Department of Mechanical Engineering

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http://hdl.handle.net/20.500.11905/1217

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ANALYSIS OF GREEN HYDROGEN PRODUCTION USING SOLAR DISH STIRLING SYSTEM IN ANKARA REGION
(2023-01-27) TROSTER, Frederick Can; DEVRİM, Yılser
The world's energy demand is growing in parallel with the world's population and economy. In today's world, fossil fuels provide most of the electricity. By damaging the environment, the usage of fossil fuels endangers our future. Renewable energy sources are becoming more popular as technology advances. These eco-friendly supplies are critical for our future. Renewable energy is defined as energy derived from natural sources such as solar, wind, and geothermal. The sun is the most basic source of energy. Many systems have been developed to generate energy from the sun. Concentrated solar energy systems are becoming increasingly popular for generating solar energy. One of the concentrated systems, Solar Dish Stirling technology, attracts attention due to its great efficiency. This system, consisting of a dish with a mirror, a receiver, and a motor, can convert solar energy to electrical energy with 32% efficiency. Energy storage, in addition to energy generation, is critical for our future. One of the energy storage strategies, hydrogen production, looks promising for the future. The energy source used in hydrogen production is categorized. Green hydrogen is hydrogen produced using ecologically friendly, renewable energy sources. This zero-emission manufacturing approach is increasing in popularity. An electrolyzer is used in the generation of hydrogen. The water is split into hydrogen and oxygen by the electrolyzer. The separated hydrogen can be compressed with the help of a compressor and stored for later use. Green hydrogen production simulation in the Ankara region was investigated in this study using Solar Dish Stirling, one of the concentrated solar energy technologies. Solar Dish Stirling, PEM water electrolyzer, hydrogen compressor, and hydrogen tank for storage are all part of the system. The electrolyzer was powered by electricity generated by the Ripasso dish Stirling system. The offsetting approach has been implemented in the system. When there is insufficient radiation, but the total daily electricity generation is sufficient to run the electrolyzer, the electrolyzer and compressor are activated, and hydrogen production begins. The system can create more electricity and hydrogen in the summer than in the winter. The LCOE value was found 0.4595 $/kWh and compared to international values. Following the offset, strategy provides an advantage for the cost of the system. The system has a capacity of 47950 kW/h per year and can produce 377 kilograms of hydrogen per year. These systems are critical for our future. It will be a good solution to environmental challenges with growing technology and reduced investment costs.
EVALUATION OF THE THERMAL PERFORMANCE OF AUTOMOTIVE BRAKE DISC
(2023-01-27) ERKILIÇ, Kaan Tamer; JAFARI, Rahim
Acceleration is a crucial dynamic for a vehicle, although deceleration is the key element for vehicle safety. A vehicle's braking system is the sole piece of equipment that can bring it to a slowdown or halt. The function of a brake system is performed with the friction between disc and the pad. The thermal performance of the components it contains must be measured precisely in the design and test steps, and the component must show the required performance under operating conditions. In this study, an experimental setup was designed and produced to observe both aerodynamic and thermal characteristics of brake discs. Parts such as disc, pad, rim and tire on the experimental setup are exactly the same as those used in a typical passenger car. The quarter weight of a passenger car was adapted to the experimental setup on the shaft with cylindrical weights. In addition, a repetitive braking scenario was used in the experimental setup and simulations of the aerodynamic and thermal outputs of braking were carried out using detailed numerical models. In the experiments and simulations, it was observed that the air flow caused by the acceleration of the vehicle reduced significantly inside the rim, despites there was a turbulent air flow that takes place with the form of eddies inside the rim. As a result of thermal simulations and experiments, the temperature distribution on the brake disc has been observed, and it has been predicted that the area where the brake disc contact with the brake pad is higher than the temperature of the area directly opposite the contact area and the temperature is not uniformly distributed across the brake disc.
