Browsing by Author "Omri M."

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    Effects of surface rotation on the phase change process in a 3d complex-shaped cylindrical cavity with ventilation ports and installed pcm packed bed system during hybrid nanofluid convection
    (MDPI, 2021) Kolsi L.; Selimefendigil F.; Omri M.
    The combined effects of surface rotation and using binary nanoparticles on the phase change process in a 3D complex-shaped vented cavity with ventilation ports were studied during nanofluid convection. The geometry was a double T-shaped rotating vented cavity, while hybrid nanofluid contained binary Ag–MgO nano-sized particles. One of the novelties of the study was that a vented cavity was first used with the phase change–packed bed (PC–PB) system during nanofluid convection. The PC–PB system contained a spherical-shaped, encapsulated PCM paraffin wax. The Galerkin weighted residual finite element method was used as the solution method. The computations were carried out for varying values of the Reynolds numbers (100 ≤ Re ≤ 500), rotational Reynolds numbers (100 ≤ Rew ≤ 500), size of the ports (0.1L1 ≤ di ≤ 0.5L1), length of the PC–PB system (0.4L1 ≤ L0 ≤ L1), and location of the PC–PB (0 ≤ yp ≤ 0.25H). In the heat transfer fluid, the nanoparticle solid volume fraction amount was taken between 0 and 0.02%. When the fluid stream (Re) and surface rotational speed increased, the phase change process became fast. Effects of surface rotation became effective for lower values of Re while at Re = 100 and Re = 500; full phase transition time (tp) was reduced by about 39.8% and 24.5%. The port size and nanoparticle addition in the base fluid had positive impacts on the phase transition, while 34.8% reduction in tp was obtained at the largest port size, though this amount was only 9.5%, with the highest nanoparticle volume fraction. The length and vertical location of the PC–PB system have impacts on the phase transition dynamics. The reduction and increment amount in the value of tp with varying location and length of the PC–PB zone became 20% and 58%. As convection in cavities with ventilation ports are relevant in many thermal energy systems, the outcomes of this study will be helpful for the initial design and optimization of many PCM-embedded systems encountered in solar power, thermal management, refrigeration, and many other systems. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
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    Combined effects of sequential velocity and variable magnetic field on the phase change process in a 3d cylinder having a conic-shaped pcm-packed bed system
    (MDPI, 2021) Kolsi L.; Selimefendigil F.; Omri M.; Ladhar L.
    Effects of sequential velocity and variable magnetic field on the phase change during hybrid nanofluid convection through a 3D cylinder containing a phase-change material packed bed (PCM-PB) system is analyzed with the finite element method. As the heat transfer fluid, 40% ethylene glycol with hybrid TiO2-Al2O3 nanoparticles is considered. Impacts of the sequential velocity parameter (K, between 0.5 and 1.5), geometric factor of the conic-shaped PCM-PB (M, between 0.2 and 0.9), magnetic field strength (Ha number between 0 and 50) and solid volume fraction of hybrid nanoparticles (vol.% between 0.02% and 0.1%) on the phase change dynamics are explored. Effects of both constant and varying magnetic fields on the phase change process were considered. Due to the increased fluid velocity at the walls, the phase change becomes higher with higher values of the sequential velocity parameter (K). There is a 21.6% reduction in phase transition time (tF) between the smallest and highest values of K both in the absence and presence of a constant magnetic field. The value of tF is reduced with higher magnetic field strength and the amount of reduction depends upon the sequential velocity parameter. At K = 1.5, the reduction amount with the highest Ha number is 14.7%, while it is 26% at K = 0.5. When nanoparticle is loaded in the base fluid, the value of tF is further reduced. In the absence of a magnetic field, the amount of phase-transition time reduction is 6.9%, while at Ha = 50, it is 11.7%. The phase change process can be controlled with varying magnetic field parameters as well. As the wave number and amplitude of the varying magnetic field are considered, significant changes in the tF are observed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
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    Investigation of phase change dynamics in a T-shaped multiple vented cylindrical cavity during nanofluid convection for PCM-embedded system
    (Emerald Publishing, 2022) Kolsi L.; Selimefendigil F.; Omri M.
