Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Experimental Investigation of a Hybrid Thermal Management System for an Electric Vehicle Battery Module(Izmir Institute of Technology, 2022) Coşkun, Turgay; Çetkin, Erdal; Çetkin, Erdal; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyEnvironmental concerns and limited energy sources of the world are driving force in electric vehicle technology improvements. One of the main components of the electric vehicles is battery cell. Using batteries in electric vehicles brings up new concerns such as safety problems, limit of range and so on. The temperature of the battery cell increases during charging/discharging and operation. There is an optimal temperature range (15ºC ─ 35ºC) for battery cells to maximize efficiency and prevent safety issues. The high temperature values in the battery cells can be result with fire and explosion. In addition, the performance of the battery cells is highly affected by operating temperatures. Therefore, thermal management of the battery cells is a necessity to overcome safety issues and maximize the battery performance. The feasibility of microchannel heat sink for battery cooling is investigated numerically and it is decided to continue with conventional length scales because of the higher pressure drop values in micro scales. Thus, a hybrid cooling system, using air and liquid solely or simultaneously, is developed and is introduced to a battery module. The battery module created by connecting three lithium-ion pouch cells in serial. According to the results, air cooling gives the more homogeneous temperature distribution. The lowest temperature values are observed in hybrid cooling system and temperature difference between the cells are reduced by 30% when compared to the water-cooling system. The temperature profile in air cooling shows that any increase in the ambient temperature (23ºC) or discharge rate will undergo a temperature rise in battery cells and optimal temperature ranges will be exceeded in that case. A step function, in a sequence of various discharge rate, is introduced to the battery module to determine cooling capacity of the air system during operation. The result show that the temperature of the cells is kept below 30ºC. The hybrid cooling is enabled to select cooling systems for the battery module with respect to operating condition; hence, the efficiency of the system is increased.Doctoral Thesis Numerical Investigation of Gas Transport Through Micro/Nano-scale Porous Media at Slip Flow Regime(Izmir Institute of Technology, 2021) Sabet, Safa; Barışık, Murat; Sabet, Safa; Barışık, Murat; 03.10. Department of Mechanical Engineering; 01. Izmir Institute of Technology; 03. Faculty of EngineeringGas flow in micro/nano-scale porous systems is observed in many applications and technologies. Gas dynamics at such small scales differ from conventional fluid dynamics estimations due to rarefaction effects. In the literature, the Knudsen number (Kn) for the characterization of rarefaction effects on permeability is calculated based on a characteristic flow height estimated from the pore size, while the geometric parameters such as pore shape and pore-throat ratios are mostly ignored. Therefore, an accurate characterization of rarefaction effects could not be ascertained. For the first time in literature, a general characterization of gas transport through systems at different porosity and pore throat size values and at different rarefaction levels was obtained using a modified Kn definition. The characteristic height required for an accurate Kn of a porous system is defined using the "equivalent diameter" calculated from the corresponding permeabilities. Pore-level calculations were performed in a wide range of systems while the observed permeability variation by porous parameters was successfully described by an extended volume-averaged model developed as a combination of the Darcy, Kozeny-Carman, and Klinkenberg models. The characterization systematic and volume-averaged model was applied for various cases of (i) two-dimensional porous, (ii) two-dimensional multi- porous, and (iii) three-dimensional complex porous system. For all these systems, the permeability values could be estimated in terms of the geometric parameters of the porous structures and rarefaction levels. In addition, the rarefaction effects on heat convection in metal foams were studied through Darcy to Forchheimer flow regimes using the Kelvin Cell structure. A 60% increase in permeability and a substantial decrease in inertial effects developed due to rarefaction, while Nusselt numbers were found mostly related to Reynolds number. Further, the influence of variation in gas thermophysical properties coupled with rarefaction as a function of increasing gas temperature for high heat flux applications was described. A 40% decrease in hydraulic conductivity for a temperature increase from 300K to 400K is observed, independent from the Kn number.Doctoral Thesis Examination of Fatigue Behaviour of Carbon Fiber Reinforced Polymer Composites(Izmir Institute of Technology, 