Browsing by Author "Chamkha, AJ"

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    MHD mixed convection of Ag-MgO/water nanofluid in a triangular shape partitioned lid-driven square cavity involving a porous compound
    Selimefendigil, F; Chamkha, AJ
    In the current study, magnetohydrodynamics mixed convective flow of Ag-MgO/water hybrid nanofluid in a triangular shaped partitioned cavity involving a porous layer is numerically investigated by using the finite element method. In the numerical simulation, various effects of pertinent parameters such as Richardson number (between 0.01 and 100), Hartmann number (between 0 and 60), magnetic field inclination angle (between 0 and 90), Darcy number (between 10(-4) and 5 x 10(-2)), location of the vertex of triangular porous region (between 0.2 and 0.8 H) and hybrid nanoparticle solid volume fraction (phi(1) between 0 and 0.01, phi(2) between 0 and 0.01) on the fluid flow and convective heat transfer features are examined. It was observed that a large vortex is established below the main vortex near the upper wall for the lowest value Ri number. At the highest magnetic field strength, multi- recirculation flow pattern is seen in the right bottom corner. The average heat transfer enhances with higher values of permeability of the porous medium, magnetic field inclination angle, distance of the porous layer vertex from the hot wall and solid nanoparticle volume fraction of each particles in the hybrid nanofluid. The impact is reverse for higher values of Richardson number and Hartmann number. In the current work, significant changes in the average Nusselt number are obtained by varying the location of the porous medium. The triangular shaped porous compound can be used as an excellent tool for convective heat transfer control.
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    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
    Selimefendigil, F; Chamkha, AJ
    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 shear-thickening 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.
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    Cooling of an isothermal surface having a cavity component by using CuO-water nano-jet
    Selimefendigil, F; Chamkha, AJ
    Purpose The purpose of this study is to numerically analyze the convective heat transfer features for cooling of an isothermal surface with a cavity-like portion by using CuO-water nano jet. Jet impingement cooling of curved surfaces plays an important role in practical applications. As compared to flat surfaces, fluid flow and convective heat transfer features with jet impingement cooling of a curved surface becomes more complex with additional formation of the vortices and their interaction in the jet wall region. As flow separation and reattachment may appear in a wide range of thermal engineering applications such as electronic cooling, combustors and solar power, jet impingement cooling of a surface which has a geometry with potential separation regions is important from the practical point of view. Design/methodology/approach Numerical simulations were performed with a finite volume-based solver. The study was performed for various values of the Reynolds number (between 100 and 400), length of the cavity (between 5 w and 40 w), height of the cavity (between w and 5w) and solid nano-particle volume fraction (between 0 and 4 per cent). Artificial neural network modeling was used to obtain a correlation for the average Nusselt number, which can be used to obtain fast and accurate predictions. Findings It was observed that cavity geometrical parameters of the cooling surface can be adjusted to change the flow field and convective heat transfer features. When the cavity length is low, significant contribution of the inclined wall of the cavity on the average Nusselt number is achieved. As the cavity length and height increase, the average Nusselt number, respectively, reduce and slightly enhance. At the highest value of cavity height, significant changes in the convective flow features are obtained. By using nanofluids instead of water, enhancement of average heat transfer in the range of 35-46 per cent is obtained at the highest particle volume fraction. Originality/value In this study, jet impingement cooling of an isothermal surface which has a cavity-like portion was considered with nanofluids. Addition of this portion to the impingement surface has the potential to produce additional vortices which affects the fluid flow and convective features in the jet impingement heat transfer. This geometry has the forward-facing step for the wall jet region with flow separation reattachment in the region. Based on the above literature survey and to the best of the authors' knowledge, jet impingement cooling for such a geometry has never been reported in the literature despite its importance in practical thermal engineering applications. The results of this study may be useful for design and optimization of such systems and to obtain best performance in terms of fluid flow and heat transfer characteristics.
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    MHD Mixed Convection and Entropy Generation in a Lid-Driven Triangular Cavity for Various Electrical Conductivity Models
    Chamkha, AJ; Selimefendigil, F; Oztop, HF
    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.
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    MHD mixed convection in a nanofluid filled vertical lid-driven cavity having a flexible fin attached to its upper wall
    Selimefendigil, F; Oztop, HF; Chamkha, AJ
    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.
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    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
    Selimefendigil, F; Oztop, HF; Chamkha, AJ
    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 105 and 106), Hartmann number (between 0 and 100), magnetic inclination angle (between 0 degrees and 90 degrees), 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.
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    Analysis of mixed convection and entropy generation of nanofluid filled triangular enclosure with a flexible sidewall under the influence of a rotating cylinder
    Selimefendigil, F; Oztop, HF; Chamkha, AJ
    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 =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 105. 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.
