Phd Degree / Doktora

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  • Doctoral Thesis
    Parametric Flow Simulation for Early Design Phase: Case Study of an Urban Regeneration Area in Izmir
    (Izmir Institute of Technology, 2022) Öner, Efe; Başaran, Tahsin
    Climate change and its effects on the planning of cities require new dynamics for designing new expansion zones or neighborhood development projects. In conceptual phases, decision-makers, architects, planners, and engineers must consider extreme weather events and increased wind speeds in cities due to climate change to ensure the safety of pedestrians. Proposed building layouts, geometrical parameters, and features should be investigated in an artificial environment to satisfy wind behavior for acceptable conditions. Computational Fluid Dynamics (CFD) software provides insight into wind effects on the pedestrian level for the proposed layout of buildings and the surrounding area. This insight can boost the design process without conducting experimental wind tunnel tests. This study aims to assess the impact of building geometry (height, width, length) and building spacings in urban development projects for the safety and comfort of users in pedestrian-level wind environments with CFD simulations. The case area of this study is the first phase of an urban regeneration area in Izmir. The proposed layout is analyzed with prevailing wind speeds and directions to identify the dangerous and comfortable regions around buildings. Sub-configurations of buildings are simulated in CFD software to compare with existing wind tunnel tests for verification and validation. A design proposal with building features is evaluated with validated CFD parameters to examine the impact on pedestrian-level wind speeds. Mean speeds for corresponding comfort and safety limits of categorized human activities are compared to findings to identify suitable locations for these activities around buildings. Design parameters of urban layout; distance between buildings, height, and balconies on facades showed significant effects on pedestrian level wind environment. Building height among these parameters proved to be a decisive feature that should be considered in the early design stages.
  • Doctoral Thesis
    An Experimental and Numerical Study on Effects of Pore To Throat Size Ratio on Macroscopic Transport Parameters in Porous Media
    (Izmir Institute of Technology, 2015) Özgümüş, Türküler; Mobedi, Moghtada; Özkol, Ünver
    Heat and fluid flow in porous media are frequently encountered in natural and industrial applications, such as oil recovery, water supply management in hydrogeology, ground heat storage, nuclear waste disposals, and ground water flow modeling. Fluid flow and heat transfer analyses in porous media have gained recent attention. The theoretical analysis of heat and fluid flow in porous media is troublesome. That’s why some methods were developed to overcome the difficulties. One of these methods is the macroscopic method in which the solid and fluid phases are combined and the porous media is represented as an imaginary continuum domain. For the application of the macroscopic method onto a porous medium, the macroscopic transport properties such as permeability and thermal dispersion of the corresponding medium should be known. Many parameters such as pore to throat size ratio, porosity, Reynolds number, solid-to-fluid thermal conductivity ratio influence the macroscopic transport parameters. In this study, the fluid flow and heat transfer in porous media are examined numerically to determine the effects of pore to throat size ratio on permeability, interfacial convective heat transfer and thermal dispersion coefficients. The heat and fluid flow in periodic porous media consisting of rectangular rods are investigated. A representative elementary volume is considered and the continuity, Navier-Stokes and energy equations are solved to determine the velocity, pressure and temperature fields in the voids between the rods. It is shown that the pore to throat size ratio is a significant parameter which should be taken into account to suggest a wide applicable correlation. Based on obtained computational results, correlations for determination of Kozeny constant and interfacial heat transfer coefficient in terms of pore to throat size ratio and other related parameters are proposed. An experimental study was conducted to validate the numerical results of the present study. In the experimental part, a porous channel of square rods is used and the permeability and thermal dispersion coefficient are validated with the aid of experimental measurements. A good agreement between the experimental and numerical results is observed.
  • Doctoral Thesis
    Design of a Continuous Flow Uv Reactor for Opaque Liquid Foods by Using Computational Fluid Dynamics (cfd)
    (Izmir Institute of Technology, 2013) Atılgan, Mehmet Reşat; Ünlütürk, Sevcan
    UV-C radiation is usually applied as an alternative non-thermal process for clear liquid food products in order to achieve microbiologically safe and shelf stable products. The main objective of this Ph.D. study was to design a UV reactor inorder to provide efficient UV dose/intensity distribution to reach minimum 5 log microbial reduction in opaque liquid foods. For this purpose, a S-shaped, thin film, continuous flow UV reactor was designed and constructed. UV dose/intensity delivered in the UV system was measured and determined by means of biodosimetric, actinometric and computational fluid dynamics (CFD) methods. Inactivation performance of the UV reactor was assesed by using both clear and freshly squeezed opaque white grape juices. The number of spoilage yeast, lactic acid bacteria and E.coli K-12 (ATCC 25253) in opaque grape juice was reduced to 1.604, 4.133 and 5.431 log at UV dose levels of 247.302, 301.113 and 273.520 mJ/cm2 respectively. For clear grape juice samples inoculated with S.cerevisiae and E.coli K-12 (ATCC 25253), 6.498 and 5.986 log reductions were achieved at UV dose levels of 1001.618 and 577.245 mJ/cm2. The microbial shelf life of freshly squeezed grape juice was extended up to fourteen days which was two times longer compared to untreated samples at refrigerated conditions. The physicochemical properties of UV-C processed grape juice were also evaluated during storage. Although pH, total soluble content (Bix %) and total titratable acidity were not affected from UV treatment, significant changes observed in pH, turbidity, color properties, total soluble content (Brix %), total titratable acidity and ascorbic acid (Vitamin C) content during storage.