Browsing by Subject "FLUID-FLOW"

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    Application and CFD-Based Optimization of a Novel Porous Object for Confined Slot Jet Impingement Cooling Systems under a Magnetic Field
    (MDPI) Aich, W; Selimefendigil, F; Ayadi, B; Ben Said, L; Alshammari, BM; Kolsi, L; Betrouni, SA; Gasmi, H
    A novel porous object for the control of the convective heat transfer of confined slot nanojet impingement is offered under magnetic field effects, while optimization-assisted computational fluid dynamics is used to find the best working conditions to achieve the best performance of the system. The flow, thermal patterns, and heat transfer characteristics were influenced by the variation in rotational Reynolds number (Rew), Hartmann number (Ha), permeability of the porous object (Da) and its location (Mx). There was a 14.5% difference in the average Nusselt number (Nu) at the highest Rew when motionless object configuration at Ha = 5 was compared, while it was less than 2% at Ha = 25. At Rew = -600, the average Nu variation was 22% when cases with the lowest and highest magnetic field strength were compared. The porous object provides an excellent tool for convective heat transfer control, while the best performance was achieved by using optimization-assisted computational fluid dynamics. The optimal sets of (Rew, Da, Mx, AR) for porous object were (-315.97, 0.0188, -1.456, 0.235), (-181.167, 0.0167, -1.441, 0.2), and (-483.13, 0.0210, -0.348, 0.2) at Ha = 5, 10, and 25, respectively. At the optimal operating point, the local Nu enhancements were 19.46%, 44.86%, and -0.54% at Ha = 5, 10, and 15, respectively, when the no-object case was compared, while the average values were 7.87%, 8.09% and 5.04%.
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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
    (MDPI) 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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    Forced Convection of Non-Newtonian Nanofluid Flow over a Backward Facing Step with Simultaneous Effects of Using Double Rotating Cylinders and Inclined Magnetic Field
    (MDPI) Kolsi, L; Selimefendigil, F; Said, LB; Mesloub, A; Alresheedi, F
    The forced convection of non-Newtonian nanofluid for a backward-facing flow system was analyzed under the combined use of magnetic field and double rotating cylinders by using finite element method. The power law nanofluid type was used with different solid volume fractions of alumina at 20 nm in diameter. The effects of the Re number (100 & LE;Re & LE;300), rotational Re number (-2500 & LE;Rew & LE;3000), Ha number (0 & LE;Ha & LE;50), and magnetic field inclination (0 & LE;gamma & LE;90) on the convective heat transfer and flow features were numerically assessed. The non-Newtonian fluid power law index was taken between 0.8 and 1.2 while particle volume fractions up to 4% were considered. The presence of the rotating double cylinders made the flow field complicated where multiple recirculation regions were established near the step region. The impacts of the first (closer to the step) and second cylinders on the heat transfer behavior were different depending upon the direction of rotation. As the first cylinder rotated in the clockwise direction, the enhancement in the average heat transfer of 20% was achieved while it deteriorated by approximately 2% for counter-clockwise directional rotation. However, for the second cylinder, both the rotational direction resulted in heat transfer augmentation while the amounts were 14% and 18% at the highest speeds. Large vortices on the upper and lower channel walls behind the step were suppressed with magnetic field effects. The average Nu number generally increased with the higher strengths of the magnetic field and inclination. Up to 30% increment with strength was obtained while this amount was 44% with vertical orientation. Significant impacts of power law fluid index on the local and average Nu number were seen for an index of n = 1.2 as compared to the fluid with n = 0.8 and n = 1 while an average Nu number of 2.75 times was obtained for the flow system for fluid with n = 1.2 as compared to case for fluid with the n value of 0.8. Further improvements in the local and average heat transfer were achieved with using nanoparticles while at the highest particle amount, the enhancements of the average Nu number were 34%, 36% and 36.6% for the fluid with n values of 0.8, 1 and 1.2, respectively.
