Browsing by Author "Kolsi, L"

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    Cooling system design for photovoltaic thermal management by using multiple porous deflectors and nanofluid
    Omri, M; Selimefendigil, F; Smaoui, HT; 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 degrees C. When cooling channel with PDs operating at lowest and highest permeability are compared, 37% rise of average Nu and 10 degrees 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 degrees 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.
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    Hybrid Nano-Jet Impingement Cooling of Double Rotating Cylinders Immersed in Porous Medium
    Selimefendigil, F; Hamzaoui, M; Aydi, A; Alshammari, BM; Kolsi, L
    A cooling system with impinging jets is used extensively in diverse engineering applications, such as solar panels, electronic equipments, battery thermal management, textiles and drying applications. Over the years many methods have been offered to increase the effectiveness of the cooling system design by different techniques. In one of the available methods, nano-jets are used to achieve a higher local and average heat transfer coefficient. In this study, convective cooling of double rotating cylinders embedded in a porous medium is analyzed by using hybrid nano-jets. A finite element formulation of the thermo-fluid system is considered, while impacts of Reynolds number, rotational speed of the double cylinders, permeability of the porous medium and distance between the cylinders on the cooling performance are numerically assessed. Hybrid and pure fluid performances in the jet cooling system are compared. It is observed that the cooling performance improves when the rotating speed of the cylinder, permeability of the medium and jet Reynolds number are increased. The heat transfer behavior when varying the distance between the cylinders is different for the first and second cylinder. Higher thermal performances are achieved when hybrid nanofluid with higher nanoparticle loading is used. An optimization algorithm is used for finding the optimum distance and rotational speeds of the cylinders for obtaining an improved cooling performance, while results show higher effectiveness as compared to a parametric study. The outcomes of the present work are useful for the thermal design and optimization of the cooling system design for configurations encountered in electronic cooling, energy extraction and waste heat recovery.
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    Numerical Study of Thermo-Electric Conversion for TEG Mounted Wavy Walled Triangular Vented Cavity Considering Nanofluid with Different-Shaped Nanoparticles
    Selimefendigil, F; Omri, M; Aich, W; Besbes, H; Ben Khedher, N; Alshammari, BM; 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.
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    Control of Magnetohydrodynamic Mixed Convection and Entropy Generation in a Porous Cavity by Using Double Rotating Cylinders and Curved Partition
    Hassen, W; Selimefendigil, F; Ben Khedher, N; Kolsi, L; Borjini, MN; Alresheedi, F
    In this work, mixed convection and entropy generation analyses in a partitioned porous cavity with double inner rotating cylinders are explored under magnetic field effects. A curved partition shape is considered with identical rotating cylinders and an inclined magnetic field, while the right vertical wall moves with a constant speed in the y-direction. Numerical simulations are performed by considering various values of Rayleigh number, Hartman number, Darcy number, inclination of the magnetic field, size of the curved partitions, and rotational speeds of the inner cylinders and their vertical locations with the cavity. Complicated flow field with multicellular structures are observed due to the complex interaction between the natural convection, moving wall, and rotational effects of inner cylinders. Improved heat-transfer performance is obtained with higher values of magnetic field inclination, higher values of permeability/porosity of the medium, and higher rotational speeds of the cylinders. Almost doubling of the average Nu number is obtained by decreasing the value of the Hartmann number from 25 to 0 or varying the magnetic field inclination from 90 to 0. When rotational effects of the cylinders are considered, average heat-transfer improvements by a factor of 5 and 5.9 are obtained for nondimensional rotational speeds of 5 and -5 in comparison with the case of motionless cylinders. An optimum length of the porous layer is achieved for which the best heat-transfer performance is achieved. As the curvature size of the partition is increased, better heat transfer of the hot wall is obtained and up to 138% enhancement is achieved. Significant increments of entropy generation are observed for left and right domains including the rotating cylinders. The magnetic field parameter also affects the entropy generation and contributions of different domains including the curved porous partition.
