Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Numerical Investigation of Y-Shaped and Csc Micromixers(01. Izmir Institute of Technology, 2022) Samancıoğlu, Umut Ege; Çetkin, Erdal; Çetkin, ErdalMicromixers are one of the key parts in microfluidic devices. Therefore, passive micromixers have become a popular research topic. In this thesis, parametric optimization of a Y-shaped micromixer with mixing chamber is documented. Design parameters are; alpha () for the angle between the two inlet angles, beta () for the angle between the z axis and one of the inlet channels and theta () for the angle between the other inlet channel, z-eccentricity (zecc) is the distance between the centerline of an inlet channel and origin of the mixing chamber along z-axis, x-eccentricity (xecc) is the distance between the intersection point of the two inlets and the origin of the mixing chamber along x-axis, ratio of the inlet and outlet channel length (L1/L2), ratio of the inlet and outlet channel diameter (D1/D2), ratio of the inlet channel length and diameter (L2/D2) and ratio of mixing chamber volume to the total volume(Vsp). = 180o - 240o range and zecc= 20m corresponds to the optimal range. Effect of each parameter on the system is discussed and the best performing 3 mixer designs are further investigated. The optimized design yields 88.16% mixing efficiency with 9244.4 Pa pressure drop when Reynolds number is 81. Furthermore, performance of this design is compared with a reference design. The comparison shows that optimized design decreases the pressure drop more than 50% for all Reynolds numbers while having a higher mixing efficiency (up to 35%) with low Reynolds numbers (0.054-3).Master Thesis Numerical and Experimental Investigations of an Air-Cooled Battery Thermal Management System(01. Izmir Institute of Technology, 2021) Göçmen, Sinan; Çetkin, ErdalElectric vehicles play an integral role in eliminating pollution related to transportation, especially if electricity is generated via renewable sources. However, storing electricity onboard requires many battery cells. If the temperature of the cells is not strictly regulated, their capacity decreases in time, and they may burn or explode due to thermal runaway. Battery thermal management systems emerged for safe operations by keeping the battery cell temperatures under limit values. However, the current solutions do not yield uniform temperature distribution for all the cells in a pack. Here, we document that constant temperature distribution can be achieved with uniform coolant distribution to the channels located between batteries. To this end, we performed both numerical and experimental investigations. The design process of the developed battery pack begins with a design used in current packs. Later, how the shape of the distributor channel affects flow uniformity is documented. Then, the design complexity was increased to satisfy the flow uniformity condition, which is essential for temperature uniformity. The design was altered based on a constructal design methodology with an iterative exhaustive search approach. The uncovered constructal design yields a uniform coolant distribution with a maximum of 0.81% flow rate deviation along channels. The developed design is palpable and easy to manufacture relative to the tapered manifold designs. The results also document that the peak temperature difference between the cells decreases from a maximum of 12 K to 0.4 K. Additionally, the developed design was simulated by using Newman, Tiedeman, Gu, and Kim (NTGK) electrochemical battery model, which provides more realistic results due to its heat generation approach in a battery cell. The electrochemical model was simulated with fluid and heat flow simultaneously at the battery pack level. The accuracy of numerical studies is validated by experimental work. The results show that the peak temperature can be kept under the desired operational temperature with a minimum deviation in the temperature difference.Master Thesis Design Optimization of an Industrial Oven Heat Exchanger(01. Izmir Institute of Technology, 2021) Nergiz, Güven; Çetkin, ErdalThe coating application of metals (especially in automotive and white goods sectors) is used in various fields to protect the metal against oxidation, corrosion, scratch, or high temperature to increase product lifetime. The most efficient technique in the coating application is powder coating where the powder is Epoxy-polyester. This process has three steps; surface pretreatment (washing), powder coating, and curing the coated metal. Metals may need to be dried and cured in ovens with 90°C and 200°C, respectively, for the required quality coating process. Burners are used as the heat source in the oven's heat exchangers. Due to high temperatures, the expanding heat exchanger is exposed to various thermal stresses. The stresses cause cracking and rupture problems. The regions where thermal stresses occur intensely are the surfaces with high-temperature differences. Various mass flow rates in the heat exchanger cause non-uniformity for how the energy to be transferred, thus non-uniform surface temperature distribution. In this study, a heat exchanger design provided by "ELECTRON – Sistem Teknik Makina" company has been studied. The mass flow rates in the heat transfer pipes (where the heat is mainly transferred) show deviations up to 75% from the ideal rate. With