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Öğe Analysis of cascade vapor compression refrigeration system using nanorefrigerants: Energy, exergy, and environmental (3E)(Elsevier, 2024) Yilmaz, Metin; Cimsit, Canan; Keven, Arzu; Karaali, RabiNanorefrigerants 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.Öğe Analysis of Some Tribological Properties of Hazelnut Oil in Gasoline Engines(2022) Keven, Arzu; Karaali, RabiIn 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.Öğe ÇEVRE ŞARTLARININ GAZ TURBİNLİ KOJENERASYON ÇEVRİMLERİNİN PERFORMANSI ÜZERİNE ETKİLERİ(2017) Karaali, Rabi; Öztürk, İlhan TekinBu çalışmada ekserji analizi metodu kullanılarak çevre şartlarının kojenerasyon çevrimlerinin performansıüzerine etkisi analiz edilmiştir. Bu kojenerasyon çevrimleri basit, hava ön ısıtmalı, hava-yakıt ön ısıtmalı ve girişhavası soğutmalı çevrimlerdir. Ayrıca bu çevrimler değişik hava yakıt kütle oranları için termodinamik açıdanincelenmiş ve performansları birbirleri ile karşılaştırılmıştır. Kompresor giriş havasının 25 0C’den 0 0C’ye soğutulmasıelektrik güç üretimini 10-15 % civarında artırmaktadır. Ancak ısı gücü giriş havasının soğutulmasından dolayı 10 %civarında düşmektedir. Kompresör giriş havasına su püskürtülerek yaz sezonunda elektrik gücü kolayca 2-7 %civarında artırılabilir. Kompresör giriş havasının basıncı 101.3 kPa’dan 70.18 kPa’ya düşürüldüğünde çevrimlerinekserji verimleri 11-13 % civarında düşmektedir. Ancak bu basınç düşüşü elektrik gücü üretiminde 25 % civarındadüşüşe yol açmaktadır. En yüksek ekserji verimi hava-yakıt ön ısıtmalı çevrimde elde edilmiştir. Dört çevrim arasındaen iyi ısı oranı ve ısı ekserjisi basit çevrimde elde edilmektedir. Bu çalışmada tüm çevre şartlarının bu çevrimlerüzerindeki etkisi aynı anda göz önüne alınarak analiz edilmiş ve birbiri ile karşılaştırılmıştır.Öğe Effects of ambient conditions on performance of gas turbine cogeneration cycles(Turkish Society for Thermal Science and Technology, 2017) Karaali, Rabi; Oztürk, Ilhan TekinIn this paper, effects of the ambient conditions on performance of cogeneration cycles are analyzed by using exergy analysis method. These cogeneration cycles are the simple cycle, the air preheating cycle, the air-fuel preheating cycle and the inlet air cooling cycle. Also, these cycles are evaluated thermodynamically for different air and fuel mass ratio and the performance of these cycles are compared. The electrical power generation increases about 10-15 % by decreasing the inlet air temperature of the compressor from 25 0C to 0 0C. However, the thermal power decreases about 10 % with decreasing inlet air temperature. During the summer, the electric power can be easily increased 2-7 % by injecting water into the inlet air of the compressor. The exergetic efficiency of cycles is decreased 11-13 %, by decreasing the compressor inlet air pressure from 101.3 kPa to 70.18 kPa. But this change decreases the electric power generation about 25 %. The highest exergy efficiency is obtained for the air-fuel preheated cycle. The simple cycle is the best among the four cycles to obtain high heat rate and heat exergy. The effects of all ambient conditions on these cycles are considered simultaneously, analyzed and compared with each other in this study. © 2017 TIBTD Printed in Turkey.Öğe EFFECTS OF AMBIENT CONDITIONS ON PERFORMANCE OF GAS TURBINE COGENERATION CYCLES(Turkish Soc Thermal Sciences Technology, 2017) Karaali, Rabi; Ozturk, Ilhan TekinIn this paper, effects of the ambient conditions on performance of cogeneration cycles are analyzed by Using exergy analysis method. These cogeneration cycles are the simple cycle, the air preheating cycle, the air-fuel preheating cycle and the inlet air cooling cycle. Also; these cycles are evaluated thermodynamically for different air and fuel mass ratio and the performance of these cycles are compared. The electrical power generation increases about 10-15 % by decreasing the inlet air temperature of the compressor from 25 degrees C to 0 degrees C. However, the thermal power decreases about 10 % with decreasing inlet air temperature. During the summer, the electric power can be easilyincreased 2-7 % by injecting water into the inlet air of the compressor. The exergetic efficiency of cycles is decreased 11-13 %; by decreasing the compressor inlet air pressure from 101.3 kPa to 70.18 kPa. But this change decreases the electric power generation about 25 %. The highest exergy efficiency is obtained for the air-fuel preheated cycle. The simple cycle is the best among the four cycles to obtain high heat rate and heat exergy. The effects of all ambient conditions on these cycles are considered simultaneously, analyzed and compared With each other in this study.