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    Jet Impingement Heat Transfer of Confined Single and Double Jets with Non-Newtonian Power Law Nanofluid under the Inclined Magnetic Field Effects for a Partly Curved Heated Wall
    Selimefendigil, F; Oztop, HF; Chamkha, AJ
    Single and double impinging jets heat transfer of non-Newtonian power law nanofluid on a partly curved surface under the inclined magnetic field effects is analyzed with finite element method. The numerical work is performed for various values of Reynolds number (Re, between 100 and 300), Hartmann number (Ha, between 0 and 10), magnetic field inclination (gamma, between 0 and 90), curved wall aspect ratio (AR, between 01. and 1.2), power law index (n, between 0.8 and 1.2), nanoparticle volume fraction (phi, between 0 and 0.04) and particle size in nm (dp, between 20 and 80). The amount of rise in average Nusselt (Nu) number with Re number depends upon the power law index while the discrepancy between the Newtonian fluid case becomes higher with higher values of power law indices. As compared to case with n = 1, discrepancy in the average Nu number are obtained as -38% and 71.5% for cases with n = 0.8 and n = 1.2. The magnetic field strength and inclination can be used to control the size and number or vortices. As magnetic field is imposed at the higher strength, the average Nu reduces by about 26.6% and 7.5% for single and double jets with n greater than 1 while it increases by about 4.78% and 12.58% with n less than 1. The inclination of magnetic field also plays an important role on the amount of enhancement in the average Nu number for different n values. The aspect ratio of the curved wall affects the flow field slightly while the average Nu variation becomes 5%. Average Nu number increases with higher solid particle volume fraction and with smaller particle size. At the highest particle size, it is increased by about 14%. There is 7% variation in the average Nu number when cases with lowest and highest particle size are compared. Finally, convective heat transfer performance modeling with four inputs and one output is successfully obtained by using Adaptive Neuro-Fuzzy Interface System (ANFIS) which provides fast and accurate prediction results.
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    Effects of a Rotating Cone on the Mixed Convection in a Double Lid-Driven 3D Porous Trapezoidal Nanofluid Filled Cavity under the Impact of Magnetic Field
    Chamkha, AJ; Selimefendigil, F; Oztop, HF
    Effects of a rotating cone in 3D mixed convection of CNT-water nanofluid in a double lid-driven porous trapezoidal cavity is numerically studied considering magnetic field effects. The numerical simulations are performed by using the finite element method. Impacts of Richardson number (between 0.05 and 50), angular rotational velocity of the cone (between -300 and 300), Hartmann number (between 0 and 50), Darcy number (between 10-4 and 5x10-2), aspect ratio of the cone (between 0.25 and 2.5), horizontal location of the cone (between 0.35 H and 0.65 H) and solid particle volume fraction (between 0 and 0.004) on the convective heat transfer performance was studied. It was observed that the average Nusselt number rises with higher Richardson numbers for stationary cone while the effect is reverse for when the cone is rotating in clockwise direction at the highest supped. Higher discrepancies between the average Nusselt number is obtained for 2D cylinder and 3D cylinder configuration which is 28.5% at the highest rotational speed. Even though there are very slight variations between the average Nu values for 3D cylinder and 3D cone case, there are significant variations in the local variation of the average Nusselt number. Higher enhancements in the average Nusselt number are achieved with CNT particles even though the magnetic field reduced the convection and the value is 84.3% at the highest strength of magnetic field. Increasing the permeability resulted in higher local and average heat transfer rates for the 3D porous cavity. In this study, the aspect ratio of the cone was found to be an excellent tool for heat transfer enhancement while 95% enhancements in the average Nusselt number were obtained. The horizontal location of the cone was found to have slight effects on the Nusselt number variations.
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    Pulsating Flow of CNT-Water Nanofluid Mixed Convection in a Vented Trapezoidal Cavity with an Inner Conductive T-Shaped Object and Magnetic Field Effects
    Chamkha, AJ; Selimefendigil, F; Oztop, HF
    Mixed convection of carbon-nanotube/water nanofluid in a vented cavity with an inner conductive T-shaped object was examined under pulsating flow conditions under magnetic field effects with finite element method. Effects of different parameters such as Richardson number (between 0.05 and 50), Hartmann number (between 0 and 30), cavity wall inclination (between 0 degrees and 10 degrees), size (between 0.1 H and 0.4 H) and orientation (between -90 degrees and 90 degrees) of the T-shaped object, and amplitude (between 0.5 and 0.9) and frequency (Strouhal number between 0.25 and 5) of pulsating flow on the convective flow features were studied. It was observed that the average Nusselt number enhanced with the rise of strength of magnetic field, solid nanoparticle volume fraction, and amplitude of the pulsation, while the effect was opposite for higher values of Ri number and cavity wall inclination angle. The presence of the T-shaped object and adjusting its size and orientation had significant impact on the main flow stream from inlet to outlet and recirculations around the T-shaped object and in the vicinity of hot wall of the cavity along with the magnetic field strength. Pulsating flow resulted in heat transfer enhancement as compared to steady flow case for all configurations. However, the amount of increment was different depending on the variation of the parameters of interest. Heat transfer enhancements were 41.85% and 20.81% when the size of the T-shaped object was increased from 0.1 H to 0.4 H. The T-shaped object can be utilized in the vented cavity as an excellent tool for convective heat transfer control. As highly conductive CNT particles were used in water, significant enhancements in the average Nusselt number between 97% and 108% were obtained both in steady flow and in pulsating flow cases when magnetic field was absent or present.
