• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.292-295
• /
• 2008

In a SCWR (SuperCritical pressure Water cooled Reactor), the coolant temperature initially at below the pseudo-critical temperature at the bottom of a reactor core increases as the coolant flows upward through the sub-channels of the fuel assemblies, and it finally becomes higher than the pseudo-critical temperature when it leaves the reactor core. At certain conditions, heat transfer deterioration occurs near the pseudo-critical temperature and it may cause a drastic rise of the fuel surface temperature resulting a fuel failure. Therefore, an accurate estimation of the heat transfer coefficient is very important for the thermal-hydraulic design of a reactor core. An experiment on heat transfer to the vertically upward flowing $CO_2$ at a supercritical pressure in a circular tube were performed at KAERI. The internal diameter of the test section is 6.32 mm, which corresponds to the hydraulic diameter of a sub-channel in the conceptional design proposed by KAERI. The test range of the mass flux is 285 to 1200 kg/m$^2$s and the maximum heat flux is 170 kW/m$^2$. The inlet pressure is maintained at 8.12 MPa, which is 1.1 times the critical pressure. A new correlation, which covers both the normal and deterioration heat transfer regimes was proposed and compared with the estimations by exiting correlations.

• 대한전기학회논문지:전력기술부문A
• /
• 제54권6호
• /
• pp.306-314
• /
• 2005

In this paper, a new approach that is based on EEAC & only with network solutions for CS&S in the transient stability assessment is developed. The proposed CS&S algorithm in conjunction with EEAC to include the capability of performing on-line TSA without TDS is used to calculate the critical clearing time for stability index. In this algorithm, all generators are represented by classical models and all loads are represented by constant impedance load models. The accelerating & synchronizing power coefficient as an index is determined at its disturbance through solving network equation directly. As mentioned above, a new index for generator is generally used to determine the critical generators group. The generator rotor angle is fixed for non-critical generators group, but has equal angle increments for critical generators group. Finally, the critical clearing time is calculated from the power-angle relationship of equivalent OMIB system. The proposed CS&S algorithm currently being implemented is applied to the KEPCO system. The CS&S result was remarkably similar to TSAT program and SIME. Therefore, it was found to be suitable for a fast & highly efficient CS&S algorithm in TSA. The time of CS&S for the 139 contingencies using proposed CS&S algorithm takes less than 3 seconds on Pentium 4, 3GHz Desktop.

• 한국자동차공학회논문집
• /
• 제16권1호
• /
• pp.121-126
• /
• 2008

The cooling heat transfer coefficient of $CO_2$ (R-744) in a horizontal and helically coiled tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater, evaporator and gas cooler (test section). The test section consists of a horizontal stainless steel tube and hellically coiled copper tube of 4.57 and 7.75 mm. The experiments were conducted at saturation temperature of 100 to $20^{\circ}C$, and mass flux of 200 to $500kg/m^2s$. The test results showed the variation of the heat transfer coefficient tended to decrease as cooling pressure of $CO_2$ increased. The heat transfer coefficient with respect to mass flux increased as mass flux increased. The experimental results were also compared with the existing correlations for the supercritical heat transfer coefficient, which generally underpredicted the measured data. However, the experimental data showed a relatively good agreement with the correlations of Pitla et al. except for the pseudo critical temperature.

• 한국환경과학회지
• /
• 제23권6호
• /
• pp.1199-1211
• /
• 2014

The momentum flux and the sensible heat flux were measured with the scintillometers and ultrasonic anemometers at 6 sites of which surface characteristics like roughness length and zero-displacement are different each other. We estimated the momentum flux and the sensible heat flux based on the bulk transfer method with the drag coefficient and the heat transfer coefficient calculated from the temperature and wind speed at two heights. The variation of bulk transfer coefficients showed a remarkable difference depending on the atmospheric stability which is less influenced by the zero-displacement than the roughness length. The estimated sensible heat fluxes were in good agreement with those measured at 3 m, showing 23.7 $Wm^{-2}$ of the root mean square error that is less than 10% of its maximum. Since the estimated momentum flux is not only effected by drag coefficient but also by wind speed square, the determination of wind speed in the bulk transfer method is critical.

