• Journal of Electrochemical Science and Technology
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• 제15권2호
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• pp.253-260
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• 2024

Proton exchange membrane water electrolysis (PEMWE) is an efficient method for utilizing renewable energy sources such as wind and solar powers to produce green hydrogen. For PEMWE powered by renewable energy sources, its durability is a crucial factor in its performance since irregular and fluctuating characteristics of renewable energy sources, especially for wind power, can deteriorate the stability of PEMWE. Triangular voltage cycle is well able to simulate fluctuating wind power, but its effect on the durability has not been investigated extensively. In this study, the performance degradation of the PEMWE cell operated with the triangular voltage cycling was investigated at different ramping rates. The measured current responses during the cycling gradually decreased for both ramping rates, and I-V curve measurements before and after the cycling confirmed the degradation of the performances of PEMWE. For both measurements, the degradation rate was larger for 300 mV s^-1 than 30 mV s^-1, and they were determined as 0.36 and 1.26 mV h^-1 (at the current density of 2 A cm^-2) at the ramping rates of 30 and 300 mV s^-1, respectively. The comparison with other studies on triangular voltage cycling also indicate that an increase in the ramping rate accelerates the deterioration of the PEMWE performance. X-ray photoelectron spectroscopy and transmission electron microscopy results showed that the Ir catalyst was oxidized and did not dissolve during the voltage cycling. This study suggests that the ramping rate of the triangular voltage cycling is an important factor for the evaluation of the durability of PEMWE cells.

• 전기화학회지
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• 제15권1호
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• pp.12-18
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• 2012

다양한 응용분야에서 활용될 수 있는 고체고분자연료전지의 경우 현재 상용화에 가장 큰 걸림돌이 되고 있는 것이 고가의 백금 촉매이다. 따라서 특히 최근 들어 산소환원반응에서 백금을 대체하는 물질을 개발하기 위한 연구가 전세계적으로 확산되고 있다. 그러나 촉매 개발 시 경제성 관점 외에 내구성도 고려해야 하는데, 이런 관점에서 백금과 유사한 물성과 활성이 기대되는 백금족 원소들이 한 대안이 될 것이다. 가장 백금과 유사한 물성, 활성을 나타내는 팔라듐과 칼코겐화물 형태의 루테늄이 지금까지 가장 많이 연구가 되었으며 상대적으로 이리듐, 로듐, 오스뮴은 산소환원 촉매로 많은 연구가 되지 않았다. RDE (rotating disk electrode)를 이용한 반쪽전지 실험이나 연료전지 MEA (membrane electrode assembly) 운전을 통하여 백금과 활성을 비교해보면 팔라듐 계열의 비백금 촉매가 가장 백금에 가까운 활성을 나타내고 있음을 알 수 있다. 이 논문에서는 각 백금족 원소들 기반의, 현재까지 문헌상으로 보고된 촉매조성들을 분석하여 비백금 산소환원 촉매 개발에 도움이 되고자 한다.

• Korean Chemical Engineering Research
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• 제56권2호
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• pp.151-155
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• 2018

고분자전해질 연료전지(PEMFC)의 고분자막 열화정도는 주로 수소투과전류밀도로 평가한다. 수소투과전류밀도는 선형주사전압전류측정법(Linear Sweep Voltammetry, LSV)으로 측정하는데 DOE프로토콜과 NEDO프로토콜이 분석방법에 차이가 있다. 본 연구에서는 PEMFC 구동 및 가속 열화 시험 과정에서 두 프로토콜을 적용해 수소투과 전류밀도를 비교하였다. DOE 방법에 의한 LSV 방법에서는 주사속도(scan rate) 변화가 수소투과 전류밀도에 영향을 주지만 NEDO 방법에서는 주사속도가 수소투과전류밀도에 영향을 주지 않았다. 고분자막 가습/건조 15,000사이클 평가과정에서 DOE 방법은 막의 열화를 민감하게 측정하였으나 NEDO방법은 DOE방법에 비해 막의 열화가 덜 민감하게 나타났다.

• Smart Structures and Systems
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• 제15권4호
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• pp.1019-1039
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• 2015

Shanghai Tower is a composite structure building with a height of 632 m. In order to verify the structural properties and behaviors in construction and operation, a structural health monitoring project was conducted by Tongji University. The monitoring system includes sensor system, data acquisition system and a monitoring software system. Focusing on the health monitoring in construction, this paper introduced the monitoring parameters in construction, the data acquisition strategy and an integration structural health monitoring (SHM) software. The integration software - Structural Monitoring/ Analysis/ Evaluation System (SMAE) is designed based on integration and modular design idea, which includes on-line data acquisition, finite elements and dynamic property analysis functions. With the integration and modular design idea, this SHM system can realize the data exchange and results comparison from on-site monitoring and FEM effectively. The analysis of the monitoring data collected during the process of construction shows that the system works stably, realize data acquirement and analysis effectively, and also provides measured basis for understanding the structural state of the construction. Meanwhile, references are provided for the future automates construction monitoring and implementation of high-rise building structures.

• Structural Engineering and Mechanics
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• 제68권4호
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• pp.459-473
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• 2018

Temperature fields and temperature deformations induced by time-varying solar radiation, shadow, and heat exchange are of great importance for the ride safety and quality of the maglev system. Accurate evaluations of their effects on the dynamic performances are necessary to avoid unexpected loss of service performance. This paper presents a numerical approach to determine temperature effects on the maglev train/guideway interaction system. Heat flux density and heat transfer coefficient of different components of a 25 m simply supported concrete guideway on Shanghai High-speed Maglev Commercial Operation Line is calculated, and an appropriate section mesh is used to consider the time-varying shadow on guideway surfaces. Based on the heat-stress coupled technology, temperature distributions and deformation fields of the guideway are then computed via Finite Element method. Combining guideway irregularities and thermal deformations as the external excitations, a numerical maglev train/guideway interaction model is proposed to analyze the temperature effect. The responses comparison including and excluding temperature effect indicates that the temperature deformation plays an important role in amplifying the response of a running maglev, and the parameter analysis results suggest that climatic and environmental factors significantly affect the temperature effects on the coupled maglev system.