    Purpose: The purpose of this study is to explore the phase change (PC) dynamics in a T-shaped ventilated cavity having multiple inlet and outlet ports during nanofluid convection with phase change material (PCM) packed bed-installed system. Design/Methodology/Approach: Finite element method was used to analyze the PC dynamics and phase completion time for encapsulated PCM within a vented cavity during the convection of nanoparticle loaded fluid. The study is performed for different Reynolds number of flow streams (Re1 and Re2 between 300 and 900), temperature difference (ΔT1 and ΔT2 between −5 and 10), aspect ratio of the cavity (between 0.5 and 1.5) and nanoparticle loading (between 0.02% and 0.1%). Findings: It is observed that phase transition can be controlled by assigning different velocities and temperatures at the inlet ports of the T-shaped cavity. The PC becomes fast especially when the Re number and temperature of fluid in the port vary closer to the wall (second port). When the configurations with the lowest and highest Re number of the second port are considered up to 54.7% in reduction of complete phase transition time is obtained, while this amount is 78% when considering the lowest and highest inlet temperatures. The geometric factor which is the aspect ratio has also affected the flow field and PC dynamics. Up to 78% reduction in the phase transition time is obtained at the highest aspect ratio. Further improvements in the performance are achieved by using nanoparticles in the base fluid. The amounts in the phase transition time reduction are 8% and 10.5% at aspect ratio of 0.5 and 1.5 at the highest nanoparticle concentration. Originality/Value: The thermofluid system and offered control mechanism for PC dynamics control can be considered for the design, optimization, further modeling and performance improvements of applications with PCM installed systems. © 2022, Emerald Publishing Limited.
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    Cooling system design for photovoltaic thermal management by using multiple porous deflectors and nanofluid
    (Elsevier Ltd, 2022) Omri M.; Selimefendigil F.; Smaoui H.T.; Kolsi L.
    A novel cooling channel system with multiple porous deflectors (PDs) and nanofluids is proposed for thermal management of photovoltaic (PV) panels. The PDs are elliptic in shape while alumina nanoparticle of cylindrical shape is considered in water which is used as the base cooling medium in the channel. Impacts of Reynolds number (Re: 200-1000), Darcy number (10-6-10-2), PD number (1-5) and aspect ratio of the PDs (0.25-1) on the cooling performance are numerically assessed while nanoparticles are used up to solid volume fraction of 3%. The flow and thermal patterns are strongly influenced by installation of PDs with lower permeability and higher aspect ratio in the cooling channel. The average Nusselt number (Nu) rises by about 56.1% at aspect ratio of 1 when lowest and highest Reynolds number cases are compared while average panel temperature drops become 8.64 °C. When cooling channel with PDs operating at lowest and highest permeability are compared, 37% rise of average Nu and 10 °C temperature drop are obtained at aspect ratio of 1. When nanofluid is used instead of pure fluid as the cooling medium, further performance improvement are achieved which depends upon the aspect ratio of the PDs in the channel. The best cooling performance is achieved when five PDs with aspect ratio of 1 are installed in the channel operating with nanofluid at solid volume fraction of 0.03. This case provides 107.5% higher average Nu and 13.7 °C lower temperature as compared to reference case. The combined utilization of PDs and nanofluid in the cooling channel provides an excellent tool for the thermal management of PV. A modeling approach with modal base is successfully used for impacts of PDs on the cooling performance of coupled cooling channel with conductive panel system. © 2022 The Authors.
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    Performance analysis of thermoelectric generator mounted chaotic channel by using non-Newtonian nanofluid and modeling with efficient computational methods
    (Elsevier B.V., 2022) Selimefendigil F.; Öztop H.F.; Kolsi L.; Omri M.
    Performance features of a thermoelectric system mounted in a chaotic channel with non-Newtonian power law fluid are numerically explored with finite element method. The analysis is performed for different values of Re number of the hot and cold fluid streams (250⩽Re⩽1000), power law indices (0.75⩽n⩽1.25) and solid volume fraction of alumina (0⩽ϕ⩽4%) in water. It is observed that the fluid type with different power law indices significantly affected the electric potential variations and power generation of the thermoelectric system. Impacts of Re number on the power generation enhancement amount depends upon the power law index. The power rises by about 123.78%, 94.13% and 52.30% at the highest Re for different power law index combinations of (0.75,0.75), (0.75,12.5) and (1.25,1.25), respectively. Thermoelectric power reduces by about 39.71% for shear thinning fluids in both channels while it rises by about 43.48% for shear thickening fluids in chaotic channels. The potential of using nanofluids is more when both channels contain shear thinning fluids. Nanofluids rise the power of thermoelectric system by about 31%, 29% and 28% for the case when the hot side fluid is shear thinning, Newtonian and shear thickening fluid types while the cold side chaotic channel is shear thinning. When constant and varying interface temperature configurations are compared, there is at most 3% variations in the generated power while the trends in the curves for varying parameters are similar. The computational cost of constant interface temperature and computations only in the thermoelectric domains are much cheaper as compared to high fidelity coupled computational fluid dynamics simulations. The temperature field in the whole computational domain is approximated by using POD based approach with nine modes. A polynomial type regression model is used for POD-modal coefficients while fast and accurate results for interface temperatures are obtained. © 2021 THE AUTHORS
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    Utilization of wavy porous layer, magnetic field and hybrid nanofluid with slot jet impingement on the cooling performance of conductive panel
    (Emerald Publishing, 2023) Ouni M.; Selimefendigil F.; Hatem B.; Kolsi L.; Omri M.
