Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Access Right: Open AccessSubject: search.filters.subject.Computational fluid dynamics

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Now showing 1 - 5 of 5
  • Master Thesis
    Numerical Detection of Cavitation in Plunger Valves
    (01. Izmir Institute of Technology, 2020) Akbulut, Bedia; Özkol, Ünver
    Cavitation is a very serious problem for control valves. Besides noise and vibration, cavitation can seriously damage mechanical parts. Experimental costs for cavitation tests are high, especially when the difficulty of testing large sized valves is considered. For these reasons, developing a Computational Fluid Dynamics (CFD) model can be an attractive solution for predicting cavitation. Cavitation; is a phase change event where the bubbles that occur when the fluid pressure drops below the vapor pressure seriously damage the parts of the machines such as pumps, impellers, and valves. The first aim of this research is to determine the onset of cavitation by performing two-phase CFD simulations in plunger valves. Then, several cavitation cages are connected to observe the change at the beginning of cavitation. A cavitation cage is used to protect the valve and valve disc when downstream pressure is too low. As a result of the analysis, it was observed that the cavitation delayed using the cavitation cage. The second purpose of this research is to design an interface program that will present the Loss and Flow Coefficient diagrams obtained from tests and CFD analysis to the user. Each valve has its own flow coefficient. This depends on how the valve is designed to allow flow through the valve. Therefore, the main differences between the different flow coefficients are due to the valve type and of course the valve opening position. The flow coefficient is important to choose the best valve to use in a particular application.
  • Master Thesis
    Computational Fluid Dynamics (cfd) Analysis of Latent Heat Storage in Heat Exchangers by Using Phase Change Materials (pcm)
    (Izmir Institute of Technology, 2020) Demirkıran, İsmail Gürkan; Çetkin, Erdal; Rocha, Luiz Aberto Oliveira
    The development of TES applications and materials takes the attention of many researchers, but the current literature rarely involves studies concerning medium temperature applications. This thesis compares available phase change materials (PCMs) for the medium temperature range. For this aim, Erythritol was defined as PCM in the numerical analyses. The effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a latent heat thermal energy storage (LHTES) application were investigated. Tube location and shell shape are essential due to the shape of the melted region, i.e., similar to the boundary layer. Results show that the S-curve of melting becomes steeper if the tubes are distributed such that the intersection of melted regions is delayed. Therefore, melted regions should be packed into a finite space which uncovers the shape of the shell that minimizes melting time and required sensible energy. Results show that, rectangular-shaped shell design where the tubes located near the bottom end decreases melting time and sensible energy from 67 minutes to 32 minutes and from 161.8 kJ/kg to 136.3 kJ/kg for %72.3 liquid fraction relative to the circular-shaped shell, respectively. In the four-tube cases, then the required melting time and sensible energy decrease 80% and 3.8% through the rectangular-shaped shell design for the PCM to melt completely, respectively. Overall, the results show that sensible energy storage and especially melting time can be decreased greatly by just varying the design.
  • Master Thesis
    Investigation of Liquid Transport in Micro and Nanoscale Porous Media at Different Pore To Throat Size Ratios
    (Izmir Institute of Technology, 2017) Kalyoncu, Gülce; Barışık, Murat; Özkol, Ünver
    Extensive usage of micro/nanoscale porous media in various applications, require comprehensive understanding of fluid transport in those systems, such as in the unconventional oil-reservoirs, micro/nano-membrane technologies and lab-on-a-chip applications. The frequently employed transport calculations in literature do not consider any effects related to size or shape of the pore. Instead, dynamically similar flow systems assumed by the porosity of a given medium that an “ability of flow” definition named permeability is employed for a given solid/liquid couple based on the corresponding porosity. However, in such small-scales, liquid flow characteristics diverge from continuum behavior and non-equilibrium effects should be considered to estimate the transport. Furthermore, geometrical parameters of pore structures and networks should be considered, in addition to porosity, for a proper characterization. Hence, pore scale analyses of fluid flow were performed by solving Navier-Stokes equation numerica lly with finite element method in a representative elementary volume. Permeability values were calculated based on the Darcy’s Law, at different pore-to-throat-size ratios, porosities, and velocity slips whose range determined by a literature review. Permeability showed a strong dependence on pore-to-throat-size ratios, and slip conditions. Using the permeability of pores across a wide range of conditions, the Kozeny-Carman (KC) relation was re-considered. An extended phenomenological Kozeny Carman model to predict micro/nanoscale liquid transport as a function of porosity, pore-to-throat size ratio, and slip length was developed. The pore-to-throat-size ratio and slip effects were found substantial on transport, which was successfully predicted by developed model.
  • Master Thesis
    Experimental Investigation of Gdi Injectoer
    (Izmir Institute of Technology, 2015) Abuzahra, Fakhry; Rodriguez, Alvaro Diez
    Among the challenges in the internal combustion - spark ignition Gasoline Direct Injection (GDI) engines stayed under spotlight for its ability to be developed in terms of fuel conversion efficiency and emission contaminants. Spray analysis is of great importance for the combustion operation and it is a prerequisite for improving the mixing capabilities of the air/fuel mixture. Momentum flux measurement technique is one of the most interesting approaches that aims to study the spray structure which can be a complement for high-speed imaging and Phase Doppler Anemometry (PDA) analysis. In the present study, two GDI single-hole research injectors, Magneti Marelli with Length to Diameter parameter (L/D)=1; 3 are investigated by means of momentum flux, global and local, under both low and high temperatures. The flash-boiling phenomenon is triggered when static pressure is below fuel saturation pressure at the same temperature which drastically affects the spray structure in terms of decrement in the penetration rate accompanied with an enlargement in the cone angle. N-heptane is used as a fuel under a temperature range 30-120 C, vessel ambient pressure range 40 303 KPa ,energizing time 1500 -3000 distance for the global momentum 5--40 mm and two horizontal planes for local momentum flux 10; 30 mm. Results of high-speed imaging were integrated in terms of cone angle and penetration rate. Furthermore, the results of this study can verify the Computational Fluid Dynamic (CFD) numerical analysis and provide wealthy understanding of the spray evolution.
  • Master Thesis
    Modification of a Computational Fluid Dynamics Model (ansys-Fluent) for the Purpose of River Flow and Sediment Transport Modeling
    (Izmir Institute of Technology, 2015) Ekmekçi, Hüseyin Burak; Elçi, Şebnem
    Precise estimation of the sediment transport and settling velocity of particle in turbulent flows is required for many engineering applications including modeling of the transport of suspended sediments and the transport of particle pollutants. This study presents an approach for modification of an existing CFD Model for sediment transport in turbulent flow based on field measurements. In the first part, synchronized 3-D velocity and temperature time series were monitored at Büyük Menderes River in Turkey where the data were utilized to characterize the turbulence characteristics and model particle – fluid interaction. Sieve and hydrometer analysis were obtained from earlier studies to understand and modify sediment transport under different conditions via ANSYS Fluent programme. The second part of the study involved numerical modeling of hydrodynamics via 3D CFD model in the selected portion of a river body through use of field measurements conducted at the study site. The k-ω turbulence model found to be the best suited when such flow around a structure as piers or flow through a water intake is considered. Effect of particle size, concentration and modeling approach for particle motion are also investigated and Rossin Rammler Logarithmic Distribution and multiphase modeling approach was the most appropriate methods. This study involved development of an approach to modify drag force on sediment particles using turbulence characteristics in the Fluent solver as well.