Browsing by Author "Öztop, HF"

Now showing 1 - 20 of 163
  • No Thumbnail Available
    Item
    Effects of elasticity and waviness of the conductive panel surface on the cooling performance and entropy generation by using nano-enhanced multiple impinging jets
    Selimefendigil, F; Öztop, HF
    The design of cooling systems is crucial for the thermal management of many energy systems including batteries, microelectro-mechanical systems, photovoltaics and many others. In this study, cooling system for elastic curved conductive panel is developed by using nano-enhanced multiple jet impingement. ALE finite element modeling of the entire coupled fluid-structure conjugate heat transfer system is employed for assessment, which considers both elastic flat and wavy panels. Type of the panel and operating parameters affect the cooling performance and entropy generation. Different effects and contributions of varying parameters such as Cauchy number (Ca), jet-cooling spacing (to the target plate and between the slots), wave amplitude and number of the conducive panel and nanoparticle loading amount in the pure fluid on the cooling performance and entropy generation features are analyzed. Increases in the Cauchy number, waveform amplitude, slot-slot distance, and slot-plate distance reduce the effectiveness of cooling, whereas increases in the nanoparticle loading have the reverse effect. When varying the Ca, there is 12.1% decrease of average Nusselt number (Nu) while average panel temperature rise becomes 3.1 & DEG;C by using nanofluid. The average Nu deteriorates by 7.7% and 6.6% when amplitude and wave number are varied while the corresponding temperature rises are achieved as 1.4 & DEG;C and 1 & DEG;C. When wavy and flat surfaces are used, using nanofluid provides 2.8 & DEG;C and 2.5 & DEG;C temperature drops. Lower entropy generation (EG) is obtained with flexible panel while higher amplitude of the wave form and increasing the nanoparticle amount result in EG reduction. The amount of EG reduction by using nanofluid becomes 21% and 27% at the highest loading.
  • No Thumbnail Available
    Item
    Mixed Convection of Pulsating Ferrofluid Flow Over a Backward-Facing Step
    Selimefendigil, F; Öztop, HF; Chamkha, AJ
    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 <= gamma <= 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.
  • No Thumbnail Available
    Item
    Impact of local elasticity and inner rotating circular cylinder on the magneto-hydrodynamics forced convection and entropy generation of nanofluid in a U-shaped vented cavity
    Selimefendigil, F; Öztop, HF; Sheikholeslami, M
    This study analyzes the effects of a partial elastic wall and rotating circular cylinder on the convective heat transfer of carbon nanotube (CNT)-water nanofluid filled U-shaped cavity with entropy generation by considering inclined magnetic field effects. Numerical simulation is performed by using ALE with finite element method (FEM). Impacts of various important parameters such as Re number, Ha number, magnetic field orientation, elastic wall size and modulus, angular velocity, and horizontal position of the rotating cylinder on the forced convection are analyzed. When the values of Re number, strength of magnetic field (up to Ha number of 50), and orientation angle are increased, the average Nu value rises while the impact is opposite for higher elastic wall size and horizontal position of the cylinder above 0.4H. When the rotational cylinder effects are considered, enhancement up to 60%is obtained at the highest speed as compared to motionless cylinder case. The average Nu variation is in the range of 9%-10.45%at the highest value when varying the size and modulus of the elastic wall. Flexible wall effects on the average Nu number variation becomes more pronounced when the angular rotational velocity is highest at the clockwise rotation and for the highest Re number. The average Nu number enhancements are 13%-14%at the highest Ha number. The entropy generation rates with varying Ha number, rotational velocity, and location of the cylinder are different for the left and right parts of the domains while impacts of elastic wall properties on the entropy generation rate are slight.
