• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3377-3382
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• 2007

In proton exchange membrane fuel cell, the heat is generated at the catalyst layer as result of exothermic electrochemical reaction. This heat increases temperature of gas diffusion layer and membrane whose conductivity is very sensitive to humidity, function of temperature. So it is very important to analysis heat transfer through fuel cell to maintain temperature at specified range. In this paper numerical simulation was done including reversible, irreversible, ionic resistance, water formation loss to source term of energy equation. Results show that irreversible and water formation loss contributes mainly to energy source term and as current density increases, all of energy source terms become increased and Nusselt number is increased as results of more heat generation. Particularly irreversible loss is found to be predominant among the all energy source and water formation at cathode channel influences the temperature distribution of fuel cell greatly.

• Korean Journal of Environmental Biology
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• v.26 no.1
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• pp.1-7
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• 2008

A mathematical model for the synergistic interaction of physical and chemical environmental agents was suggested for quantitative prediction of irreversibly damaged cells after combined exposures. The model took into account the synergistic interaction of agents and was based on the supposition that additional effective damages responsible for the synergy are irreversible and originated from an interaction of ineffective sublesions. The experimental results regarding the irreversible component of radiation damage of diploid yeast cells simultaneous exposed to heat with ionizing radiation ($^{60}Co$) or UV light (254 nm) are presented. It was shown that the cell ability of the liquid holding recovery decreased with an increase in the temperature, at which the exposure was occurred. A good correspondence between experimental results and model prediction was demonstrated. The importance of the results obtained for the interpretation of the mechanism of synergistic interaction of various environmental factors is discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.2
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• pp.87-95
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• 2017

The concept of entransy has been proposed recently as a potential heat transfer mechanism and could be useful in analyzing and optimizing the heat-work conversion systems. This work presents an entransy analysis for the irreversible Carnot cycle by systematic balance formulations of the entransy loss, work entransy, and entransy dissipations, which are consistent with exergy balances. Additionally, several forms of system efficiency are introduced based on entransy for the appreciation of the optimal system performance. The effects of the source temperature and irreversible efficiencies on the optimal conditions for system efficiencies are systematically investigated for both dumping and non-dumping cases of used source fluid. The results show different trends in entransy efficiencies when compared to the conventional efficiencies of energy and exergy, and represent another method to assess the effective use of heat source in power generation systems.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.16 no.3
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• pp.305-314
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• 1987

Thermodynamic analysis of a mixed refrigerant refrigeration cycle has been performed by computing thermodynamic properties of various refrigerants. The analyses are carried cut to identify the sources and distribution of the energy degradation by irreversible processes. Heat exchange process with the surroundings produces the entropy and the irreversible loss can be reduced by the mixed refrigerant whose phase change temperature varies during the phase change processes in the evaporator and the condenser. The concept has been applied to find the minimum compression work and thus the minimum energy loss in the overall system, specifically in the case of the mixed refrigerant of R12 and R114. Parametric studies have been added to recognize the various factors affecting the system performance.

• Korean Journal of Materials Research
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• v.7 no.4
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• pp.287-294
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• 1997

(NdㆍDy)-(FeㆍCoㆍAIㆍM)-B 합금에 Sn,Mo등을 첨가하여 그에 따른 미세구조와 열적안정성 및 자기적 특성 변화를 조사하였다. Sn과 Mo의 첨가는 (NdㆍDy)-(FeㆍCoㆍAIㆍM)-B 합금리본의 큐리온도를 크게 향상시켰으며 자기특성, 특히 보자력을 1KOe이상 증가시켰다. 그리고 이러한 현저한 보자력 증가는 입계형 defect인 disturbed grain boundary defect에 기인하는 것이라 판단되었다. 또한 Sn과 Mo 첨가원소는 irreversible loss를 각각 4%와 6% 감소시켜 리본자석의 열적안정성을 향상시켰다. 이는 Sn과 Mo의 첨가가 보자력을 크게 증가시켰기 때문이다. 한편 (NdㆍDy)-(FeㆍCoㆍAIㆍM)-B 리본자석들의 열저항온도(heat resistance temperature)는 irreversible loss와 직선관계를 이루었다.

• Fibers and Polymers
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• v.4 no.2
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• pp.84-88
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• 2003

The properties of a woven fabric made of poly(trimethylene terephthalate) (PTT) were investigated. The PTT fab-ric of draw textured yarn (DTY) showed excellent stretch as good as a fabric containing spandex. However, the unique stretch of the PTT fabric reduced dramatically by simple heat-treatment even at as low as $80^{\circ}C$. To understand the phenomenon, the crimp rigidity of the DTY was observed by SEM. It was found that the drastic reduction of stretch was caused by irreversible uncrimping of PTT DTY after heat-treatment. Conclusively, it is of importance to optimize the texturing conditions for PTT DTY to make the crimp more stable.

• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.1
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• pp.27-33
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• 2003

Excessive heat generation at the implant-bone interface may cause irreversible bone damage and loss of osseointegration. The effect of heat generation in vitro at the implant surface caused by abutment reduction with high-speed dental turbine was examined. Titanium-alloy abutments connected to a titanium alloy screw-implant embedded in an acrylic-resin block in a $37^{\circ}C$ water bath were prepared. Temperature changes were recorded via embedded thermocouples at the cervix and apex of the implant surface. Analysis of variance for repeated measures was used to compare seven treatment groups. Fifty seconds of continuous cutting with air and water coolant caused a mean temperature increase of $1.24^{\circ}C$ at apex and $5.77^{\circ}C$ at cervix. Similar intermittent cutting caused increase of $2.50^{\circ}C$ at apex and $1.64^{\circ}C$ at cervix. But, continuous cutting with air coolant caused a mean temperature increase of $6.47^{\circ}C$ at apex and $5.77^{\circ}C$ at cervix. Similar intermittent cutting caused increase of $6.47^{\circ}C$ at apex and $5.77^{\circ}C$ at cervix. Preparation of implant abutment does not lead to detrimental effect on peri-implant tissues provided that adequate cooling. However, without water cooling, extreme overheating could be provoked, reaching the critical temperature that would lead to irreversible bone damage within only a few seconds.

• Restorative Dentistry and Endodontics
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• v.20 no.1
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• pp.235-249
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• 1995

This study was designed to identify the lymphocytes present and to examine the relation between lymphocytes population and clinical symptoms of the pulps clinically diagnosed as normal and irreversible pulpitis. We recorded the history and severity of the pain and performed several clinical tests, before extirpation of vital, irreversibly inflamed pulps in routine endodontic treatment. Then the teeth were divided into two groups. Five teeth, categorized in acute symptom group, had severe spontaneous pain, particularly at night and were extremely sensitive to cold and heat. The other 15 teeth with history of mild to moderate pain and with or without cold or heat responses were categorized as chronic symptom group. Inflamed pulps were also classified into 8 minor groups by presence or absence of signs or symptoms related to the involved teeth, including the presence of pain on percussion, pain on heat and cold stimuli and the periodontal pocket depth. All extirpated pulps were immediately immersed in ultra low-temperature freezer($-74^{\circ}C$), and they were sectioned $6{\mu}m$ in thickness. Specimens were stained using three-stage indirect immunoperoxidase techniques(DAKO, LSAB kit) and monoclonal antibodies for detecting the presence of T lymphocytes(T), B lymphocytes(B) and helper(T4) and suppressor(T8) lymphocytes. Following results were obtained; 1. All the examined normal and inflamed pull) tissues had positive staining for T lymphocytes and T helper and T suppressor cells. But B cells were observed only in inflamed pulp. 2. Statistically more T and B cells were observed in acute symptom group as compared with chronic symptom group(p<0.05). 3. Cell ratio of BIT in acute symptom group were significantly higher than that of chronic symptom group(p<0.05). 4. Only B cells were significantly increased in the percussion positive group than the number of B cells in percussion negative group(p<0.05). 5. No differences were observed in the number of different cell types among other minor groups.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.527-532
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• 2009

Recently, Interior Permanent Magnet Machine(IPM) is widely used for traction motor in the high speed train. Due to the high efficiency and high power density of the IPM, it has lots of heat sources such as iron loss and copper loss. These heat sources can cause the demagnetization of permanent magnet, losses in output power and even irreversible defect of the IPM. To prevent the power loss caused by heat sources, the accurate thermal analysis has to be carried out. For the thermal analysis of the IPM, the thermal network is designed for this traction motor. The thermal analysis has executed at rated speed operation. The result of thermal network analysis can be used for the IPM design process.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.431-438
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• 2000

The major irreversibilities in absorption chillers are associated with the transfer of heat into and out from the machine and irreversible process inside the machine. By modeling only external irreversibilities(endo-reversible), a model was formulated to predict the ideal performance of a single-effect absorption chiller. Its actual performance including both external and internal irreversibilities was calculated with a in-house simulation program. The optimization of heat transfer area distribution was performed for both endo-reversible cycle and actual cycle. The equation of endo-reversible modeling was found to give about 2times higher cooling capacity than the simulation program. At optimal distribution, it was found that heat transfer area of the evaporator was about 30% of total area, that of the generator was 20%, and the rest 50% was for the absorber and condenser. The system COP for endo-reversible cycle was slightly higher than that for actual cycle. In the case of LiBr-water single-effect absorption chiller, the maximum cooling capacity was obtained near the condition that LMTD is same at all heat exchangers.