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    Effects of phase shift on the heat transfer characteristics in pulsating mixed convection flow in a multiple vented cavity
    (ELSEVIER SCIENCE INC) Selimefendigil, F; Öztop, HF
    In the current study, numerical investigation of pulsating mixed convection in a multiple vented cavity with phase shift is carried out for the range of parameters; Richardson number (0.25 <= Ri <= 4), phase shift (0 <= phi <= pi) and Strouhal number is fixed at 1. The governing equations are solved with a general purpose finite volume based solver. The effects of Ri number and phase shift parameters on the fluid flow and heat transfer characteristics are numerically studied. It is observed that the flow field and heat transfer enhancement are influenced by the variation of these parameters. Furthermore, recurrence plot analysis is applied for the analysis of the time series (spatial averaged Nusselt number along the vertical wall of the cavity) and for a combination of different parameters, the systems are identified using recurrence quantification analysis parameters including recurrence rate, laminarity, determinism, trapping time and entropy. (C) 2014 Elsevier Inc. All rights reserved.
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    Combined effects of using multiple porous cylinders and inclined magnetic field on the performance of hybrid nanoliquid forced convection
    (ELSEVIER) Selimefendigil, F; Öztop, HF
    Effects of combined utilization of inclined magnetic field and multiple porous cylinders on the forced convection in a vented cavity are numerically assessed by using finite element method. Effects of Reynolds number (Re: 200-1000), magnetic field strength (Ha: 0-75), inclination of magnetic field (gamma: 0-90), permeability of the porous cylinders (Da: 10(-4) - 10(-1)) and size of the cylinders (R: 0.04 H-0.15 H) on the fluid flow convective heat transfer performance are studied. The presence of the cylinder and their permeability can be used for controlling the heat transfer. When cylinders at the highest permeability is used, there is 77% additional contribution to the overall thermal performance when lowest and highest Re cases are compared. There is significant contribution of the magnetic field on the suppression of the vortices in the cavity for the case with lower permeability of the cylinders. The magnetic field strength is more effective on the flow field and heat transfer as compared to its inclination. Up to 123% increment in the heat transfer is obtained at the highest strength of magnetic field for the highest permeability of the cylinders while it is only 12% when cylinders with the lowest permeability are used. When variation in the magnetic field inclination is considered, average heat transfer variation up to 19.8% is obtained for the multiple cylinders with the highest permeability. The size of the porous cylinders generally contributes positively to the overall thermal performance. Heat transfer enhancements up to 88% can be obtained by using highest cylinder size as compared to lowest size when the permeability is lowest while it is only 15% for the highest permeability case. The optimum set of parameters at Re = 200 is found as Ha, gamma, Da) = (74.4, 1.3, 10(-5)) and at Re = 1000, it is (Ha, gamma, Da) = (75, 0.35, 10(-5)). Significant variations in the average heat transfer is obtained when optimum case is compared with the parametric study case.
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    3D numerical study of heat and mass transfer of moving porous moist objects
    (ELSEVIER) Çoban, SÖ; Selimefendigil, F; Öztop, HF
    Heat and moisture transfer of two moving moist objects in a channel with convection of hot dry air is investigated numerically. A moving mesh approach is used for providing movement by means of the Arbitrary LagrangianEulerian (ALE) framework. Governing equations for flow field and porous objects are solved by finite element discretization method for the 3D transient problem. Effects of drying air velocity and temperature are simulated by means of temperature, moisture content and heat transfer distributions. Results showed the importance of varying parameters on drying behavior. It was observed that the air velocity also has an increasing effect on evaporation and most reduction in moisture content is obtained at 0.8 m/s air velocity with 63.12% loss. Besides, there are insignificant differences between heat transfer values for fixed and moving objects, differences in average heat transfer values calculated between 6 and 13% for static bed and moving bed.
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    Mixed convection in a lid-driven cavity filled with single and multiple-walled carbon nanotubes nanofluid having an inner elliptic obstacle
    (ELSEVIER SCI LTD) Selimefendigil, F
    In this study, numerical analysis and optimization in a single and multiple walled carbon nanotube-water nanofluid filled lid driven cavity having an inner elliptic obstacle were performed by using finite element method and COB YLA optimization solver. The top wall is moving with constant speed and vertical walls are kept at constant temperatures. An optimal size of the inner elliptic obstacle was determined by using an optimization study to maximize the average heat transfer along the hot wall of the cavity. Numerical simulation was performed by for various values of Richardson numbers (between 0.05 and 50) and various solid particle volume fraction (between 0 and 0.06) for single and multiple-walled carbon nanotubes water nanofluid. A larger obstacle (higher values of radii in the major and minor axis) with lower values of Richardson number results in higher heat transfer rates. The average Nusselt number versus solid particle volume fraction shows a linear trend and the discrepancy between the average Nusselt number for the cavity with the optimized obstacle and other obstacles becomes higher with higher particle volume fraction. The average heat transfer enhances significantly which is about 120.20% for single wall carbon nanotube-water nanofluid at solid volume fraction of 0.06 when compared to pure water. The discrepancy between the average Nusselt number for single and multiple walled carbon nanotubes becomes higher for higher values of Richardson number and solid particle volume fraction. A polynomial type correlation was proposed for the average Nusselt number along the hot wall which is fifth order for Richardson number an first order for nanoparticle volume fraction. (C) 2019 Beihang University. Production and hosting by Elsevier B.V.