DESIGN, FABRICATION, INSTRUMENTATION AND TESTING OF AN EDUCATIONAL WIND TUNNEL
(2022-05-22) KILIÇKAYA, Murat Çığıl; AKAY, Hasan Umur; JAFARI, Rahim; TÜRKAKAR, Göker
An educational wind tunnel with a test section of 350x350 mm dimensions and 650 mm length, in which the maximum air velocity reaches up to 11.3 m/s with Reynold’s number of 267,000, was designed and built in 2019 by the author of this thesis with the help of a team of students in the Automotive Engineering Laboratory in Atılım University. In the scope of instrumentation studies, three force balance systems for drag/lift force measurements were designed, produced and tested. First balance sys tem was capable of measuring drag and lift force at only 90 degree angle of attack. Using it, a circular disc and rectangular plate the drag coefficient values of which are available on textbooks were tested and two velocity data were obtained. These two velocity data matched with a relative to each other percentage error with a maximum value of 2 in percent. Having obtained a velocity data and verified the reliability of drag load cell with first balance system, a second force balance system with angle adjusting capability was manufactured but lift load cell’s reliability could not verified due to high noise occurred during wind tunnel measurements and to the suspect that some components of second force balance may have interfered to the aerodynamics of test specimens. So, a third force system all components of which are outside the wind tunnel test section and that is still in use, was designed, manufactured and tested using the same test specimens that had been used during testing second force balance. They are/were NACA 2418 (Chord=80 mm and Span=80 mm) in 2D air flow, 81×81×2 mm Square Plate in 2D flow, and 81×81×2 mm Square Plate in 3D flow. All these wind tunnel measurements were compared using CFD analyses results (with ANSYS and COMSOL), 2D Thin Airfoil Theory, and a similar study presented with a paper. The outcomes were promising because in the case of no or low noise, wind tunnel measurements were close enough to the compared studies. Especially, some impor tant results were obtained about 2D Thin Airfoil Theory. All these studies show that wind tunnel setup can create a reliable flow in wind tunnel test section and in the case of no or low noise, a force balance system with strain gauge load cells can work well. The common solution to noise problem that is a Faraday Cage should be integrated to the upcoming force balance system(s). Furthermore, a moment balance system to be integrated to wind tunnel test setup can be a useful tool for producing scientific knowledge using this educational wind tunnel.
COATING OF SURGICAL NEEDLES WITH BN (BORON NITRIDE) AND RESEARCH ON THEIR MEDICAL PERFORMANCES
(2022-09-14) AYDOĞAN, Asude; KAFTANOĞLU, Bilgin
In this thesis, surgical needles are coated with Boron Nitride (BN) to improve their both medical and mechanical properties. BN coatings of needles are performed by using both magnetron sputtering (MS) method and Inductively Coupled Plasma (ICP) technology in the Physical Vapor Deposition (PVD) system. Also, stainless steel specimen produced from the raw material of needles, D2 steel and silicon are coated with BN. As a result of the obtained BN coatings, thickness, crystal structure, hardness, adhesion, and friction coefficient are measured. The performances of BN-coated needles are evaluated by suture attachment test and penetration test. As a result, the effect of ICP power on SS is observed for the first time and positive results such as increased hardness and adhesion are obtained. Also, D2 steel and silicon results are improved after ICP usage. According to the medical application results, the success of the suture attachment test increased with increasing substrate voltage. As ICP power is increased, both needle body bending, and average needle tip deviation are decreased. In addition, to support another theoretical study and fill the scientific gap about BN coatings, three different experiments are performed by changing the coating parameters such as increasing magnetron power, substrate voltage and Ar/N2 gas amount. Also, the effect of target plate-substrate distance is investigated. As a result, thickness and the intensity of BN coatings is decreased within the increasing target plate-substrate distance. The more substrate is closer to target plate the more thickness is obtained. Also, hardness and adhesion are increased.