  • No Thumbnail Available
    Item
    Nanoliquid Jet Impingement Heat Transfer for a Phase Change Material Embedded Radial Heating System
    Selimefendigil, F; Öztop, HF
    Nanoliquid impingement heat transfer with a phase change material (PCM) installed radial system is considered. The study is performed by using the finite element method for various values of Reynolds numbers (100 <= Re <= 300), height of PCM (0.25H <= h(pcm) <= 0.75H), and plate spacing (0.15H <= h(s) <= 0.40H). Different configurations using water, nanoliquid, and nanoliquid + PCM are compared in terms of heat transfer improvement. Thermal performance is improved by using PCM, while best performance is achieved with nanoliquid and PCM-installed configuration. At Re = 100 and Re = 300, heat transfer improvements of 26% and 25.5% are achieved with the nanoliquid+ PCM system as compared to water without PCM. The height of the PCM layer also influences the heat transfer dynamic behavior, while there is 12.6% variation in the spatial average heat transfer of the target surface with the lowest and highest PCM heights while discharging time increases by about 76.5%. As the spacing between the plates decreases, average heat transfer rises and there is 38% variation.
  • No Thumbnail Available
    Item
    Effects of flexible fins on melting process in a phase change material filled circular cavity
    Akbal, Ö; Selimefendigil, F; Öztop, HF
    In this study, melting process in a phase change material (PCM) filled annular closed space by using flexible fins is analyzed. Cases with different number of flexible fins and without fin are compared in terms of phase change dynamics while two-way fluid structure interaction analysis is used. Temperature differences of 30 degrees C and 60 degrees C are considered between the walls of the circular enclosure while flexible fin numbers are varied between 0 and 10. It is observed that the melting is significantly accelerated by using the elastic fins. Due to the deflection of the elastic fins, melt process dynamics is influenced by varying fin number and its elastic modulus. Further reduction in the full phase transition occurs when the temperature difference is increased. As compared to un-finned case at temperature difference of 30 degrees C by using 10 flexible fins at Delta T = 60 degrees C, there is 87 % reduction in the complete phase transition time. The ANFIS (Adaptive Neuro-Fuzzy Interface System) based modeling approach is used for phase transition dynamics in circular enclosure equipped with flexible fins.
  • No Thumbnail Available
    Item
    Cooling of a Partially Elastic Isothermal Surface by Nanofluids Jet Impingement
    Selimefendigil, F; Öztop, HF
    Numerical study of nanofluid jet impingement cooling of a partially elastic isothermal hot surface was conducted with finite element method. The impingement surface was made partially elastic, and the effects of Reynolds number (between 25 and 200), solid particle volume fraction (between 0.01 and 0.04), elastic modulus of isothermal hot surface (between 10 4 and 10 6), size of the flexible part (between 7.5 w and 25 w), and nanoparticle type (spherical, cylindrical, blade) on the fluid flow and heat transfer characteristics were analyzed. It was observed that average Nusselt number enhances for higher Reynolds number, higher values of elastic modulus of flexible wall, smaller size of elastic part, and higher nanoparticle solid volume fraction and for cylindrical shaped particles. It is possible to change the maximum Nusselt number by 50.58% and 33% by changing the elastic modulus of the hot wall and size of elastic part whereas average Nusselt number changes by only 9.33% and 6.21%. The discrepancy between various particle shapes is higher for higher particle volume fraction.
  • No Thumbnail Available
    Item
    Mixed convection of nanofluid filled cavity with oscillating lid under the influence of an inclined magnetic field
    Selimefendigil, F; Öztop, HF
    In this study, mixed convection of an oscillating lid-driven cavity filled with nanofluid under the influence of an inclined uniform magnetic field was numerically investigated. The cavity is heated from below and cooled from above while side walls are assumed to be adiabatic. The top wall velocity varies sinusoidally while no-slip boundary conditions are imposed on the other walls of the cavity. The governing equations was solved by Galerkin weighted residual finite element formulation. The numerical investigation was performed for a range of parameters: Richardson number (10(-1) <= Ri <= 10(2)), Hartmann number (0 <= Ha <= 60), inclination angle of the magnetic field (0 <= gamma <= 90), non-dimensional frequency of the oscillating lid (0.001 <= St <= 1) and solid volume fraction of the nanoparticle (0 <= phi <= 0.04). It is observed that the flow and thermal patterns within the cavity are affected by the variation of these parameters. The heat transfer process becomes inefficient for high Strouhal number, high Hartmann number and high Richardson number. Maximum enhancement of averaged heat transfer and the damping of the convection within the cavity due to the Lorentz forces caused by magnetic field are attained for magnetic inclination angles of gamma = 90 degrees and gamma = 60 degrees. As the solid volume fraction of nanoparticles increases averaged heat transfer enhancement of 28.96% is obtained for volume fraction of phi = 0.04 compared to base fluid. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Analysis of hybrid nanofluid and surface corrugation in the laminar convective flow through an encapsulated PCM filled vertical cylinder and POD-based modeling
    Selimefendigil, F; Öztop, HF
    In the present work, performance assessment of a PCM filled three dimensional vertical cylinder is con-ducted under the combined effects of surface corrugation and presence of binary nanoparticles in the heat transfer fluid. The numerical simulation is performed by using finite element method with varying values of Reynolds number (100 <= Re <= 750 ), number (1 <= N <= 8) and height (H/10 <= h <= H/2 ) of rect-angular type corrugation form and volume fraction of particles (0 <= phi <= 0.02) in unsteady configuration. Thermal transport features are enhanced while charging time is reduced for higher values of Reynolds number, solid volume fraction of the binary mixture in the heat transfer fluid. Complete charging time is reduced by 57 % with increase of Reynolds number from 100 to 750 while it is reduced by 23 % when nanofluid at the highest solid volume fraction is used instead of water. However, the corrugation param-eters have reverse effects on the charging process. A computational framework for reconstruction of heat transfer fluid and PCM temperatures for the unsteady parametric configuration in the computational do-main is offered by utilizing proper orthogonal decomposition (POD) technique with 25 modes for heat transfer fluid and 75 modes for PCM. (C) 2021 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    PERFORMANCE PREDICTIONS OF AIR-COOLED CONDENSERS HAVING CIRCULAR AND ELLIPTIC CROSS-SECTIONS WITH ARTIFICIAL NEURAL NETWORKS
    Selimefendigil, F; Öztop, HF
    In this study, mathematical models of air cooled condensers with circular and elliptic cross-sections were developed and performances were evaluated with artificial neural networks. Air velocity, orientation angle and ambient temperature were used as the input to the neural network structure while heat transfer rate to the air was used as the output. The data sets were generated from high fidelity, computationally inefficient expensive three dimensional computational fluid dynamics simulations. It was observed that artificial neural network model replaces computational fluid dynamics model and based on the mathematical model with artificial neural network, elliptic condensers perform better in terms of heat transfer compared to circular ones.
  • No Thumbnail Available
    Item
    Identification of forced convection in pulsating flow at a backward facing step with a stationary cylinder subjected to nanofluid
    Selimefendigil, F; Öztop, HF
    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 phi 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. (C) 2013 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    MHD mixed convection of nanofluid in a flexible walled inclined lid-driven L-shaped cavity under the effect of internal heat generation
    Selimefendigil, F; Öztop, HF
    In this study, mixed convective flow of nanofluid in an inclined L-shaped cavity which has elastic walls is numerically analyzed under the effects of internal heat generation and magnetic field by using the finite element technique with the Arbitrary-Lagrangian-Eulerian method. Simulations are performed for different values Richardson number (between 0.03 and 30), inclination angle of the cavity (between 0 degrees and 180 degrees), Hartmann number (between 0 and 50), orientation angle of the magnetic field (between 0 degrees and 90 degrees), internal Rayleigh number (between 10(4) and 10(6)), solid nanoparticle volume fraction (between 0 and 0.04), flexible wall elastic modulus (between 104 and 108) and aspect ratio (between 0.2 and 0.7) of the L-shaped cavity. It was observed that the effects of elastic wall on the convective heat transfer features are significant for the lowest value of Richardson number and lowest values of elastic modulus while 11% of discrepancy is obtained in the average Nusselt number when cavity with elastic and rigid walls is compared. The impact of the magnetic inclination angle is significant when compared to magnetic field strength for the variation of the average Nusselt number. Cavity inclination angle has significant impacts on the variation of the average Nusselt number for water and nanofluid. A higher size of the cold wall (aspect ratio) increases the heat transfer rate while the internal Rayleigh number reduces it. Enhancement in the average Nusselt number is about 15%-19% at highest nanoparticle volume fraction of the nanofluid while the trends in the convective heat transfer features with respect to changes in the pertinent parameters are similar for water and nanofluid. (C) 2019 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Mixed convection of nanofluids in a three dimensional cavity with two adiabatic inner rotating cylinders
