Authors:Batuhan ÜĞÜDÜR; Ümit İŞKAN, Mehmet DİREK Abstract: This study aimed to assess the effectiveness of an ejector refrigeration cycle, using a laboratory-scale experimental system operating in different configurations. The investigated configurations consisted of a conventional vapour compression refrigeration (CVCR) system and a dual evaporator ejector system (DEES) operated in two modes: DEES with a single thermal expansion valve (DEESA) and DEES with dual thermal expansion valves (DEESB). The findings revealed that the utilization of the ejector enhanced the refrigerant's mass flow rate. Additionally, the DEESA configuration achieved higher cooling capacities compared to the CVCR. Moreover, the DEESA configuration achieved up to 21% higher coefficient of performance (COP) values. On the other hand, when the system was operated in the DEESB configuration, it yielded lower evaporation temperatures and higher superheating degrees in comparison to DEESA. Based on the evaluations, it can be concluded that the ejector operates more efficiently in systems with dual evaporators, thereby making positive contributions to overall system performance. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Edip TAŞKESEN; Ruzgar UREN Abstract: Nanofluids are fluids that contain nanoparticles that improve thermal characteristics. The thermal efficiency of systems that use nanofluids is higher than that of systems that use water as the working fluid. Solar thermal energy and systems, nanofluids and their structures, nanofluid integration into solar thermal systems, and the positive and negative consequences of nanofluid usage in these systems were all addressed in this study, emphasizing the importance of their integration. This study describes a study on using nanofluids in solar thermal systems. This research aims to examine the potential benefits of employing nanofluids, such as increased efficiency and lower prices. Furthermore, the study demonstrates that using nanofluids can reduce the size of the solar collector required to achieve the same performance level, which can lead to a decrease in the overall cost of the solar thermal system. This study's results indicate that using nanofluids in solar thermal systems can significantly enhance efficiency and reduce costs. However, further research is needed to fully explore the benefits and limitations of using nanofluids in solar thermal systems. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Sameh YOUNİS; Güven TUNÇ Abstract: This study examines the electricity crisis in the Gaza Strip and its impact on public well-being. Adopting a sequential exploratory mixed-methods approach, data were collected from 350 households and key institutions. The research assesses the current state of renewable power technologies applicable to the region and develops a performance matrix to identify the most suitable technology for providing clean and affordable electricity. The findings highlight solar energy as the most viable solution for addressing the electricity shortage in the Gaza Strip. Moreover, the study underscores the adverse effects of electricity shortages on vital services, including health, water, and sanitation, as well as the fragile economy. The research recommends strategic investments in solar energy as a reliable and cost-effective solution that is readily accessible to meet the energy needs of the Gaza Strip and Palestine at large. This study provides a valuable resource for national and international NGOs, offering insights into the strengths, weaknesses, opportunities, and threats within the Gaza Strip's electricity sector. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Gonca KETHUDAOGLU; Fatih AKTAŞ, Salih KARAASLAN, Seyfi POLAT, Nureddin DİNLER Abstract: Numerical methods are commonly used for analyzing combustion characteristics. Besides, they provide an opportunity to predict emissions of an engine. In this paper, the conversion of a single-cylinder diesel engine to HCCI combustion model is investigated with AVL Boost v2021R2. The model was used to simulate the power, emission, bsfc value. In-cylinder pressure results also are obtained from the model. Verification of the model is conducted with experimental data from the literature. The differentiation between the numerical and experimental results remained below 8.9% for the power, below 6.62% for bsfc. In addition to this, the model gave maximum pressure values with an accuracy of ± 1%, and maximum HRR values with an accuracy of ± 2%. Maximum HRR values and in-cylinder pressure curves for 1200-2400 rpm were obtained with acceptable accuracy. Besides, the operating range of an HCCI engine fueled with n-heptane was investigated using a zero-dimensional single-zone model with reduced fuel chemistry. The compression ratio and inlet air temperature effect on HCCI combustion were analyzed. The increasing the air inlet temperature to 40oC from 20oC, increases the lowest air-fuel ratio about 6.6% which the engine can operate without entering the knock zone, at 17.5 CR at 1200rpm. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Fatih OĞUZALP; Musa TERKES, Alpaslan DEMİRCİ Abstract: The recent increase in renewable energy generation can balance consumption and reduce carbon emissions. With battery energy storage optimizing supply and demand, it is more important than ever to manage charge control to the benefit of all stakeholders. In this paper, the developed and proposed energy management control methods based on the technical operating criteria of battery energy storage (BESS) and considering self-consumption rate (SCR), self-supply rate (SSR) and curtailment rate are compared in terms of environmental index and economics for daily and annual demand profiles for various household prosumer demand profiles in Istanbul and Antalya. Considering the supply-demand matching based on demand profile, feed-in damping, fixed feed-in, schedule mode, schedule mode with constant charging power and self-consumption control methods are proposed for optimum operation for each prosumer profile. The results show that feed-in damping and fixed feed-in methods can reduce household prosumer costs by up to 22.3% in the daily analysis. Moreover, similar control methods can increase SCR by up to 29.5% and reduce costs by up to 10.62% for higher irradiances in the annual analysis. Proper management of BESS charge control can facilitate sustainable development goals by assisting plans of many stakeholders. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Kemal BİLEN; Batukan Cem TARHAN, Selahattin ÇELİK Abstract: The operating parameters of proton exchange membrane fuel cells (PEMFCs) are very effective at generating heat. The study examined and evaluated parameters that can help determine fuel cell (FC) performance. The parameters and structures used in systems have been examined. In this context, performance evaluations have been made by performing electrochemical analyses of PEMFCs. Evaluations about how the study parameters affect the performance was made on MATLAB® and the results were presented. As a result of the study, it was seen that the operating temperature increased the efficiency until it reached certain limits. On the other hand, although the performance-enhancing effects of the working pressure are observed, high pressure appears as an obstacle. Air stoichiometric rate is another variable that affects FC performance. While high stoichiometric rates improve performance, they can adversely affect the membrane. According to the simulation result, it was found that the working temperature, working pressure and air stoichiometry should be optimized together. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Afşin Kılıçarslan ÖZBEK; Serhat KARYEYEN Abstract: Air vehicles have began to develop with advancing technology. In order to increase the thrust and reduce pollutant levels at high speeds, researchers focus on different combustion techniques. For this purpose, within the scope of this study, A Scramjet engine combustor has been studied. The effect of reduced oxygen concentration in the air on Scramjet engine combustion was investigated. A hydrogen fueled Scramjet engine is used. In order to seek oxygen concentration effects on combustion characteristics of the Scramjet engine combustor, oxygen concentration in the oxidizer (by mass) was reduced, and the concentration conditions were performed at 23.2%, 21%, 20%, 19%, 18%, 17%, 16%, and 15%. Fort he modelings Reynolds Average Navier-Stokes (RANS) standard turbulence model is preferred for turbulent modeling. A combination of Eddy Dissipation and Finite Rate combustion model was selected to model combustion. The data obtained through the modelings were compared with the experimental data, and the results are in good agreement with the measurements. The results predicted are evaluated, and it was concluded that the velocity increased as the oxygen concentration was increased. It was also predicted that the temperature difference caused by the oxygen concentration decreased with moving away the flame position from the combustor. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Buğrahan ALABAŞ; Zeliha TÜRKKAHRAMAN Abstract: NOX emissions and flame characteristics in gas turbine burners are a current issue. Different combustion methods are tested for the solution of NOX emissions. One of these methods is oxy-colorless distributed combustion. In this method, CO2 is used as a diluent instead of N2 gas in the air. In this way, nitrogen does not enter the combustion chamber and theoretically NOX emissions are planned to be zero. In this study, a premixed and swirl assisted gas turbine combustion chamber used experimentally was verified numerically. Analyzes were carried out by keeping 3 kW thermal power, 1 swirl ratio and 0.7 equivalence ratios constant. The oxy-colorless distributed combustion method was applied to the pure methane flame at different O2/CO2 ratios. Analyzes were carried out with the O2 ratio of 26%, 21%, 19%, 17% and 15% by volume. The results showed that the colorless distributed combustion conditions were achieved as the CO2 ratio increased. Thanks to the oxy-colorless distributed combustion method, almost zero NOX emissions have been achieved. In addition, as the O2 ratio in the oxidizer mixture decreased, a significant decrease in the flame temperature was detected. Thanks to this study, the effect of oxy-colorless distributed combustion conditions in a premixed and swirl supported combustion chamber was investigated. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Meltem KOŞAN Abstract: In recent years, the use of refrigerants, which increase the global warming potential by creating a greenhouse effect, has begun to be restricted in refrigeration systems. More environmentally friendly and more efficient synthetic mixtures and natural refrigerants are replacing refrigerants with high global warming potential. In this study, R404A refrigerant, which is frequently preferred in refrigeration systems and has a high global warming potential, was discussed. Six different refrigerants (R407H, R448A, R454C, R468A, R290, R1270) that could be alternatives to R404A refrigerant were examined and compared with R404A. Energy, exergy, and environmental analyzes were performed under the same conditions according to -10 ℃, -5 ℃, and 0 ℃ evaporating temperatures. Among the refrigerants, R290 had the best value with a coefficient of performance of 4.11 and an exergy efficiency of 40.04%. The values of R1270 refrigerant were also almost the same as R290. Even if R468A shows the lowest performance, it can be preferred over R404A because its global warming potential is lower than R404A. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Erhan ARSLAN Abstract: In this study, single-pass and double-pass photovoltaic thermal collectors were designed and analyzed numerically. Energy efficiency and heat transfer coefficients of the PV module were calculated in the study. For case studies two different meteorological conditions (winter and summer) choosed. Case studies were performed with three different Reynolds number (15059, 17805, 22061). Avarage thermal efficiencies obtained for single and double-pass PV-T calculated in winter 65.15% and 67.88% ; summer 56.09%, and 58.46% conditions, respectively. For double- as PV-T, these values are It has been determined that the temperature of the PV module decreases with the increase in flow rate. Avarage electrical efficiency for single pass PVT in winter condition determined as 13.68% where for summer it was calculated as 13.24%. For double pass PVT these values obtained as 14.40% and 13.94%, respectively. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Eren AKÜZÜM; Erdem ÇİFTÇİ Abstract: Today, energy needs are increasing rapidly. Since our country imports a large part of its energy resources, it is extremely important to use energy efficiently and protect the environment in order to leave a livable world to future generations. One of the losses in energy transmission is transmission loss. In order to prevent this loss all over the world, "distributed energy production" method should be encouraged. Through combined heat and power systems, we can generate heat and electricity and save energy. Cogeneration systems can generally pay for themselves within 1.5-4 years. The aim of this study is to contribute to science with a broad literature review including the design of combined power systems and the technical and economic evaluation of their most efficient applications. The systems in the literature are investigated and comparisons are made. Hydrogen fuel cell types for domestic applications are detailed and hydrogen is considered to be a logical choice. The effects of design and performance parameters are analysed. This combined power system does not harm the nature; it utilises natural resources such as wind, sun and hydrogen, which can also be obtained by electrolysis of water. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:İsmail ATA; Burak AKGÜL Abstract: In this study, hybrid-electric propulsion systems, which have become a focal point in aviation in recent years, were addressed. In order to see the effects of hybrid-electric propulsion systems on fuel consumption, greenhouse gas emissions and flight costs, five different flight times (60, 90, 120, 150, 180 min) and five different cruise altitudes (1200, 1800, 2400, 3000, 3600 m) were compared with conventional flights. The widely used Cessna 172S aircraft was taken as a reference for the conceptual applications in the study. As a result of the study, the hybrid-electric propulsion system achieved the highest fuel and cost savings of 15.1% and 14.2%, respectively, for 120 minutes flight time and 2400 m altitude, while the lowest fuel and cost savings of 9.7% and 9.1% were achieved for 60 minutes flight time and 1200 m cruise altitude. The highest CO2 reduction was 6.86 kg per hour for 120 minutes and 1200 m altitude flight, while the lowest CO2 reduction was 4.47 kg for 180 minutes and 3600 m altitude flight. It has been determined that flights with hybrid-electric configuration have advantages over conventional flights. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Murat TAŞTAN; Kamil MUTLU, Serdar ÇETİNTAŞ Abstract: In this study, the instability and emission changes of hydrogen-enriched methane-propane fuel under external acoustic application in a premixed and vortex assisted system were investigated. In the experiment, 67% -33% and 63,5% -31,5% -5% were studied under different acoustic stresses as fuel mixtures. It is known that hydrogen can reduce the emission parameters polluting the environment and its effect on combustion stability. For this reason, interest in the use of hydrogen fuel with other fuels has increased. It may be possible to improve the combustive performance properties of compatible methane and propane mixtures by adding hydrogen. Also, the effects of acoustic applications were examined. Addition of hydrogen to the methane/propane flame increased the heating value of the mixture and caused flame instability due to the increase in laminar flame velocity. There was an increase of 12.2% in light intensity. When the amount of hydrogen increased, the flame was more resistant to acoustic stress. High dynamic pressure fluctuations occurred with 90 Hz acoustic forcing. The emission capacity of the mixture to which hydrogen is added by acoustic forcing has consistently higher values. This was attributed to the change in reaction kinetics due to the increased content. