Browsing by Author "Abu-Hamdeh N."
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Item Natural convection and entropy generation in nanofluid filled entrapped trapezoidal cavities under the influence of magnetic field(MDPI AG, 2016) Selimefendigil F.; Öztop H.F.; Abu-Hamdeh N.In this article, entropy generation due to natural convection in entrapped trapezoidal cavities filled with nanofluid under the influence of magnetic field was numerically investigated. The upper (lower) enclosure is filled with CuO-water (Al2O3-water) nanofluid. The top and bottom horizontal walls of the trapezoidal enclosures are maintained at constant hot temperature while other inclined walls of the enclosures are at constant cold temperature. Different combinations of Hartmann numbers are imposed on the upper and lower trapezoidal cavities. Numerical simulations are conducted for different values of Rayleigh numbers, Hartmann number and solid volume fraction of the nanofluid by using the finite element method. In the upper and lower trapezoidal cavities magnetic fields with different combinations of Hartmann numbers are imposed. It is observed that the averaged heat transfer reduction with magnetic field is more pronounced at the highest value of the Rayleigh number. When there is no magnetic field in the lower cavity, the averaged Nusselt number enhances as the value of the Hartmann number of the upper cavity increases. The heat transfer enhancement rates with nanofluids which are in the range of 10% and 12% are not affected by the presence of the magnetic field. Second law analysis of the system for various values of Hartmann number and nanoparticle volume fractions of upper and lower trapezoidal domains is performed. © 2016 by the authors.Item Mixed convection due to rotating cylinder in an internally heated and flexible walled cavity filled with SiO2-water nanofluids: Effect of nanoparticle shape(Elsevier Ltd, 2016) Selimefendigil F.; Öztop H.F.; 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 103 and 5×105), internal Rayleigh number (between 104 and 106), Young's modulus of the flexible wall (between 5×102 and 106), angular rotational speed of the cylinder (between -2000 and 2000) and nanoparticle 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. © 2015 Elsevier Ltd.Item Forced convection of Fe 3 O 4 -water nanofluid in a bifurcating channel under the effect of variable magnetic field(MDPI AG, 2019) Selimefendigil F.; Oztop H.F.; Sheremet M.A.; Abu-Hamdeh N.In this study, forced convection of Fe 3 O 4 –water nanofluid in a bifurcating channel was numerically studied under the influence of variable magnetic. Galerkin residual finite element method was used for numerical simulations. Effects of various values of Reynolds number (between 100 and 500), Hartmann number (between 0 and 3), and solid nanoparticle volume fraction (between 0% and 4%) on the convective heat transfer characteristics were analyzed. It was observed that location and size of the re-circulation zones established in the walls of the bifurcating channel strongly influenced by the variable magnetic field and Reynolds number. Average Nusselt number versus Hartmann number showed different characteristics for hot walls of the vertical and horizontal branching channels. The average Nusselt number enhancements were in the range of 12–15% and 9–12% for hot walls of the branching channel in the absence and presence of magnetic field (at Hartmann number of 3). © 2019 by the authors.Item Impacts of conductive inner L-shaped obstacle and elastic bottom wall on MHD forced convection of a nanofluid in vented cavity(Springer Science and Business Media B.V., 2020) Selimefendigil F.; Öztop H.F.; Abu-Hamdeh N.Forced convection of nanofluid in a vented cavity with elastic bottom wall is studied by using an inner conductive L-shaped object and magnetic field. Simulations are performed using the finite element method when the impacts of various pertinent parameters, such as Reynolds number (between 100 and 500), Hartmann number (between 0 and 40), elastic modulus of the flexible wall (between 10 5 and 10 9), solid nanoparticle volume fraction (between 0 and 0.04), size (between 0.1 and 0.4H), inclination (between − 90 and 90) and location (xc between 0.25 and 0.75 H and yc between 0.15 and 0.65H) of the L-shaped object on the fluid flow and heat transfer features, are investigated. It was observed that wall flexibility effects are influential for the configuration with strong convection and maximum of 11 % enhancement in the average heat transfer rate for the bottom wall is achieved. Suppression of the recirculations in the vented cavity and around the L-shaped object is observed with magnetic field. It is observed that impact of magnetic field on heat transfer enhancement is different for different segments of hot wall. When the cases with the highest magnetic field and in the absence of magnetic field are compared, the average heat transfer enhancement of 5.5 % is achieved for bottom elastic wall while 24.5 % of reduction in the average heat transfer is seen for upper hot wall. The overall Nusselt number reduces slightly when the magnetic field strength is increased. Significant impacts of the size, inclination and location of the of the L-shaped conductive object on the fluid flow such as branching of the main flow stream, size of the vortex below the inlet port and heat transfer are observed. 