Master Degree / Yüksek Lisans Tezleri

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

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Author: search.filters.author.Çetkin, ErdalPublisher: search.filters.publisher.Izmir Institute of Technology

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Now showing 1 - 9 of 9
  • Master Thesis
    Numerical and Experimental Investigation of an Electric Vehicle Battery Module Thermal Management System
    (Izmir Institute of Technology, 2022) Gediksiz, Çağlar; Çetkin, Erdal
    Today, electric vehicles play an essential role in preventing pollution from fossil sources. Therefore, it is vital to develop battery technology in electric vehicles. The biggest problem experienced is the thermal runaways, which is a phenomenon that may cause burning and explosions following the decrease in battery capacities. The thermal runaway problem can be solved by using the thermal management system to keep the temperature range under control. In this study, a 6.7 kWh battery pack was produced. Battery pack operation consists of two parts, mechanical and thermal. In the mechanical part, battery pack assembly and drop tests, one of the mechanical tests, were carried out. At the end of the battery pack assembly, voltage measurements were made, and the accuracy of the assembly was demonstrated. Besides, a numerical and experimental study supported drop tests. As a result of this study, the battery case did not show permanent deformation (2.529x 108 N/m2) as suggested in the numerical experiments (1.263x 108 N/m2). Discharge characteristics and battery module model were discussed in the thermal management part. The information in the literature confirmed the discharge characteristic. The gap between the battery cells reached its most efficient value at 8 mm. In the developed battery module, thermal management was attempted using a heat plate and a cooling pipe. According to the numerical results, the battery module reaches 311.37K at 10C discharge. In the experimental process, the battery pack was charged with 15 amps and discharged with 30 amps. Moreover, the temperature values reached a maximum of 31 degrees. In the experiment on electric vehicles, a maximum discharge level of 255 A was observed. In this experiment, the battery pack reached a maximum of 36 degrees.
  • Master Thesis
    Numerical Investigation of Various Heat Transfer Mechanisms on Thermal Management of a Lithium-Ion Battery Pack
    (Izmir Institute of Technology, 2022) Şahin, Resul Çağtay; Çetkin, Erdal
    Lithium-ion battery packs are preferred in Electrical and Hybrid Vehicles (EVs and HEVs) due to their efficient and stable energy storage characteristics. Battery Thermal Management Systems (BTMS) have vital importance in EVs and HEVs to keep the batteries in desired temperature range to maximize performance and lifetime. Air cooling is a well-known method with the advantages of being simple and light but main concern for air cooling is effectiveness and pressure drops due to low heat capacity and thermal conductivity of air. This work compared various cooling designs for battery modules based on the surface temperature of batteries and the parasitic power consumption. Modules were built with COMSOL Multiphysics 5.5, and their accuracy was validated by experiments. Each module involves an equal number of batteries whose thermal characteristics were simulated by the electrochemical-thermal battery model, the P3D multiscale model. As a result, the maximum temperature was reduced by 5% (1.8°C) for inline alignment with baffles and 7.2% (2.8°C) for staggered modules, and the temperature gradient was reduced by 40% (1.7°C) for inline and 35% (1.5°C) for staggered alignments. While fan power consumption of inline alignment with triangle baffles (0.98W) was 3.5 times higher than the base design (0.27W), it was 0.23W for staggered design. Moreover, the cooling performance of different winglet parameters was compared and documented.
  • 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
    Hydraulic Design Optimization and Performance Evaluation for a Dishwasher
    (Izmir Institute of Technology, 2019) Erik, Ömer Berhan; Çetkin, Erdal
    Hydraulic 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, Erdal
    n 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, Erdal
    In 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.
  • Master Thesis
    Snowflake Shaped High Conductivity Inserts for Heat Transfer Enhancement
    (Izmir Institute of Technology, 2018) Konan, Hasel Çiçek; Çetkin, Erdal
