• 설비공학논문집
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• 제9권3호
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• pp.354-363
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• 1997

The purpose of the present work is to show the best thermal storage material and the sensitivity of the parameters on the thermal performance by experimentally investigating the effects of the parameters on the thermal performance of the spherical capsule system using paraffins superior to the commercial one. The paraffins were n-Tetradecane and the mixture of n-Tetradecane 40% and n-Hexadecane 60%. The experimental parameters were the Reynolds number of 8, 12, and 16 and the inlet temperature of-7, -4, -1, and $2^{\circ}C$. The charging and the discharing time, the dimensionless thermal storage amount, and the averge heat transfer coefficient in the tank were obtained by utilizing the local temperature variation in the tank. The local charging and discharging time in the tank was axially and radially different a lot. The effects of the inlet temperature on the charging and the discharging time were larger during the charging process than during the discharging process, but the effects of the Reynolds number on the charging and the discharging time were in reverse order. The paraffins were better by 11~72% than the water with the inorganic material in the charging time aspect, but no difference in the discharging time aspect. The effects of the Reynolds number on the dimensionless thermal storage amount were smaller than the effects of the inlet temperature during the charging process, but in reverse order during the discharging process within the working range of the experimental parameters. The effects of the inlet temperature and the Reynolds number on the average heat transfer coefficient were larger during the discharging process than during the charging process. The average heat transfer coefficient for the paraffins was larger by 40% maximum than that for the commercial material during the charing and the discharging process.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1146-1148
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• 2007

This paper proposes a method to improve the charging speed and discharging performance of a high voltage capacitor used in a portable medical device. The improvement of the charging speed was achieved by duty cycle control. The discharging performance was carried out by varying the phase duration and the leading edge voltage of the output according to the transthoracic impdedance of the patient. As a result, the improvement in the charging speed and the performance of the discharging parameters shorten the patient treatment time.

• 한국정밀공학회지
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• 제22권4호
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• pp.27-36
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• 2005

Some studies have shown that unstable factors are inherent in WEDM process, causing the instability of the discharging pulse to reach about 40∼60％ in normal machining. Transient stability is an important subject in WEDM process since there is a close relationship between stability and machining performance, such as the characteristics of a machined surface, machining speed and problem of instability like wire rupture phenomenon. Among the many machining parameters affecting WEDM machining state, three specific parameters (Vr, Ip, off time ) are major controllable variables that can be applied in transient stability control. And, this research investigates the implementation and analysis of real-time micro control of the discharging stability of WEDM (Wire Electric Discharge Machining) process.

• Journal of Advanced Marine Engineering and Technology
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• 제41권1호
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• pp.1-7
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• 2017

두 판을 맞대기 용접할 경우 용접부 시종단부 측면에 열전도도가 큰 금속(예를 들어 구리)으로 만든 엔드 탭을 장착하고 용접을 진행하면 용접부 끝부분의 비드흘러내림과 결함을 방지할 수 있다. 본 논문에서는 엔드 탭의 방열 성능을 강화시키기 위하여 자연 대류에 의한 방열 특성이 뛰어난 것으로 알려진 평판 휜 모양을 적용하였고, 실험 및 수치해석을 통하여 엔드 탭에 평판 휜 모양의 구멍이 있는 형상이 구멍이 없는 형상보다 방열 성능이 더 뛰어남을 확인하였다. 그리고 열, 유동해석을 통하여 엔드 탭의 휜 형상에 대한 냉각 속도를 평가하여, 방열 성능 측면으로 도움이 될 형상 인자적인 특성을 파악하였다. 그 결과, 엔드 탭에 수직 휜이 있으며 휜 간 간격에 최적 휜 간 간격 식을 적용한 구조가 우수한 형상으로 판단되었다.

• 한국전기전자재료학회논문지
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• 제35권4호
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• pp.322-332
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• 2022

Energy storage capacitors based on dielectric ceramics with superior polarization properties and dielectric constant can provide much higher output power density due to their very fast energy charging/discharging rates, which are particularly suitable for operating pulsed-power devices. For an outstanding energy storage performance of dielectric capacitor, a large recoverable energy density could be derived by introducing a slim polarization-electric field hysteresis loop into dielectric materials by various technical approaches. Many research teams have explored various dielectric capacitor technologies to demonstrate high output power density and ultrafast charging/discharging behavior. This article reviews the recent research progress in high-performance dielectric capacitors for pulsed-power electronic applications.