INVESTIGATION OF THE EFFECTS OF MOOD STATES ON USERS’ THERMAL COMFORT
(2022-06-14) ÇETER, Aydın Ege; TURHAN, Cihan; ALKAN, Neşe
Providing indoor thermal comfort to the users has a great importance since most of the people spend 90% of their time in interior zones. On the other hand, accurate calculation of the thermal comfort has been a problematic issue and is the first priority in providing thermal comfort. Recent studies in this field have shown that there is a vital difference between the calculated thermal comfort and thermal sensation. Additionally, researchers have investigated the effects of human psychology, which is thought to be one of the important reasons for this difference. However, ongoing studies have only addressed the physical responses of the human body under psychological disturbance. Moreover, the mood state of the people is an important parameter of the human psychology. Therefore, this thesis investigates the effect of mood states on users’ thermal sensation and offers a novel “Mood State Correction Factor (MSCF)” on the existing thermal comfort model. For this reason, a series of experiments were conducted in a study hall of Atılım University between 16th of August, 2021 and 15th of April, 2022. Predicted Mean Vote (PMV), Actual Mean Vote (AMV) and Profile of Mood States (POMS) were used to investigate the effect of mood state on the thermal sensation. The results of the study indicated that the most effective mood state classes on thermal sensation of the users are very pessimistic, very optimistic and pessimistic, moreover, the users feel significantly warmer than the measurement results. Additionally, the MSCFs are calculated as -0.125, -0.114 and -0.075 for very pessimistic, very optimistic and pessimistic mood state classes, respectively.
SOLUTION OF STORE SEPARATION PROBLEMS USING OPENFOAM
(2022-03-12) ABUHANIEH, Saleh; AKAY, Hasan
In this thesis, the ability of OpenFOAM to solve the store separating from an air ve hicle (store separation problem) using a dynamic mesh (Overset/Chimera) technique for an industry-class (transonic/supersonic and generic) benchmark test case has been evaluated and improved. The major limitations of the standard libraries have been determined. To tackle these challenges, a new strategy has been proposed and imple mented using only open-source libraries and tools. The strategy combines porting, modifying and adapting an overset library from the OpenFOAM fork platform (foam extend) to the standard OpenFOAM platform (ESI). Furthermore, in order to over come the well-known weakness of the standard OpenFOAM compressible solvers, the newly adapted overset library was integrated with an open source, density-based and coupled solver (HiSA: High Speed Aerodynamic), which uses the OpenFOAM technology. HiSA solver has been used after the necessary validation process for steady-state, transient and overset simulations. For steady-state validation, the DLR F6, the steady-state Eglin and the steady-state SDM results have been used. Whereas, for transient and overset validations, the pitching airfoil case has been used. These validation results are presented in this thesis. Additionally, a new force restrained model was developed to consider the externally applied forces on the store by the store ejectors. The results of the developed strategy have been compared with the wind tunnel tests of the Eglin case and with the solutions of two well-known com mercial codes, showing good agreements with them. While the study has focused on simulations with inviscid Euler equations (typical of the test case considered here), the viscosity effect on the solution has also been studied with Navier-Stokes equa tions and compared with other results in the literature, showing minor differences. Additionally, mesh and time step independence studies have been conducted using the same test case (Eglin). Furthermore, the Eglin test case at supersonic regime has been solved too using the developed strategy in this work. The obtained results were in good agreement with the experiment and other results in literature. To the best of our knowledge, this is the first work which studies and validates the store separation problem in transonic and supersonic regimes with OpenFOAM.
DEVELOPMENT OF BORON NITRIDE COATINGS FOR SINGLE AND MULTI – LAYER FILMS FOR MECHANICAL AND BIOMEDICAL APPLICATIONS
(2022-06-15) HACALOĞLU, TUĞÇE; Kaftanoğlu, Bilgin
In this thesis, Boron Nitride (BN) coatings are performed with the Physical Vapor Deposition (PVD) system by magnetron sputtering technique. D2 steel is used as a main substrate in all experiments. In addition, PVD magnetron sputtering system is supported by additional power source, Inductively Coupled Plasma (ICP), which is a newly developed technology that has not been used before. In this study, BN coatings are applied on medical instruments, multi-layered coatings and with applied ICP power. Different substrates are coated with BN by applying different parameters. As a result of obtained BN coatings, thickness of coating, the crystal structure of the obtained BN film, the nanohardness of the thin film, adhesion of the BN coating and the friction coefficient of the BN coated surface are measured. Furthermore, it is discovered that BN coated orthopedically implants are prevented biofilm formation and accelerated bone healing. The thickness of the BN coating on electroless nickel-plated aluminum substrate is measured as the thickest coating in multi-layer coatings. The aim of BN coatings performed with an ICP supported PVD magnetron sputtering system to enhance the ionization energy as the ICP power is increased. As a result, allotropes of BN are optimized.
