• Title/Summary/Keyword: Water channels

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Experimental and Numerical Assessment of Liquid Water Exhaust Performance of Flow Channels in PEM Fuel Cells (고분자 전해질 연료전지 유로의 수분배출 특성의 실험 및 해석적 평가)

  • Kim, Hyun-Il;Nam, Jin-Hyun;Shin, Dong-Hoon;Chung, Tae-Yong;Kim, Young-Gyu
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.2
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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.

Thermal managing effects by cooling channels on performance of a PEMFC (냉각채널 열관리에 따른 고분자연료전지의 성능영향 연구)

  • Sohn, Young-Jun;Kim, Min-Jin;Park, Gu-Gon;Kim, Kyoung-Youn;Lee, Won-Yong
    • 한국신재생에너지학회:학술대회논문집
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    • 2009.06a
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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.

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Sympathetic and parasympathetic regulation of sodium transporters and water channels in rat submandibular gland

  • Jung, Hyun;Ryu, Sun-Youl
    • Journal of the Korean Association of Oral and Maxillofacial Surgeons
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    • v.32 no.1
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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.

Lateral Migration Features of the Alluvial Channels in Hapyeong Intake Station, Nakdong River (해평취수장 부근에서 충적하천의 저수로 이동 특성)

  • Jang, Chang-Lae;Lee, Gang-Man;Kim, Gye-Hyun
    • Journal of Korea Water Resources Association
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    • v.41 no.4
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    • pp.395-404
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    • 2008
  • It is important to understand the complex, various migration features of the alluvial channels for river engineering. In this study, the morphological changes and migration features of alluvial channels were investigated by analyzing the aerial photographs of active channels between 1972 and 2004 in Hapyeong Intake Station, Nakdong river. The lower channels were migrated from left bank to right bank and showed the features of braided channel in 2004. The instability of lower channels was increased due to the increased channel slope and width. The sinuosity of lower channels was decreased with time. As time increased, the increasing rate of lower channel and lateral migration rate were decreased. As a result of meso-scale regime analysis by using bankfull discharge, multiple row bars were developed, and suspended sediment load was governed in the flow as a sand bed channel.

Autonomic Neural Regulation of Sodium Transporters and Water Channels in Rat Submandibular Gland

  • Ryu, Sun-Yeol;Jung, Hyun;Kim, Ki-Yung;Kim, Mi-Won;Lee, Jong-Un
    • The Korean Journal of Physiology and Pharmacology
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    • v.10 no.2
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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.

Study on flow characteristics of the grit chamber using VOF multi-phase flow simulations (VOF 다상유동 해석을 이용한 침사지 유동특성 연구)

  • Yoon, Jong-Hwan
    • Journal of the Korean Society of Visualization
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    • v.19 no.2
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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.

A Comparison Study of CFD Analysis and Flow Visualization on Behavior of Liquid Water in Cathode Channels of PEM Fuel Cells (PEM 연료전지 공기극 유로에서 물의 거동에 대한 CFD 해석과 가시화 실험의 비교 연구)

  • Kim, Hyun-Il;Nam, Jin-Hyun;Shin, Dong-Hoon;Chung, Tae-Yong;Kim, Young-Gyu;Seo, Won-Seok;Lee, Jung-Woon
    • Proceedings of the Korea Society for Energy Engineering kosee Conference
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    • 2008.04a
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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.

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Migration characteristics with Forms of Channels and Bed Conditions (수로의 형상과 하상조건에 따른 이행특성)

  • 차영기;이종석
    • Water for future
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    • v.26 no.1
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    • pp.103-114
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    • 1993
  • Migration characteristics with forms of channels and bed conditions are studied by constant-radius curve (CRC), sine-generated curve (SGC) and small-wave theory (SWT) method. For channels which are meandering and of which bed conditions are of coarse materials, transverse bed slope, depth and velocity distributions are predicted by CRC and SGC method, and the results are compared with measured field data, And for fine bed-materials of the sinuous channels, lateral and downvalley migration rates are computed by SWT method. It is confirmed from this investigation that transverse mass-flux factor plays significant roles in determining of magnitude and direction of meander migration.

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Ecological Change in Drainage Channel Site Renovated by Environment Friendly Methods (환경친화적 정비에 따른 배수로의 생태변화)

  • Yang, Yong-Seok;Kim, Sun-Joo;An, Min-Woo;Choi, Kyoung-Young
    • Journal of Korean Society of Rural Planning
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    • v.12 no.3 s.32
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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.

CFD Analysis on Two-phase Flow Behavior of Liquid Water in Cathode Channel of PEM Fuel Cell (PEM 연료전지 공기극 유로에서 물의 가동에 대한 CFD 해석)

  • Kim, Hyun-Il;Nam, Jin-Hyun;Shin, Dong-Hoon;Chung, Tae-Yong;Kim, Young-Gyu
    • New & Renewable Energy
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    • v.3 no.4
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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.

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