentrates on the transient entropy generation and mixed convection due to a rotating hot inner cylinder within a square cavity having a flexible side wall by using the finite element method and arbitrary Lagrangian-Eulerian formulation. Effects of various relevant parameters like Rayleigh number (104⩽Ra⩽107), angular rotational velocity (-1⩽Ω⩽1), dimensionless elasticity modulus (1012⩽E⩽1015) on the convective heat transfer characteristics and entropy generation rates are analyzed for dimensionless time 10-8⩽τ⩽3.5. It is observed that various complex shaped wall deformations are established depending on the non-dimensional elastic modulus of the flexible right wall and cylinder rotation direction. The local and average Nusselt numbers rise with Ra and secondary peaks in the local Nusselt number are established for lower values of Ra. The local heat transfer along the hot cylinder does not change for the case of clockwise rotation of the heated cylinder even if there is a wall deformation in the positive x-direction. The highest average heat transfer and global entropy generation rates are achieved for the case of counter-clockwise rotation of the circular cylinder and for lower values of the flexible wall deformation. © 2019 Elsevier Ltd