UTILIZING ARTIFICIAL NEURAL NETWORKS TO PREDICT HUMAN BODY EXERGY CONSUMPTION
(2022-03-10) Layth, Yousif; TURHAN, Cihan; LOTFISADIGH, Bahram
The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) defines thermal comfort as "the state of mind that conveys happiness with the thermal environment”. Energy and Matter can scatter as a system and move toward equilibrium with their surrounding environment, and this is referred to as exergy in thermodynamics. Predicted Mean Vote (PMV)/Percentage of Predicted Dissatisfied (PPD) model and adaptive thermal comfort approach are the two most widely used methods for assessing thermal comfort. However, it is also possible to apply the exergy notion to the human body system as an index of thermal comfort. The relationship between a person's exergy balance and their level of thermal comfort is that effectively dissipating heat and water from the body is essential to human well-being. For this reason, the lowest human body exergy consumption rate mostly gives the optimum thermal comfort level. In this thesis, an Artificial Intelligence-based work was conducted in a room of engineering faculty of the Atilim University, Ankara, Turkey, with an occupant being inside the room to obtain the best condition for his exergy and thermal comfort. Human body exergy consumption is extracted via a computer programme and environmental parameters are measured by objective sensors. Then, an Artificial Neural Network (ANN) model is developed in Python environment. A back propagation and sigmoid function is used in the neural network technique. A total of 133 data are included in the ANN model, with 75% (99 datasets) being used for training and the remaining for testing. A Mean Absolute Percentage Error (MAPE) of 1.98 and an accurate prediction rate (R2 ) of 0.91 are found under the provided conditions, indicating a good coordination between the artificial neural network model outputs and the human body exergy data. Simplicity, speed of analysis, and learning from restricted data sets are all features of an ANN model over human body exergy simulation. This thesis presents a novel concept that uses an ANN model to determine how much exergy rate people consume (HBExC). This is because artificial neural networks (ANNs) are the most commonly used artificial intelligence technique in the field of buildings and thermal comfort fields. After all, they can handle nonlinear variables' interactions rapidly and correctly, especially, exergy concept which has complex nonlinear relationships between its variables.
MODELLING, SIMULATION AND DESIGN OF A GREEN HYDROGEN BASED HYBRID ENERGY SYSTEM
(2022-03-01) Özkök, Duygu; DEVRİM, Yılser
As global warming increases and fossil fuel sources are depleted, renewable energy sources gain importance. Clean energy sources such as sunlight, wind, geothermal energies, and hydro energies constitute renewable energy sources. The fact that the sun and wind are endless sources makes renewable energy more important day by day. In addition, reducing foreign dependency increases the importance of renewable energy sources even more. Turkey has a very productive position in terms of both solar radiation and wind potential. This makes electricity generation from solar and wind energy even more important. However, the current high initial costs and low energy conversion efficiencies of renewable energy sources reduce the availability of renewable energy. Failure to produce electricity from solar energy in the evening also leads to blackouts. Therefore, the integration of solar and wind energy systems is used as complementary systems. The use of two or more renewable energy sources together is called hybrid systems. Rather than using a single renewable energy source, the use of a hybrid system is more advantageous in terms of both cost and efficiency. The system established in solar-wind energy integration can solve the problem of intermittent electricity that may occur from the sources installed as a single system. The fact that the sun produces electricity during the daytime and the wind produces electricity in the evening provides complementary features. Another problem that can be encountered in renewable energy sources is storage. As is known, batteries used in solar energy do not store seasonally. This shows that the electricity produced in excess cannot be used. Therefore, hydrogen energy comes into play as an alternative energy source. Storage of energy in the form of hydrogen (H2) provides solutions for both daily and seasonal storage. With the help of the electrolyzer, water molecules are decomposed into hydrogen (H2) and oxygen (O2) and stored as H2 and O2 in high pressure tanks. Fuel cells are also a source that converts the chemical energy created by hydrogen into electrical energy in this system. Fuel cells integrated into the solar wind system are also an alternative solution in terms of increasing energy conversion. There are six types of fuel cells. Among them, the proton exchange membrane fuel cell (PEMFC) is the most attractive due to its quiet operation and lower corrosion, high power density, low local emissions, low operating temperatures. Therefore, they can be powered by a PEMFC for hybrid systems with photovoltaic panels and wind turbines. The most important process in the studies of renewable energy sources is the simulation steps. This thesis study was carried out to meet the 25 kW electricity needs of Ankara Atilim University from hybrid systems without being connected to the grid. To solve the system storage problem, hydrogen energy and, accordingly, the fuel cell were designed. The Proton Exchange Membrane Fuel cell design, which will operate for 5 hours a day, was designed through the MATLAB program and integrated into the TRNSYS software program. System simulation was done using the TRNSYS program. The optimum number of panels was determined according to a fixed number of selected wind turbines for the operation of the electrolyzer. Finally, the leveled cost calculations were calculated, and the optimum system was selected.