this study, deviations have been reduced to the level of ±10%. The results show that the maximum thermal stress on the heat exchanger was reduced by 24% with this improvement. In general, the uniform mass flow rates obtained in the heat transfer pipes provided a more homogeneous distribution of the surface temperatures, thus decreased thermal stresses.Master Thesis Four-way refrigerant piping system design for variable speed compressor(01. Izmir Institute of Technology, 2021) Karadoğan, Ceren; Çetkin, ErdalIn the study, a new refrigerant piping system was designed for an air conditioner with a capacity of 12 000 BTU. The purpose of designing a new piping system is to eliminate the vibration problem that occurs at low frequencies. This vibration problem causes an undesired sound level in the device acoustically. With the new refrigerant pipe group, the vibration rate has been reduced by 30% on average, in areas where problems were experienced. The pressure, temperature, and velocity distributions in the developed design and the existing design were analyzed numerically with ANSYS 2021 R1 software. At the same time, a new capillary pipe system has been designed for the refrigerant pipe group. By designing the capillary tube, it is aimed to optimize the capacity of the existing system. In addition to numerical studies, experimental studies have also been carried out on which the capillary system is more suitable for the developed system by applying performance tests to both the existing system and different capillary systems. The phase change, pressure, temperature, and velocity distributions in the capillary tubes obtained in the experimental performance tests were used to verify the numerical model. The Volume of Fluids (VOF) model, which is a two-phase flow model, was used in numerical analysis. The lengths of the phase transition in the capillary tube system were also examined within the scope of the study. It has been determined that the phase change zone in the current system with 1.7 mm × 900 mm + 1.7mm × 300 mm capillaries have a shorter distance than the 1.5 mm × 700 mm capillary group. Thanks to the verification of the numerical model results with experiments, a validated numerical model was obtained to be used in future studies.Master Thesis Numerical Investigation of Thermal Management in Photovoltaic Cells With Phase Changing Materials (pcm) and High Conductivity Inserts(01. Izmir Institute of Technology, 2021) Kyaligonza, Sylevaster; Çetkin, ErdalPhotovoltaic cells' electrical conversion efficiency from incident solar radiation heavily depends on the cell temperature. A novel thermal management strategy aimed at keeping the cell temperature in the same order to maximize PV cell electrical conversion efficiency is proposed in this study. The study compares four solar module configurations: a conventional photovoltaic module (PVT module), a hybrid of conventional with PCM (PVT/PCM-I), an internally finned configuration with PCM (PVT/PCM-II), and a configuration where the bottom surface of PVT/PCM-II was cooled via convection (PVT/PCM-III). The developed 3D numerical model was solved via ANSYS software involving the solar ray tracing radiation model for incident solar radiations and a transient melting-solidification thermo-fluid model for modeling of the PCM. Numerical results were validated by comparing them against experimental results published in the literature. Results show that the conversion efficiency of PV cells reaches 16.84%, 18.65%, 18.83%, and 18.98% after 120 minutes for PVT module, PVT/PCM-I, PVT/PCM-II, and PVT/PCM-III, respectively while the specific electrical power produced reaches 75.30W/m2, 83.39W/m2, 84.19W/m2, and 89.42W/m2 for solar radiation of 540W/m2 and 26°C ambient temperature. A 5 mm increase in the fin height for PVT/PCM-II results in a 0.22% increase in efficiency while a 0.5m/s increase in the inlet velocity of the cooling air for PVT/PCM-III results in about 0.06% efficiency increase. Furthermore, performance evaluation of PVT/PCM-III was carried out with sample weather data of the Indian Institute of Technology-Delhi and the Algiers site. The hourly average of overall conversion efficiency for the respective sites reaches 16.70% and 16.84% for a conventional PV module and 19.04% and 19.19% for PVT/PCM-III where the conversion efficiency increases by 14% and 13.7% respectively.Master Thesis Investigation of Microchannels Heat Exchangers for Condensers(01. Izmir Institute of Technology, 2021) Sevencan, Furkan Tuğberk; Çetkin, ErdalThere are limited types of condenser types/designs in the market although there are many distinct heat exchangers available. One reason is related to the complexity of the phase-change mechanism and how it is affected by the geometric parameters of the heat exchanger. Technological requirements force the size of any component to become smaller and condensers are no exception for this trend. However, there is a limit for scaling down the current condensers, and their compactness cannot be decreased due to their serpentine design. The transition from serpentine designs to parallel microchannels is promising as the required coolant volume would decrease significantly for the same cooling due to enhanced heat exchange surface area. However, parallel channel designs are challenging to implement due to irregularities in pressure distribution which would yield phase change and