Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleAçık Erişim2024Scopus SJRQ3Thermoeconomic Analyses of Heat Pumps
Öztekin, Erman Kadir; Gür, Mehmet Murat; Karaali, Rabi
Recently, the rapid development of technology and the increase in energy costs and needs have made reducing the costs and efficient use of energy and exergy important. The thermoeconomic analysis method, which is the best cost analysis method of energy and exergy, gives the ways to reduce costs and increase efficiency that can be applied a facility. It has been found that the most suitable thermoeconomic solution for winter heating and summer cooling of a facility is a vertical underground source heat pump and the most high-performance working fluid that should be used is R32. If the heating is done with a ground source heat pump instead of electrical energy, 4.25 kW of heating energy will be obtained for each kW of electrical energy given for heating, since the costs are COPIP 4.25. Here the earnings increase by around 325%. In other words, heating costs decrease by around 77.5 percent, that is, from one hundred liras to 22. 5 liras.
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İncele - MakaleYayıncıda açık erişim2024Scopus SJRQ1Energy, exergy, environmental, and enviroeconomic (4E) analysis of cascade vapor compression refrigeration systems using nanorefrigerants
Yılmaz, Metin; Cimşit, Canan; Keven, Arzu; Karaali, Rabi
The refrigerants used in traditional vapor compression refrigeration systems are harmful to the ozone layer and contribute to global warming. The demand for refrigeration is increasing because of global warming. In this study, for the first time, an energy, exergy, environmental, and enviroeconomic (4E) analysis was performed using different refrigerants and nanoparticles to reduce the energy required in low-temperature vapor compression cascade refrigeration systems and to determine more environmentally friendly nanorefrigerants. The R290 refrigerant was used for the Low-Temperature Circuit (LTC), while the High-Temperature Circuit (HTC) used RE170, R1234yf, R600, R600a, and R450A refrigerants. The nanoparticles used in the analysis were Al2O3, CNT, CuO, TiO2, ZnO, and SiO2. The R600 nanorefrigerant performed the best, whereas the R1234yf nanorefrigerant performed the worst. The results indicate that the CuO nanoparticles provided the highest performance. In addition, the results showed that the R290+R600-CuO nanorefrigerant emitted 11 % less CO2 than the pure R290+R600 refrigerant. The nanorefrigerants provide a more environmentally sustainable option because of their high efficiency and lower energy consumption than conventional refrigerants.
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İncele - MakaleAçık Erişim2024Scopus SJRQ1Analysis of cascade vapor compression refrigeration system using nanorefrigerants: Energy, exergy, and environmental (3E)
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, TiO2 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 CO2 emissions compared to the pure refrigerants. The nanorefrigerants play a crucial role in reducing energy consumption and promoting environmental protection compared to traditional refrigerants.
AtıfScopus16WoS16OpenAlex17İncele - MakaleAçık Erişim2024Scopus SJRQ3Exergetic Analyses of Detonation Engine Cogeneration Plants
Çakmak, Bahar; Karaali, Rabi
Efficiency 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.
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İncele - MakaleYalnız künye2023Exergetic Analyses of Hypersonic Flows
Topal, Esra Nur; Karaali, Rabi
Hypersonic 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.
AtıfScopus2İncele - MakaleAçık Erişim2023Performance Analyses of Combined Cycle Power Plants
Karaali, Rabi
In 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.
AtıfScopus3OpenAlex6İncele - MakaleYalnız künye2022Analysis of Some Tribological Properties of Hazelnut Oil in Gasoline Engines
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.
AtıfOpenAlex1TR Dizin2İncele - MakaleAçık Erişim2022Scopus SJRQ2Investigation of inlet air pressure and evaporative cooling of four different cogeneration cycles
Karaali, Rabi
The 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%.
AtıfOpenAlex4İncele - MakaleAçık Erişim2022Scopus SJRQ3Evaluation of four different cogeneration cycles by using some criteria
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.
AtıfScopus20WoS18OpenAlex30İncele - MakaleAçık Erişim2022Scopus SJRQ3Exergy analyses of two and three stage cryogenic cycles
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%.
AtıfScopus6WoS3OpenAlex9İncele - MakaleYalnız künye2017Exergy Analyses of Half-Effect, Single-Effect and Double-Effect Absorption Cooling Cycles
Karaali, Rabi
This work presents exergy and energy analysis of a half effect parallel flow, single effect and double effect absorption systems for comparison. For the thermodynamic properties of lithium bromide-water solutions a computer program is developed by the author in FORTRAN codes for th e energy and exergy analysis. It is found that the coefficient performance (COP) and the exergetic coefficient performance (ECOP) of the double effect parallel flow absorption systems are higher than the single effect and the half effect cycles. For the do uble effect cycle COP and ECOP are found as 1.196 and 0.284, and for the single effect cycle COP and ECOP are found as 0.68 and 0.254, respectively. For the half effect cycle COP and ECOP are found as 0.455 and 0.24, respectively. The exergy loss is calculated for each component. Most of the irreversibilities are found in the evaporator and in the absorber. It is concluded that the performance of the absorber and the evaporator is crucial for the three cycles. Improving and better design of the evaporator and the absorber will directly affect positively and improve the performance and the working conditions of the three cycles
- MakaleYalnız künye2017Scopus SJRQ3Gaz türbinli kojenerasyon tesislerinin performans analizleri
Karaali, Rabi; Öztürk, İlhan Tekin
In this study, some improving methods of gas turbine cogeneration cycles are applied on a simple cogeneration cycle. These methods are preheating air, preheating air and fuel, inlet air cooling by using evaporative cooling and absorption cooling. These cogeneration systems are evaluated with respect to energy efficiency (energy utilization factor), exergetic efficiency, electric and heat power, electric-heat energy rate, artificial thermal efficiency and fuel energy saving ratio and are compared with each other. In these analyses, the thermodynamic parameters such as compressing ratio, air and fuel mass ratio and compressor inlet temperatures of the cycles are used. It is concluded that these parameters can be listed from most effective to least effective as air fuel ratio, pressure ratio and compressor inlet temperature. It is also concluded that the most efficient cycle is found to be the air-fuel preheated cycle for obtaining more electric power and less heat power, and the simple cycle is the most suitable one for obtaining more heat power and less electric power
AtıfTR Dizin1İncele - MakaleAçık Erişim2017Exergetic Comparison of Single and Double Effect Absorption Cooling Cycles
Karaali, Rabi
Absorption 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.