THERMAL COMFORT INVESTIGATION AND RETROFITTING STRATEGIES OF AN EDUCATIONAL BUILDING
(2022-03-01) Ghazi, Sanarya; TURHAN, Cihan
In terms of global sustainable development, buildings are one of the largest energy consumers. Although technology advancements actively assist in constructing environmentally friendly buildings, current structures still consume a large amount of energy. Thus, we shall investigate educational facilities, one of the essential architectural types. It is vital to establish high-quality school structures to give a high-quality education to future generations. While numerous factors influence the building, thermal comfort significantly impacts the pupils. The pleasure a person feels in their thermal environment is thermal comfort. A suitable temperature environment aids physical and mental well-being. This study considers these aspects and attempts to evaluate the possibility of improving thermal comfort in educational buildings by making minor changes to the architecture rather than reconstructing them. At Atilim University in Ankara, Turkey, Design-Builder Software assessed an existing building model. The simulation was then run on the building's adjusted cases, totally seven retrofitting cases. Changing the window and frame types, as well as installing a Trombe wall, are some of the retrofitting options. In addition, the insulation material was replaced with three different materials in each case. A solar collector was added, the set temperature and airtightness were changed, and the light systems were changed to the led type. The Design-Builder ran the model for annual energy usage and recorded the result considering the building's modification. We conducted a comparative examination of the cases. The most compelling case for student thermal comfort was the use of Rockwool insulating material, which reduced student discomfort hours by 17% and was also the most effective for lowering CO2 emissions and energy consumption, none of the instances affected airtightness. Furthermore, using a solar collector was the most expensive choice.
MODELING AND COMPARISON OF MICRO INVERTER AND STRING INVERTER IN PHOTOVOLTAIC SYSTEMS
(2022-02-14) Durmuş, Gizem Nur Bulanık
Photovoltaic panels are structures that convert solar energy directly into electrical energy using photovoltaic cells connected in series and parallel. Several reasons are affecting photovoltaic panel efficiency negatively. Shading on the panel temporarily or permanently is one of the reason reduction of the efficiency. Panels can be exposed to the shading due to the clouding, buildings, or any other obstacles like dust, bird or leaf. Additionally, constant shadowing generates a hot spot effect. This situation causes some failures in the long-term on the panel or the panel group. Another problem is about connecting photovoltaic panels. In mostly, photovoltaic panels are connected in series at the plant-based systems. Serial connected panels reach very high voltages, and the high voltage based failure can occur. In these systems, photovoltaic panels can be arranged in limited ways in photovoltaic systems where the string inverter is used. Conversely, micro inverters are panel based systems and more comfortable to install. There is not any necessity to arrange the panels concerning the inverter. Although micro inverters are preferred for small scale photovoltaic systems, in some cases, they are used for large scale photovoltaic systems. Since each panel produces its own AC power, the high voltage problem is eliminated. However, due to their high costs and lower efficiencies, they are not preferred especially in large scale plants. In this thesis, considering these problems, 24 kWp installed power photovoltaic system in Ankara Province was simulated with three different shading densities with both string and micro inverters and these simulations were compared.
