Makine Mühendisliği Bölümü Koleksiyonu
https://hdl.handle.net/20.500.12440/92
2024-03-29T08:16:05Z
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Influence of post processing on the mechanical properties and wear behavior of selective laser melted Co-Cr-Mo-W alloys
https://hdl.handle.net/20.500.12440/6161
Influence of post processing on the mechanical properties and wear behavior of selective laser melted Co-Cr-Mo-W alloys
Varol, Temel; Aksa, Hüseyin Can; Yıldız, Fatih; Akçay, Serhatcan Berk; Kaya, Gürkan; Beder, Murat
In the study, the effect of laser energy density and post-processes (sintering, cold rolling, and hot rolling) on the properties of Co-Cr-Mo-W alloys fabricated by selective laser melting (SLM) are investigated. The samples are fabricated at 83, 125, and 167 J/mm3 of laser energy density to compare their properties. XRD results show that the samples in which ε-Co martensitic phase dominates γ-Co phase are the samples exposed to hot rolling. The highest hardness values obtained with the hot rolling applied after SLM. The hardness for SLM1hr, SLM2hr and SLM3hr is 489.2, 500.4 and 509.8 HV, respectively. The lowest wear rate values are also obtained after the hot rolling post-process, where the highest hardness values and lowest average COFs were obtained. © 2024 Elsevier Ltd
2024-01-01T00:00:00Z
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Effect of thickness and melting temperature of phase change material integrated into exterior wall on building energy performance and CO2 emission reduction
https://hdl.handle.net/20.500.12440/6120
Effect of thickness and melting temperature of phase change material integrated into exterior wall on building energy performance and CO2 emission reduction
İlgar, Gamze; Terhan, Meryem
In the study, the effect of phase change materials integrated into the building's external wall has been investigated in terms of material type, thickness, and melting temperature of phase change material on the building energy performance for İzmir Province. A villa residential project has been modelled in 3D using DesignBuilder energy simulation software and two different external wall configurations have been designed by changing the position, thickness and melting temperature of the PCMs into the wall. The amount of CO2 emission reductions that PCMs will provide according to the fuel type of the building's heating system has been calculated. Using PCMs in the external wall not only provides high heating and cooling energy savings but also increases thermal comfort indoors by reducing temperature fluctuations. The PCM melting temperature of 23℃ performs quite well compared to other temperatures in both cooling energy and heating energy demand reduction. By increasing the triple thickness of the PCM, 18.81% in heating energy and 22.85% in cooling energy savings can be achieved. Depending on the external wall and phase change material types, different thicknesses and melting temperatures of PCM, annual total energy saving of the phase-change material is calculated between 10,349.50-83,345.98 kJ/m2.year and the annual CO2 emission reduction according to fuel types has been found as 0.672-14.284 kgCO2/m2.year. © 2024 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.
2024-01-01T00:00:00Z
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Waste Heat and Mass Recovery from Boiler Exhaust Gases in a New Generation District Heating System: Energy and Exergy Analysis
https://hdl.handle.net/20.500.12440/6093
Waste Heat and Mass Recovery from Boiler Exhaust Gases in a New Generation District Heating System: Energy and Exergy Analysis
Terhan, Meryem
The study performs energy and exergy analyses for each component such as boilers, buildings, distribution networks and heat exchangers of a new generation district heating system. Energy and exergy efficiencies are compared for all system components, and energy and exergy losses are presented using Sankey and Grassman diagrams. Three flue gas condensers with finned bundles are designed for different capacities of boilers that intend to recover water and heat from the waste flue gas in the district heating system due to high flue gas energy losses. Colburn-Hougen and one-dimensional finite difference methods are used to design the flue gas condensers with the MATLAB program. The exergy analysis showed that the exergy input to the system is lost by 4.52% from the distribution networks, 4.15% from all buildings and 2.18% from the flue gas. In the system, the energy and exergy efficiencies of the boilers are calculated to be 87.23% and 17.32%, respectively, and the heat loss from the flue gas is found to be 12%. The design results show that the values of mass convection coefficient (km) for all flue gas condensers decrease from 0.0706 at the inlet condensation zone to 0.0354 towards the outlet. The total condensation rate and condensation efficiency are found to be 86 kg/h and 60%, respectively, for the 2500 kW boiler. © 2023, King Fahd University of Petroleum & Minerals.
2023-01-01T00:00:00Z
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Wong-Zakai approximation for stochastic models of smoking
https://hdl.handle.net/20.500.12440/6089
Wong-Zakai approximation for stochastic models of smoking
Sengul, Sueleyman; Bekiryazici, Zafer; Merdan, Mehmet
In this study, Wong-Zakai approximation method has been used to obtain approximate solutions for two compartmental models of smoking dynamics. Stratonovich stochastic differential equation systems are obtained for these two stochastic models for the application of Wong-Zakai method. Wong-Zakai method is used together with the predictor-corrector deterministic approximation method where Adams-Bashforth method is used as the predictor pair and Adams-Moulton method is used as the corrector pair. Stochastic Runge-Kutta IV, Euler-Maruyama and stochastic Runge-Kutta strong order 1.0 schemes are also used to investigate the models and the results are compared to the results from Wong-Zakai approximation. The comparison shows that Wong-Zakai method is a reliable tool for the analysis of stochastic models and can be considered as an alternative investigation method for modeling studies. Solution graphs, error graphs and numerical results have been given as evidence to show that Wong-Zakai method can also be a reliable method for analyzing various models. An alternate technique for parallelizing the algorithm has also been given to decrease CPU times for Wong-Zakai method. This technique is suggested to overcome the extra calculation load that comes with Wong-Zakai method.
2023-01-01T00:00:00Z