• Nuclear Engineering and Technology
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• 제54권1호
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• pp.220-225
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• 2022

Perlite is one of the major constituents of the radioactive thermal insulation waste (RTIW) originating from nuclear power plants and, for proper waste management, a significant reduction in its volume is required prior to disposal. In this work, the volume reduction of perlite is studied by high-temperature treatment method with using K₂CO₃ as a flux. The perlite is ground with 0-30 wt% K₂CO₃, and differential thermal analysis/thermogravimetric analysis is used to monitor the glass transition temperature (T_g) and weight loss. The Tg varied between ~772.2 and 837.1 ℃ with the minima at ~643.5 ℃ with the addition of ~10 wt% K₂CO₃. It is observed that compared to the pure perlite the volume reduction ratio (VRR) increases with the addition of K₂CO₃. The VRR of 11.20 is observed with 5 wt% K₂CO₃ at 700 ℃, as compared to VRR of 5.56 without K₂CO₃ at 700 ℃. The X-ray photoelectron spectroscopy and scanning electron microscopy are used to characterize perlite samples heat-treated without/with 5 wt% K₂CO₃ at 700 ℃. Moreover, the atomic absorption spectroscopy indicates that the proposed heat-treatment procedure is able to completely retain the radionuclides present in the perlite RTIW.

• Journal of the Korean Society of Safety
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• 제38권3호
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• pp.27-34
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• 2023

With the technological development of the semiconductor industry, the roles of electrical and thermal energy supply and control of semiconductor equipment in ultrafine processes have become very important. However, instances of electrical fires in the chiller heater, which is used for cooling in the semiconductor manufacturing process, are increasing. A fire occurs in combustibles due to high heat at the connection part of the chiller heater, that is, when the number of electrical wires in the connection part is reduced or when the wires are completely disconnected. In this study, the temperature characteristics were compared and analyzed through experiments and 3D simulations. The number of electrical wires, which is the connection part of the chiller heater, was reduced by 90%, 50%, 30%, 10%, and 5%, and the wires were completely disconnected. When the number of electrical wires was reduced by 5%, heat of up to 80℃ was generated, which is a relatively high temperature but insufficient to cause a fire in combustibles. Complete disconnection occurred due to the vibration of the motor and other components, and sparks and arcs were generated, resulting in a rapid increase in temperature to up to 680℃. When completely disconnected, the temperature increase was sufficient to cause a fire in the combustibles covering the terminal block. Therefore, in this study, the causes of electrical fires in chiller heaters were investigated and preventive measures were proposed by analyzing abnormal signals and thermal characteristics caused by the electrical wiring being reduced and completely disconnected.

• Korean Chemical Engineering Research
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• 제55권3호
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• pp.322-331
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• 2017

District heating was first introduced in Korea in 1985. As the service life of the underground thermal piping network has increased for more than 30 years, the maintenance of the underground thermal pipe has become an important issue. A variety of complex technologies are required for periodic inspection and operation management for the maintenance of the aged thermal piping network. Especially, it is required to develop a model that can be used for decision making in order to derive optimal maintenance and replacement point from the economic viewpoint in the field. In this study, the analysis was carried out based on the repair history and accident data at the operation of the thermal pipe network of five districts in the Korea District Heating Corporation. A failure probability model was developed by introducing statistical techniques of qualitative analysis and binomial logistic regression analysis. As a result of qualitative analysis of maintenance history and accident data, the most important cause of pipeline damage was construction erosion, corrosion of pipe and bad material accounted for about 82%. In the statistical model analysis, by setting the separation point of the classification to 0.25, the accuracy of the thermal pipe breakage and non-breakage classification improved to 73.5%. In order to establish the failure probability model, the fitness of the model was verified through the Hosmer and Lemeshow test, the independent test of the independent variables, and the Chi-Square test of the model. According to the results of analysis of the risk of thermal pipe network damage, the highest probability of failure was analyzed as the thermal pipeline constructed by the F construction company in the reducer pipe of less than 250mm, which is more than 10 years on the Seoul area motorway in winter. The results of this study can be used to prioritize maintenance, preventive inspection, and replacement of thermal piping systems. In addition, it will be possible to reduce the frequency of thermal pipeline damage and to use it more aggressively to manage thermal piping network by establishing and coping with accident prevention plan in advance such as inspection and maintenance.