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    Effects of magnetic field, binary particle loading and rotational conic surface on phase change process in a PCM filled cylinder
    Ghachem, K; Selimefendigil, F; Öztop, HF; Almeshaal, M; Alhadri, M; Kolsi, L
    In the present work, coupled effects of forced convection, rotational conic surface and magnetic field on the phase change dynamics are numerically explored by using finite element method for a phase change material (PCM) filled 3D cylindrical reactor. The PCM filled region has a conic shape and it is rotating. The study is conducted for various values of rotational Re number (between 0 and 2500), magnetic field strength (Hartmann number between 0 and 30) and conic surface aspect ratio (between 1 and 2). It is observed that the coupled interactions between the rotational surface and magnetic field significantly affect the phase change process dynamics and convective heat transfer between different phases. Optimum value of rotational Reynolds number for minimum complete phase transition time is achieved at Rew = 1000. The magnetic field has a positive impact on the phase change process while it is impact is profound without surface rotation. There are 98% and 65% reductions in the complete phase transition times when configurations at Rew = 1000 are compared with motionless conic surface case in the absence and presence of magnetic field. The effects of rotation are profound when different aspect ratios of the PCM filled region is considered. The transition time is increased up to 553% without rotation while this value is only 86% when cases with lowest and highest aspect ratio are compared. A modal analysis with 30 mode is used to capture the phase change dynamics and coupled interactions between the rotational surface and magnetic field on the variation of liquid fraction.
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    Enhancing the performance of a greenhouse drying system by using triple-flow solar air collector with nano-enhanced absorber coating
    Selimefendigil, F; Sirin, C; Ghachem, K; Kolsi, L; Alqahtani, T; Algarni, S
    In this research, the impacts of utilizing nano-embedded absorber coating in an auxiliary heater of a greenhouse drying system on the thermal and drying performances have been surveyed empirically. In this context, triple-flow solar air collectors with and without CuO nano-enhanced absorber coating have been designed and manufactured. Designed collectors then integrated to even-span greenhouse dryers to be used as an auxiliary heating device. In the experiments, greenhouse dryers have been tested with and without auxiliary heaters at constant flow rate which is 0.014 kg s(-1). According to the experimental findings, utilizing triple-flow solar air heating device with and without nano-embedded paint decreased the drying time as 35.71% and 26.66%, respectively. Thermal and exergetic efficiencies for newly developed collectors were found between the range of 70.39-75.11% and 9.05-10.18%, respectively. In addition, specific energy consumption values were decreased by using collectors with and without nano-enhanced modification from 2.51 to 2.11 and from 2.61 to 2.18 kWh/kg, respectively. Attained outcomes of this study showed the successful utilization of nano-enhanced absorber coating in the auxiliary heating system of the greenhouse dryer.
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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
    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, gamma, sx) = (1,000, 30, 0.07558, 86.28, 2.585) for flat surface and (Re, Ha, Da, gamma, 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.
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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
    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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    Performance Optimization of a Thermoelectric Device by Using a Shear Thinning Nanofluid and Rotating Cylinder in a Cavity with Ventilation Ports
    Ben Khedher, N; Selimefendigil, F; Kolsi, L; Aich, W; Ben Said, L; Boukholda, I
    The combined effects of using a rotating cylinder and shear thinning nanofluid on the performance improvements of a thermoelectric generator (TEG)-installed cavity with multiple ventilation ports are numerically assessed. An optimization algorithm is used to find the best location, rotational speed and size of the cylinder to deliver the highest power generation of the TEG. The power generation features with varying Rew are different for the first nanofluid (NF1) when compared to the second one (NF2). The power rises with higher Rew when NF1 is used, and up to 49% enhancement is obtained. The output power variation between nanofluids NF1 and NF2 is the highest at Rew = 0, which is obtained as 68.5%. When the cylinder location is varied, the change in the output power becomes 61% when NF2 is used. The optimum case has 11.5%- and 161%-higher generated power when compared with the no-object case with NF1 and NF2. The computational effort of using the high-fidelity coupled system is reduced when optimization is considered.