Öğe Evaluation of four different cogeneration cycles by using some criteria(De Gruyter Poland Sp Z O O, 2022) Karaali, Rabi; Keven, ArzuThe 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.Öğe Exergetic analyses of air-fuel preheated cogeneration plants in food production(EDP Sciences, 2024) Keven, Arzu; Karaali, RabiLower 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.Öğe Exergetic Analyses of Detonation Engine Cogeneration Plants(Prof.Dr. İskender AKKURT, 2024) Çakmak, Bahar; Karaali, RabiEfficiency improvements are very important in all research and technology. Detonation engines are high technology devices. In the last decades they attracted attention by many researchers. However, detonation engines for cogeneration are not researched efficiently. This article is about the detonation engines cogeneration cycles which analysed by using 1. and 2. law of thermodynamics and exergy analyses methods by the authors. The exergetic performance analyses, their advantage and disadvantages of the ZND-HRSG detonation engine cogeneration cycles were obtained. The exergetic performance analyses were done for various excess air rates to obtain the variations of the combustion exit pressures and temperatures, exergy efficiencies, electric heat rates, SFC and other parameters of their performance. Also, an optimization analysis was done for the ZND-HRSG by searching the optimum values for different excess air rates. The results showed that, the ZND-HRSG cycle have the optimum values of the performance at 1.6-1.8 of the excess air rates. © IJCESEN.Öğe Exergetic Analyses of Hypersonic Flows(Prof.Dr. İskender AKKURT, 2023) Topal, Esra Nur; Karaali, RabiHypersonic devices and vehicles and hypersonic flows are very important and competitive advanced technology in science and in the World. Hypersonic technology is rapidly spreading and turning into competition in developed countries, especially in space studies and defense industry. This technology is vital for developed countries. Because of shock waves emerging in hypersonic devices during hypersonic flow, the energy and exergy destructions they cause are the most important difficulties, obstacles and problems which arise in this vital technology. To overcome these problems and difficulties, to prevent or reduce or minimize energy and exergy destruction, aerodynamic analysis and energy and exergy analysis methods are applied. The data and the results that can be guiding and useful for the calculations and the design have been obtained. In this study optimal design and optimum calculations ways of the energy and exergy destructions of hypersonic devices and instruments are discussed. It is obtained and shown that how much exergy destruction and entropy production occurs at which altitude and hypersonic velocities and also at which oblique shock angles. © IJCESEN.Öğe Exergetic Comparison of Single and Double Effect Absorption Cooling Cycles(2017) Karaali, RabiAbsorption cooling cycles are environmental and can use solar or waste heat for cooling with very small electric power. This workpresents exergy analysis of a double effect parallel flow and single effect absorption cooling systems for comparison. A computerprogram is developed for the thermodynamic properties of lithium bromide-water solutions by the author in FORTRAN codes forthe exergy analysis. The double effect parallel flow absorption systems have better advantages than the single effect absorption system.The coefficient performance (COP) and the exergetic coefficient performance (ECOP) of the double effect parallel flow