Browsing by Subject "Element method"
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Item Effects of flow separation and shape factor of nanoparticles in heat transfer fluid for convection thorough phase change material (PCM) installed cylinder for energy technology applications(Elsevier Ltd, 2021) Selimefendigil F.; Öztop H.F.In this study, flow separation effects on the performance of PCM embedded thermo-fluid system is numerically analyzed by using the finite element method. In the heat transfer fluid, shape effects of nanoparticles are considered. Spherical, blade, brick and cylindrical shaped alumina nanoparticles are used in water. The numerical work is performed for different values of Reynolds number (between 100 and 300), expansion ratio of the channel (0.35 and 1), nanoparticle volume fraction (between 0 and 2%) and different shape of particles. The PCM material is paraffin wax with spherical shaped capsules of 20 mm in diameter. There is significant impact of channel expansion and flow separation zone on the performance of the system. When the area expansion is introduced in the straight channel, the configuration with the highest Reynolds number resulted in performance degradation due to flow recirculation extended in the PCM region. The charging time for a straight channel is reduced by about 84% when comparison is made with the channel having an expansion ratio of 0.35. The shape factor of the alumina nanoparticles significantly affects the flow recirculations and thermal exchange between the PCM and heat transfer fluid. Among various particles, cylindrical shaped one performs best while 23.8% reduction in charging time is obtained at the highest solid volume fraction when comparison is made with pure water as heat transfer fluid. © 2021 Elsevier LtdItem Analysis of hybrid nanofluid and surface corrugation in the laminar convective flow through an encapsulated PCM filled vertical cylinder and POD-based modeling(Elsevier Ltd, 2021) Selimefendigil F.; Öztop H.F.In the present work, performance assessment of a PCM filled three dimensional vertical cylinder is conducted under the combined effects of surface corrugation and presence of binary nanoparticles in the heat transfer fluid. The numerical simulation is performed by using finite element method with varying values of Reynolds number (100≤Re≤750), number (1≤N≤8) and height (H/10≤h≤H/2) of rectangular type corrugation form and volume fraction of particles (0≤ϕ≤0.02) in unsteady configuration. Thermal transport features are enhanced while charging time is reduced for higher values of Reynolds number, solid volume fraction of the binary mixture in the heat transfer fluid. Complete charging time is reduced by 57% with increase of Reynolds number from 100 to 750 while it is reduced by 23% when nanofluid at the highest solid volume fraction is used instead of water. However, the corrugation parameters have reverse effects on the charging process. A computational framework for reconstruction of heat transfer fluid and PCM temperatures for the unsteady parametric configuration in the computational domain is offered by utilizing proper orthogonal decomposition (POD) technique with 25 modes for heat transfer fluid and 75 modes for PCM. © 2021 Elsevier LtdItem Phase change dynamics in a cylinder containing hybrid nanofluid and phase change material subjected to a rotating inner disk(Elsevier Ltd, 2021) Selimefendigil F.; Öztop H.F.; Doranehgard M.H.; Karimi N.In this numerical study, the phase change dynamics of a 3D cylinder containing hybrid nanofluid and phase change material (PCM) is investigated with a finite element solver. The PCM consists of spherical encapsulated paraffin wax, and the flow is under the forced convection regime. The dynamic features of the phase change process are studied for different values of the Reynolds number (between Re=100 and 300), the rotational Reynolds number of the inner disk (Rew=0 and 300), and the size of the rotating disk (length between 0.1L and 0.55L; height between 0.001H2 and 0.4H2). The flow dynamics and separated flow regions are found to be greatly influenced by the rotational speed and size of the inner disk. As Re is increased, the difference between the transition times at different rotational disk speeds decreases. At Re=100, a 21% reduction in the phase transition time is observed when the inner disk rotates at the highest speed as compared to the motionless case. Up to a 26% variation in the phase transition time occurs when the size of the inner rotating disk is varied. A 5 input-1 output feed-forward artificial neural network is applied to achieve fast and reliable predictions of the phase change dynamics. This study shows that introducing rotational effects can have a profound effect on the phase change dynamics of a hybrid nanofluid system containing phase change material. © 2021Item Thermoelectric generation in bifurcating channels and efficient modeling by using hybrid CFD and artificial neural networks(Elsevier Ltd, 2021) Selimefendigil F.; Öztop H.F.Thermoelectric power generation within TEG mounted branching channels is considered with finite element method. In the heat transfer fluid of bifurcating channels, nanodiamond + Fe3O4 binary particles are used for further system performance improvement. It was observed that when compared to non-bifurcating channels, TEG power will be reduced with the use of branching channels while branching location also affects the interface temperature variations. At (Re1, Re2)=(1000, 200), TEG power is reduced 34.7% when both channels are branching while it is 9.9% for only upper channel branching case as compared to non-branching channel case. Up to 18% variation of power is obtained when location of the upper branching channel varies. Highest powers are achieved when both channels are filled with hybrid nanofluid while at (Re1,Re2)=(1000,200) TEG power rises by about 33% and 15.5% with nanofluid in both channels and with nanofluid in only one channel cases when compared to fluid in both channel configuration. The computational cost of electric potential and power generation in TEG device is drastically reduced from 6 hours with fully coupled high fidelity CFD to 3 minutes by using hybrid CFD and artificial neural networks. The proposed approach will very helpful in the efficient design and optimization of TEG installed renewable energy systems. © 2021 Elsevier LtdItem 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