• International Journal of Concrete Structures and Materials
• /
• 제10권1호
• /
• pp.61-73
• /
• 2016

In predicating the probability distribution of chloride diffusion coefficient of recycled aggregate concrete ($D_{RAC}$), the morphological characteristics of three phases, i.e., the old attached mortar, the natural aggregate and the new mortar, should all be taken into account. The present paper attempts to develop a probability density evolution method (PDEM) to achieve this. After verifying the derived PDEM results with experimental results, the effects of old attached mortar to the $D_{RAC}$ are examined in a quantitative manner. It is found that (1) the variation of the attached mortar content is much sensitive to $D_{RAC}$; (2) given the probability distribution of the content and chloride diffusion coefficient of old mortar, the probability distribution of DRAC can be analysed based on the PDEM; and (3) the critical chloride diffusion coefficient at a certain assurance rate can be obtained by the PDEM. The analysis results of this investigation will be valuable to the durability design for RAC.

• Tuberculosis and Respiratory Diseases
• /
• 제72권6호
• /
• pp.467-474
• /
• 2012

Background: The objective of this study was to assess the validity and reliability of the Korean version of chronic obstructive pulmonary disease assessment test (CAT) and Dyspnea-12 Questionnaire for patients with bronchiectasis or tuberculous destroyed lung. Methods: For 62 bronchiectasis patients and 37 tuberculous destroyed lung patients, 3 questionnaires including St. George's Respiratory Questionnaires (SGRQ), CAT, and Dyspnea-12 were obtained, in addition to spirometric measurements. To assess the validity of CAT and Dyspnea-12, correlation with SGRQ was evaluated. To assess the reliability of CAT and Dyspnea-12, Cronbach's ${\alpha}$ coefficient was calculated. Results: The mean ages of the patients were $60.7{\pm}8.3$ years in bronchiectasis and $64.4{\pm}9.3$ years in tuberculous destroyed lung. 46.8% and 54.1% were male, respectively. The SGRQ score was correlated with the score of the Korean version of CAT (r=0.72, p<0.0001) and Dyspnea-12 (r=0.67, p<0.0001) in bronchiectasis patients. The SGRQ score was correlated with the score of CAT (r=0.86, p<0.0001) and Dyspnea-12 (r=0.80, p<0.0001) in tuberculous destroyed lung patients. The Cronbach's ${\alpha}$ coefficient for the CAT and Dyspnea-12 were 0.84 and 0.90 in bronchiectasis, and 0.88 and 0.94 in tuberculous destroyed lung, respectively. Conclusion: We found that Korean version of CAT and Dyspnea-12 are valid and reliable in patients with tuberculous destroyed lung and bronchiectasis.

• 한국콘텐츠학회논문지
• /
• 제16권5호
• /
• pp.612-622
• /
• 2016

본 연구는 간호대학생의 문제해결능력, 비판적 사고 성향, 창의성, 자기효능감, 간호과정 수행능력 정도와 이 들 변수 간의 상관관계를 파악하기 위한 서술적 조사연구이다. 연구대상은 일 간호대학에서 간호과정 교과목을 수강한 2학년 학생 246명을 대상으로, 2015년 6월 10일부터 20일까지 구조화된 설문지를 통해 자료를 수집하였다. 대상자의 일반적 특성별 문제해결능력, 비판적 사고 성향, 창의성, 자기효능감, 간호과정 수행능력과의 차이는 t-test, ANOVA, Kruskal-wallis 검정으로, 대상자의 문제해결능력, 비판적 사고 성향, 창의성, 자기효능감과 간호과정 수행능력과의 관계는 Pearson correlation coefficient로 분석하였다. 프로그램을 이용하여. 본 연구결과 문제해결능력, 비판적 사고 성향, 창의성은 지원동기, 전공 만족도와 통계적으로 유의한 차이가 있었으며, 자기효능감, 간호과정 수행능력은 전공 만족도에 따라 통계적으로 유의한 차이가 있었다. 간호대학생의 문제해결능력, 비판적 사고 성향, 창의성, 자기효능감과 간호과정 수행능력과의 관계를 분석한 결과, 문제해결능력과 비판적 사고 성향, 창의성 및 자기효능감은 통계적으로 유의한 정적 상관관계로 나타났으나 간호과정 수행능력은 문제해결능력, 비판적 사고 성향, 창의성 및 자기효능감과 상관관계가 없는 것으로 나타났다. 본 연구 결과에 따라 이에 대한 지속적인 연구와 함께 간호대학생들의 자기효능감 증진 및 간호과정 수행능력 향상을 위한 지지 및 교육적 기반을 갖춘 프로그램 모색이 필요함을 제시하고자 한다.