    Purpose: The purpose of this study is to analyze the impacts of combined utilization of multi-jet impinging cooling of nanofluids with magnetic field and porous layer on the cooling performance, as effective cooling with impinging jets are obtained for various energy systems, including photovoltaic panels, electronic cooling and many other convective heat transfer applications. Design/methodology/approach: Finite element method is used to explore the magnetic field effects with the inclusion of porous layer on the cooling performance efficiency of slot nanojet impingement system. Impacts of pertinent parameters such as Reynolds number (Re between 250 and 1,000), strength of magnetic field (Ha between 0 and 30), permeability of the porous layer (Da between 0.001 and 0.1) on the cooling performance for flat and wavy surface configurations are explored. Findings: It is observed that the average Nusselt number (Nu) rises by about 17% and 20.4% for flat and wavy configuration while temperature drop of 4 K is obtained when Re is increased to 1,000 from 250. By using magnetic field at the highest strength, the average Nu rises by about 29% and 7% for flat and wavy cases. Porous layer permeability is an effective way of controlling the cooling performance while up to 44.5% variations in the average Nu is obtained by varying its value. An optimization routine is used to achieve the highest cooling rate while the optimum parameter set is obtained as (Re, Ha, Da, γ, sx) = (1,000, 30, 0.07558, 86.28, 2.585) for flat surface and (Re, Ha, Da, γ, sx) = (1,000, 30, 0.07558, 71.85, 2.329) for wavy surface configurations. Originality/value: In thermal systems, cooling system design is important for thermal management of various energy systems, including fuel cells, photovoltaic panels, electronic cooling and many others. Impinging jets are considered as effective way of cooling because of its ability to give higher local heat transfer coefficients. This paper offers novel control tools, such as magnetic field, installation of porous layer and hybrid nano-liquid utilization for control of cooling performance with multiple impinging jets. © 2022, Emerald Publishing Limited.
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    MHD hybrid nanofluid convection and phase change process in an L-shaped vented cavity equipped with an inner rotating cylinder and PCM-packed bed system
    (Elsevier B.V., 2023) Ouri H.; Selimefendigil F.; Bouterra M.; Omri M.; Alshammari B.M.; Kolsi L.
    In this study, convective heat transfer and phase change process are analyzed for an L-shaped vented cavity equipped with an inner rotating cylinder and phase change material-packed bed (PCM-PB) system under magnetic field during hybrid nanofluid convection. The numerical work is performed for different values of Reynolds number (Re between 200–1000), rotational Reynolds number (Rew between −1000–1000), size of the cylinder (R between 0.05H-0.15H) and Hartmann number (Ha between 0–40) while hybrid Ag/MgO nanoparticle loading amount in water is 2%. It is observed that the vortex size and their distributions in the cavity and within the PCM-PB system can be controlled by varying rotating cylinder size and rotational speed along with the magnetic field. With higher cylinder size, phase change becomes fast while complete phase transition time (tP) is reduced by about 22% and average Nusselt number (Nu) rises by about 86% at Rew = −1000. Rotational direction of the cylinder is effective for phase transition dynamics while at Rew = −1000, tP rises up to 27% when compared to non-rotating cylinder case. Magnetic field strength is a good parameter for vortex suppression. At the highest strength, phase change becomes fast and average Nu rises up to 26.5% at Rew = −1000. ANFIS based modeling approach is used for impacts of rotating cylinder on the phase change dynamics in the L-shaped vented cavity. © 2022 THE AUTHORS
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    CFD Study of MHD and Elastic Wall Effects on the Nanofluid Convection Inside a Ventilated Cavity Including Perforated Porous Object
    (MDPI, 2023) Kolsi L.; Selimefendigil F.; Omri M.; Rmili H.; Ayadi B.; Maatki C.; Alshammari B.M.
