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.Article Citation - WoS: 2Citation - Scopus: 2Sleep Quality: Design of Bedroom Ventilation and Evaluation Within the Scope of Current Standards(Elsevier Science Sa, 2025) Karadeniz, Ziya Haktan; Toksoy, Macit; Sofuoglu, Sait Cemil; Toksoy, Macit; 03.06. Department of Energy Systems Engineering; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyIndoor air pollution is one of the leading environmental risks to public health considering people now spending nearly 90 % of their day in indoor environments. A significant portion of this time indoors is devoted to sleeping, making it crucial to address the impact of indoor environmental conditions on sleep quality. International ventilation standards such as ASHRAE and CEN, as well as country-specific guidelines, offer valuable recommendations for ventilation design in residential buildings, including bedrooms. This study aims to evaluate the importance of determining ventilation rates in sleeping spaces using Indoor Air Quality Procedure (IAQP) compared to Ventilation Rate Procedure (VRP) in accordance with current standards. Here, the IAQP approach for determining air flow rate is based on the CO2 balance by maintaining CO2 levels in any sleeping environment below specified upper limits of 750 ppm and 1000 ppm. This study focused on the adult population, which forms the majority of society, with analyses conducted for both single and double occupancy sleeping conditions. The volume of environment where ventilation is not required during sleep (Vf) is inaccessible in conventional sleeping environments (10-21.6 m3 per person). Therefore, proper ventilation is of great importance for any sleeping space that is smaller than the Vf. The results of the analyses show that for the conventional sleeping volumes, CO2 levels reach 750 ppm (upper limit for comfortable sleep) in the first hour and increase to the disturbed sleep zone in about 2 h. Additionally, a chart outlining the necessary ventilation flow rates is suggested for maintaining maximum CO2 concentrations of 750 and 1000 ppm during different sleep durations and in various sleeping environments with varying volumes. Finally, the ventilation rates determined based on unit area and/or occupancy levels in standards (referred to as VRP) may not always be adequate or may be excessive in order to maintain CO2 concentrations below the recommended limits of 750 and 1000 ppm. It is advised to utilize demand-controlled ventilation by considering the system design as recommended by IAQP.