Browsing by Subject "Pressure coefficients"
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Item Impacts of double rotating cylinders on the forced convection of hybrid nanofluid in a bifurcating channel with partly porous layers(Elsevier Ltd, 2021) Kolsi L.; Selimefendigil F.; Öztop H.F.; Hassen W.; Aich W.Impacts of using double rotating cylinders and partly porous layers in the bifurcating channels on the hydro-thermal performance were numerically assessed. Hybrid nanoparticles were used in water and finite element method was selected as the solver. Effects of Reynolds number, rotational speeds of the cylinders and their locations in the bifurcating channels, porous layer sizes and nanoparticle solid volume fractions on the hydro-thermal performance features were explored. The contribution of different hot wall parts was changed with varying Reynolds number and rotational velocity of the cylinders. Depending upon the rotational direction of the cylinders, the vortex occurrence and size at the bifurcations change significantly. Heat transfer considering all hot walls rise with higher rotational speeds in both directions. The amount of improvement in the heat transfer rate becomes 25% and 19% with varying speeds of the cylinders as compared to motionless cylinders. The pressure coefficient reduces with increasing the second cylinder speed in clockwise direction and this is favorable for thermal performance since the heat transfer also increases. The overall impact of the varying horizontal locations of the cylinders on the heat transfer rate is slight. The separated zones at the branching depends on the porous layer sizes. The overall heat transfer behavior becomes opposite when varying the sizes of the porous layers in the horizontal and vertical channels. By using nanoparticles in the base fluid, 35.75% improvement in the heat transfer rate is achieved for vertical wall at Re = 350 while pressure drop coefficient rises by about 8.5%. The overall improvement in the heat transfer rate by using nanofluid is 26%. Owing to diverse use of bifurcating channels in thermal engineering from fuel cells to electronic cooling, the proposed methods of heat transfer enhancement techniques can be considered simultaneously for effective control the thermal performance of those systems. © 2021 The Author(s).Item Performance of TEG integrated channel with area expansion by using advanced passive techniques(Elsevier Ltd, 2021) Selimefendigil F.; Öztop H.F.In this study, flow separation effects on the power generation and conversion efficiency of a thermoelectric generator integrated channel flow with area expansion are numerically studied. Impacts of using an eccentric conic object near the thermoelectric device on the performance enhancement of the system are explored with numerical simulation using finite element method. Hybrid nano sized particles are also included in the heat transfer fluid to improve thermal transport features of the base fluid. Impacts of Reynolds number (between 200 and 1000), expansion ratio of the channel (between 0.25 and 0.6), aspect ratio (between 0.1 and 1.5), location (between -1 and 5) and size (between 0.05 and 0.25) of the eccentric cone and solid nanoparticle volume fraction (between 0 and 0.02) on the fluid flow and generated power characteristic are numerically studied. It is observed that the vortex behind the step extends over the thermoelectric device surface at the highest Reynolds number while vortcies are also established behind the eccentric cone. When the expansion ratio is increased, thermo electric device power reduction is observed while the amounts are 34% and17.8% for cases at R1=0.25 with Reynolds number of 200 and 1000 as compared to upper channel with R1=0.6. The conversion efficiency also rises with higher expansion ratio while the pressure coefficient has its lowest values at R1=0.4. When the cone aspect ratio, size and its horizontal location from the step are increased, resizing of the vortex behind the upper channel step is observed while more fluid deflection toward the thermoelectric device is obtained. Therefore, the power of the device is increased and the power enhancement is in the range of 10%-12% for varying size and aspect ratio of the cone while it is up to 20% for different horizontal locations of the cone. There is significant enhancement in the pressure drop with higher size and aspect ratio of the conic object even though the conversion efficiency rise. However, changing the object location is favorable as compared to increasing the size and aspect ratio of the cone on the power generation, conversion efficiency and pressure drop features. The potential in the device power enhancement with nanoparticle inclusion is higher for lower Reynolds number and lower higher expansion ratio while up to 18% increment of the power is obtained with nanoparticle inclusion at the highest amount. Conversion efficiencies also rise while pressure drop slightly vary with higher solid nanoparticle volume fractions. A predictive model based on artificial neural networks has been developed that estimates the power generated in the thermoelectric device accurately and fast as compared to high fidelity three dimensional computational fluid dynamics simulations. © 2020Item Effects of a rotating tube bundle on the hydrothermal performance for forced convection in a vented cavity with Ag–MgO/water hybrid and CNT–water nanofluids(Springer Science and Business Media B.V., 2022) Selimefendigil F.; Öztop H.F.In this study, effects of rotating tube bundle on the hydrothermal performance for the forced convection in a vented cavity are numerically studied with a mixture of Ag and MgO nanoparticles suspended in water, forming a hybrid nanofluid and CNT–water nanofluid. The finite volume method is used for the numerical simulations. The simulation study is performed for various values of Reynolds number (between 100 and 1000), rotational Reynolds number (between − 100 and 100), size (between 0.01H and 0.12H), vertical (between 0.3H and 0.65H) and horizontal locations (between 0.3H and 0.65H) of the cylinder in the tube bundle and nanoparticle volume fraction (between 0 and 0.02). An experimental correlation was used for the description of the Ag–MgO/water hybrid nanofluid. Results indicated that the rotational effects of the tube bundle contribute to the hydrothermal performance. The average Nusselt number enhancements are 8.95% and 40% when CNT–water is used for solid volume fraction of 0.02 at the highest speed, while these values are 31.5% and 37.7% for hybrid nanofluid. The pressure coefficients are higher for negative value of Re ω and hybrid nanofluid. The size of the tube bundle is effective at the highest size, while the increment amount is 16.8% both for CNT–water and for hybrid nanofluids. The center location of the tube bundle resulted in heat transfer enhancement which is in the range of 11% and 18%. As the solid volume fraction of nanoparticles becomes higher, discrepancies between the average Nu values of CNT–water nanofluid and Ag–MgO/water hybrid nanofluid become higher which is also observed for the pressure coefficient. It is advantageous to use CNT particles since higher heat transfer coefficients with lower values of pressure coefficient are obtained. © 2020, Akadémiai Kiadó, Budapest, Hungary.