• Korean Chemical Engineering Research
• /
• 제61권1호
• /
• pp.19-25
• /
• 2023

PEM (Proton Exchange Membrane) 수전해의 성능향상에 대해 많은 연구개발이 진행되었으나, 내구성에 대한 연구는 아직 초기 단계라고 할 수 있다. 본 연구는 성능향상을 위해 PEM 수전해 구동 온도를 상승시켰을 때, 수전해 내구성에 미치는 영향에 대해 연구하였다. 50~80 ℃ 온도 범위에서 일정 전류 조건으로 구동하면서 전압변화, I-V, CV (Cyclic Voltammetry), LSV (Linear Sweep Voltammetry), Impedance, FER (Fluoride Emission Rate) 등을 측정했다. 운전온도가 상승할수록 열화속도가 증가했다. 50~65 ℃에서는 IrO₂ 전극 촉매 열화가 PEM 수전해 셀의 내구성에 주로 영향을 주었다. 80 ℃에서는 고분자 막과 전극 열화가 비슷하게 진행되어 short 저항이 1.0 kΩ·cm² 이하로 감소하면서 shorting 현상에 의해 구동한지 144시간 만에 성능이 초기의 약 1/3로 감소하였다.

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

• 대한전기학회논문지:시스템및제어부문D
• /
• 제50권7호
• /
• pp.325-331
• /
• 2001

A dynamic anti-windup method for state delayed control systems with input saturation is considered. Under the assumption that a linear controller has been designed for a state delayed control system based on the existing design technique which shows desirable nominal performance, an additional compensator is incorporated to provide a graceful performance degradation despite of input saturation. By regarding the difference of the controller states in the absence and presence of input saturation as an objective function, the dynamic compensator which minimizes it is determined explicitly. The proposed dynamic compensator is the closed form of plant and controller parameters. The proposed method not only provides graceful performance degradation, but it also guarantees the total stability of resulting systems. An illustrative example is provided to show the effectiveness of the proposed method.

• Computers and Concrete
• /
• 제19권1호
• /
• pp.87-98
• /
• 2017

In recent year, the coat layer drops and the rebar rust of bridge parapets, which caused the structural performance degradation. In order to achieve the comprehensive rehabilitation, ultra high performance cementitious composites is proposed to existing RC parapet rehabilitation. The influence factors of UHPCC rehabilitation includes two parts, i.e., internal factors related with material, such as UHPCC layer thickness, corrosion ratio of rebars, fiber volume fraction, and external factors related with the load, such as impact speeds, impact angles, vehicle mass. The influence of the factors was analyzed in this paper based on the nonlinear finite element. The analysis results of the maximum dynamic deformation and the peak impact load of parapets revealed the influence of the internal factors and the external factors on anti-collision performance and degree degradation. This research may provide a reference for the comprehensive multifunctional rehabilitation of existing bridge parapets.

• 한국수소및신에너지학회논문집
• /
• 제14권4호
• /
• pp.291-297
• /
• 2003

As an alternative bipolar plate material for polymer electrolyte membrane fuel cell (PEMFC), TiN-coated 316 stainless was evaluated in terms of electrical contact resistance and water contact angle. Performance and lifetime of the TiN-coated 316 bipolar plates were measured in comparison with those of graphite and bare 316 bipolar plates. At a cell voltage of 0.6 V, current density of the single cells using graphite, AISI 316, and TiN/316 bipolar plates was 996, 796, and $896mA/cm^2$, respectively. By coating 316 stainless steel with TiN layer, performance degradation rate determined to be the voltage degradation rate at a cell voltage of 0.6 V was reduced from 2.3 to 0.43 mV/h.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
• /
• pp.176-183
• /
• 2000

The performance of gas turbines decreases as their operating hours increase. Compressor fouling is the main reason for this time-dependent performance degradation. Airborne particles adhere to the blade surface and results in the change in the blade shape. It is difficult to exactly analyze the mechanism of the compressor fouling because the growing process of the fouling is very slow and the dimension of the fouled depth is very small compared with blade dimensions. In this study, an analytic method to predict the motion of particles and their deposition inside axial flow compressors is proposed. The analytic model takes into account the blade shape and the flow within the blade passage. Comparison of simulation result with field data shows the feasibility of the model. Influence of the particle distribution on the compressor fouling is also examined.

• Advances in concrete construction
• /
• 제9권2호
• /
• pp.115-123
• /
• 2020

The performance of steel fiber reinforced geopolymer concrete beam column joints under cyclic loading was investigated. The volume fraction of fibers considered were 0.25% (19.62 kg/㎥), 0.5% (39.24 kg/㎥), 0.75% (58.86 kg/㎥) and 1% (78.48 kg/㎥). A total of fifteen specimens were prepared and tested under reverse cyclic loading. Test results were analyzed with respect to first crack load, ultimate load, energy absorption capacity, energy dissipation capacity, stiffness degradation and load deflection behavior. Test results revealed that the addition of steel fibers enhanced the performance of geopolymer concrete beam column joints significantly. The joints were analyzed using finite element software ANSYS. The analytical results were found to compare satisfactorily with the experimental values.

• 항공우주시스템공학회지
• /
• 제1권1호
• /
• pp.53-59
• /
• 2007

Inlet distortion test was performed at Korea Aerospace Research Institute in order to evaluate the degradation of engine performance under the distorted inlet condition. In this paper, only the inlet pressure distortion was taken into consideration. During the development process of the inlet distortion test technique, variable distortion screen was designed and evaluated under various test conditions to establish the experimental database of distortion for engine test. The result of inlet distortion test for engine shows that the operating point was changed toward the worse direction and the degradation of engine performance by inlet distortion was verified.

• 품질경영학회지
• /
• 제24권3호
• /
• pp.37-49
• /
• 1996

For highly reliable devices it is often defined to "fail" when its performance degrades below a specified value. In this paper we consider a method for optimally designing accelerated degradation tests(ADTs) in which the performance over exposure time and stress has Weibull distribution. For the product whose performance has Weibull distribution, the optimum plan - low stress level and sample proportions allocated to each test condition - is obtained, which minimize the asymptotic variance of maximum likelihood estimator of a stated quantile at design stress. We also present compromise ADTs plan that can be used for the practical purpose.

• 전자공학회논문지D
• /
• 제34D권7호
• /
• pp.23-29
• /
• 1997

The performance degradation of CMOS differential amplifiers due to hot carrier effect has been measured and analyzed. Two-state CMOS amplifiers whose input transistors are PMOSFETs were designed and fabriacted using the ISRC CMOS 1.5.mu.m process. It was observed after the amplifier was hot-carrier stressed that the small-signal voltage gain and the input offset voltage increased and the phase margin decreased. The performance variation results from the increase of the transconductances and gate capacitances of the PMOSFETs used as input transistors in the differential input stage and the output stage and also resulted from the decrease of their output conductances. After long-term stress, the amplifier became unstable. The reason might be that its phase margin was reduced due to hot carrier effect.