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    Single-channel cooling system design by using perforated porous insert and modeling with POD for double conductive panel
    Selimefendigil, F; Benabdallah, F; Ghachem, K; Albalawi, H; Alshammari, BM; Kolsi, L
    In this study, a single cooling channel system is suggested for conductive double panel systems. The cooling channel for the vertical component uses perforated porous insert (PP-I) and porous insert (P-I), while cylinders are used in the PP-I case. The permeability of the porous channel (Da between 1 0 - 5 1{0}<^>{-5} and 1 0 - 1 1{0}<^>{-1} ), size of the cylinders (Rc between 0 and 0.25), and location of the PP plate (Yp between 1 and 4.5) are all taken into account when calculating the effectiveness of the cooling system using finite element method. It is found that PP-I can effectively control the vortex size and enhance cooling performance, particularly for vertical plate. Nusselt number is enhanced in the absence of cylinders in the vertical channel by 92% as contrasted to 51% in the presence of cylinders. When cylinders are used for the vertical channel, the temperature drop of 1 3 degrees C 1{3}<^>{<^>\circ }{\rm{C}} is computed. The flow field noticeably changes when the permeability of the P-I and PP-I is altered. The equivalent temperature increases for P-I and PP-I with setups at Da = 1 0 - 5 {\rm{Da}}=1{0}<^>{-5} and Da = 1 0 - 2 {\rm{Da}}=1{0}<^>{-2} are 7.7 degrees C {\text{7.7}}<^>{<^>\circ }{\rm{C}} and 4.4 degrees C {\text{4.4}}<^>{<^>\circ }{\rm{C}} , respectively. The performance of cooling for the vertical plate is influenced favorably by the higher values of the porous plate's vertical placement. By moving the porous object, it is possible to reduce the temperature by 8 degrees C {8}<^>{<^>\circ }{\rm{C}} . For panel surface temperature, a proper orthogonal decomposition (POD)-based reconstruction model with 12 POD modes is used. The POD-based model accurately captures the effects of utilizing P-I and PP-I on the panel temperature.
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    Multiple slot nano-jet impingement cooling of a sinusoidal hot surface by using active rotating cylinders under magnetic field
    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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    Performance analysis of thermoelectric generator mounted chaotic channel by using non-Newtonian nanofluid and modeling with efficient computational methods
    Selimefendigil, F; Öztop, HF; 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 <= phi <= 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. (C) 2021 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University.
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    Impacts of rotating surface and area expansion during nanofluid convection on phase change dynamics for PCM packed bed installed cylinder
    Ghachem, K; Selimefendigil, F; Öztop, HF; Alhadri, M; Kolsi, L; Alshammari, N
    Phase change dynamics under the rotational surface effects, area expansion and nanoparticle loading in the base fluid are explored for forced convective flow of hybrid nanofluid in a phase change packed bed installed cylindrical reactor. The study is performed with finite element method for different parameters of rotational Reynolds number, fluid stream Reynolds number and concentration of nanoparticle. The hybrid nanofluid properties are based on experimental data for binary particle of Al2O3-TiO2 in 40% ethylene-glycol. Complete phase transition time is estimated with ANFIS based model. The recirculation zone due to the area expansion within the phase change installed region is controlled by the complex interactions between the forced flow, rotation of the surface and nanoparticle amount. Higher values of Reynolds number and nanoparticle concentration result in fast phase change process at rotational Reynolds number of 0 while the effects become reverse in the presence of rotations. Complete phase transition time reduces by about 49% and 10.5% at the highest Reynolds number and at the highest concentration in the absence of rotation while it is increased by about 88% and 6.5% when rotational effects are considered at the highest rotational speed. When only rotational effects are considered, phase change process completion time reduces by about 60% at the highest speed. (C) 2021 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University.
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    Effects of using sinusoidal porous object (SPO) and perforated porous object (PPO) on the cooling performance of nano-enhanced multiple slot jet impingement for a conductive panel system
    Selimefendigil, F; Benabdallah, F; Ghachem, K; Albalawi, H; Alshammari, BM; Kolsi, L
    Cooling system design for thermal management of electronic equipment, batteries and photovoltaic (PV) modules is important for increasing the efficiency, safety operation, and long life span the products. In the present study, two different cooling systems are proposed with nano-enhanced multiple impinging jets for a conductive panel. The present cooling systems can be used in electronic cooling and PV modules. Perforated porous object (PPO) and sinusoidal porous object (SPO) are used in the jet cooling system. 2D numerical analysis using finite volume method is conducted considering different values of permeability of the objects (Darcy number ( Da ) between 10-6 and 10-1 ). When PPO is used in the cooling system, number of cylinders (between 1 and 6), and size of the cylinders (between 0.015 and 0.075) are considered. In the case of using SPO, amplitude (between 0.1 and 2) and wave number (between 1 and 12) are varied. Alumina-water nanofluid with cylindrical shaped nanoparticles is used as the heat transfer fluid. When permeability is changed for PPO, the average temperature increases by roughly 3.89 degrees C for a single cylinder and drops by roughly 0.57 degrees C for a sixcylinder cases. Increasing the size of the cylinder in the PPO case at highest permeability results in temperature drop of 5.3 degrees C. When changing the number of cylinders, cooling rate varies by about 3.6%. Wave number of SPO is more influential on the cooling performance enhancement as compared to amplitude and permeability of the SPO. The average surface temperature drops by 12.4 degrees C when the wave number is increased to 12. As compared to reference case of jet impingement cooling without porous object, using PPO and SPO along with the nanofluid result in temperature drop of 12.3 degrees C and 14.4 degrees C. (c) 2024 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).