- MakaleYalnız künye2017Scopus SJRQ3EFFECTS OF AMBIENT CONDITIONS ON PERFORMANCE OF GAS TURBINE COGENERATION CYCLES
Karaali, Rabi; Öztürk, Ilhan Tekin
In 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.
AtıfWoS3İncele - MakaleYalnız künye2017Scopus SJRQ3Performance analyses of gas turbine cogeneration plants
Karaali, Rabi; Oztürk, Ilhan Tekin
In this study, some improving methods of gas turbine cogeneration cycles are applied on a simple cogeneration cycle. These methods are preheating air, preheating air and fuel, inlet air cooling by using evaporative cooling and absorption cooling. These cogeneration systems are evaluated with respect to energy efficiency (energy utilization factor), exergetic efficiency, electric and heat power, electric-heat energy rate, artificial thermal efficiency and fuel energy saving ratio and are compared with each other. In these analyses, the thermodynamic parameters such as compressing ratio, air and fuel mass ratio and compressor inlet temperatures of the cycles are used. It is concluded that these parameters can be listed from most effective to least effective as air fuel ratio, pressure ratio and compressor inlet temperature. It is also concluded that the most efficient cycle is found to be the air-fuel preheated cycle for obtaining more electric power and less heat power, and the simple cycle is the most suitable one for obtaining more heat power and less electric power.
AtıfScopus6İncele - MakaleAçık Erişim2017Scopus SJRQ2Efficiency improvement of gas turbine cogeneration systems; [Poboljšanje učinkovitosti kogeneracijskih sustava plinske turbine]
Karaali, Rabi; Öztürk, İlhan Tekin
In this study eight methods are evaluated for a gas turbine cogeneration cycle to improve the efficiency. These methods are increasing gas turbine inlet air temperature, cooling the inlet air of the compressor, air preheating, fuel preheating, increasing compressor inlet air pressure, increasing air excess rates, steam injection, and humidification of the inlet air of the compressor. These methods are studied in order to compare their effects on the performance of the systems. The effects of these methods on the exergetic efficiency depend on the kind of the cogeneration cycle. By combining recuperation, preheating fuel and steam injection methods high efficiency can be achieved. The combined methods give the best results under variable heat demands of the market. An appropriate combination of the efficiency improvement methods may increase the exergetic efficiency about 20 %. The results show that efficiency improvement methods must be applied together whenever it is possible.
AtıfScopus8WoS6OpenAlex15İncele - MakaleYalnız künye2016Scopus SJRQ3Thermodynamic optimization of a zero CO2 emission cogeneration cycle
Karaali, Rabi; Ozturk, Ilhan Tekin
CO2 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.
AtıfScopus3İncele - MakaleYalnız künye2015Thoermodynamic Analyses of Steam Injected Gas Turnine Cogeneration Cycles
Karaali, Rabi; Öztürk, İlhan Tekin
In 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.
- MakaleYalnız künye2015Scopus SJRQ1Thermoeconomic optimization of gas turbine cogeneration plants
Karaali, Rabi; Öztürk, Ilhan Tekin
In this study, a novel thermoeconomic optimization method that is simple and efficient, for real complex cycles is introduced. First, a thermoeconomic analysis method that is called non-linear simplex direct search method is improved for the purposes of this study. The objective of this paper is to apply this method to four cogeneration cycles that are simple cycle, inlet air cooling cycle, air preheated and air-fuel preheated cycles for analyzing and optimizing. The four cycles are thermoeconomically optimized for constant power and steam mass (30 MW and 14 kg/s saturated steam flow rate at 2000 kPa), for constant power (30 MW) and for variable steam mass, and for variable power and steam mass by using the cost equation method and the effect of size on equipment method. The results obtained by the effect of size on equipment and by the cost equations methods are very different from each other. For the case of global optimization, the optimum electricity costs which also correspond to minimum are obtained as 0,0432 $/kWh for simple cycle, 0,0514 $/kWh for inlet air cooling cycle 0,0577 $/kWh for air preheated cycle and 0,058 $/kWh for air-fuel preheated cycle by using cost equations method. (C) 2014 Elsevier Ltd. All rights reserved.
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