• 한국수소및신에너지학회논문집
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• 제31권6호
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• pp.637-645
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• 2020

In this paper, entransy analysis is carried out for combined heat and power (CHP) generation system driven by low-grade heat source compared with energy and exergy analyses. The system consists of a regenerative organic rankine cycle (ORC) and an additional process heater in a series circuit. Special attention is paid to the effects of the turbine inlet pressure, source temperature, and the working fluid on the thermodynamic performance of the system. Results showed that the work efficiency of entransy is higher than that of energy but lower than that of exergy, wheress the process heat efficiency of entransy is lower than that of energy but higher than that of exergy. Entrance analysis showed the potential to complement the exergy analysis in the optimal design of the energy system.

• 한국수소및신에너지학회논문집
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• 제32권1호
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• pp.77-85
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• 2021

In this paper, entransy analysis is carried out for combined heat and power (CHP) generation system driven by low-grade heat source compared with energy and exergy analyses. The system consists of an organic Rankine cycle (ORC) and an additional process heater in a parallel circuit. Special attention is paid to the effects of the source temperature, turbine inlet pressure, and the working fluid on the thermodynamic performance of the system. Results showed that the work efficiency of entransy is higher than that of energy but lower than that of exergy, wheress the process heat efficiency of entransy is lower than that of energy but higher than that of exergy. Entrancy analysis showed the potential to complement the exergy analysis in the optimal design of the energy system.

• 한국수소및신에너지학회논문집
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• 제30권6호
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• pp.621-628
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• 2019

The use of the ammonia-water zeotropic mixture as a working fluid in the power generating system has been considered as a proven technology for efficient recovery of low-grade heat sources. This paper presents a thermodynamic performance analysis for ammonia-water evaporator using low-grade heat source, based on the exergy and entransy which has been recently introduced as a physical quantity to describe the heat transfer ability of an object. In the analysis, effects of the ammonia mass fraction and source temperature of the binary mixture are investigated on the system performance such as heat transfer, effectiveness, exergy destruction, entransy dissipation, and entransy dissipation based thermal resistance. The results show that the ammonia mass concentration and the source temperature have significant effects on the thermodynamic system performance of the ammonia-water evaporator.

• 한국수소및신에너지학회논문집
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• 제31권1호
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• pp.105-111
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• 2020

The organic Rankine cycle (ORC) and the Kalina cycle system (KCS) are being considered as the most feasible and promising ways to recover the low-grade finite heat sources. This paper presents a comparative exergetical performance analysis for ORC and Kalina cycle using ammonia-water mixture as the working fluid for the recovery of low-grade heat. Effects of the system parameters such as working fluid selection, turbine inlet pressure, and mass fraction of ammonia on the exergetical performance are parametrically investigated. KCS gives lower lower exergy destruction ratio at evaporator and higher second-law efficiency than ORC. The maximum exergy efficiency of ORC is higher than KCS.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.1140-1151
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• 2023

Fully Ceramic Microencapsulated (FCM) fuel is emerging advanced fuel material for the future nuclear reactors. The fuel pellet in the FCM fuel is composed of matrix and a large number of TRistructural-ISOtopic (TRISO) fuel particles which are randomly dispersed in the SiC matrix. The minimum layer thickness in a TRISO fuel particle is on the order of 10^-5 m, and the length of the FCM pellet is on the order of 10^-2 m. Hence, the heat transfer in the FCM pellet is a multi-scale phenomenon. In this study, three multi-scale heat conduction models including the Multi-region Layered (ML) model, Multi-region Non-layered (MN) model and Homogeneous model for FCM pellet were constructed. In the ML model, the random distributed TRISO fuel particles and coating layers are completely built. While the TRISO fuel particles with coating layers are homogenized in the MN model and the whole fuel pellet is taken as the homogenous material in the Homogeneous model. Taking the results by the ML model as the benchmark, the abilities of the MN model and Homogenous model to predict the maximum and average temperature were discussed. It was found that the MN model and the Homogenous model greatly underestimate the temperature of TRISO fuel particles. The reason is mainly that the conventional equivalent thermal conductivity (ETC) models do not take the internal heat source into account and are not suitable for the TRISO fuel particle. Then the improved ETCs considering internal heat source were derived. With the improved ETCs, the MN model is able to capture the peak temperature as well as the average temperature at a wide range of the linear powers (165 W/cm~ 415 W/cm) and the packing fractions (20%-50%). With the improved ETCs, the Homogenous model is better to predict the average temperature at different linear powers and packing fractions, and able to predict the peak temperature at high packing fractions (45%-50%).