TOPOLOGY OPTIMIZATION OF A SANDWICH STRUCTURAL COMPONENT AGAINST HIGH IMPULSE LOADINGS
(2022-01-21) Şenel, Barkın; Aslan, Özgür; Baranoğlu, Besim
Sandwich structures are used in many areas today due to their lightness, economy and durability. Application in armoured military vehicles is one of these areas. Accord ing to previous studies in the literature, sandwich structures provide a great advantage over monolith structures. Today, researchers try to develop sandwich structures in terms of material or topology optimization to further increase this advantage. Nu merical analysis trials applied before experimental studies, on the other hand, help this development in terms of time and cost. In this thesis, different core geometry types selected are modelled in the SolidWorks package program. Then, the analy ses were made in the ABAQUS/Explicit finite element program. Initially, analyses were performed under fixed parameters for evaluation and comparison purposes only. According to the results, the material parameters were determined according to the material parameters to be used in production and the analyses continued in this way. However, in this study, no material optimization was made, only the topology was focused. In addition, while the geometries are modelled, it is aimed to determine the selected geometry types in a way that will not cause problems in terms of production. With these determined parameters and analyses, an optimum core geometry has been proposed, which is also easy in terms of production.
DESIGN AND ANALYSIS OF THE CHASSIS OF NEW GENERATION ELECTRIC OVEN COOKER IN VIEW OF MANUFACTURING AND FLUID FLOW
(2022-01-17) TEKE, Ethem; BARANOĞLU, Besim; AKAY, Hasan U.
Built-in ovens are cooking devices that are embedded in kitchen furniture. Built-in ovens placed in a standardized furniture size are subject to international safety standards. During the cooking process, the cooking cavity, which can reach up to 250˚C, heats the regions around it. The temperature of the kitchen furniture and the temperature of the areas that the user can contact such as the oven door are very important parameters. There are cooling groups placed on the oven cooking cavity to keep this temperature at a certain level. Cooling group keeps the temperature under control by sucking hot air from the cooking cavity, the space between the oven and the furniture and between the glass doors of the cooking cavity. The industrial competition forces manufacturers to design with larger cooking cavities. The growth of the cooking cavity narrows the place of cooling groups and requires smaller and more efficient cooling group designs. The air leaving the cooling group must be homogeneous in order to cool the glass doors of the cooking cavity uniformly. In order to optimize the flow and homogeneity of air outlets, the geometry of the sheet metal cover in which the cooling group fan is located should be optimized. In this study the formability of the sheet metal cover containing the impeller is verified with the Finite Element Method (FEM) simulations and then the homogeneity and the volumetric flow rate of the air flows are calculated with Computational Fluid Dynamics (CFD) are applied. The results yielded into a better design for a press formable sheet metal cover with adequate flow characteristics.
MODELLING AND OPTIMIZATION OF HARNESS DESIGN AND COST ANALYSIS USING SOFTWARE TOOLS
(2022-01-11) Tankut, Mehmet Kemal; Lotfisadigh, Bahram; Kara, Ali
A harness is a cable web or an assembly of cables that transmits electrical power, signals, or information between two or multiple sources. It also may have some other subcomponents such as connectors, backshells, wires, boots, transitions, shields, jackets, and splices. Since a harness may consist of various materials and subcomponents, determining required materials is critical in the harness design and production process. The selection of appropriate components requires an excessive amount of time to browse through standards and datasheets, therefore. Time losses are depending heavily on the designer's experience level and complexity of the ordered harness. In this research, to reduce time losses during harness design and meanwhile reduce the risk of error in component selection software is developed. This study encapsulates the impacts and results of such an attempt to improve harness design process considering harness complexity, user experience. According to experimental results, consumed time on projects per month for each designer is calculated and a cost model developed. Finally, the contribution of prepared software is evaluated and results show that application of this software in the design and development process of harness regardless of harness complexity and user experience is beneficial.

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