    Cost-effective, lightweight design alternatives for the thermal management of heat transfer equipment are required. In this study, porous plate and perforated-porous plates are used for nanoliquid convection control in a flexible-walled vented cavity system under uniform magnetic field effects. The finite element technique is employed with the arbitrary Lagrangian–Eulerian (ALE) method. The numerical study is performed for different values of Reynolds number ((Formula presented.)), Hartmann number ((Formula presented.)), Cauchy number ((Formula presented.)) and Darcy number ((Formula presented.)). At Re = 600, the average Nusselt number (Nu) is 6.3% higher by using a perforated porous plate in a cavity when compared to a cavity without a plate, and it is 11.2% lower at Re = 1000. At the highest magnetic field strength, increment amounts of Nu are in the range of 25.4–29.6% by considering the usage of plates. An elastic inclined wall provides higher Nu, while thermal performance improvements in the range of 3.6–6% are achieved when varying the elastic modulus of the wall. When using a perforated porous plate and increasing its permeability, 22.8% increments of average Nu are obtained. A vented cavity without a plate and elastic wall provides the highest thermal performance in the absence of a magnetic field, while using a porous plate with an elastic wall results in higher Nu when a magnetic field is used. © 2023 by the authors.
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    Numerical Study of Thermo-Electric Conversion for TEG Mounted Wavy Walled Triangular Vented Cavity Considering Nanofluid with Different-Shaped Nanoparticles
    (MDPI, 2023) Selimefendigil F.; Omri M.; Aich W.; Besbes H.; Ben Khedher N.; Alshammari B.M.; Kolsi L.
    The effects of the combined utilization of wavy wall and different nanoparticle shapes in heat transfer fluid for a thermoelectric generator (TEG) mounted vented cavity are numerically analyzed. A triangular wave form of the cavity is used, while spherical and cylindrical-shaped alumina nanoparticles are used in water up to a loading amount of 0.03 as solid volume fraction. The impacts of wave amplitude on flow and output power features are significant compared to those of the wave number. The increment in the generated power is in the range of 74.48–92.4% when the wave amplitude is varied. The nanoparticle shape and loading amount are effective in the rise of the TEG power, while by using cylindrical-shaped nanoparticles, higher powers are produced as compared to spherical ones. The rise in the TEG power by the highest loading amount is achieved as 50.7% with cylindrical-shaped particles, while it is only 4% with spherical-shaped ones. Up to a 194% rise of TEG power is attained by using the triangular wavy form of the wall and including cylindrical-shaped nanoparticles as compared to a flat-walled cavity using only pure fluid. © 2023 by the authors.
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    Analysis of MHD nanofluid forced convection and phase change process in a PCM mounted corrugated and partly elastic partitioned channel system with area expansion
    (Elsevier B.V., 2024) Omri M.; Selimefendigil F.; Besbes H.; Ladhar L.; Alshammari B.M.; Kolsi L.
    In this study, effects of using wall corrugation and nano-enhanced magnetic field in a channel with area expansion and elastic interface on the phase change and thermal process are examined by using finite element method with ALE (Arbitrary Lagrangian-Eulerian). A range of values for the relevant parameters are included in the simulations: the flow Reynolds number (Re) between 100 and 1000; the elasticity of the flexible partition (E between 105 and 109); the Hartmann number (Ha) between 0 and 60; the amplitude of the wavy wall (A between 0.01 and 0.35); and the wave number of corrugation (N between 2 and 20). Complete phase transition (tF) with Re shows non-monotonic behavior while variations of tF up to 57 % and 50 % are obtained for the upper and lower PCM under wavy wall with varying Re. For upper PCM, the variation of tF with elastic modulus becomes 21 %-25 %. When E is changed, the average Nu increment with a corrugated wall is 11 %. When the magnetic field is applied with maximal strength, thermal performance is enhanced and the phase transition process is accelerated. For the upper and lower PCM zones, reduction of tF with Ha yields 44 % and 33 %, respectively. For the upper and lower PCM zones, the full transition time decreases with higher corrugation amplitudes by 14.7 % and 12.5 %, respectively. Average Nu increments of 10 % and 7.5 % are found by raising the corrugation amplitude and wave number to their maximum values. A significant reduction of tF, around 54 %, is obtained with the introduction of wavy walls with magnetic field and nanofluid when compared to the reference case (flat channel using base fluid and without magnetic field effects). Although the upper wall's corrugation further enhances thermal performance, magnetic field has a bigger impact on thermal performance than wavy shape. © 2024 The Authors