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    Conductive panel cooling by using coupled effects of nano-jet impingement, double rotating cylinders and magnetic field under cross-flow
    (EMERALD GROUP PUBLISHING LTD) Selimefendigil, F; Oztop, HF
    PurposeThis study aims to examine the effects of cross-flow and multiple jet impingement on conductive panel cooling performance when subjected to uniform magnetic field effects. The cooling system has double rotating cylinders.Design/methodology/approachCross-flow ratios (CFR) ranging from 0.1 to 1, magnetic field strength (Ha) ranging from 0 to 50 and cylinder rotation speed (Rew) ranging from -5,000 to 5,000 are the relevant parameters that are included in the numerical analysis. Finite element method is used as solution technique. Radial basis networks are used for the prediction of average Nusselt number (Nu), average surface temperature of the panel and temperature uniformity effects when varying the impacts of cross-flow, magnetic field and rotations of the double cylinder in the cooling channel.FindingsThe effect of CFR on cooling efficiency and temperature uniformity is favorable. By raising the CFR to the highest value under the magnetic field, the average Nu can rise by up to 18.6%, while the temperature drop and temperature difference are obtained as 1.87 degrees C and 3.72 degrees C. Without cylinders, magnetic field improves the cooling performance, while average Nu increases to 4.5% and 8.8% at CR = 0.1 and CR = 1, respectively. When the magnetic field is the strongest with cylinders in channel at CFR = 1, temperature difference (Delta T) is obtained as 2.5 degrees C. The rotational impacts on thermal performance are more significant when the cross-flow effects are weak (CFR = 0.1) compared to when they are substantial (CFR = 1). Cases without a cylinder have the worst performance for both weak and severe cross-flow effects, whereas using two rotating cylinders increases cooling performance and temperature uniformity for the conductive panel. The average surface temperature lowers by 1.2 degrees C at CFR = 0.1 and 0.5 degrees C at CFR = 1 when the worst and best situations are compared.Originality/valueThe outcomes are relevant in the design and optimization-based studies for electric cooling, photo-voltaic cooling and battery thermal management.
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    A comparative experimental thermal performance analysis of conical pin fin heat sink with staggered and modified staggered layout under forced convection
    (ELSEVIER) Abuska, M; Corumlu, V
    In contrast to the common practice of evaluating heat sinks with inline or standard staggered fin placement, this research investigated the thermo-hydraulic performance of conical pin-fin heat sinks with staggered-(CPFHSst) and modified staggered-(CPFHSmst) fin placements. The heat sinks with cross-cut pin-fins oriented parallel-(CCPFHSpar) and perpendicular-(CCPFHSperp) to the airflow and a flat heat sink (FHS) are also used for com-parison. The effect of heat sink fin placement on the parameters became remarkable with increasing Re, so the modified staggered fin placement was 2-7 degrees C lower than the staggered surface and junction temperatures. Rth of the modified model compared to the staggered was 5.3 %, 5.8 %, and 3.5 % lower, while the highest Delta P is in CCPFHSperp with 6.7, 6.9, and 7.4 Pa. CCPFHSperp provided a 29.9 % advantage of Nu to the modified model, whereas the modified model provided a 6.4 % over CCPFHSperp and a 17.4 % over the staggered model for the test powers. The modified model provides the highest THP performance, with a 13.3 % advantage over CCPFHSperp, 12 %, and 10.9 % over the staggered model for the test powers. The CPFHSmst is superior regarding thermo-hydraulic performance and is an appropriate option among many heat sink models in the literature.