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.623-628
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• 2009

Desiccant based air conditioning system offers a promising alternative to conventional one using vapour compression refrigeration for energy saving and greenhouse gas reduction. It is a heat driven cycle which has high potential for the use of low grade heat source such as the waste heat from the cogeneration plant or the solar thermal energy. In this study, the cooling performance of a desiccant cooling system incorporating a regenerative evaporative cooler was characterized in various operation conditions through numerical simulation. The cooling capacity and COP were evaluated at various outdoor conditions, regeneration temperatures, and supply flow rates. Based on the performance characteristics, the optimal control scheme was discussed to minimize the cooling cost at part load condition.

• 한국수소및신에너지학회논문집
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• 제31권2호
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• pp.242-249
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• 2020

The Kalina cycle (KC) is considered as one of the most efficient systems for recovery of low grade heat. Recently, Kalina based power and cooling cogeneration cycles (KPCCCs) have been suggested and attracted much attention. This paper presents an energy and exergy analysis of a recently suggested KPCCC with flexible loads. The cycle consists of a KC (KCS-11) and an aqua-ammonia absorption refrigeration cycle. By adjusting the splitting ratios, the cycle can be operated with four modes of pure Kalina cycle, pure absorption cooling cycle, Kalina-cooling parallel cycle, and Kalina-cooling series cycle. The effects of system variables and the operating modes on the energetic and exergetic performances of the system are parametrically investigated. Results show that the system has great potential for efficient utilization of low-grade heat source by adjusting loads of power and cooling.

• 한국수소및신에너지학회논문집
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• 제29권5호
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• pp.490-496
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• 2018

Recently, the power and refrigeration cogeneration based on Kalina cycle has attracted much attention for more efficient utilization of low-grade energy. This study presents a thermodynamic performance analysis of a cogeneration cycle of power and absorption refrigeration based on Kalina cycle. The cycle combines Kalina cycle (KCS-11) and absorption cycles by adding a condenser and an evaporator between turbine and absorber. The effects of ammonia mass fraction and separation pressure were investigated on the system performance of the system. Results showed that the energy utilization of the system could be greatly improved compared to the basic Kalina cycle.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2011년도 춘계학술발표대회 논문집
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• pp.191-194
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• 2011

Low-grade waste heat has generally been discarded in industry due to lack of efficient recovery methods. In recent years, organic Rankine cycle(ORC) has become a field of intense research and appears as a promising technology for conversion of heat into useful work of electricity. In this work thermodynamic performance of ORC with superheating of vapor is comparatively assessed for various working fluids. Special attention is paid to the effects of system parameters such as the evaporating temperature on the characteristics of the system such as maximum possible work extraction from the given source, volumetric flow rate per 1 kW of net work and quality of the working fluid at turbine exit as well as thermal efficiency.

• 한국수소및신에너지학회논문집
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• 제31권4호
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• pp.363-371
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• 2020

Recently, the technologies to utilize the cold energy of liquefied natural gas (LNG) have attracted significant attention. In this paper, thermodynamic performance analysis of combined cycles consisting of ammonia Rankine cycle (AWR) and organic Rankine cycle (ORC) with LNG Rankine cycle to recover low-grade heat source and the cold energy of LNG. The mathematical models are developed and the effects of the important system parameters such as turbine inlet pressure, ammonia mass fraction, working fluid on the system performance are systematically investigated. The results show that the thermal efficiency of AWR-LNG cycle is higher but the total power production of ORC-LNG cycle is higher.