• 한국산학기술학회논문지
• /
• 제19권12호
• /
• pp.825-835
• /
• 2018

본 연구의 목적은 간호대학생을 대상으로 셀프리더십 정도에 따른 비판적 사고성향, 임상수행능력, 간호전문직 자아개념의 관계를 확인하는 서술적 조사연구이다. K도 C시 소재 C대학교 간호학과 3.4학년 165명을 대상으로 자가 보고식 설문지를 이용하여 자료를 수집하였고, 수집된 자료는 t-test, ANOVA, Pearson's correlation coefficient, Multiple Regression으로 분석하였다. 일반적 특성에 따른 셀프리더십은 학년, 학업성적, 입학동기, 전공만족도에 따라 유의한 차이가 있었고, 셀프리더십은 비판적 사고성향, 임상수행능력, 간호전문직 자아개념과 순상관관계가 있는 것으로 확인되었다. 셀프리더십에 영향을 미치는 일반적 특성과 비판적 사고성향, 간호전문직 자아개념 및 임상수행능력의 영향을 분석하였을 때 49.9%의 설명력을 보였고, 이 중 비판적 사고성향이 가장 중요 요인이었다. 이를 통해 간호대학생의 비판적 사고성향을 증진함으로써 셀프리더십을 효과적으로 향상시킬 수 있을 것으로 사료된다. 또한 본 연구는 일 대학교를 대상으로 하여 연구결과를 일반화하는데 무리가 있으며, 현실적으로 전공이수 체계상의 문제점 등 여러 어려움이 있지만 다양한 방법을 모색하여 간호대학생에게 셀프리더십을 강화시켜 나갈 지속적인 교육프로그램을 운영할 필요가 있음을 제언한다.

• Nuclear Engineering and Technology
• /
• 제27권5호
• /
• pp.701-709
• /
• 1995

RELAP5 /MOD3/KAERl의 임계유동모델을 위한 실제적인 배출계수들을 9개의 MARVIKEN 임계유동실험 의 평가계산을 통하여 과냉각과 이상임계유동에 대하여 구하였다. 선택된 실험에는 높은 초기 과냉각도와 큰 노즐 세 장비(L/D)인 것들이 포함되었다. 코드의 평가결과는 RELAP5/MOD3/KAERI은 과냉각임계유동을 크게 예측하고 이 상임계유동은 작게 예측함을 보이고 있다. 이러한 결과들을 이용하여 임계유동모델의 실제적인 배출계수들을 반복법으로 정량화 하였다. 실제적인 배출계 수는 과냉각임계유동이 0.89 그리고 이상임계유동이 1.07로 결정되었으며 관련 표준편차는 각 각 0.0349과 0.1189이다. 본 연구로부터 얻어진 결과는 대형냉각재 상실사고의 실제적인 계통반응 계산과 비상노심냉각계통 성능평가에 적용할 수 있다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2001년도 하계학술대회 논문집
• /
• pp.955-958
• /
• 2001

The structure characteristics of varistor of Zn oxide to depend on the breakdown voltage has been investigated to annealing condition by additive material of Sb$_2$O$_3$ system. The breakdown voltage that has not doping Sb$_2$O$_3$ was 235[V]. ZnO varistors was shown ohmic properties when it's applied voltage was below critical voltage. It was shown non-ohmic properties over critical voltage, because current was increased with decreasing resistance. High voltage ZnO varistors had high breakdown voltage, but it had bad electrical stability with various surge. Sb$_2$O$_3$was increased non-linear coefficient in ZnO varistors grain boundary.