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    Coupled Effects of Using Magnetic Field, Rotation and Wavy Porous Layer on the Forced Convection of Hybrid Nanoliquid Flow over 3D-Backward Facing Step
    (MDPI) Ghachem, K; Selimefendigil, F; Alshammari, BM; Maatki, C; Kolsi, L
    In the present study, the effects of using a corrugated porous layer on the forced convection of a hybrid nanofluid flow over a 3D backward facing step are analyzed under the coupled effects of magnetic field and surface rotation. The thermal analysis is conducted for different values of the Reynolds number (Re between 100 and 500), the rotational Reynolds number (Rew between 0 and 2000), the Hartmann number (Ha between 0 and 15), the permeability of the porous layer (the Darcy number, Da between 10(-5) and 10(-2)) and the amplitude (ax between 0.01 ap and 0.7 ap) and wave number (N between 1 and 16) of the porous layer corrugation. When rotations are activated, the average Nusselt number (Nu) and pressure coefficient values rise, while the increment of the latter is less. The increment in the average Nu is higher for the case with a higher permeability of the layer. When the corrugation amplitude and wave number are increased, favorable impacts of the average Nu are observed, but at the same time pressure coefficients are increased. Successful thermal performance estimations are made by using a neural-based modeling approach with a four input-two output system.
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    Mixed convection in a two-sided elastic walled and SiO2 nanofluid filled cavity with internal heat generation: Effects of inner rotating cylinder and nanoparticle's shape
    (ELSEVIER SCIENCE BV) Selimefendigil, F; Öztop, HF
    In this study, mixed convection in a cavity with volumetric heat generation and filled with nanofluid having an inner rotating cylinder and two flexible side walls is numerically investigated. The top wall of the cavity is at constant cold temperature while the bottom wall is kept at hot temperature. Two flexible side walls and the surface of the inner rotating cylinder are accepted as adiabatic. The finite element formulation is used to solve the governing equations. The Arbitrary-Lagrangian-Eulerian method is used to describe the fluid motion with the flexible side walls of the cavity in the fluid-structure interaction model. The influence of external Rayleigh number, elastic modulus pair of the flexible side walls, angular rotational speed of the cylinder, internal Rayleigh number and nanopartide volume fraction on the fluid flow and heat transfer are numerically simulated by using different solid nanoparticle shapes (spherical, cylindrical, brick and blade type). It is observed that the local and averaged heat transfer enhances as the external Rayleigh number, nanoparticle volume fraction and absolute value of the angular rotational velocity of the cylinder increase and as the internal Rayleigh number decreases. The elastic modulus of the side walls can be used to control the fluid flow and heat transfer inside the cavity. Utilizing cylindrical nanopartides gives the best performance in terms of heat transfer enhancement. (c) 2015 Elsevier B.V. All rights reserved.
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    Effects of using a porous disk on the dynamic features of phase change process with PCM integrated circular pipe during nano-liquid forced convection in discharging operation mode
    (ELSEVIER) Selimefendigil, F; Öztop, HF
    Impacts of using a porous disk on the performance of a phase change material filled cylindrical container during forced convection of nanoliquid in discharging mode are investigated with finite element method. Simulations are performed for various values of porous disk permeability (10(-5) <= Da <= 5 x 10(-2)), radius (0 <= p(r)<= h(r)) and height (0:2h(z)<= p(z)<= 0.8h(z)) of the porous disk while time is considered between 0 and 40 min. As the heat transfer fluid, nanoliquid of water containing cylindrical shaped alumina nanoparticle is considered with solid volume fraction of 2%. It was observed that the flow field, temperature and phase change process dynamic features are influenced by varying the porous disk permeability and its geometrical parameters. An optimum permeability value of the disk is observed at Darcy number of 5 x 10(-3) for which the discharging time is minimum and its reduction is 40.7% as compared to case with the lowest permeability of the disk. The phase change process becomes fast with higher radius of the porous disk while the effect is reverse for higher height of the disk. The reduction is discharging time is 22% with highest radius while is it increased by about 61% at the highest height. A predictive model based on feed-forward artificial neural networks is considered with 25 neurons in the hidden layer which delivers accurate results for the effects of porous disk on the dynamic features of phase change process. (C) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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    Mixed convection due to rotating cylinder in an internally heated and flexible walled cavity filled with SiO2-water nanofluids: Effect of nanoparticle shape