• Tribology and Lubricants
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• 제33권3호
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• pp.112-118
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• 2017

Tilting pad journal bearings(TPJBs) are widely used for high speed rotating machinery owing to their rotordynamic stability and thermal management feature. With increase in the rotating speed of such machinery, an increasingly important aspect of TPJB design is the prediction of their thermal behaviors. Researchers have conducted detailed investigations in the last two decades, which provided design tools for the TPJBs. Based on these previous studies, this paper presents a thermohydrodynamic(THD) analysis model for TPJBs. To calculate pressure distribution, we solve the generalized Reynolds equation and to predict the lubricant temperature, we solve the 3D energy equation. We employ the oil mixing theory to calculate pad inlet temperature; further, to consider heat conduction via the pad, we solve the heat conduction equation for the pads. We assume the shaft temperature as the averaged oil film temperature and apply natural convection boundary conditions to the pad side and back surfaces. To validate the analysis model, we compare the predicted pad temperatures with those from previous research. The results show good agreement with previous research. In addition, we conduct parametric studies on a TPJB which was used in a gas turbine simulator system. The predicted results show that film temperature largely depends on the rotating speed and oil supply condition.

• Proceedings of the Korean Nuclear Society Conference
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• 한국원자력학회 1996년도 춘계학술발표회논문집(1)
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• pp.185-190
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• 1996

RFSP is a computer program to do fuel management calculations for CANDU reactors. Its main function is to calculate neutron flux and power distributions using two-energy-group, three dimensional neutron diffusion theory. However, up to now the treatment has not been true two-group but actually "one-and-half groups". In other words, the previous (1.5-group) version of RFSP lumps the fast fission term into the thermal fission term. This is based on the POWDERPUFS-V Westcott convention. Also, there is no up-scattering term or bundle power over cell flux (H1 factor) for the fast group. While POWDERPUFS-V provides only 1.5 group properties, true two-group cross sections for the design and analysis of CAUDU reactors can be obtained from WIMS-AECL. To treat the full two-group properties, the previous RFSP version was modified by adding the fast fission, up-scatter terms, and H1 factor. This two-group version of RFSP is a convenient tool to accept lattice properties from any advanced lattice code (e.g. WIMS-AECL DRAGON, HELIOS...) and to apply to advanced fuel cycles. In this study, the modification to implement the true two-group treatment was performed only in the subroutines of the ＊SIMULATE module of RFSP. This module is the appropriate one to modify first, since it is used for the tracking of reactor operating histories. The modified two-group RFSP was evaluated with true two-group cross sections from WIMS-AECL. Some tests were performed to verify the modified two-group RFSP and to evaluate the effects of fast fission and up-scatter for three core conditions and four cases corresponding to each condition. The comparisons show that the two-group results are quite reasonable and serve as a verification of the modifications made to RFSP. To assess the long-term impact of the full 2-group treatment, it is necessary to simulate a long period (several months) of reactor history. It will also be necessary to implement the full two-group treatment of reactivity devices and assess the reactivity-device worths.ce worths.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제21권3호
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• pp.585-593
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• 2020

Until now, 29 fire accidents have occurred; 22 of them were caused by the interconnection of renewable energy sources that occurred during the rest period after the lithium-ion battery had been fully charged regardless of the seasons. The fire accidents of ESS were attributed to thermal runaway due to the overcharging of a few cells with the phenomenon of self-energy balancing, which is unintentional current flow from cells with a high SOC to the low cells if the SOC condition of each cell connected in parallel is different. Therefore, this paper proposes a novel configuration and operation algorithm of the BMS to prevent the self-energy balancing of ESS and presents a hybrid SOC estimation algorithm. From the test results of the self-energy balancing phenomenon between aging and normal cells based on the proposed algorithm and BMS, it was confirmed the possibility of self-energy balancing, which is unintentional current flow from cells with a high SOC to cells with a low SOC. In addition, the proposed configuration of the BMS is useful and practical to improve the safety of lithium-ion batteries because the BMS can reliably disconnect a parallel connection of the cells if the self-energy balancing current becomes excessively high.

• Transactions of the Korean hydrogen and new energy society
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• 제22권5호
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• pp.609-615
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• 2011

A 5 kW class SOFC system for cogeneration power units was consisted of a hot box part and cold BOPs. High temperature components such as a stack, a fuel reformer, a catalytic combustor, and heat exchanges are arranged in the bot box considering their operating temperatures for the system efficiency. The hot box was made of ceramic boards for the thermal insulation. A 5 kW class SOFC stack was composed of 2 sub-modules and each module had 64 cells with $15{\times}15cm^2$ area and stainless steel interconnects. The 5 kW class SOFC system was operated with a hydrogen and a city gas. With a hydrogen, the total power of the stacks was about 7.1 kWDC and electrical efficiency was about 49.3% at 80 A. With a city gas, the total power of the stacks was about 5.7 $kW_{DC}$ and electrical efficiency was about 38.8% at 60 A. Under self-sustained operating condition, the system efficiency including a power conditioning loss and a consumed power by BOPs was about 30.2%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제22권7호
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• pp.492-507
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• 2010