condensation temperature significantly. In the present thesis, a microchannel heat exchanger was selected and the imperfections related to the pressure distribution irregularities were progressively developed numerically. Geometrical parameters were optimized to eliminate the flow maldistribution resulted from non-homogeneous pressure distribution in the condenser. The effects of header shape (from rectangular to tapered) on flow uniformity are not dramatic. Then, manifold channels were relocated with given protrusion depths which were optimized using an iterative approach. Relocating the channels enables the pressure uniformity. Finally, the condensation behavior of the design developed with the aim of enabling uniform flow resistance was documented. Under the given operational conditions, three different height channel design is 100% condensed R410a from the vapor phase into the liquid phase. A and B design were condensed the refrigerant fluid in a low Reynolds number meanwhile, C design was condensed in a high range of Reynold number. All in all, effects of maldistribution on flow regime were tried to be eliminated with new geometric design approaches and condensation effect in new geometries was able to be seen 100% at low flow rates.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 OliveiraThe 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 Hydraulic Design Optimization and Performance Evaluation for a Dishwasher(Izmir Institute of Technology, 2019) Erik, Ömer Berhan; Çetkin, ErdalHydraulic designs of dishwashers with 12 (2 baskets) and 15 (3 baskets) place settings with diverter which distributes the water to bottom and upper spray arms separately were analyzed. First, both hydraulic systems were modeled analytically, so continuous and local losses were calculated based on them. Besides, operating point of systems were determined based on the curve of the pump and head loss. All parameters were also verified by experimental tests. An asynchronous circulation pump (fixed pump rpm and outlet pressure) with the same hydraulic outlet pressure is used in both products. Hydraulic design is evaluated with parameters obtained from the analytical model and then the design of equipment along the hydraulic path was improved. Once parameters improving the designs are determined, modified parts were analyzed numerically with finite volume method. The results were also validated with experimental studies. Lastly, prototype with improved design parameters was produced and installed on a dishwasher. Dishwasher performance index was calculated according to IEC standards to see the effect of new design on dishwasher washing performance. The results show that the energy requirement decreases 25% whereas performance index stays the same.Master Thesis Investigation of Compressor Cycle Operating Point for Various Air Conditions(Izmir Institute of Technology, 2019) Yaşar, Soykan; Çetkin, Erdal; Çetkin, Erdaln this study, operating point of compression cycle for various conditions is documented with the consideration of all the equipment of vapor-compression refrigeration cycle. An algorithm which characterizes all the equipment, simulation of the cycle and enabling of the calculation of capacitive values is proposed. The algorithm includes compressor capacitive value polynomial coefficients, air and refrigerant side pressure drop and heat transfer correlations (for finned heat exchangers) which were taken from the literature to uncover the operating point and performance of each equipment in the cycle. e-Ntu and LMTD relations are discussed and proper correlations are included on the thesis. Furthermore, the mathematical models in the literature were surveyed in order to uncover circuiting analysis performed in the cycles.Master Thesis Numerical Investigation of Thermal Management for an Airfoil Profile To Prevent Ice Formation(Izmir Institute of Technology, 2019) Kök, Çağatay; Çetkin, ErdalIn this study, we present a design alternative to prevent the icing of a wind turbine blade in the cold climate wind zones. The main objective is to create a thin film around the wing profile that can protect the surface from ice formation. In order to form this insulating layer, the leading edge, which is the region where the icing started first, the circular openings that could provide hot air to the outside of the wing, were added to geometries. By means of these openings, it has been tried to provide a solution that will prevent ice on the surface without the need to heat the entire wing. At the same time, the effect of these openings on the wing, the distance between the openings and the positions and diameters of the wings on the lifting performance of the wing were investigated. Throughout the study, the design parameters were all proportional to the chord length of the wing. In the model stage, instead of the entire wing, only one section of the wing was modeled using symmetry boundary conditions in order to use the existing limited computing power more efficiently. In this way, both the number of network elements and the calculation time can be modeled in such a way that the distance between the openings is equal to the width of the section. The results show that the lifting force, as can be expected, is small. As the width, i.e. the distance between the openings increased, the lifting force became more stable, while the film layer temperature decreased.