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    Analysis of cascade vapor compression refrigeration system using nanorefrigerants: Energy, exergy, and environmental (3E)
    (Elsevier, 2024) Yilmaz, Metin; Cimsit, Canan; Keven, Arzu; Karaali, Rabi
    Nanorefrigerants are considered the most efficient heat transfer fluids for improving heat transfer properties in the refrigeration and air conditioning equipment. For the first time in this study, energy, exergy, and environmental evaluation (3E) analyses were performed by the addition of different nanoparticles to a low GWP refrigerant pair such as R290/R1233ZDE in a cascade refrigeration system. CNT, CuO, and, TiO 2 nanoparticles were added to the refrigerant. The effect of nanoparticles on the cascade refrigeration system was analyzed using a model based on density changes. A detailed thermodynamic analysis was performed of the cascade refrigeration system at different evaporator temperatures and mass ratios. The power consumption of the compressor decreases as the evaporator temperature increases for all types of nanoparticles, resulting in an increase in COP values. The analyses showed that CuO nanoparticles had the highest performance. It has been observed that the energy and exergy efficiency increase as compressor work decreases with increasing mass ratios in all nanorefrigerants. In addition, the results indicated that all nanorefrigerants emit lower monthly CO 2 emissions compared to the pure refrigerants. The nanorefrigerants play a crucial role in reducing energy consumption and promoting environmental protection compared to traditional refrigerants.
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    Analysis of Some Tribological Properties of Hazelnut Oil in Gasoline Engines
    (2022) Keven, Arzu; Karaali, Rabi
    In this article, oil obtained from vegetable was used to lubricate a single-cylinder 2-stroke gasoline engine as lubricating oil, and tribological function of the obtained oil was investigated. To investigate the tribological functions of the lubricating oils, a 2-stroke single-cylinder gasoline engine was used. For mineral oil and hazelnut oil, the test engine was run for 100 hours for each one and were used to lubricate in the test engine as lubricating oils. Samples were prepared for the aim of the determining the wear on the cylinder surface, and also EDS (Energy Dispersive Spectrograph) analysis were obtained. The results of the analyses showed that, the wear on the cylinder surface were increased in the studies using hazelnut oil and the C content of the cylinder sample increased compared to the study with mineral oil. Al element was detected in the cylinder sample in the hazelnut study, that the reason for this, is the transport of the Al element during the friction event in the piston material to the cylinder surface.
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    Evaluation of four different cogeneration cycles by using some criteria
    (De Gruyter Poland Sp Z O O, 2022) Karaali, Rabi; Keven, Arzu
    The purpose of this article is to evaluate four different gas turbine cogeneration cycles which are basic, absorption cooling, air heating and air fuel heating cogeneration cycles by using the most important six evaluation criteria for different excess air coefficient, different compression rates, and different compressor inlet air temperatures. These six evaluation criteria are electrical heat ratio, exergy efficiency, incremental heat rate, artificial thermal efficiency, fuel energy saving ratio, and specific fuel consumption. It is seen that the air-fuel heating cogeneration cycle is the most efficient among the cycles examined for a certain compressor compression ratio, followed by the air heating, basic, and absorption cooling cycles.
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    Exergetic analyses of air-fuel preheated cogeneration plants in food production
    (EDP Sciences, 2024) Keven, Arzu; Karaali, Rabi
    Lower emissions and better performances in food production also affect the cost, the environmental effects, and the quality of the products of the agriculture and food industry. The aim of this study is to investigate and to analyze the exergetic performance of the production of heat exergy and power, to reuse waste heat and to give optimum reaction and to adapt to changing demands of the food production process and agriculture. Because of those reasons, an air fuel preheated (recuperative) cogeneration plant is taken to analyze the exergetic performance and working conditions by using exergy analysis and 1st and 2nd laws of thermodynamics. Energy and exergy efficiencies, combustion chamber and gas-turbine outlet temperatures, electric-heat exergy rates, specific works, and total electric and heat energies and exergies are calculated by taking various environmental temperatures and various excess air coefficient. Effects of the environmental temperatures and the excess air coefficient on the exergetic performance of the recuperative cogeneration plants were calculated, obtained, and discussed. For the best exergetic performance and working conditions, some recommendations were done for agriculture and for the food production process. In that study, it is found that, the recuperative cogeneration plants can obtain and give the best solutions and can adapt to changing demands of heat and electric rates. Also, it was found that, lower ambient temperatures give better electric efficiency, but lower heat exergy and electric rates. However, higher excess air coefficient increases the performance of the recuperative (air fuel preheated) cogeneration plants. © The Authors, published by EDP Sciences.
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    Exergy analyses of two and three stage cryogenic cycles
    (De Gruyter Poland Sp Z O O, 2022) Atasbak, Musa; Keven, Arzu; Karaali, Rabi
    Cryogenics has an important influence on industry and science. In this study, optimum working conditions are obtained by applying exergy analysis and local optimization methods to two- and three-stage vapor compression cascade cryogenic cycle. The first and second laws of thermodynamics, exergy analysis, and local optimization methods are applied to the two- and three-stage cascade cryogenic cycle. By considering the needs and demands, it is possible to create new cycles by adding new devices and/or new stages to these cycles. The results of the optimum operating conditions are obtained for the two- and three-stage vapor compression cascade cryogenic cycle. It is seen that to achieve high COP values and high efficiency; it is necessary to reduce the compression ratio of the compressor as much as the fluid allows. For the two-stage cycle, the minimum total work required for cryogenic cooling is around P (7) = 2,400 kPa. The COP value is 0.30 between P (7) = 2,400 and 2,800 kPa, and the maximum exergy efficiency is obtained around 0.235. It is seen operating the first-stage compressor at high pressures increases the total losses of the entire cycle from 7,500 to 18,550 kW. The increase in total exergy losses is around 247%, and operating the first-stage compressor at high pressures increases the exergy efficiency of the entire cycle. The increase in total exergy efficiency is around 160%. When the second-stage compressor is operated at low pressure, the COP value increases by 2%, the exergy efficiency increases by 20%, and the exergy losses decrease by around 40%.
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    Performance analyses of basic cogeneration basic cogeneration plants in agriculture and food production
    (EDP Sciences, 2024) Karaali, Rabi; Keven, Arzu
    Energy in agriculture and in food production have vital importance that affect directly the cost and the quality of the products. Micro cogeneration plants are widely used in the World to produce heat and electricity at the same time in a same plant. The aim of this study, to analyze the performance of the production of power and heat for the food production process and the agricultural needs. For that reason, a basic cogeneration plant is taken to analyze the performance by using 1st and 2nd laws of thermodynamics and exergy analysis method. The electric-heat exergy rates, the energy and exergy efficiencies, the combustion chamber and the gas turbine outlet temperatures, the total electric and heat energies and exergies, and the specific works were calculated for various ambient temperatures and for various excess air rates of the basic cogeneration plants fueled with methane. The effects of the various ambient temperatures and the various excess air rates on the performance of the basic cogeneration plants were obtained, discussed and analyzed. For the best performance and for the best working conditions of the basic cogeneration plants in agriculture and food production process and food industry recommendations were done. It was found that, lower ambient temperatures give higher electric efficiency, but lower heat efficiency. However, an optimum excess air rates for the best performance was found at the value 2.3 of the excess air rates of the basic cogeneration plants fueled with methane. © The Authors, published by EDP Sciences.