absorptionsystems are higher than the single cycles. For the double effect cycle COP and ECOP are found as 1.195 and 0.28, and for the singleeffect cycle COP and ECOP are found as 0.68 and 0.23, respectively. For each component the exergy loss and exergy destruction iscalculated. Most of the irreversibilities are found in the evaporator and in the absorber which about 74 % for the double effect, and 72% for the single effect of the total irreversibility. It is concluded that the performance of the evaporator and the absorber is crucial forthe two cycles. Improving and better design of these two components will directly improve and affect positively the working conditionsand the performance of the cycles.Öğe Exergy analyses of two and three stage cryogenic cycles(De Gruyter Poland Sp Z O O, 2022) Atasbak, Musa; Keven, Arzu; Karaali, RabiCryogenics 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%.Öğe Investigation of inlet air pressure and evaporative cooling of four different cogeneration cycles(De Gruyter Poland Sp Z O O, 2022) Karaali, RabiThe objective of this study was to search the effects of the inlet air compressor pressure and evaporative cooling of four different cogeneration plants that are absorption cooling (ab), basic (bsc), air heating (airh), and air fuel heating (airfh) cogeneration systems by using the first law and the second law of thermodynamics, and the exergy analysis methods. For analysis, a program is written by the author in the FORTRAN programming language. Decreasing the atmospheric pressure or increasing the installation altitude of the plants increases the Z factor (ratio of lost exergy to useful exergy) of the four cycles about 10-13%. Also, decreasing inlet air pressure decreases the specific work about 25-28%, and the fuel energy saving ratio of the four cycles decreases about 29-30%. The method of water spray cooling of the compressor inlet air especially in the summer months, the humidity increases and the evaporative cooling can be obtained. By using this method, the ratio of lost exergy to useful exergy can be decreased for the four cycles about 0.5-2%. Also, the specific work of the four cycles can be increased about 1.2-6%.Öğe Performance analyses of basic cogeneration basic cogeneration plants in agriculture and food production(EDP Sciences, 2024) Karaali, Rabi; Keven, ArzuEnergy 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.Öğe Performance Analyses of Combined Cycle Power Plants(Prof.Dr. İskender AKKURT, 2023) Karaali, RabiIn this article, different compressor pressure and different excess air rates for a gas turbine based combine cycle power plant with steam Rankine cycle as bottoming cycle were analyzed by using 1. and 2. laws of thermodynamics and exergy analyses methods to obtain the best performances of the cycle. Exergy efficiency of the cycle, net powers of the gas and steam turbines and the overall cycle, exergy loss of the components, the efficiencies of the components are obtained, compared and discussed. It was found that, increasing the compressor pressure increases exergy efficiency of cycle, gas turbine and total plant power, and the combustion chamber, the HRSG and the compressor efficiencies. However, increasing compression rates decreases steam turbine power, combustion chamber, steam turbine, and HRSG exergy losses and the gas turbine efficiency. Also, it is found that, increases in excess air ratios gives an optimum or a maximum exergy efficiency, at 2.5 excess air rate of the cycle. © IJCESEN.Öğe PERFORMANCE ANALYSES OF GAS TURBINE COGENERATION PLANTS(2017) Karaali, Rabi; Öztürk, İlhan TekinBu çalışmada, gaz türbinli kojenerasyon çevrimlerinin geliştirilmesinde kullanılan bazı yöntemler basit bir kojenerasyon çevrimi üzerinde uygulanmıştır. Bu yöntemler havanın ön ısıtılması, hava ve yakıtın ön ısıtılması ve giriş havasının evaporatif ve absorpsiyonlu soğutma ile soğutulmasıdır. Bu kojenerasyon sistemleri enerji verimi (enerji kullanım faktörü), ekserji verimi, elektrik ve ısı gücü, elektrik ısı enerjisi oranı, yapay termal verim ve yakıt enerjisi kazanım oranı yönünden değerlendirilmiş ve birbirleri ile karşılaştırılmışlardır. Bu