• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.4
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• pp.202-211
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• 2017

In this study, the exergy that can be reflected in the energetic and economic values was used to assess the heat tariff of a district heating (DH) system instead of the enthalpy. It is difficult to directly apply the exergy to the current heat-charge system because of the complicated calculation; therefore, the difference between the supply and return temperatures was converted to the exergy-temperature difference for the ease of the heat-amount calculation. As a result of the exergy analysis for a DH substation, the exergy-temperature difference did not affect the surrounding temperature and pressure loss. The supply temperature and the maximum difference between the supply temperature and the return temperature exerted the main effect on the exergy-temperature difference. The new heat charge of a DH user was slightly reduced in winter compared with the previous charge, but the heat charges in the other seasons are almost the same. It is concluded from the assessment of the heat tariff for which the exergy is used that this tariff is more feasible for both DH suppliers and consumers compared with enthalpy.

• Journal of the Korean Society of Industry Convergence
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• v.13 no.1
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• pp.31-39
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• 2010

An exergy analysis is carried out for the regenerative gas turbine cycle which has a potential of enhanced thermal efficiency and specific power owing to the more possible water injection than that of inlet fogging under the ambient conditions. Using the analysis model in the view of the second law of thermodynamics, the effects of pressure ratio, water injection ratio and ambient temperature are investigated on the performance of the system such as exergetic efficiency, heat recovery ratio of recuperator, exergy destruction or loss ratios, and on the optimal conditions for maximum exergy efficiency. The results of computation for the typical cases show that the regenerative gas turbine system with afterfogging can make a notable enhancement of exergy efficiency.

• Clean Technology
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• v.12 no.2
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• pp.95-100
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• 2006

Fractionation and hydrodealkylation (HDA) units, subparts of BTX plant, were thermodynamically analyzed using the notion of exergy. Exergy values were calculated as the sum of physical and chemical exergies due to the existence of chemical reactions. The analysis was based on the simulation results with the aid of real operating data. Driving and material exergy losses were separately defined and quantified. Locations and the reason of major exergy losses were identified and improvement strategies were suggested. It was noted that the exergy analysis could provide a sound base for adopting the concept of industrial ecology and developing loss prevention schemes.

• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.55-60
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• 2012

The energy conservation and exergy loss of a fully thermally coupled distillation commercialized as the divided wall column are compared with those of a conventional two-column system for ternary separation. The used example for the comparison is the benzene-toluene-m-xylene separation process widely used in a petrochemical plant. The design procedure of the fully thermally coupled distillation column is explained, and the energy requirement is compared using the HYSYS. When the same numbers of trays are utilized, the fully thermally coupled distillation column uses 28.2% less energy and 10.4% more exergy loss. The increase of the exergy loss is due to the additional mixing from the bidirectional inter-linking and the temperature elevation in the reboiler from the increased pressure at the bottom of the main column.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.4
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• pp.45-54
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• 2009

An exergy analysis is carried out for the regenerative steam-injection gas turbine systems which has a potential of enhanced thermal efficiency and specific power. Using the analysis model in the view of the second law of thermodynamics, the effects of pressure ratio, steam injection ratio, ambient temperature and turbine inlet temperature are investigated on the performance of the system such as exergetic efficiency, heat recovery ratio of heat exchangers, exergy destruction, loss ratios, and on the optimal conditions for maximum exergy efficiency. The results of computation show that the regenerative steam-injection gas turbine system can make a notable enhancement of exergy efficiency and reduce irreversibilities of the system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.593-600
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• 2012

The exergy characteristics for R245fa and water working fluids have been analyzed for an electric generation system utilizing the Rankine cycle to recover heat from the wasted exhaust gas from a diesel engine used for the propulsion of a large ship. The theoretical calculation results showed that the efficiencies of exergy and system exergy improved as the turbine inlet pressure increased for R245fa at a fixed mass flow rate. Furthermore, the exergy destruction rates of the condenser and evaporator were relatively larger than those in other components. The exergy efficiency of the system increased with increasing mass flow rate. For a water working fluid, although the exergy destruction rate of the evaporator was similar to that for R245fa, the exergy loss rate varied significantly in response to variations in the pressure and mass flow rates at the turbine inlet.

• Journal of Energy Engineering
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• v.29 no.2
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• pp.40-60
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• 2020

When various kinds of products are produced from a single energy system, the methodology which allocates the common cost to each product cost is very important because it is directly related with the profit and loss of producer and purchaser. In the cost allocation methodology of electricity and heat for CHP, there are heat method, work method, benefit distribution method, exergy method, and so on. Benefit distribution method is the most widely known worldwide, and exergy method is widely recognized among thermal engineers. As a result of review, it is judged that the rationality of benefit distribution method is low because the result deviates from common sense, and the rationality of exergy method is high because the result consistent with common sense. In accounting, it is calculated as merit methodology and the result is used for negotiations between producer and buyer, but In thermal engineering, the rationality of exergy methodology is described only as a thesis. The purpose of this study is to compare and examine the rationality of merit methodology and exergy methodology, and the aim is to describe in detail in order that producer and buyer can understand the rationality of each methodology.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.3
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• pp.235-243
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• 1989

The purpose of this paper is to obtain enthalpy balance and exergy analysis for the energy losses in a steam power plant. The enthalpy and exergy analysis of the steam power plant were carried out on the various output of steam turbine. While enthalpy analysis shows that circulating loss in the condenser is maximum, exergy evaluation of the power plant shows that the losses of the boiler and turbine are considerably larger than those of condenser and feed water heater. Most irreversible losses of the power plant occur at the boiler. For improving the performance, the precise study about the irreversible losses of the boiler is necessary.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1001-1008
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• 2011

This paper describes an analysis on performance and exergy of R744-R404A cascade refrigeration system with internal heat exchanger to optimize the design for the operating parameters of this system. The operating parameters considered in this study include subcooling and superheating degree, internal heat exchanger and compression efficiency, evaporation and condensation temperature in the R744 low- and R404A high- temperature cycle, respectively. The main results are summarized as follows : As the evaporation temperature of cascade heat exchanger increases, the COP of R404A high-temperature cycle increases. But the COP of R744 low-temperature cycle decreases, and the COP of total cascade cycle is almost constant. As cascade evaporation temperature increase, the exergy loss in the R404A condenser and the R744 internal heat exchanger is the largest and the lowest among all components, respectively. Therefore, the exergy loss in the condenser and compressor of R404A must be decreased to enhance the COP of R744-R404A cascade refrigeration system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.6
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• pp.550-560
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• 2000

In order to minimize compression power and analyze the cause of exergy loss for a dry ice production cycle with 3-stage compression, the variation of compression power was investigated and the exergy analysis was peformed for the cycle. In this cycle, $CO_2$, is used both as a refrigerant and as a raw material for dry ice. The behavior of compression power and irreversibility in the cycle were examined as a function of intermediate pressure. From this result, the conditions for the minimum compression power were obtained in terms of the first stage or the third stage pressure. In addition, the irreversibilities for the cycle were investigated with respect to the efficiency of compressor. Result shows that the optimum pressure is not consistent with the conventional pressure obtained from the equal-pressure-ratio assumption. This is mainly due to the change in mass flow rate of the intermediate stage compressor by the flash gas evaporation from the flash drums. Most important is that the present exergy analysis enabled us to find bad performance components for the cycle and informed us of methods to improve the cycle performance.