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Gökhan ARSLAN; Seda YÜKSEL Abstract: A thermal analysis of a forced circulation solar water heating system (SWHS) was carried out. Three different models were analyzed: SWHS without an auxiliary heater, SWHS with an auxiliary heater, and electric heater only. The study was carried out for the province of Mersin-Turkiye. Flat plate collectors with different structural properties were used in simulations, the best results were obtained with the collector with black chrome absorber coating. This system met 55% of the hot water requirement on the design day without requiring any auxiliary heater. During the season, 18.7% of hot water needs were met in January, 20.42% in February, 37.6% in March, 31.2% in November, and 20.5% in December. SWHS with an auxiliary heater, consumed 1130.3 kWh of electrical energy during the heating season, resulting in 540.3 kg of CO2 emissions. 33 % reduction in greenhouse gas (GHG) emissions is achieved with this system compared to a base system powered by electricity only. The hot water use profile is an essential factor in the design of the SWHS. Since the systems using fossil fuels can meet the needs of the users, energy storage techniques must be adapted to the SWHS to be an alternative. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Uğur KILIÇ; Ömer ÇAM Abstract: The short-haul flights have higher emission values than medium or long-haul flights when emissions per distance are considered. In this study, the potential to reduce greenhouse gas emissions by replacing short-haul flights which carried out by a narrow-body commercial aircraft from/to Konya City in Turkey with regional jets or high-speed trains (HSRs) has been investigated. The flight trajectory is selected from Konya Airport to İstanbul Sabiha Gökçen Airport, and that trajectory is a frequently performed domestic flight between Konya and İstanbul. The IMPACT platform is used for the calculation of fuel burn and gas emissions. According to the results, traveling with regional jets or high-speed trains from/to Konya City which is the most 15th polluted city in Europe, provides advantages in terms of environmental impact. Traveling with HSR which is the best traveling option in this study, provides approximately 3.3 times more green travel than the currently used narrow-body passenger aircraft between Konya and İstanbul. In addition, this mode of transportation can become more environmentally friendly by using renewable energy sources to produce its electricity needs. It is expected that this study will serve as a guide for airline and high-speed rail operators and regulators to determine the most environmentally efficient travel options based on fuel burn and emission parameters. PubDate: Fri, 22 Sep 2023 00:00:00 +030
Authors:Pooya LOTFABADİ Abstract: Energy is a significant part of socio-economic development of modern societies. Increasing fossil fuel consumption is almost the main source of energy throughout the world. Thus, it is essential to search for more sustainable alternatives or a method to decrease this huge amount of usage. On the other hand, the building industry is known as one of the biggest energy consumers. Among building energy efficiency measures, openings are playing a key role in declining energy consumption, especially in the hot summers of Cyprus. Therefore, this study carries out a field measurement of various opening sizes in the case study in order to make a satisfactory situation both from energy efficiency and visual comfort considerations. Meanwhile, a studio in a faculty of architecture, Famagusta, North Cyprus, has been selected as an experimental examination to show the effectiveness of the method. In order to analyze its energy performance, the calculation simplified method is chosen. Outcomes are intended to illustrate the benefits of the calculation method and to authorize opening size comparisons to display the differences in energy conservation measures inherent in the various compliance methods allowable by the regulations. Finally, the results obviously display that by decreasing the window-to-wall ratio, the heat loss significantly reduces. But, by considering the daylight factor (DF) in the standard defined range and applying 750lux as an essential lighting requirement for the studio, finding the minimum WWR seems more meaningful. Therefore, according to the mentioned criteria in this special case, an optimum amount of WWR can be considered in the range of 10 to 20%, which gives architects some flexibility to apply in their designs. PubDate: Fri, 22 Sep 2023 00:00:00 +030
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