31.6 % rise of the average heat transfer for left vertical wall and 34.6 % reduction of average heat transfer for bottom wall are achieved when the minimum and maximum of the orientation angles are compared. The location of the L-shaped object has a significant impact on the flow and thermal pattern variations. The highest variation in the contribution to the overall heat transfer is seen for right vertical hot wall segment when the Nusselt numbers at the lowest and highest values of the horizontal and vertical locations of the object are compared. L-shaped object was found to be an efficient tool to control the heat transfer features of the vented cavity. Nanofluid inclusion resulted in heat transfer enhancement in the range of 8.5–16.5% while amount of enhancement is different for different hot wall segments either in the absence or in the presence of magnetic field effects. Finally, a polynomial-type correlation for the average Nusselt number of each hot wall segments of the vented cavity is proposed for water and for nanofluid at ϕ= 0.04. © 2019, Akadémiai Kiadó, Budapest, Hungary.Item Analysis of melting of phase change material block inserted to an open cavity(Elsevier Ltd, 2022) Öztop H.F.; Coşanay H.; Selimefendigil F.; Abu-Hamdeh N.A numerical work has been conducted to explore the effects of opening parameters on melting of phase change material (PCM) during natural convection in a partially open enclosure. A finned heater is located on bottom wall while the remaining parts are insulated. Paraffin wax is used as PCM and two-dimensional time dependent analysis is performed by using the finite volume method for the parameters of location of opening and temperature difference. The governing parameters for the study are chosen for the range of Ra = 1.45 × 108 ≤ Ra ≤ Ra = 1.97 × 108, 0.25 ≤ w/H ≤ 0.75 and 0.25 ≤ c/H ≤ 0.75. It is found that both opening ratio and opening length are effective parameter on melting time and these can be used as control parameters for improving the energy efficiency. Also, heat transfer can be controlled by using PCM inserted block and opening parameters. Among different cases of opening ratios and locations of opening, the most favorable configuration is obtained at Ra = 1.97 × 108, w/H = 0.25, c/H = 0.25 while average heat transfer enhancement by about 60% is achieved. At the lowest and highest value of Rayleigh numbers, the most favorable location of the opening is obtained at c/H = 0.25 in order to have the highest reduction amount of phase completion time. © 2022 Elsevier LtdItem Optimization of phase change process in a sinusoidal-wavy conductive walled cylinder with encapsulated-phase change material during magnetohydrodynamic nanofluid convection(Elsevier Ltd, 2022) Selimefendigil F.; Öztop H.F.; Abu-Hamdeh N.A novel method of controlling the phase transition dynamics in encapsulated phase change material (PCM) installed container is proposed by using combined utilization of magnetic field and wavy conductive wall during hybrid nanoliquid convection. The study is performed for different values of Reynolds number (Re: 100–500), strength of magnetic field (Ha: 0–30), amplitude (Af: 0–0.2), wave number (Nf: 2–16) of the wavy partition and conductivity ratio (Kr: 0.1–50). Binary nanoparticle loading with solid volume fraction of 2% is considered. The complete phase transition time (PT) is reduced by about 46.7% and 22.5% for flat and wavy conductive walls between the lowest and highest Re cases. The impact of using magnetic field is favorable for phase transition while as compared to flat wall by using wavy wall, PT is reduced by further about 9% with the magnetic field at the highest strength. Corrugation amplitude and wave number are good control parameters for affecting the phase transition dynamics while PT variation is 30% when cases with lowest and highest wave number of corrugation are compared. Phase change is faster with higher conductivity ratio while up to 42.3% reduction in PT is obtained by varying conductivity ratio. Optimization assisted computational fluid dynamics is used to achieve the fastest phase transition dynamics while optimum set of parameters are obtained as (Ha, Af, Kr)=(30, 0.067, 2.7) at Re=100 and (Ha, Af, Kr)=(30, 0.007, 1.30) at Re=500. © 2022 Elsevier LtdItem Phase change dynamics in a triangular elastic walled vented cavity having phase change material packed bed during nanofluid forced convection; [纳米流体强制对流过程中充填相变材料的三角形弹性壁通气腔内的相变动力学](Central South University of Technology, 2023) Selımefendıgıl F.; Öztop H.F.; Abu-Hamdeh N.In this study, phase change process dynamics in a triangular shaped elastic walled vented cavity is explored during nanofluid forced convection in the laminar flow regime. Impacts of Reynolds number (Re), Cauchy number (Ca) and port size of the cavity on the flow field and phase change dynamics are explored by finite element method. It is observed that the flow recirculation below the inlet port and phase change dynamics are affected by the variation of Re, Ca and port size. The phase transition time (TF) is reduced first when increasing Re from 100 to 200 and then increases. Hybrid nanofluid results in fast phase change while TF is reduced by about 26% at Re=100. Up to 12.5% reduction of TF is achieved at the highest value of Ca. The port size has a negative impact on the phase transition while TF is increased up to 19% with varying the port size. © 2023, Central South University.Item Numerical analysis of conjugate convection heat transfer in an open cavity with different phase change materials surrounded by plexiglass(Taylor and Francis Ltd., 2024) Öztop H.F.; Selimefendigil F.; Coşanay H.; Abu-Hamdeh N.Phase change (PC) process and convection inside an open cavity equipped with two different PCMs are analyzed with the finite volume method with ANSYS Fluent. The analysis is conducted for three different Grashof number (Gr) values for fully and partly open configurations. It is observed that the PC becomes fast when the object is closer to the exit for the fully open case. The partly open case results in higher thermal performance improvements while the average Nusselt number (Nu) increment is 94.5% for PCM-18. PC and heat transfer characteristics are influenced by both material and location of the PCM. At Gr = 3.79 × 108, the average Nu rises by about 50% when PCM-22 is used instead of PCM-18. Location and type of PCM provide excellent tool for controlling the phase transition and heat transfer dynamics with a fully and or partly open cavity. © 2023 Taylor & Francis Group, LLC.