2021) Tanoğlu, Metin; Tanoğlu, Metin; Tanoğlu, Metin; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThis PhD thesis aims to examine the fatigue behavior of sandwich panels fabricated from adhesively bonded aluminum honeycomb core and carbon fiber reinforced polymer composite face sheets. Initially, sandwich panels were manufactured with three different amounts of adhesive in their interface. Static flexural behavior was characterized with three-point bending tests. Load-displacement curves and static flexural failure modes were obtained and utilized to compare the static flexural behavior of fabricated sandwich. Fatigue behavior of sandwich panels were characterized with the three-point bending fatigue tests. Stiffness degradation curves were used to identify the failure cycles of sandwich panels. Fatigue failure modes and S-N curves were obtained to find out the effect of amount of adhesive on fatigue behavior of sandwich panels. The other study within this thesis was made to investigate the effect of core thickness on the fatigue behavior of the sandwich panels based on aluminum honeycomb core and carbon fiber reinforced polymer composite face sheets. Sandwich panels were fabricated by using three different aluminum honeycomb core thickness. Static flexural tests were carried out to determine the static flexural behavior of developed sandwich panels. Load-displacement curves and failure modes were obtained from flexural tests. In addition to this, core shear tests were performed to investigate the core shear strength of the honeycomb cores with different core thickness. Effect of core thickness on fatigue behavior of sandwich panels were characterized with fatigue failure modes and S-N curves. Stiffness degradation method was used to determine the fatigue failure cycles of the sandwich panels.Doctoral Thesis Molecular Dynamics Studies on Interface Heat Transfer Control Using Electric Field(Izmir Institute of Technology, 2021) Barışık, Murat; Barışık, Murat; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThermal management is considered as a bottleneck for the development of next generation micro/nano-electronics with high heat dissipation rates. When component sizes decrease to nanoscales, increase in surface to volume ratio leads the interfacial thermal resistance (ITR) to dominate the heat transfer behavior. The current study focuses on characterizing ITR at molecular level and exploring smart thermal management concepts for nano-scale systems. In sequence, the effect of solid thickness on ITR was investigated such that the altered phonon spectrum inside the solid domain creating the size dependency on thermal conductivity was also found to create a size dependency in ITR. Next, an active and local manipulation of heat transfer between water and various solids by an applied uniform and/or non-uniform electric field was examined. When the water molecules underwent electric field induced orientation polarization and liquid dielectrophoresis (LDEP), a substantial increase in heat transfer was developed due to the decrease in ITR and increment in thermal conductivity. Finally, an interface-localized heat transfer control technique was proposed, where interdigitated electrodes (IDEs) were embedded into the heat dissipating surface. IDEs created an electric field gradient exclusively near the electrode surface which resulted in LDEP forces on the water dipoles at near surface region enhancing solid/liquid interface energy and almost eliminating the ITR. We developed semi-empirical and theoretical relations to describe ITR variation by the electric field, which will be important for thermal management of current and future technologies.Doctoral Thesis Development and Characterization of Innovative Fiber Reinforced Prepregs and Their Composites Containing Functional Fillers(Izmir Institute of Technology, 2021) Uz, Yusuf Can; Tanoğlu, Metin; Tanoğlu, Metin; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThis Ph.D. thesis aims to prepare laboratory-scale carbon fiber reinforced prepregs and improve the performance of their composites by incorporating functionalized single-wall carbon nanotubes (SWCNTs). The effect of nano-scale functional fillers on the characterization of prepregs and their composites was investigated to develop innovative materials for primary structures. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with the carboxyl (-COOH) group using acid treatment. The modified resin system containing 0.05, 0.1, and 0.2 wt. % F-SWCNTs were developed with novel multi-step dispersion techniques. FTIR spectroscopy was performed to identify new bonding groups formed after the covalent functionalization. Unidirectional carbon fiber reinforced prepregs with/without F-SWCNTs were prepared using a drum-type winding technique by utilizing the solvent-dip (solution impregnation) process. The effect of F‐SWCNTs on the curing process and kinetic parameters of the carbon fiber/epoxy-based prepregs were investigated using non‐isothermal DSC. The activation energy of the curing reaction was calculated by the isoconversional methods. Also, the new numerical approach called GMN was developed to determine the activation energy of the thermosetting materials. For the fabrication of prepreg-based composite laminates, the vacuum bag-only (VBO) method was performed. The fiber volume fractions of the CFRP samples changed between 55.3% and 50.16%. The mechanical and thermomechanical properties of prepreg-based CFRP composites with/without F-SWCNTs were investigated. The optimum mechanical properties of F-SWCNTs filled CFRP composite was achieved at 0.05 wt.