Browsing by Publisher "Taiwan Institute of Chemical Engineers"

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    MHD mixed convection of nanofluid filled partially heated triangular enclosure with a rotating adiabatic cylinder
    (Taiwan Institute of Chemical Engineers, 2014) Selimefendigil F.; Öztop H.F.
    MHD mixed convection of Cu-water nanofluid filled triangular enclosure with a rotating cylinder is investigated numerically. A partial heater is added on the left vertical wall of the cavity and the right inclined wall is kept at constant temperature. Other walls of the triangular cavity and cylinder surface are assumed to be adiabatic. The governing equations are solved using the finite element method. The effects of the Grashof number, Hartmann number, angular rotational speed of the cylinder and volume fraction of the nanoparticle on fluid flow and heat transfer are investigated numerically. The second law of thermodynamics is also applied to the flow and heat transfer corresponding to different combinations of parameters. It is observed that with increasing the Hartmann number the total entropy generation, local and averaged heat transfer decrease. Averaged Nusselt number increases with the Grashof number. Averaged heat transfer and total entropy generation increase with increase in the angular rotational speed of the cylinder. 50.4% and 37.4% of heat transfer enhancements are obtained for ω= 20 and ω= -20 compared to motionless cylinder ω= 0. Heat transfer and total entropy generation increase as the solid volume fraction of nanoparticle increases. © 2014 Taiwan Institute of Chemical Engineers.
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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
    (Taiwan Institute of Chemical Engineers, 2015) Selimefendigil F.; Öztop H.F.
    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 (104 ≤ RaE ≤ 106), internal Rayleigh number (104 ≤ RaI ≤ 106), Hartmann number (0 ≤ Ha ≤ 50), and solid volume fraction of the nanofluid (0 ≤ ϕ ≤ 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 ReE. 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 RaI = 106. 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. © 2015 Taiwan Institute of Chemical Engineers.
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    Mixed convection of nanofluid filled cavity with oscillating lid under the influence of an inclined magnetic field
    (Taiwan Institute of Chemical Engineers, 2016) Selimefendigil F.; Öztop H.F.
    In this study, mixed convection of an oscillating lid-driven cavity filled with nanofluid under the influence of an inclined uniform magnetic field was numerically investigated. The cavity is heated from below and cooled from above while side walls are assumed to be adiabatic. The top wall velocity varies sinusoidally while no-slip boundary conditions are imposed on the other walls of the cavity. The governing equations was solved by Galerkin weighted residual finite element formulation. The numerical investigation was performed for a range of parameters: Richardson number (10-1≤Ri≤102), Hartmann number (0 ≤ Ha ≤ 60), inclination angle of the magnetic field (0 ≤ γ ≤ 90°), non-dimensional frequency of the oscillating lid (0.001 ≤ St ≤ 1) and solid volume fraction of the nanoparticle (0 ≤ φ ≤ 0.04). It is observed that the flow and thermal patterns within the cavity are affected by the variation of these parameters. The heat transfer process becomes inefficient for high Strouhal number, high Hartmann number and high Richardson number. Maximum enhancement of averaged heat transfer and the damping of the convection within the cavity due to the Lorentz forces caused by magnetic field are attained for magnetic inclination angles of γ=90{ring operator} and γ=60{ring operator}. As the solid volume fraction of nanoparticles increases averaged heat transfer enhancement of 28.96% is obtained for volume fraction of φ=0.04 compared to base fluid. © 2016 Taiwan Institute of Chemical Engineers.
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    Mixed convection in a partially heated triangular cavity filled with nanofluid having a partially flexible wall and internal heat generation
    (Taiwan Institute of Chemical Engineers, 2017) Selimefendigil F.; Öztop H.F.
    Numerical study of mixed convection in a partially heated nanofluid-filled lid driven cavity with internal heat generation and having a partial flexible wall was performed. The bottom wall of the triangular enclosure is moving with constant speed and left vertical wall is partially heated. The inclined wall of the cavity is cooled and partially flexible. The governing equations are solved with Galerkin weighted residual finite element method. The effects of Richardson number (between 0.05 and 50), internal Rayleigh number (between 104 and 108), size and elastic modulus of the partial flexible wall and nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and heat transfer were numerically investigated. It was observed that the local and averaged heat transfer reduce as the value of the Richardson number and internal Rayleigh number increase. As the value of the elastic modulus of the inclined wall and nanoparticle volume fraction increase, local and average heat transfer enhance. The discrepancy between the averaged Nusselt number increase for different sizes for the lower values of elastic modulus of the flexible wall. When heat transfer process is effective adding nanoparticles to the base fluid is advantageous. © 2016 Taiwan Institute of Chemical Engineers
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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
    (Taiwan Institute of Chemical Engineers, 2021) Selimefendigil F.; Öztop H.F.
    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≤5×10−2), radius (0≤pr≤hr) and height (0.2hz≤pz≤0.8hz) 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 × 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. © 2021 Taiwan Institute of Chemical Engineers
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    Impacts of elasticity and porosity of the channels on the performance features of thermoelectric module mounted system and efficient computations with multi-proper orthogonal decomposition approach
    (Taiwan Institute of Chemical Engineers, 2021) Selimefendigil F.; Öztop H.F.; Doranehgard M.H.