    Selimefendigil, F; Öztop, HF
    In this study, mixed convection of nanofluids in a three dimensional cavity with two inner adiabatic rotating circular cylinders were analyzed by using finite element method. Vertical surfaces are kept at constant temperature while other walls and rotating cylinder surfaces were taken as adiabatic. The three dimensional cavity was filled with water and various types of nanoparticles (Cu, Al2O3 and TiO2). The water-Cu nanofluid provided the highest heat transfer rate and at the highest value of Rayleigh number, 4% higher average heat transfer rate is obtained when compared to other particles. When cylinders rotate, depending on the rotational direction either enhancement or deterioration of average Nusselt number is observed. For the highest value of rotational speed of the cylinders, 8.5% discrepancy between the average Nusselt number is observed for the nanofluid with Cu and Al2O3 nanoparticles. For Cu-water nanofluid at the highest volume fraction as compared to base fluid, 38.10% of enhancement in the average heat transfer is obtained. A correlation for the average Nusselt number in polynomial form was developed which is a function of Rayleigh number and angular rotational speed of the cylinders. (C) 2017 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Mixed convection of ferrofluids in a lid driven cavity with two rotating cylinders
    Selimefendigil, F; Öztop, HF
    Mixed convection of ferrofluid filled lid driven cavity in the presence of two rotating cylinders were numerically investigated by using the finite element method. The cavity is heated from below, cooled from driven wall and rotating cylinder surfaces and side vertical walls of the cavity are assumed to be adiabatic. A magnetic dipole source is placed below the bottom wall of the cavity. The study is performed for various values of Reynolds numbers (100 <= Re <= 1000), angular rotational speed of the cylinders (-400 <= Omega <= 400), magnetic dipole strengths (0 <= gamma <= 500), angular velocity ratios of the cylinders (0.25 <= Omega(i/) Omega(j) <= 4) and diameter ratios of the cylinders (0.5 <= Di/Dj <= 2). It is observed that flow patterns and thermal transport within the cavity are affected by variation in Reynolds number and magnetic dipole strength. The results of this investigation revealed that cylinder angular velocities, ratio of the angular velocities and diameter ratios have profound effect on heat transfer enhancement within the cavity. Averaged heat transfer enhancements of 181.5 % is achieved for clockwise rotation of the cylinder at Omega = -400 compared to motionless cylinder case. Increasing the angular velocity ratio from Omega(2)/Omega(1) = 0.25 to Omega(2)/Omega(1) = 4 brings about 91.7 % of heat transfer enhancement. (C) 2015 Karabuk University. Production and hosting by Elsevier B.V.
  • No Thumbnail Available
    Item
    A Fuzzy-Pod Based Estimation of Unsteady Mixed Convection in a Partition Located Cavity with Inlet and Outlet Ports
    Selimefendigil, F; Öztop, HF
    In the present study, a novel approach based on Proper Orthogonal Decomposition (POD) and fuzzy clustering method is utilized to predict the flow field and heat transfer for the unsteady mixed convection in a square enclosure with two ventilation ports. An adiabatic thin fin is placed on the bottom wall of the cavity and all walls of the enclosure are kept at constant temperature. An oscillating velocity is imposed at the inlet port for a range of Strouhal numbers between 0.1 and 1. Reduced order models of the system are obtained with fuzzy-POD approach for Richardson number of 1 and 100. The estimation data set is obtained for Strouhal numbers 0.1 and 0.5, and the validation data set is obtained for Strouhal number of 0.25. A comparison of the modal coefficients obtained from the proposed approach compares well with the modal coefficients obtained by projecting the CFD data at Strouhal number of 0.25 onto the POD modes. The proposed approach is computationally efficient and the problem of numerical instability in the computation with the conventional Galerkin-POD approach can be circumvented.
