• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.19-26
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• 2015

The present paper presented and applied an exergy analysis method to evaluate the magnitudes and the locations of exergy losses in the conventional desuperheating and depressurizing process of high pressure and temperature steam delivery system. In addition, for the reduction of exergy losses occurred in conventional process, the present study proposed new alternative processes in which the pressure reducing valve and the desuperheater of conventional process are substituted with steam turbine and heat exchanger, and their effects on exergy loss reduction and exergy efficiency improvement are theoretically investigated and compared. From the present analysis results, the total exergy loss caused in conventional desuperheating and depressurizing process accounted for 66.5% of exergy input and 85% of the total exergy loss was due to the mixing between steam and cold water(e.g desuperheating). However, it was shown from the present analysis results that the present alternative processes can additionally reduce exergy loss by maximum 92.7% of the total exergy loss in conventional process, and can also produce additional and useful energy, the electricity of 220.6 kWh and the heat of 54.3 MJ/hr.

• Clean Technology
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• v.6 no.2
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• pp.129-137
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• 2000

A methanol synthesis process via reverse-water-gas-shift and methanol formation reactions has been analyzed using the notion of exergy. The analysis has been based on the simulation results with the aid of real operating data. Driving and material exergy losses have been defined and quantified, respectively. Locations and the reason of major exergy losses have been pinpointed and improvement strategies have been suggested. It had been noted that the exergy analysis can provide a sound scientific base for adopting the concept of industrial ecology and developing loss prevention schemes.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.145-150
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• 2002

The distillation column is one of large energy consumable units in the cryogenic air separation process and the accurate energy analysis of this unit is necessary for choice of energy saving process. In this work, the energy method was adopted for energy analysis of a cryogenic nitrogen distillation column. In order to designing the energy saving distillation column, the exergy distribution of feed air, exergy efficiency and exergy loss for process condition was investigated and the optimal process condition to minimize the exergy loss was found. The result from this work can be used as a guideline for the choice of the process design conditions and efficiency improvement of cryogenic distillation column.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.4
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• pp.363-370
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• 2000

Experiments have been peformed, using pure refrigerant R134a and a zeotropic refrigerant mixture R290/R600a(60%/40%) and their performances have been analyzed by the first and second laws(exergy method) of thermodynamics. From the experimental results, variations of compressor speed and air temperature have a great effect on the performance of the system. The sum of exergy losses in compressor and evaporator is about 60% of total exergy loss, using refrigerant R134a, so it is necessary to improve the performance of compressor and evaporator. According to the experimental results using refrigerant mixture of R290/R600a(60%/40%), the exergy losses in heat exchange processes are decreased but the exergy loss in throttling process is increased. The performance of the system has been improved by 20∼30% compared with that of R134a and exergy losses have been also reduced.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.169-172
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• 1999

The exergy method is used for analysis and evaluation of the cryogenic nitrogen production process which is operated by expansion turbene and liquid nitrogen. The exergy loss and thermodynamic effeciency are calculated for the each process. Also the operating efficiency and the exergy distribution are examined for each unit of proces. The optimal conditions to minimize the exergy loss of nitrogen column are found that nitrogen recovery ratio is maximum and operating pressure is 5.0 kg/cm2g. The exergy method can be used to design a plant and to evaluate its process.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.827-832
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• 2009

Exergy is the amount of reversible work obtainable when some matter is brought to a state of thermodynamic equilibrium with ambient. This exergy is availability or useful work induced from carnot cycle, and this can calculate the irreversible loss work which occurs within any thermal or power cycle. The exergy ratio is the value of exergy divided by enthalpy of ambient reference, where the quality of energy or enthalpy in substances is evaluated by exergy ratio. Exergy is very important in optimal design method of thermal system or each component, and the value of exergy at given state is calculated by equation. Here, designer can easily understand and find the value of enthalpy because enthalpy is graphically drawn in chart, however exergy did not. In this paper, exergy and exergy ratio of air were drawn on temperature-entropy chart, and we wish to this chart is a help to design, analysis and education.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2928-2938
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• 2020

A light water nuclear Reactor has been exergy analyzed, and the rate of irreversible exergy loss and exergy destruction is calculated for each of its components. The ratio of these losses compared to the total input exergy loss is calculated, which shows that most irreversible losses occur in the reactors, turbines, steam generators, respectively, as well as in the downstream operations. The main aim of this paper is to optimize the power plant using an innovative firefly algorithm and then to propose a novel strategy to improve the overall performance of the plant. As shown in the results, the exergy destruction rate of the plant decreased by 1.18% using the firefly method, and the exergy efficiency of the plant reached 29.3% comparing to the operational amount of 28.99%. Also, the results of the firefly optimization process compared to the Genetic algorithm and gravitational search algorithm to study the accuracy of the model for exergy analysis fitness problems in the power plants and the results of this comparison has shown that the results are nearly similar in the mentioned methods. However, the firefly is faster and more accurate in limited iterations.

• Journal of Energy Engineering
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• v.18 no.2
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• pp.93-100
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• 2009

An exergy analysis is carried out for the regenerative wet-compression Brayton cycle which has a potential of enhanced thermal efficiency owing to the reduced compression power consumption and the recuperation of exhaust energy. Using the analysis model, the effects of pressure ratio and water injection ratio are investigated on the exergy efficiency of system, exergy destruction ratio for each component of the system, and exergy loss ratio due to exhaust gas. The results of computation for the typical cases show that the regenerative wet-compression gas turbine cycle can make a notable enhancement of exergy efficiency. The injection of water results in a decrease of exergy loss of exhaust gas and an increase of net power output.

• Advances in Energy Research
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• v.8 no.4
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• pp.213-222
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• 2022

Our overdependence on the limited supply of fossil fuel with the burden of emission as a consequence of its utilization has been a major concern. Biodiesel is emerging as a potential diesel substitution for its similar performance, with the additional benefits of emitting lesser emissions. Due to the easy availability of feedstock for Biogas production, Biogas is studied for its use in CI engines. In this study, we considered Linseed Biodiesel and Biogas to run on dual fuel mode in a CI engine. An energy and exergy analysis was conducted to study the rate of fuel energy and exergy transformation to various other processes. Exergy relocation to exhaust gases was observed to be an average of 5% more for dual fuel mode than the diesel mode, whereas exergy relocation to the diesel mode was observed to be more than the dual fuel modes. Also, exergy loss to exhaust gas is observed to be more than the exergy transferred to cooling water or shaft. The exergy efficiency observed for biodiesel-biogas mode is only lesser by 3% compared to diesel-biogas mode, suggesting Biodiesel can be a substitute fuel for diesel.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.912-918
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• 2008

In this study, the exergy which could be reflected on energetic and economic value was used to assess on heat tariff of district heating system instead of enthalpy. Exergy is difficult to apply directly to present heat charge system because of complex calculation. Therefore, the difference between supply and return temperature was converted to the exergy temperature difference for easily calculating the amount of heat. As a result of exergy analysis for a DH substation, the exergy temperature difference were not affected on surrounding temperature and pressure loss. Supply temperature, maximum difference between supply temperature and return temperature had a main effect on the exergy temperature difference. The new heat charge of a DH user was slightly reduced in winter compared with previous heat charge. Heat charges in other seasons were almost same. It is thought that heat tariff using exergy will be appropriate in terms of both DH supplier and consumer.