Browsing by Subject "Heat transfer reductions"

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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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    Effects of a rotating partition on mixed convection of hybrid nanofluid in a lid-driven cavity under different magnetic fields
    (American Institute of Physics Inc., 2024) Selimefendigil F.; Oztop H.F.
    There are many thermal engineering applications that employ partitions, such as heat exchangers, cryogenics, electronic cooling, and mixture separation. In this study, a novel type rotating partition is proposed and its performance is numerically assessed by the consideration of mixed convection in a lid-driven cavity with an inner isothermal blockage under magnetic field. A number of numerical simulations are run for various values of the Richardson number ( 0 ≤ Ri ≤ 50 ), rotational Reynolds number ( 0 ≤ Rew ≤ 50 ), Hartmann number of the inner domain ( 0 ≤ Ha ≤ 50 ), and non-dimensional size of the rotating partition (between 0.2 and 0.35). The experimental validation of the mixed convection for a lid-driven cavity is performed. It is observed the effects of rotation of the partition become important when natural convection effects become dominant. At the highest rotational speed, heat transfer reduction of 15% is obtained with increasing the Ri from 0.5 to 50, while at Ri = 50, partition rotation considering highest speed results in average Nusselt number (Nu) reduction by about 5.5%. Streamlines and isotherms are significantly affected by the size of the partition, while slight changes are obtained by varying the magnetic field strength. The reduction of Nu is obtained in the range of 8.5% and 8.8% with a higher magnetic field strength. The increments in the heat transfer by using the highest partition size are obtained in the range of 22.6% and 27.3%. When comparisons are made with non-partitioned lid-driven cavity, average Nu is reduced between 41.6% and 50% by using rotating partition. In the natural convection dominated case, heat transfer reduction will be 4% higher when rotations become active as compared to stationary partition. Feed forward recurrent network model with 25 neurons is used for accurate prediction of the thermal system of lid-driven cavity with rotating partition under magnetic field. © 2024 Author(s).