    In this study we show numerically how thermal resistance in a two-dimensional domain with a point heat source can be reduced with embedded high-conductivity snowflake shaped pathways. The external shape of the domain is square, and its boundaries are adiabatic. Rectangular fins were used as high-conductivity pathways in order to minimize maximum excess temperature (Tmax). The geometry of the inserted pathways was optimized with consideration of Constructal Theory for minimum Tmax. In the first assembly, optimum number of mother (big) fins was uncovered as the area fraction increases. The results of the first assembly indicate that the increase in the number of mother fins does not increase heat transfer after a limit number for the fins, i.e., optimum number of mother fins exits. After uncovering the mother pathway geometry corresponding to the minimum Tmax, the daughter (small) fins inserted at the tip of them, i.e. second assembly. In the second assembly, the fin ratios, small fin location and angle between daughter fins were discovered when the area fraction is fixed. In addition, in the third assembly, larger daughter fins were attached to mother fins. The results of the second and third assemblies document what should be the geometric length scales and the number of daughter fins in order to minimize Tmax. The optimized design uncovers that the fins should be designed similar to snowflake shape. Therefore, the results also uncover snowflakes correspond to the designs with minimum thermal conductivity, i.e., not mimicking the nature but understanding it with physics.
  • Master Thesis
    The Effect of T-Shaped Fin Geometries on Heat Transfer Rate Enhancement
    (Izmir Institute of Technology, 2017) Çetin, Eylem; Çetkin, Erdal
    In this study, we show that maximum excess temperature on a heat generating cylindrical solid domain can be minimized with numerically optimized rectangular cavities and T-shaped fins. The effects of the cavities and the fins on heat transfer rate enhancement were compared while their volume fractions in a unit volume element were fixed. Furthermore, the designs correspond to the minimum thermal resistance were uncovered for two types of flows; parallel and cross-flow. The governing equations of the heat transfer and the fluid flow were solved simultaneously in order to show the effects of flow characteristics and the design on the thermal performance. Two-dimensional solution domain was used to uncover the thermal performance in cross-flow case. Because the flow direction is perpendicular to the heat transfer surface area of the heat generating domain. However, three-dimensional domain was used in parallel flow case because the fluid flows along the outer surface of the heat generating domain and the heat transfer surface area. For the cross-flow case, the results show that T-shaped assembly of fins with longer stem and shorter tributaries corresponds to thelower peak temperature. In addition, the results also show that there is an optimal cavityshape that minimizes the peak temperature. This optimal shape becomes thinner when thenumber of the cavities increase. In parallel flow case, fins with thicker and shorter stemand longer tributaries corresponds to the minimum excess temperature. In addition, longand thin cavity shapes increase the thermal performance in parallel flow case.
  • Master Thesis
    Numerical and Experimental Investigation of Radial and Tree-Shaped Vascular Channels for Self-Cooling Structures
    (Izmir Institute of Technology, 2016) Yenigün, Onur; Çetkin, Erdal
    In this study, we show experimentally and numerically how a plate which is subjected to a constant heat load can be kept under an allowable temperature limit. Vascular channels in which coolant fluid flows have been embedded in the plate. Three types of vascular channel designs were compared: radial, tree-shaped and their hybrid. The effects of channel design on the thermal performance for different volume fractions (the fluid volume over the solid volume) are documented. In addition, the effects of the number of channels on cooling performance have been documented. Changing the design from radial to tree-shaped designs decreases the order of pressure drop. Hence increase in the order of the convective heat transfer coefficient is achieved. However, tree-shaped designs do not bathe the entire domain. Therefore, additional channels were inserted at the uncooled regions (hybrid design). The best features of both radial and tree-shaped designs are combined in the hybrid of them: the flow resistances to the fluid and heat flow become almost as low as the tree-shaped and radials designs, respectively. Furthermore, this thesis shows how delaying the inlet of the coolant fluid for a given time interval affects the peak temperature. The effect of design on the maximum temperature shows that there should be an optimum design for a distinct set of boundary conditions, and this design should be varied as the boundary conditions change. This result is in accord with the constructal law, i.e. the shape should be varied in order to minimize resistances to the flows.