• 한국의류산업학회지
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• 제10권3호
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• pp.289-297
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• 2008

This paper was to examine the salesperson's service that the consumer demands in different types of fashion retailing formats including department store, discount store and outlet store. Data has been collected from June to August in 2005 in Pusan and Seoul on subject of 1000 adult over18 years old and 979 pieces were used to analyze. Data analysis was conducted by factor analysis, regression using the SPSS statistics package program. Services in common in 3 fashion retailing formats were "individual concerning", "kindness, courtesy/customer respect", "quick correspondence/convenience", and "product knowledge". Unique services that consumer demanded for the department store were professional and polite attitude; for the discount store, honesty and convenience for refund and exchange; for the outlet store, wide range of product selection. The results has shown that the part of salesperson's service dimensions influenced the consumer's purchase, repurchasing intention and the level of satisfaction. Therefore fashion marketers need to carefully implicate operation and service management depending on the retailing formats.

• 한국초전도ㆍ저온공학회논문지
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• 제23권1호
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• pp.7-11
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• 2021

Cryogenic vessels are special equipment that requires periodic evaluation of their thermal insulation performance. At the current standard, the test is considered as the loss product or heat leakage of cryogenic vessel, which takes over 72 h to evaluate; consequently, a large amount of working medium is discharged to the environment in the process. However, hydrogen is flammable and explosive, and the discharged gas may be dangerous. If liquid hydrogen is replaced with liquid nitrogen before testing, the operation then becomes complicated, and the loss product or heat leakage cannot respond to the thermal insulation performance of cryogenic vessels for liquid hydrogen. Therefore, a novel method is proposed to evaluate the heat leakage of cryogenic vessels for liquid hydrogen in self-pressurization. In contrast to the current testing methods, the method proposed in this study does not require discharge or exchange of working medium in all test processes. The proposed method is based on one-dimensional heat transfer analysis of cryogenic vessels, which is verified by experiment. When this method is used to predict the heat leakage, the comparison with the experimental data of the standard method shows that the maximum error of heat leakage is less than 5.0%.

• 전력전자학회논문지
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• 제13권5호
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• pp.344-351
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• 2008

본 논문의 배경은 제주지역의 안정적 전력공급을 위하여 최적의 전력공급체계를 분석한 논문이다. 본 논문에서 검토한 내용은 제주도 전력공급 현황파악 및 문제점 분석, 전력계통 운영측면에서 최적의 전력설비건설 타당성 검토 그리고 경제성 및 신뢰도 검토이다. 결론적으로 2011년에 HVDC 연계 선을 제주에 건설하는 경우에 경제성 평가(30년간 2011년 현가합 비교)를 한 경우 HVDC 연계선 추가건설이 기력(중유)발전이나 LNG 발전 보다 경제적임을 보여주고 있다. 그리고 신뢰도 측면에서도 좋은 역할을 할 것으로 기대되어진다.

• 한국산학기술학회논문지
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• 제13권5호
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• pp.1954-1962
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• 2012

최근 유럽과 아시아 사이의 물류 증가는 철도수송에 있어서 사회적/경제적으로 좋은 기회이며, 동시에 커다란 도전이 될 수 있다. 유라시아 대륙에는 다양한 궤간이 존재하고 있다. 이러한 궤간의 차이는 철도에 의한 화물수송시 장애요인중의 하나이다. 궤간 차이를 극복하기 위한 방법은 수송 화물의 유형에 따라 달라질 수 있으며, 국경 지점에 보관 창고 및 환적 설비와 같은 넓은 기반 시설과 많은 운영 인력수요와 같은 철도 수송 시스템의 운영에 많은 영향을 준다. 따라서 철도 수송 시스템의 효율성은 복잡한 하역 및 교환 기술에 관련된 궤간 극복 방법에 매우 의존한다. 본 논문은 궤간 극복 방법에 대한 기술적 평가를 기반으로 수송 시나리오의 효율성을 검토하고, 각 시나리오의 운영에서 요구되는 기술적 요소들을 기술하였다.

• 한국입자에어로졸학회지
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• 제9권2호
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• pp.103-110
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• 2013

The electrostatic precipitator (ESP) has been used for degrading atmospheric pollutants. These devices induce the electrical forces to facilitate the removal of particulate pollutants. The ions travel from the high voltage electrode to the grounded electrode by Coulomb force induced by the electric field when a high voltage is applied between two electrodes. The ions collide with gas molecules and exchange momentum with each other thus inducing fluid motion, electrohydrodynamic (EHD) flow. In this study, for the simulation of electric field and EHD flow in ESPs, an open source EHD solver, "espFoam", has been developed using open source CFD toolbox, OpenFOAM(R) (Open Field Operation and Manipulation). The electric potential distribution and ionic space charge density distribution were obtained with the developed solver, and validated with experimental results in the literature. The comparison results showed good agreement. Turbulence model is also incorporated to simulate turbulent flow; hence the developed solver can analyze laminar and turbulent flow. In distributions of electric potential and space charge, the distributions become distorted and asymmetric as the flow velocity increases. The effect of electrical drift flow was investigated for different flow velocities and the secondary flow in a flow of low velocity is successfully predicted.