  • No Thumbnail Available
    Item
    Magnetic field effects on the forced convection of CuO-water nanofluid flow in a channel with circular cylinders and thermal predictions using ANFIS
    Selimefendigil, F; Öztop, HF
    Numerical simulation of forced convection of CuO-water nanofluid over circular cylinders within a channel was conducted under the influence of a uniform magnetic field by using the finite element method. In the channel, four circular cylinders which are arranged in a two by two matrix configuration are used and they are kept at constant temperature. Effects of various pertinent parameters of the configuration such as the Reynolds number (between 100 and 1000), Hartmann number (between 0 and 10), solid particle volume fraction (between 0 and 0.04) and horizontal distance between the circular cylinder centers (between 0.5 and 8 times of the channel height) on the fluid flow and convective heat transfer were analyzed. The potential use of magnetic field in the reduction of the wake region behind the circular cylinder and augmentation of the heat transfer in the presence of nanoparticle inclusion to the base fluid was examined. It was observed that the established secondary peaks of local Nusselt number along the hot surface for moderate and higher values of Reynolds number reduces with Hartmann number and disappears at the highest value of Hartmann number. When the Hartmann number is increased from Ha = 0 to Ha = 10, 23% of the average heat transfer enhancement is achieved for cylinder which is located in the first row and second column (some distance far away from the wake of the first column cylinder). The average Nusselt number was found to augment by about 17-20 % at the highest and lowest values of Reynolds number and Hartmann numbers for circular cylinders which are placed at (first row first column) and (first row second column). Highly accurate and fast predictions of the average Nusselt number for the circular cylinders are obtained with Adaptive-Network-Based Fuzzy Inference System (ANFIS) modeling.
  • No Thumbnail Available
    Item
    MIXED CONVECTION IN A SINGLE-WALLED CARBON NANOTUBE-WATER NANOFLUID FILLED PARTIALLY HEATED TRIANGULAR LID-DRIVEN CAVITY HAVING AN ELASTIC BOTTOM WALL
    Selimefendigil, F; Öztop, HF
    In this study, mixed convection of nanofluid filled triangular cavity with a partial heater and having an elastic bottom wall is analyzed with finite element method. Left vertical wall is partially heated while the inclined wall is kept at constant lower temperature. The bottom wall is flexible and inclined wall is moving at constant speed. Influences of Richardson number, elastic modulus of flexible wall, solid nanoparticle volume fraction on the convective heat transfer characteristics are analyzed. It was observed that, lower values of Richardson number, elastic modulus of the flexible wall and higher values of nano-particle volume fraction resulted in higher local and average heat transfer enhancements. Average heat transfer enhanced significantly when solid particle volume fraction of nanoparticle was increased. Enhancements up to 121% were obtained at solid volume fraction of 0.04 as compared to pure water at Richardson number of 1. Effects of elastic modulus of the bottom wall were found to be marginal and at Ri=1, enhancements up to 2% were achieved by using a more flexible wall.
  • No Thumbnail Available
    Item
    Optimization assisted CFD for using double porous cylinders on the performance improvement of TEG mounted 3D channels
    Selimefendigil, F; Öztop, HF
    Performance of a thermoelectric generator (TEG) mounted into a channel is analyzed by using double porous cylinders in channel flow with finite element method. COBYLA (Constrained Optimization BY Linear Approximations) algorithm is used to obtain the optimum size and permeability of the porous objects to achieve the highest power. As compared to a non-object channel configuration, the installation of the porous object results in higher power generation. A lower permeability of the double cylinders increases the TEG power while 10.5% increment is obtained when lowest and highest permeability configurations are compared. When sizes of the porous objects are varying up to 19% rise in the TEG power is attained as compared to no-object channel case. The optimum set of parameter to achieve the highest power is obtained as ap1 = 0.232hz, ap2 = 0.75hz and Da = 10-6. At the optimum conditions, there is 22.5% rise of TEG power when hot side Reynolds number is increased from 200 to 600 while this value is 18% for the no-object case. At the highest nanoparticle loading, 20.5% higher power is obtained at the optimum case when compared to no-object channel case. The optimization assisted computational fluid dynamics (CFD) study of TEG installed channel flow with passive methods is very effective in achieving the best performance as compared to computationally expensive high fidelity multi-parametric CFD. As thermoelectric energy conversion and related devices are used in diverse energy systems technologies including solar-thermal applications, thermal management in different thermal systems, refrigeration and many others, the outcomes and computational methods will be useful for efficient design and optimization studies.