analizlerde basınç oranı, hava-yakıt kütleleri oranı ve çevrimlerin kompresör giriş sıcaklıkları gibi termodinamik parametreler kullanılmıştır. Bu parametrelerin en çok etkili olanından en az etkili olanına göre, hava-yakıt kütleleri oranı, basınç oranı ve kompresör giriş sıcaklıkları şeklinde sıralandığı anlaşılmıştır. Ayrıca daha çok elektrik ve daha az ısıl güç yönünden en verimli çevrimin hava-yakıt ön ısıtmalı çevrim ve daha çok ısıl güç daha az elektrik gücü için basit çevrimin en uygun çevrim oldukları ortaya çıkarılmıştırÖğe THERMODYNAMIC OPTIMIZATION OF A ZERO CO2 EMISSION COGENERATION CYCLE(Parlar Scientific Publications (P S P), 2016) Karaali, Rabi; Ozturk, Man TekinCO2 emissions that have the greatest negative impact on the greenhouse and the global warming that should be decreased or kept at the same rates. Today fossil fuels share 60 % of total electricity production of the world, which plays an important role on CO2 emissions. Thermal cogeneration and zero CO2 emission cycles have potential for reducing this effect. By taking into consideration the most applicable and important zero CO2 emission cycles, a new cycle is designed. Thermodynamic analyses and optimization of this cycle is studied with FORTRAN code. The optimization results of this cycle show that the maximum exergy efficiency of this new cycle is 64 %, which is 17.6 % higher than (0,544) the one for the air preheated cogeneration cycle (APHCC) and 18.7 % higher than (53,9) the absorption cooling zero CO2 emission cycle (ACZEC). In the introduced new cycle, steam and CO2 in the exhaust gases are condensed so that the condensing energy of them is regained. For that reason, the heat output and the electrical power of the introduced cycle is better than the other cogeneration cycles.Öğe Thoermodynamic Analyses of Steam Injected Gas Turnine Cogeneration Cycles(2015) Karaali, Rabi; Öztürk, İlhan TekinIn this study, air preheating, air-fuel preheating and simple cycles where steam injected in to combustion chamber are analyzed. The effects of steam injection on thermodynamic performance are calculated and obtained for the three different gas turbine cogeneration systems. Simulation programs written by the authors in FORTRAN code are obtained for the analyses by applying the first law of thermodynamics and the exergy analysis method. Thermodynamic performance of these three different cycles for variable mass of injected steam and different stages are obtained and compared with the results of the literature. The effects of injection steam into combustion chambers of those three cycles for variable compressing ratios, on power, efficiencies and performance are obtained. Consequently, the advantages and the disadvantages of injection steam are evaluated and all results of this study are compared with the literature. Injection steam into combustion chamber increases the electricity power and the electricity efficiency but decreases the heat power of the cycles.Öğe Yarım Etkili, Tek Etkili ve Çift Etkili Absorpsiyonlu Soğutma Çevrimlerin Ekserji Analizi(2017) Karaali, RabiBu çalışmada yarım, tek ve çift etkili absorpsiyonlu sistemlerin ekserji analizleri yapılmış ve birbirleri ile karşılaştırılmıştır. Lityum bromid-su çözeltisinin termodinamik özelliklerinin hesabı için yazar tarafından FORTRAN dilinde bir program yazılmış ve ekserji analizinde kullanılmıştır. Soğutma etkinlik katsayısı (COP) ve ekserjetik soğutma etkinlik katsayısı (ECOP) çift etkili absorpsiyonlu sistemde diğer iki sisteme göre daha yüksek bulunmuştur. Çift etkili absorpsiyonlu sistemde COP ve ECOP sırasıy la 1.196 ve 0.284 bulunurken, tek etkili sistemde COP ve ECOP sırasıyla 0.68 ve 0.254 bulunmuştur. Yarım etkili sistemde ise COP ve ECOP sırasıyla 0.455 ve 0.24 bulunmuştur. Sistemleri oluşturan cihazların ekserji kayıpları hesaplanmıştır. Ekserji kayıplarının çoğunluğunun evaporator ve absorberde olduğu görülmüştür. Her üç s istem için evaporator ve absorberin performansının önemli olduğu görülmüştür. Evaporator ve absorberin performansının geliştirilmesinin ve daha iyi tasarlanmasının her üç sistemin performansını ve çalışma koşullarını olumlu etkileyecektir