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    Investigation of phase change dynamics in a T-shaped multiple vented cylindrical cavity during nanofluid convection for PCM-embedded system
    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 (Re-1 and Re-2 between 300 and 900), temperature difference (Delta T-1 and Delta T-2 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.
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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
    Ouri, H; Selimefendigil, F; Bouterra, M; Omri, M; Alshammari, BM; 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 Rey-nolds number (Rew between-1000-1000), size of the cylinder (R between 0.05H-0.15H) and Hart-mann 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 tran-sition 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. (c) 2022 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
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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
    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.
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    Exergy and environmental analysis of an active greenhouse dryer with Al2O3 nano-embedded latent heat thermal storage system: An experimental study
    Selimefendigil, F; Sirin, C; Ghachem, K; Kolsi, L
    In this study, influences of integrating nanoparticles into paraffin-based latent heat thermal energy storage system on the thermal and drying behaviors of a greenhouse dryer have been analyzed. The major goal of this survey is improving the drying performance of a greenhouse dryer by employing nano-embedded latent heat storage unit. In this regard, two even-span greenhouse dryers have been produced and modified with paraffinbased and Al2O3 nano-embedded paraffin-based thermal energy storage units. Tests have been conducted at two flow rates that are 0.010 kg/s and 0.016 kg/s. According to the findings, average specific moisture extraction rates for the systems with and without nanoparticles were attained between 1.01 and 1.37 and 0.83-1.20 kg/ kWh, respectively. Average exergy efficiency metrics were found as 3.45% and 2.74%, respectively in the test done at 0.016 kg/s flow rate for the greenhouse dryers with and without nanoparticles. These values were found as 3.01% and 2.40%, respectively in the test conducted at 0.010 kg/s. In addition, energy payback time, mean annual CO2 emission and net CO2 mitigation in lifetime values were obtained between 2.34 and 2.92 years, 33.04-34.28 kg/year and 8.45-9.08 tons, respectively. Results indicated the successful utilization of Al2O3 nanoparticle-embedded latent heat storage unit in a greenhouse dryer.
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    Ternary nanofluid cooling of an elastic plate by using double sinusoidal wavy channels under different magnetic fields
    Selimefendigil, F; Hadrich, B; Kriaa, K; Maatki, C; Kolsi, L
    A novel cooling system for a hot elastic plate is considered by combined utilization of magnetic field, wavy channels and ternary nanofluid. Some applications can be found in electronic cooling, material processing and convective heat transfer control. The elastic object is placed between sinusoidal wavy channels where magnetic field of different strengths is imposed. Ternary nanofluid is used as cooling medium in both channels. Cooling performance assessment is made by various values of Reynolds number (Re, between 250 and 1000), Hartmann number of different channels (Ha, between 0 and 15), amplitude (A, between 0.05 and 0.3) and wave number (N, between 1 and 4) of corrugation, and nanoparticle loading (svf between 0 and 0.03). Entropy generation analysis is also considered. Thermal performance enhancement factor for the maximum and lowest Re configurations in the rigid and elastic object cases are 1.70 and 1.65, respectively. The amount of cooling performance improvement generated by imposing magnetic field at the highest strength is 58.5% and 80% with rigid and elastic objects, respectively. The cooling performance is improved by the wavy form amplitude; however, the wave number relation is non-monotonic. When comparing the wavy channel with the flat one, the increments of thermal performance for stiff and elastic plates are 52% and 57%. Using elastic and stiff objects with nanofluid results in increases in cooling performance of 47.2% and 55.5% when compared to the use of base fluid alone. The best thermal performance is always provided by a rigid item with wavy channels. The least amount of cooling is achieved by using an elastic plate and flat channel. The best options are to increase the magnetic field strength and amplitude of the wavy channel as thermal performance improves and entropy generation drops.
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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
    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 & LE;Re & LE;500), rotational Reynolds numbers (100 & LE;Rew & LE;500), size of the ports (0.1L1 & LE;di & LE;0.5L1), length of the PC-PB system (0.4L1 & LE;L0 & LE;L1), and location of the PC-PB (0 & LE;yp & LE;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.