% of F-SWCNTs. However, mechanical properties were decreased due to the addition of higher content of F-SWCNTs, in comparison with neat CFRP.Doctoral Thesis Multiphysics Modeling of Surface Charge and Pressure-Driven Electrokinetic Flow in Micro/Nano Scale Porous Media(Izmir Institute of Technology, 2021) Şen, Tümcan; Barışık, Murat; Barışık, Murat; 01. Izmir Institute of Technology; 03.10. Department of Mechanical Engineering; 03. Faculty of EngineeringAccurate characterization of fluid transport in micro/nano confinements is essential for numerous applications from industrial, agricultural, and medical sciences. In these applications, electrokinetic interactions dominate the fluid behavior, which causes conventional fluid dynamics to become incomplete. Specifically, near-wall hydrodynamics and liquid/solid coupling at the interface varies by electrokinetic effects. Therefore, the current study focuses on characterization of the fluid transport at various porous systems and ionic conditions. The Poisson-Nernst-Planck (PNP) equations were numerically solved coupled with the Navier-Stokes (NS) equations. Charge regulation (CR) boundary condition is employed to calculate the charging behavior of the surfaces. First, the surface charging of nano-scale systems was analyzed by considering the electric double layer (EDL) overlap and inlet/outlet effects. While EDL overlap decreased the surface charge, inlet/outlet effects presented an opposite behavior. Then, transport is characterized by calculating the hydraulic conductivity from Darcy's law under electrokinetic and boundary slip effects. The results showed that electrokinetic effects decrease the hydraulic conductivity with increasing concentrations and decreasing confinement sizes. At slipping condition with a constant slip length applied, velocity slip developing on surface showed strong dependence on porosity and ionic conditions. For low porosities and high concentrations almost no-slip conditions were observed even at high slip lengths. Results showed that the transport in micro/nano-scale porous systems is dominated by electrokinetic interactions depending on porous system parameters and ionic conditions.Doctoral Thesis Performance Improvement of Composite Materials Used as Hydrogen Storage Tanks by Microstructural Modifications(Izmir Institute of Technology, 2020) Ay, Zeynep; Ay, Zeynep; Tanoğlu, Metin; Tanoğlu, Metin; 01. Izmir Institute of Technology; 03.10. Department of Mechanical Engineering; 03. Faculty of EngineeringThe goal of this Ph.D. thesis is to improve the performance of the cylindrical composites manufactured by filament winding method by using the toughened matrix resin with nano-sized filler (noncovalently functionalized with ethoxylated alcohol chemical-vapor-deposition-grown SWCNTs). The effect of SWCNT concentration on the mechanical performance of these composites was investigated and discussed. One of the main focus of this thesis is to examine the effect of nano-sized filler type and filler concentration on the performance of the epoxy-based composites. For this purpose, epoxy-based nanocomposites with different nano-sized filler types (SWCNT, TEGO, and HNT) at varying concentrations were developed by a calendaring (3-roll-mill) method. A series of mechanical tests were performed for reference composite and developed nanocomposites. The scanning electron microscopy (SEM) was used to reveal the morphology and toughening mechanisms by examining the fractured surface of nanocomposites. The rheological behaviors and contact angle measurements with glass fiber of the selected filler (SWCNT) incorporated epoxy suspensions were investigated to determine the suitability of suspensions for the filament winding process. The reference and SWCNT modified glass fiber (GF)-based cylindrical fiber-reinforced polymeric composites (CFRPCs) with an inner diameter of 60 and 275 mm were manufactured by the filament winding method. The split-disk and three-point bending tests were performed for GF-based CFRPCs. The double cantilever beam (DCB) test was also carried out for the reference and SWCNT modified GF-based CFRPCs to investigate the effect of SWCNT existence on the interlaminar fracture toughness of CFRPCs. The fractured surfaces after the DCB test were analyzed under the SEM to comprehend the toughening mechanisms, and micro-and nano-sized filler morphologies. Consequently, it was revealed that blending and hence toughening the epoxy resin with SWCNT improves the interlaminar properties of the GF-based composites.Doctoral Thesis Desing and Production of Light-Weight Pressure Resistant Composite Tank Materials and Systems for Hydrogen Storage(Izmir Institute of Technology, 