  • No Thumbnail Available
    Item
    An efficient method for optimizing the unsteady heat and mass transport features for convective drying of two porous moist objects in a channel
    Selimefendigil, F; Coban, SO; Öztop, HF
    In the present study, an efficient methodology is proposed for optimizing the convective drying performance of multiple porous moist objects in a channel. As the first step of the method, a PDE constraint optimization routine is utilized to obtain the optimum values of distance between the objects for maximizing the transfer rates while in the second part, unsteady coupled field equations for the channel and porous moist object domains are invoked for convective drying of multiple objects for the optimum spacing values. Finite element method is used for the numerical simulations. It was observed that the recirculation zones established behind the rectangular objects are profoundly affected with the distance between the objects. There is 12.5 % variation in the average Nu for the first block with varying the horizontal distance between the objects. The effects of vertical spacing on the average Nu is profound for the second object. while up to 80 % enhancement in the average Nu is obtained when the value is changed from sy = 0 to sy = 1.5hp. However, the optimum values of the distance that maximize the heat transfer are obtained as sx = 1.1hp and sy = 1.931hp for the horizontal distance and vertical distance. At this optimum values of parameters, reduction in the moisture content becomes 33.4 % and 98.015 % for drying times at 1000 s and 5000 s. These values are also checked with the parametric unsteady coupled field equations for the porous moist objects which shows the improved time dependent drying features for the two blocks at the optimum points.
  • No Thumbnail Available
    Item
    Multijet impingement heat transfer under the combined effects of encapsulated-PCM and inclined magnetic field during nanoliquid convection
    Selimefendigil, F; Öztop, HF
    In this study, convective heat transfer performance for confined multiple jet impinging system with phase change-packed bed (PCM-PB) installed sub-system under magnetic field effects is numerically assessed during hybrid nanoliquid convection. Both phase transition and heat transfer dynamics are analyzed by using finite element method. Numerical study is conducted for different magnetic field strength (Hart-mann number-Ha between 0-40), inclination (between 0-90), distance between the slots (between 3w-6w) and nanoparticle loading (between 0-2 % ) for the cases with and without PCM-PB zone. Phase tran-sition and heat transfer dynamics are influenced by the presence of magnetic field and varying its am-plitude/inclination. Complete phase change time (TP) is reduced by about 15 % and 11.7 % for pure liquid and nanoliquid when varying Ha from 0 to 10. Inclination of gamma = 0 provides the fastest phase transi-tion dynamics. Spatial average Nusselt number (Nu) rises by about 13.5 % by using impinging system with PCM+nanoliquid at the highest Ha as compared to system using only pure liquid. Phase transi-tion becomes slower for higher distance values between the slots while the average Nu rises by about 48.8 % . As the reference case of system using pure liquid without magnetic filed and without PCM are used, up to 84.88 % rise of average Nu is achieved by using PCM+nanoliquid under magnetic field at the highest strength. Dynamic fit for the thermal performance of the impinging system installed with PCM+nanoliquid under magnetic field with system identification is obtained.(c) 2022 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Numerical Study and POD-Based Prediction of Natural Convection in a Ferrofluids-Filled Triangular Cavity with Generalized Neural Networks
    Selimefendigil, F; Öztop, HF
    The effects of a magnetic dipole source on the natural convection of ferrofluids in a triangular cavity are studied. A partial heater is added to the left vertical wall of the cavity while the right vertical wall is kept at the constant temperature. A magnetic dipole source is placed outside the cavity close to the heater. The governing equations of a coupled multi-physics system are solved with a commercial solver using the finite element method. Computations are performed for different ranges of parameters: Rayleigh number (10(4) <= Ra <= 10(6) ), strength of the magnetic dipole (0 <=gamma <= 8), horizontal and vertical location of the magnetic dipole (-2.5H <= a <=-0.5H, 0.2H <= b <= 0.8H). It is observed that the interaction between natural convection and ferrofluid convection under the influence of magnetic dipole affects the flow and thermal field in such the triangular enclosure. The external magnetic field acts in such a way to decrease local heat transfer in some locations and increase it in others for certain combinations of flow parameters and therefore it can be used as a control parameter for fluid flow and heat transfer. Furthermore, an interpolation method based on Proper Orthogonal Decomposition and Generalized Neural Networks is proposed to predict the thermal performance of the system. This approach gives satisfactory results in terms of local and averaged heat transfer values.