    (PERGAMON-ELSEVIER SCIENCE LTD) Selimefendigil, F; Öztop, HF; Abu-Hamdeh, N
    In this study, numerical investigation of mixed convection in a square cavity filled with SiO2 nanofluid and volumetric heat generation is performed under the effect of an inner rotating cylinder and a flexible side wall. The top wall of the cavity is kept at constant cold temperature while the bottom wall is at hot temperature and the other walls of the cavity and the cylinder surface are assumed to be adiabatic. The finite element method 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 effects of external Rayleigh number (between 10(3) and 5 x 10(6)), internal Rayleigh number (between 10(4) and 10(6)), Young's modulus of the flexible wall (between 5 x 10(2) and 10(6)), angular rotational speed of the cylinder (between - 2000 and 2000) and nano particle volume fraction (between 0 and 0.03) on the fluid flow and heat transfer are numerically studied for different solid nanoparticle shapes (spherical, cylindrical, brick and blade). It is observed that as the value of external Rayleigh number increases, internal Rayleigh number and elastic modulus of the flexible wall decrease, the local and averaged heat transfer enhances. The averaged heat transfer enhances with cylinder rotation in both directions for all nanoparticle types. Among all nanoparticle shapes, cylindrical ones show the best performance and spherical ones show the worst performance for heat transfer enhancement. (C) 2015 Elsevier Ltd. All rights reserved.
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    Multiple slot nano-jet impingement cooling of a sinusoidal hot surface by using active rotating cylinders under magnetic field
    (ELSEVIER) Selimefendigil, F; Ghachem, K; Alwadai, N; Alshammari, BM; Kolsi, L
    In this study, cooling performance of a multi-slot jet impingement system for a wavy surface are explored under the triple combined effects of using magnetic field (MG-F), double active rotating cylinders and nanofluid. Double rotating cylinders which provide additional cooling are used while Galerkin weighed residual finite element method is used for the solution of the governing equations. Effects of Rew (rotational Reynolds number, between -1000 and 1000), Ha (MG-F strength between 0 and 30), MG-F inclination (between 0 and 90) and sub-cooling temperature of the active cylinders (dT between 0 and 10) on the cooling performance are assessed. Rotations of the double cylinders generally provide higher Nusselt number (Nu) while 41% and 18.9% increment in the Nu is obtained when using pure fluid and nanofluid. The average Nu behavior is different when using MG-F depending upon the rotations are active or not. Average Nu is sharply reduced by about 25.1% without rotations but it rises by about 89% at Ha = 10 by using rotations. The impacts of sub-cooling is very effective when rotations are active while up to 37.9% rise of Nu is obtained at Rew = -1000. When no cylinders are used, using MG-F reduced the average Nu by about 15.4%. The best cooling performance case in the absence of MG-F with cylinders is obtained at Rew = -1000 and dT = 10.
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    Natural convection and entropy generation of nanofluid filled cavity having different shaped obstacles under the influence of magnetic field and internal heat generation
    (ELSEVIER) Selimefendigil, F; Öztop, HF
    In this study, natural convection in a nano-fluid filled cavity having different shaped obstacles (circular, square and diamond) installed under the influence of a uniform magnetic field and uniform heat generation was numerically investigated. The cavity was heated from below and cooled from the vertical sides while the top wall was assumed to be adiabatic. The temperatures of the side walls vary linearly. The governing equations were solved by using Galerkin weighted residual finite element formulation. The numerical investigation was performed for a range of parameters: external Rayleigh number (10(4) <= ROE <= 10(6)), internal Rayleigh number (10(4) <= Ra-I <= 10(6)), Hartmann number (0 <= Ha <= 50), and solid volume fraction of the nanofluid (0 <= phi <= 0.05). It is observed that the presence of the obstacles deteriorates the heat transfer process and this is more pronounced with higher values of Re-E. Averaged heat transfer reduces by 21.35%, 32.85% and 34.64% for the cavity with circular, diamond and squared shaped obstacles compared to cavity without obstacles at Ra-I = 10(6). The effect of heat transfer reduction with square and diamond shaped obstacles compared to case without obstacle is less effective with increasing values of Hartmann number. Second law analysis was also performed by using different measures for the normalized total entropy generation. (C) 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.