2020) Tanoğlu, Metin; Kartav, Osman; Tanoğlu, Metin; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThis thesis focuses on the development of high-pressure resistant composite tanks for hydrogen storage. For this aim, composite tanks with aluminum liners were designed and manufactured by filament winding technique with various lay-up configurations and tested. The main objective of this study was to develop composite tanks with 700 bar working pressure and 1400 bar burst pressure. Furthermore, composite doily layers were incorporated into the filament winding technique and inserted at the front and end dome sections of the composite tanks to improve the burst pressure performance of the composite tanks and to develop the manufacturing process. Before the manufacturing process, the winding simulations were completed using CADWINDTM CAM software. The manufactured composite tanks were hydrostatically loaded with increasing internal pressure up to the burst pressure. During loading, the deformations over the composite tanks and liners were measured locally using strain gauges. Besides, composite plates were manufactured by filament winding technique to determine the mechanical and the thermo-mechanical properties, and the fiber mass fractions of composite sections were determined. Additionally, a preliminary study was carried out to investigate the effect of hybrid fiber usage on the burst pressure performance of steel liner based composite tanks. The effect of filament winding parameters on the burst pressure performance of composite tanks was investigated experimentally. The aimed burst pressure value of more than 1400 bar was obtained in this study for aluminum liner-based carbon fiber reinforced composite tanks. Also, a desired safe burst mode that is expected to occur in the mid-region of the composite tanks was successfully obtained. This study may be useful for the development of composite tanks for high-pressure hydrogen storage especially for the automotive industry and can be helpful to decrease the usage of fossil fuels.Doctoral Thesis Design of a Robot Assisted Minimally Invasive Surgical System for Pituitary Tumor Surgery Based on Safety Features(Izmir Institute of Technology, 2020) Dede, Mehmet İsmet Can; Dede, Mehmet İsmet Can; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThe study is on the designing a robot assisted endonasal endoscopic surgical system; NeuRoboScope, the pituitary tumor resection surgery system. This system comprises a passive and an active arm. The passive arm positions the active arm in the surgery zone while the active arm assists the surgeon by positioning the endoscope during the surgery. The focus of this thesis is the mechanical and control safety features that can be implemented in the system. The safety enhancement methods of robot assisted minimally invasive surgery systems are investigated. Among the seventeen robot assisted endoscope holders, sixteen of them have been implemented in pituitary tumor and sinus surgeries. Safety is the main criterion that advances the progress of these systems and places them in operation rooms. Accordingly, two optimization procedures have been applied during the design of the NeuRoboScope system that have a direct effect on the suggested safety features. A novel optimization technique is proposed by employing a redundancy resolution method. The most suitable fixing point of the passive arm and its first link length is optimized to achieve the maximum manipulability with restrictions imposed by a modified condition number index and impedance of the passive arm. The active arm's partial gravity compensation is studied. Three spiral springs are used as counter-springs as the most compact and lightweight partial gravity compensation method. Particle swarm optimization method is employed for the optimization of the design parameters: spiral spring stiffnesses and preload angles. Consequently, at least 66% of actuator loads are compensated.Doctoral Thesis Improvement of It-Sofc by Tailoring the Microstructure of Lscf Cathode and Gdc Electrolyte(Izmir Institute of Technology, 2019) Sındıraç, Can; Akkurt, Sedat; Akkurt, Sedat; Büyükaksoy, Aligül; 03.09. Department of Materials Science and Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThe high operating temperature of solid oxide fuel cells (SOFC) brings about some restrictions like the high cost of fuel cell, long start-up time, thermal stress, and decreasing lifetime. Thus, lowering the operating temperature is vital for improvement of SOFC. However, reducing the operating temperature leads to some negative effects on solid oxide fuel cell performance by increasing the electrolyte and electrode resistances. This dissertation focuses on tailoring the cathode and/or electrolyte layers to obtain improved electrochemical performances. For this purpose, some strategies are proposed. These are (i) thin film cathode nanocomposite cathode layer formation, (ii) infiltration of porous GDC by LSCF/LSCF+GDC, (iii) infiltration of porous GDC by GDC solution to improve densification at lower temperature and finally (iv) electrochemical characterization of GDC densified by infiltration.