• 설비공학논문집
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• 제26권7호
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• pp.301-307
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• 2014

This paper presents a numerical study on the constrained melting of a phase change material inside various capsule containers, using water and HDPE (High Density Polyethylene) as a PCM and a capsule material, respectively. The computations are based on an iterative, finite-volume numerical procedure that incorporates a single-domain enthalpy formulation for simulation of the phase change phenomenon. Using the enthalpy method, various capsule configurations, such as a capsule from E company, an isochoric cylinder capsule, an equivalent diameter sphere capsule, and an isochoric sphere capsule, are used to investigate the effect of capsule configurations on the charging and discharging performance. A transient three-dimensional model is used for each case. The simulation results show that the capsule from E company results in a higher melting and solidification rate of the PCM, than the other capsule configurations considered in this research.

• 한국재료학회지
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• 제31권2호
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• pp.84-91
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• 2021

To cope with automobile exhaust gas regulations, ISG and charging control systems are applied to HEV vehicles for the purpose of improving fuel economy. These systems require quick charge-discharge performance of high current. Therefore, a Module of the AGM battery with high energy density and EDLC(Electric Double Layer Capacitor) with high power density are constructed to study the charging and discharging behavior. In CCA, which evaluates the starting performance at -18 ℃ & 30 ℃ with high current, EDLC contributed for about 8 sec at the beginning. At 0 ℃ CA (Charge Acceptance), the initial Charging current of the AGM/EDLC Module, is twice that of the AGM lead acid battery. To play the role of EDLC during high-current rapid charging and discharging, the condition of the AGM lead-acid battery is optimally maintained. As a result of a Standard of Battery Association of Japan (SBA) S0101 test, the service life of the Module of the AGM Lead Acid Battery/EDLC is found to improve by 2 times compared to that of the AGM Lead Acid Battery.

• 대한기계학회논문집B
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• 제39권7호
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• pp.625-631
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• 2015

이번 연구는 패킹 모듈로 채워진 축열조의 방열 성능을 수치해석 하였다. 해석에는 PCM의 상변화 현상을 계산하기 위해 엔탈피-공극률 방법을 이용하였다. 이 방법을 통해서 방열 시 축열조 상부로부터 열전달유체가 흐를 때 모듈에서의 녹는 현상을 계산하였다. 축열조 디자인에 모듈 배치, 모듈 수 등의 다양한 인자가 있지만, 본 해석에서는 유량의 변화에 따라 나타나는 축열조 출구온도, 전체 PCM의 시간에 따른 녹은 양 및 축열밀도를 확인하였다. 결과적으로 유량이 증가할수록 출구온도가 높게 형성되었으며, 전체 PCM이 녹는데 필요한 시간이 짧아지고 축열 밀도 역시 증가하여 목표치의 93% 수준에 도달하는 것으로 나타났다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.280-285
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• 2001

This paper presents a modelling of thermal discharge performance for a static ice-on-coil ice-storage tank. Through the present study, discharging characteristics were examined with the existing results of theoretical and numerical heat transfer analyses. Also, an experiment was conducted to obtain a real set of discharge performance. The thermal effectiveness, the ratio of the actual heat transfer rate to the maximum possible heat transfer rate, decreased when the stored energy decreased during discharging period. And the effectiveness increased as the coolant flow rate through the storage increased, of which increasing rate decreased abruptly near the maximum and the minimum stored energy. An empirical correlation was obtained from the experimental and the numerical analysis data.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.315-318
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• 2009

Hydrogen is the ideal candidate as an alternative energy carrier, so many hydrogen storage methods are investigated. The hydrogen storage method using metal hydride is good candidate as energy sources for portable devices because hydrogen-storage as metal hydride shows large volumetric storage density. In this study, we investigated the variations of hydrogen charging/discharging performance of metal hydride tanks at different temperature conditions. We charged metal hydride tanks with hydrogen in low temperature because of the exothermic reactions of hydrogen absorption while we discharged in high temperature to provide sufficient heat because of the endothermic reactions of desorption. In addition, we investigated the difference of hydrogen charging/discharging performance between two tanks having different sizes.