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2009. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends of thermal and fluid engineering have been surveyed as groups of general thermal and fluid flow, fluid machinery and piping, and new and renewable energy. Various topics were covered in the field of general thermal and fluid flow such as an expander, a capillary tube, the flow of micro-channel water blocks, the friction and anti-wear characteristics of nano oils with mixtures of refrigerant oils, etc. Research issues mainly focused on the design of micro-pumps and fans, the heat resistance reliability of axial smoke exhaust fans, and hood systems in the field of fluid machinery and piping. Studies on ground water sources were executed concerning two well type geothermal heat pumps and multi-heat pumps in the field of new and renewable energy. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics and industrial heat exchangers. Researches on heat transfer characteristics included the heat transfer in thermoelectric cooling systems, refrigerants, evaporators, dryers, desiccant rotors. In the area of industrial heat exchangers, researches on high temperature ceramic heat exchangers, plate heat exchangers, frosting on fins of heat exchangers were performed. (3) In the field of refrigeration, papers were presented on alternative refrigerants, system improvements, and the utilization of various energy sources. Refrigeration systems with alternative refrigerants such as hydrocarbons, mixed refrigerants, and $CO_2$ were studied. Efforts to improve the performance of refrigeration systems were made applying various ideas of suction line heat exchangers, subcooling bypass lines and gas injection systems. Studies on heat pump systems using unutilized energy sources such as river water, underground water, and waste heat were also reported. (4) Research trend in the field of mechanical building facilities has been found to be mainly focused on field applications rather than performance improvements. In the area of cogeneration systems, papers on energy and economic analysis, LCC analysis and cost estimating were reported. Studies on ventilation and heat recovery systems introduced the effect on fire and smoke control, and energy reduction. Papers on district cooling and heating systems dealt with design capacity evaluation, application plan and field application. Also, the maintenance and management of building service equipments were presented for HVAC systems. (5) In the field of architectural environment, various studies were carried to improve indoor air quality and to analyze the heat load characteristics of buildings by energy simulation. These studies helped to understand the physics related to building load characteristics and to improve the quality of architectural environment where human beings reside in.

• Journal of the Korean Wood Science and Technology
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• 제44권5호
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• pp.685-694
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• 2016

In this study, the thermal degradation behavior of biomass during torrefaction was studied by thermogravimetric and byproduct gas analysis. Torrefaction temperature, time, and heating rate were $220{\sim}300^{\circ}C$, 110 min, and $10{\sim}30^{\circ}C/min$, respectively. The degradation rate of yellow poplar was 8.01~8.81% at $220^{\circ}C$ and 71.86~77.38% at $300^{\circ}C$ depending on heating rate. The degradation rate significantly increased at temperature over $240^{\circ}C$. On the other hand, degradation rate of larch was relatively low as 49.58~54.15% at $300^{\circ}C$. The activation energy of yellow poplar was 87.32~91.24 kJ/mol; these values did not significantly change with heating rate. The activation energy of larch was 83.85~91.60 kJ/mol. The major components of the gas generated during torrefaction were derived from hemicellulose. The component types and concentrations increased with torrefaction severity. High concentrations of furfural and acetic acid were detected during torrefaction of yellow poplar.

• International Journal of Automotive Technology
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• 제7권7호
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• pp.867-872
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• 2006

Fuel cells are devices that convert chemical energy directly into electrical energy. Owing to the high efficiency of the fuel cells, a large number of research work have been done during these years. Among many kinds of the fuel cells, a polymer electrolyte membrane fuel cell is such kind of thing which works under low temperature. Because of the specialty, it stimulated intense global R&D competition. Most of the major world automakers are racing to develop polymer electrolyte membrane fuel cell passenger vehicles. Unfortunately, there are still many problems to be solved in order to make them into the commercial use, such as the thermal and water management in working process of PEMFCs. To solve the difficulites facing the researcher, the analysis of the inner mechanism of PEMFC should be implemented as much as possible and mathematical modeling is an important tool for the research of the fuel cell especially with the combination of experiment. By regarding some of the assumptions and simplifications, using the finite element technique, a two-dimensional electrochemical mode is presented in this paper for the further comparison with experimental data. Based on the principals of the problem, the equations of electronic charge conservation equation, gas-phase continuity equation, and mass balance equation are used in calculating. Finally, modeling results indicate some of the phenomenon in a unit cell, and the relationships between potential and current density.