WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Conference Object On the Correct Modeling of Flow Characteristics in Double Pipe Heat Exchangers With Inner Dimpled Tube(Begell House, inc, 2022) Cobanoglu, Nur; Karadeniz, Ziya H.; 01. Izmir Institute of TechnologyDouble pipe heat exchangers (DPHXs), which are made up of two concentric or eccentric ducts, are generally used in industrial applications due to the simplicity of the geometry. Passive heat transfer improvement techniques have been investigated to improve the heat transfer ability of the DPHX by the orientation of flow propagation and changing heat transfer area. Dimpled surfaces are considered as the promising passive heat transfer improvement method because of their low weight, small pressure drop penalty, simple fabrication, and small maintenance costs. Since dimples improve the convective heat transfer by flow reattachment, flow impingement, and upwash flow at the downstream region of the dimples, the correct determination of the flow regime is important for accurate prediction of the heat transfer performance especially in small Re numbers. This numerical study presents a sensitivity analysis on the correct modeling of flow characteristics for the investigation of heat transfer performance of DPHXs working with small Re numbers (Re = 500) in low-temperature applications. The effects of laminar flow and turbulent flow solutions on flow propagation and heat transfer performance have been investigated by developing a transient 3D numerical model. The k - omega model was employed to evaluate the influence of dimples on turbulent flow. A constant temperature (T-c=253.15 K) boundary condition was applied at the inner pipe. Ethylene glycol-water mixture (50:50) enters the annuli at T-i=293.15 K. The influence of the dimpled geometry in annular flow propagation is discussed by considering velocity and temperature distributions at the critical cross-sections of the geometry.Conference Object The Effect of Permanent Magnet Location on The Performance of Ferrofluid Based Spncml(Begell House, inc, 2022) Bozkir, Selim Can; Karadeniz, Ziya Haktan; Cobanoglu, Nur; Doganay, Serkan; Karadeniz, Ziya Haktan; Turgut, Alpaslan; 03.06. Department of Energy Systems Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyFerrofluids are suspensions of ferromagnetic nanoparticles (iron, cobalt, nickel, magnetite, hematite, etc.) dispersed in non-magnetic base fluids. They have application potential in many fields due to the tunable thermophysical properties and the manipulation capability of the ferromagnetic nanoparticles under the influence of an external magnetic field. This numerical study investigates the effect of external magnetic field location on the performance of ferrofluid-based single phase natural circulation mini loop (SPNCmL) in which the driving mechanism is resulting buoyancy forces of density gradient caused by temperature difference. Since the working fluid exhibits higher magnetization at low temperatures, effects of the magnetic field have been investigated for the low-temperature side of the SPNCmL by placing a permanent magnet at the cooling-end outlet and heating-end inlet. The steady 3D numerical model was developed in the COMSOL Multiphysics by coupling three different physics: magnetic field (no current), heat transfer in fluid, and laminar flow. The performance of the SPNCmL working with water-based Fe3O4 ferrofluid under an external magnetic field was evaluated in terms of the maximum temperature (T-max), the temperature difference between heater inlet and outlet (Delta T-heater), the effectiveness (epsilon), and the flow distribution. In addition, the magnetic field effect on the fluid flow was visualized by velocity and the temperature distributions at the critical cross-sections.