• 대한기계학회논문집B
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• 제33권2호
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• pp.85-92
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• 2009

Polymer electrolyte membrane (PEM) fuel cells are a promising technology for short-term power generation required in residential and automobile applications. Proper management of water has been found to be essential for improving the performance and durability of PEM fuel cells. This study investigated the liquid water exhaust capabilities of various flow channels having different geometries and surface properties. Three-pass serpentine flow fields were prepared by patterning channels of 1 mm or 2 mm width onto hydrophilic Acrylic plates or hydrophobic Teflon plates, and the behaviors of liquid water in those flow channels were experimentally visualized. Computational fluid dynamics (CFD) simulations were also conducted to quantitatively assess the liquid water exhaust capabilities of flow channels for PEM fuel cells. Numerical results showed that hydrophobic flow channels have better liquid water exhaust capabilities than hydrophilic flow channels. Flow channels with curved corners showed less droplet stagnation than the channels with sharp corners. It was also found that a smaller width is desirable for hydrophobic flow channels while a larger width is desirable for hydrophilic ones. The above results were explained as being due to the different droplet morphologies in hydrophobic and hydrophilic channels.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.373-373
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• 2009

Relative humidity, membrane conductivity and water activity are critical parameters of polymer electrolyte membrane fuel cells (PEMFC) for high performance and reliability. These parameters are closely related with temperature. Moreover, the ideal values of these parameters are not always identical along the channels. Therefore, the cooling channel design and its operating condition should be well optimized along the all location of the channels. In the present study, we have performed a numerical investigation on the effects of cooling channels on performance of a PEMFC. Three-dimensional Navier-Stokes equations are solved with the energy equation including heat generated by the electrochemical reactions in the fuel cell. The present numerical model includes the gas diffusion layers (GDL) and serpentine channels for both anode and cathode gas flows, as well as cooling channels. To accurately predict the water transport across the membrane, the distribution of water content in the membrane is calculated by solving a nonlinear differential equation with a nonlinear coefficient, i.e., the water diffusivity which is a function of water content as well as temperature. Main emphasis is placed on the heat transfer between the solid bipolar plate and coolant flow. The present results show that local current density is affected by cooling channels due to the change of the oxygen concentration and the membrane conductivity as well as the water content. It is also found that the relative humidity is influenced by the generated water and the gas temperature and thus it affects the distribution of fuel concentration and the conductivity of the membrane, ultimately fuel cell performance. Unit-cell experiments are also carried out to validate the numerical models. The performance curves between the models and experiments show reasonable results.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제32권1호
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• pp.1-7
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• 2006

The present study was aimed to explore the role of sympathetic and parasympathetic nerves in the regulation of sodium transporters and water channels in the salivary gland. Rats were denervated of their sympathetic and parasympathetic nerves to the submandibular gland, and the glandular expression of sodium transporters and water channels was determined by Western blot analysis. The expression of either ${\alpha}1$ or ${\beta}1$ subunit of Na, K-ATPase was not significantly affected either by the sympathetic or by the parasympathetic denervation. The expression of subunits of epithelial sodium channels was significantly increased both in the denervated and contralateral glands either by the sympathetic or by the parasympathetic denervation. Neither the sympathetic nor the parasympathetic denervation significantly altered the expression of aquaporin-1 (AQP1). Nor was the expression of AQP4 affected significantly by the parasympathetic or the sympathetic denervation. On the contrary, the expression of AQP5 was significantly increased not only by the parasympathetic but also by the sympathetic denervation. These results suggest that sympathetic and parasympathetic nerves have tonic regulatory effects on the regulation of certain sodium transporters and AQP water channels in the salivary gland.

• 한국수자원학회논문집
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• 제41권4호
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• pp.395-404
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• 2008

충적하천의 복잡하고 다양한 이동특성을 파악하고 이해하는 것은 하천공학적으로 매우 중요하며, 본 연구에서는 저수로의 이동 및 하상저하로 인하여 취수문제가 있는 경상북도 구미시에 위치한 해평취수장 주변에 대하여 항공사진 분석을 통하여, 시간에 따른 하천의 지형변화, 저수로의 이동 특성을 조사하고 분석하였다. 저수로는 좌안에서 우안으로 이동해 가고 있으며, 저수로는 강턱유량에 대하여 복렬사주가 발달하는 특성을 보여주고 있다. 이는 하천의 경사가 급하고 하폭이 넓고 수심이 얕은 곳에서 발생하는 현상으로서, 저수로의 불안정성이 증가하기 때문이다. 또한 저수로의 사행도가 감소하면서 저수로 폭이 증가하는 것은 제한된 범위 안에서 저수로의 분류와 합류가 활발하게 발생하는 것을 의미한다. 시간의 증가에 따라 저수로 하폭의 증가율과 측방향 이동율은 감소하고 있다. 강턱유량을 이용하여 중규모 영역구분을 수행한 결과, 복렬사주가 발달하는 하천의 특성을 보여주었으며, 모래하천으로서 부유사가 지배적인 하천으로 판단되었다.

• The Korean Journal of Physiology and Pharmacology
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• 제10권2호
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• pp.65-69
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• 2006

The present study was undertaken to explore the role of autonomic nerves in the regulation of sodium transporters and water channels in the salivary gland. Rats were denervated of their sympathetic or parasympathetic nerves to the submandibular gland. One week later, the expression of Na,K-ATPase, epithelial sodium channels (ENaC), and aquaporins (AQP) was examined in the denervated and contralateral glands. The sympathetic denervation slightly but significantly decreased the expression of ${\alpha}1$ subunit of Na,K-ATPase, whereas the parasympathetic denervation increased it. The expression of ${\alpha}$-subunit of ENaC was significantly increased in both the denervated and contralateral glands either by the sympathetic or parasympathetic denervation. The sympathetic denervation significantly increased the expression of AQP5 in both the denervated and contralateral glands, whereas the parasympathetic denervation decreased it. It is suggested that the autonomic nerves have a tonic effect on the regulation of sodium transporters and AQP water channels in the salivary gland.