    Effects of wall elasticity and porosity of the channel on the performance characteristics of TEG module integrated system are explored numerically with finite element method. A porous layer in the lower channel is introduced with hybrid nanoparticles in the fluid. Effects of different values of elastic modulus of the top and bottom channel walls (5×103≤E1, E2 ≤ 1010), Darcy number (5×10−4 ≤ Da ≤ 5×10−1), porous layer height (0.2H ≤ py ≤ 0.8H) and length in flow direction (0.25L ≤ px ≤ 0.85L), Reynolds number (200 ≤ Re ≤ 1000) and hybrid nanoparticle volume fraction (0 ≤ϕ≤ 2%) on the convection and power generation are analyzed. The presence of elastic walls may affect the flow field in local regions but the overall impact on the power variation is slight while 2.8% variation is obtained. The presence of the porous layer altered the power generation features while increasing the permeability and height of the porous layer resulted in higher thermoelectric power generation. The increment amounts are 32% for the highest permeability and 17% for the highest porous layer height. The length of porous layer in the flow direction has slight impact on power generation features while introducing nano-sized particles further enhanced the power by about 15% at the highest ϕ. The computational cost of generated power is drastically reduced from 2.5 h for full coupled model to two minutes by using a multi-POD approach. © 2021 Taiwan Institute of Chemical Engineers
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    Modeling and identification of combined effects of pulsating inlet temperature and use of hybrid nanofluid on the forced convection in phase change material filled cylinder
    (Taiwan Institute of Chemical Engineers, 2021) Selimefendigil F.; Öztop H.F.
    Effects of pulsating heat transfer fluid temperature and hybrid nano-additive inclusion in the base fluid are numerically studied for laminar forced convection through a phase change material embedded thermo-fluid system with finite element method. Effects of different values of Reynolds number (between 250 and 1000), amplitude (between 0 and 0.05) and frequency (Strouhal number between 0.01 and 0.5) of pulsating inlet temperature, nanoparticle volume fraction of hybrid particles (between 0 and 0.02) on the dynamic features of the system with performance characteristics are analyzed. It is observed that the phase change material onset temperature becomes oscillating with drastically reduction of full completion time as the Reynolds number and amplitude of pulsation are increased. The amount of reduction in the full phase transition is 63% when cases at Re=100 to Re=400 are compared. When lowest and highest amplitude configurations are compared, 62% reduction in the complete phase transition time is observed while the impact of frequency is marginal at higher frequencies. When the hybrid nanoparticles are introduced in the base fluid, transition time and dynamic features of onset temperatures are affected. Successful results that capture the dynamic behavior of the phase change embedded thermal system is achieved with a nonlinear dynamic system modeling approach. © 2021 Taiwan Institute of Chemical Engineers
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    Effects of cooler shape and position on solidification of phase change material in a cavity
    (Taiwan Institute of Chemical Engineers, 2024) Öztop H.F.; Kiyak B.; Biswas N.; Selimefendigil F.; Coşanay H.
    Background: For balancing the imbalance between the energy supply and demand, phase-change materials (PCMs) provide an efficient means in terms of thermal energy storage and release. The performance of the energy storage is primarily dependent on the melting as well as the solidification process of the storage medium. Faster charging or discharging of the thermal energy is a primary concern for any thermal energy storage unit. On this background, the present study explores the novel approach for enhancing the solidification process of PCM considering the effects of cooler shape (namely semi-circular, triangular, and rectangular) and their position (namely top, side, and bottom) in a molten PCM-filled enclosure. The middle portion of the cooler wall is curved; whereas the remaining cooler wall is straight maintaining the same cooler wall length. Methods: To analyze the solidification process, the involved transport equations are solved numerically following a finite volume-based computational approach using Ansys Fluent solver in conjunction with the appropriate boundary conditions. The computational model is generated for all the geometry comprising different shapes, as well as positions of the cooler wall. The third-order upwind scheme (QUICK) technique is utilized to discretize the momentum and energy equations. This scheme is well capable to accurately capture the gradients in the temperature and flow domains. Furthermore, the semi-implicit pressure-linked equation (SIMPLE) technique is utilised to address the pressure-velocity coupling. The resolved data are then saved as selective variables (U, V, and θ), which undergo post-processing to produce a local thermo-fluid flow field and extract average data. Significant findings: The shape, as well as the position of a cooler, dictates the solidification process in an energy storage system. Thermal energy storage with a triangular-shaped cold wall positioned at the top could be opted as an appropriate design approach of an efficient energy storage system compared to a semi-circular or rectangular-shaped cooler model. The shortest solidification time of PCM occurs when the cooler wall is positioned at the top. The top position of the cooler having a triangular shape with higher Grashof number (Gr) values leads to a faster solidification process. Some ideas for possible future research areas in this field are provided after a comprehensive examination. © 2024 Taiwan Institute of Chemical Engineers