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    Magnetohydrodynamics mixed convection in a power law nanofluid-filled triangular cavity with an opening using Tiwari and Das' nanofluid model
    Selimefendigil, F; Chamkha, AJ
    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.
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    Fluid-structure-magnetic field interaction in a nanofluid filled lid-driven cavity with flexible side wall
    Selimefendigil, F; Öztop, HF; Chamkha, AJ
    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: (10(4) N/m(2) <= E <= 2.5 x 10(5) N/m(2)), 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 <= phi <= 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 = 10(4) N/m(2) compared with E = 2.5 x 10(5) N/m(2). 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. (C) 2016 Elsevier Masson SAS. All rights reserved.
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    Mixed convection in a partially layered porous cavity with an inner rotating cylinder
    Chamkha, AJ; Selimefendigil, F; Ismael, MA
    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 10(3) and 10(6)), 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 = 10(5). 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.
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    Mixed convection in superposed nanofluid and porous layers in square enclosure with inner rotating cylinder
    Selimefendigil, F; Ismael, MA; Chamkha, AJ
    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 10(3) and 10(6)), 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 Omega = 6000 compared to motionless cylinder case at Omega = 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.
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    MHD mixed convection of nanofluid in a cubic cavity with a conductive partition for various nanoparticle shapes
    Selimefendigil, F; Öztop, HF; Chamkha, AJ
    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.
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    MHD mixed convection of nanofluid due to an inner rotating cylinder in a 3D enclosure with a phase change material
    Chamkha, AJ; 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$(boolean AND)5$ and 10$(boolean AND)6$), 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.
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    Analysis of mixed convection of nanofluid in a 3D lid-driven trapezoidal cavity with flexible side surfaces and inner cylinder
    Selimefendigil, F; Öztop, HF; Chamkha, AJ
    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 10(5)), side wall inclination angle (between 0 degrees and 20 degrees) 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 degrees and 10 degrees. Average Nusselt number enhances by about 9.80% when the value of the elastic modulus is increased from 1000 to 10(5) for side wall inclination angles of theta = 0 degrees. 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.
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    Fluid-structure interaction analysis of entropy generation and mixed convection inside a cavity with flexible right wall and heated rotating cylinder
    Alsabery, AI; Selimefendigil, F; Hashim, I; Chamkha, AJ; 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 (10(4) <= Ra <= 10(7)), angular rotational velocity (-1 <= Omega <= 1), dimensionless elasticity modulus (10(12) <= E <= 10(15)) on the convective heat transfer characteristics and entropy generation rates are analyzed for dimensionless time 10(-8) <= tau <= 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. (C) 2019 Elsevier Ltd. All rights reserved.
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    Role of magnetic field on forced convection of nanofluid in a branching channel
    Selimefendigil, F; Öztop, HF; Chamkha, AJ
    Purpose Numerical study of nanofluid forced convection within a branching channel was performed under the influence of a uniform magnetic field. The purpose of this study is to enhance the heat transfer performance of the separated flow at the branching channel with the use of magnetic field and nanofluid. The use of magnetic field and enhancement in both the thermal conductivity and electrical conductivity with the inclusion of the nanoparticles provides favorable thermophysical properties of the nanofluid when it used as a heat transfer fluid in a branching channel. The results of this study may be used to control the thermal performance in a branching channel and further optimization studies in the presence of magnetic field. Design/methodology/approach Galerkin weighted residual finite element method was used for the simulations. The numerical simulation results are performed by changing the inclination angle of the lower branching channel (between 0 degrees and 90 degrees), thermophysical properties of the fluid via inclusion of nanoparticles (between 0 and 0.04), Reynolds number (between 100 and 400) and magnetic field strength (Hartmann number changes between 0 and 15). Findings It was observed that the recirculation zones and reattachment length of the upper and lower branching channels are affected by the variation of those parameters. Reattachment lengths increase with the augmentation of the Reynolds number and deterioration of the Hartmann number. Average Nusselt number becomes higher for higher values of Hartmann number and solid particle volume fraction. Inclusion of the nanoparticle to the base fluid is very effective for the configuration with higher values of Hartmann number. An optimum value of the inclination angle of the lower branching channel is observed, beyond which heat transfer rate is significantly reduced due to the establishment of a large vortex in the upper branching channel and restriction of the fluid motion. Originality/value In this study, forced convection of nanofluid flow in a branching channel under the effect of magnetic field was numerically studied. Magnetic field effects with nanoparticle inclusion to the base fluid on the convective heat transfer was analyzed for various inclination angles of the lower branching channel. Flow separation at the junction of the channels and thus convective heat transfer rate are influenced by the variation of these parameters. There are many studies related to application of the magnetic field with nanofluids, and a few of them are related to configurations with separated flows. To the best of the authors' knowledge, there exist no studies for the application of nanofluids and magnetic field for the convective heat transfer in a branching channel. This topic is of importance as there are many engineering applications of the branching channels.
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    Forced Convection of Pulsating Nanofluid Flow over a Backward Facing Step with Various Particle Shapes
    Chamkha, AJ; 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.