• 한국가시화정보학회지
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• 제19권2호
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• pp.63-73
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• 2021

It is essential to accurately predict the change in water level, velocity, and flow rate for each passage of the grit chamber according to the operating conditions of the pump. In this study, VOF multiphase flow analysis was performed, and the flow characteristics of the grit chamber were predicted. As a result of simulations, the sedimentation phenomenon after the entrance of the grit chamber channel is expected to occur on the side walls. When 6 channels are used, the average speed of the channels is about 52% of the design standard, and when 4 channels are used, the value increases to 74% of the design standard. The average water level in the channels tends to decrease as the flow velocity increases, and the water level in the absorption well with a larger flow rate is maintained lower than that in the absorption well with a smaller flow rate.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2008년도 춘계학술 발표회
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• pp.101-108
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• 2008

Polymer electrolyte membrane (PEM) fuel cells are promising power generation devices which are ideal for residential and automobile applications, thanks to their fast transient characteristics. However, liquid water produced in PEM fuel cells should be properly managed to enhance the performances and durabilities of the cells. In this study, a visualization experiment was conducted to investigate the flow behavior of water droplets in cathode channels. The visualization experiment was done with four different model flow channels which were made by varying the material (Acrylic and Teflon) and the channel width (1 mm and 2 mm). Acrylic is hydrophilic (contact angle is about $80^{\circ}$) while Teflon is hydrophobic (contact angle is about $120^{\circ}$). A computational fluid dynamics (CFD) analysis was also performed to compare the observed and the simulated two-phase water/air flow characteristics in cathode channels. The computational models were made to be consistent with the geometries and surface properties of the model flow channels. Both the experimental and numerical results showed that the Teflon cathode channel with 1 mm width has the best water management performance among four model flow channels considered. A close correlation was found between the experimental visualization results and the numerical CFD simulation results.

• 물과 미래
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• 제26권1호
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• pp.103-114
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• 1993

수로의 형상과 하상조건에 따른 이행특성을 일정반경곡선(CRC), 정현곡선(SGC) 및 미소지폭파 이론(SWT)의 방법에 의해 연구하였다. 수로의 형상이 사행이고, 하상조건이 거친 하상입자인 사행하천의 경우에는 CRC 및 SGC의 방법을 적용하여 횡방향 하상경사, 수심 및 유속분포의 예측치를 구하고, 이를 실측치와 비교하였다. 또한 가는 입자의 준사행하천(Sinuous Channels)에 대해서는 SWT의 방법을 이용하여 횡방향과 흐름방향의 사행이행량을 각각 구하였다. 그 결과 횡방향 질량이송계수는 사행이행의 크기 및 방향을 결정하는데 중요한 계수임이 확인되었다.

• 농촌계획
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• 제12권3호
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• pp.19-28
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• 2006

This study has been conducted to perform the survey on the ecological systems, scenary, and water quality change for agriculturally purposed drainage channels constructed with the application of environment-friendly methods and thus to evaluate the environment-friendly redevelopment effects of them. The main results of this study are as follow: 1. The channels not looking good aesthetically before redevelopment had changed into graceful scenic views from the aspect of landscape architecture as natural-type gently waterside to the channel and naturally-looking water stream. In the village parks developed for the rest of residents, an enough view was secured and thus a wide prospect scope could be obtained. 2. The flora in the channels have increased to 35 families and 82 species from 19 families and 32 species before renovation. As the growth speed of them are slower than externally-brought plants, they can cause some risks to the stability of land slope, including scour by erosion. From that reason, it is necessary to adequately combine the species of the plants both natively growing there and externally-brought planted. 3. In case of water quality, it turned out that, from more than a year after redevelopment, plants began to take roots and the water quality improved. On the contrary, there have been some cases, partly found, that aggravated the quality of water due to the causes like as retention of floating matters by withered plants or plant bodies after the growth of plants in the channels under survey became active, and therefore it is judged that a periodic maintenance of waterways is needed. 4. In case of fishes, all species before renovation have revived, and the population and the number of species have increased after works the formation of puddles in the channels. In waterside grasslands, amphibia and reptiles have not only increased but also been diversified.

• 신재생에너지
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• 제3권4호
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• pp.8-15
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• 2007

Liquid water in flow channel is an important factor that limits the steady and transient performance of PEM fuel cells. A computational fluid dynamics study based on the volume-of-fluid [VOF] multi-phase model was conducted to understand the two-phase flow behavior of liquid water in cathode gas channels. The liquid water transport in $180^{\circ}{\Delta}$ bends was investigated, where the effects of surface characteristics (hydrophilic and hydrophobic surfaces], channel geometries (rectangular and chamfered corners], and air velocity in channel were discussed. The two-phase flow behavior of liquid water with hydrophilic channel surface and that with hydrophobic surface was found very different; liquid water preferentially flows along the corners of flow channel in hydrophilic channels while it flows in rather spherical shape in hydrophobic channels. The results showed that liquid water transport was generally enhanced when hydrophobic channel with rounded corners was used. However, the surface characteristics and channel geometries became less important when air velocity was increased over 10m/s. This study is believed to provide a useful guideline for design optimization of flow patterns or channel configurations of PEM fuel cells.