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
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%.
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.
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 1 st and 2 nd 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.
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 1 st and 2 nd 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.
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.
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
= 2,400 kPa. The COP value is 0.30 between
= 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%.
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.
Dünya’da enerjiye talebin artması, sınırlı fosil kaynaklar ve çevre kirliliği gibi faktörlerden dolayı temiz ve verimli enerjinin önemini artırmış ve dikkatleri atık ısıların değerlendirilmesine ...çevirmiştir. Gaz türbininden çıkan sıcak egzoz gazlarının ısı enerjisi atmosfere atılmadan önce ısıtmada kullanılmak üzere sıcak su ya da buhar üretiminde (kojenerasyon), hem ısıtmada hem de soğutmada (absorpsiyonlu) kullanılması (trijenerasyon), güç üretiminde ya da başka amaçlarla kullanılması da mümkündür. Gaz türbinli güç çevrimlerinin atık egzoz gazı ısısından tekrar güç elde etmek için sisteme buharlı ya da organik Rankine çevrimi eklemek son yapılan araştırmalarda en iyi çözümlerden biri olarak ortaya çıkmıştır. Gaz türbinli güç tesisine buharlı Rankine çevrimi eklenerek elde edilen sisteme Termodinamiğin birinci ve ikinci kanunu ile ekserji analizi metotları uygulanarak analiz edilmiştir. Bunun için Fortran dilinde bir program yazılarak çalıştırılmış ve elde edilen sonuçlar Literatürdeki çalışmalarla karşılaştırılmıştır. Gaz türbinli güç çevrimi ile gaz türbinli kombine çevrimin değişen kompresör sıkıştırma oranlarına ve değişen hava fazlalık katsayılarına göre ekserji verimi, güç artışı ve diğer performans özellikleri değişimi karşılaştırılarak avantaj ve dezavantajları ortaya konmuştur. Ekonomik analiz ve maliyet analizi yapılmadan yakıttan elde edilen tasarruf, birim kilo Watt için her iki durumdaki harcanan yakıt miktarları ve performanstaki iyileşmeler gösterilmiştir. En iyi performans değerlerini elde etmek için çalışılması gereken kompresör sıkıştırma oranı ve hava fazlalık katsayısı yani optimum çalışma şartları elde edilerek gösterilmiş ve tartışılmıştır.
Dünya’da enerji maliyetinin ve talebinin artması, çevre kirliliği ve sınırlı kaynaklar gibi problemlerden dolayı güç üretiminde ve diğer proseslerde ortaya çıkan atık ısıların enerjilerinin atmosfere ...atılmadan önce nasıl değerlendirilebileceği konusu araştırmacılar için önemli bir konu haline gelmiştir. Proseslerden ya da çeşitli ısı kaynaklarından ortaya çıkan ısı enerjisi ile gaz türbini ya da motorlardan çıkan sıcak egzoz gazlarının ısı enerjisini çeşitli proseslerde kullanmak mümkündür. Bu kullanılmayan atık ısı enerjisi atmosfere atılmadan önce kojenerasyonda (aynı anda güç ve buhar üretimi), trijenerasyonda (güç, sıcak su ve soğutma) ya da başka amaçlarla kullanılması ile verim artışı sağlanabileceği gibi maliyet düşüşleri ve yakıttan tasarrufta sağlanabilir. Gaz türbinli rekuperatörlü güç çevrimlerine buharlı ya da organik Rankine çevrimi ekleyerek gaz türbininden çıkan egzoz gazının ısısından buhar türbini vasıtası ile tekrar güç elde etmek mümkündür. Kombine çevrim denilen bu çevrimlerin hesabı için Fortran dilinde bir program yazılarak Termodinamiğin 1. ve 2. kanunu ile ekserji analizi metotları uygulanmıştır. Elde edilen sonuçlar da Literatürdeki çalışmalarla karşılaştırılarak tartışılmıştır. Gaz türbinli rekuperatörlü güç çevrimi ile gaz türbinli rekuperatörlü kombine çevrimin değişik hava fazlalık katsayılarına ve değişik kompresör sıkıştırma oranlarına göre güç değişimi, ekserji verimi ve diğer performans özellikleri değişimleri karşılaştırılmış ve avantajları gösterilmiştir. Ekonomik ve maliyet analizleri yapılmadan her iki çevrimin birim güç için harcanan yakıt değerleri ve performanstaki artışlar hesaplamıştır. Optimum performans değerleri için çalışılması gereken hava fazlalık katsayısı ile kompresör sıkıştırma oranları elde edilmiştir.
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