• Title, Summary, Keyword: concentration polarization

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Visualization of Ion Transport and pH Change in Ion Concentration Polarization (농도 분극 현상에서의 이온의 흐름과 pH 변화의 가시화)

  • Ko, Sung-Hee;Kang, Kwan-Hyoung
    • Journal of the Korean Society of Visualization
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    • v.8 no.4
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    • pp.38-42
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    • 2010
  • Ion concentration polarization is an electrokinetic phenomenon which occurs in membrane systems, such as in an electrodialysis and fuel-cell system. But the phenomenon is not fully understood because hydrodynamics, electrokinetics and electrochemistry are coupled with each other. Here, we report that there occurs a change of pH value of buffer solution in concentration polarization phenomenon. To visualize the change of pH, the litmus solution which is one of the pH indicators was used. It is conjectured that the pH of solution changes because hydrogen ions were concentrated in cathodic side and hydroxide ions were concentrated in anodic side. We anticipate that this work may contribute to the fundamental understanding on the ion concentration polarization phenomenon.

Development of Optical Fiber Hydrogen Sensor Based on Polarization-Diversity Loop Configuration Using Pd-Coated Polarization-Maintaining Fiber (팔라듐 코팅된 편광 유지 광섬유를 이용한 편광 상이 배치 구조 기반 광섬유 수소 센서의 개발)

  • Noh, Tae-Kyu;Kim, Young-Ho;Lee, Yong-Wook
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.27 no.3
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    • pp.1-6
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    • 2013
  • In this study, we propose a fiber-optic hydrogen sensor using a polarization-diversity loop configuration composed of a polarization beam splitter, two quarter-wave plates, and a polarization-maintaining fiber coated with palladium whose thickness is ~400nm. One transmission dip of the output interference spectrum of the proposed sensor, chosen as a sensor indicator, was observed to spectrally shift with the increase of the hydrogen concentration, and the sensing indicator showed a wavelength shift of ~2.48nm at a hydrogen concentration of 4%. Except for a hydrogen concentration of 4%, the response time of the proposed sensor was measured as less than 12.5s and did not show significant dependence on the hydrogen concentration. In particular, the proposed fiber hydrogen sensor is more durable and highly resistant to external stress applied on a transverse axis of an optical fiber, compared with other hydrogen sensors based on side-polished fibers or fiber gratings.

Uncertainty in Potentiodynamic Polarization Resistance Measurement (동전위 분극저항 측정에서의 불확도)

  • Kim, Jong Jip
    • Corrosion Science and Technology
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    • v.8 no.5
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    • pp.193-196
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    • 2009
  • For the estimation of uncertainty in potentiodynamic polarization resistance measurement, the type A uncertainty was measured using type 316 stainless steel in an acidified NaCl solution. Sensitivity coefficients were determined for measurand such as scan rate of potential, temperature of solution, concentration of NaCl, concentration of HCl, surface roughness of specimen and flow rate of purging gas. Sensitivity coefficients were large for the measurand such as the scan rate of potential, temperature of solution and roughness of specimen. However, the sensitivity coefficients were not the major factors influencing the combined standard uncertainty of polarization resistance due to the low values of uncertainty in measurements of the measurands. A major influencing factor was the concentration of NaCl. The value of type A uncertainty was 1.1 times the value of type B uncertainty, and the combined standard uncertainty was 10.5 % of the average value of polarization resistance.

Concentration of Sodium Chloride, Sodium Acetate and Sodium Citrate Solutions by using Polyamide Reverse Osmosis Membrane (폴리아미드 역삼투막을 이용한 염화나트륨, 아세트산나트륨, 구연산나트륨 용액의 농축)

  • Lee, Heungil;Kim, In Ho
    • Korean Chemical Engineering Research
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    • v.56 no.5
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    • pp.679-686
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    • 2018
  • Reverse osmosis (RO) concentration of sodium chloride, sodium acetate, and sodium citrate solutions has been performed by polyamide RO membrane. Concentration polarization phenomena was also studied by changing pressure, solute kinds, and initial solution concentration. Pressure effect on permeation flux was that the increase of flux was accompanied by the increase of pressure. Flux increase was observed by the decrease of initial solution concentration. Surface concentration on the RO membrane increases and so flux declines due to the concentration polarization. In the later phase of concentration, concentration polarization effect was decreased by the back diffusion of solute from the polariztion layer. In case of sodium citrate, its large ion size and charge density resulted in the discrepancy between theory and experimental data of concentration polarization. It may be due to electric repulsion on the membrane surface.

Concentration Polarization Phenomena in Ion-Exchange Membranes (이온교환막에서의 농도분극 현상)

  • 최재환;문승현
    • Membrane Journal
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    • v.12 no.3
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    • pp.143-150
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    • 2002
  • Electrodialysis(ED) is a reliable and effective process for the separation and concentration of ionic compounds. However, commercial uses of ED are often hindered by the cost of the stack that mainly resulted from the ion-exchange membrane cost. In order to minimize the membrane cost, it is desired to operate ED at the highest practicable current density. In an actual ED system the high current operation is limited by the concentration polarization phenomenon. This article illustrates the transport phenomena of ions through ion exchange membranes using current-voltage relations as a characterizing method. Also recent studies on electroconvection and water-spitting phenomena caused by concentration polarization were reviewed.

Evaluation on Damage Behavior of Al-4.5%Mg-0.6%Mn Al Alloy with Potentiostatic Experiment Time (Al-4.5%Mg-0.6%Mn 알루미늄 합금의 정전위 시간 변수에 따른 손상거동 평가)

  • Kim, Seong-Jong;Woo, Yong-Bin;Han, Min-Su;Jang, Seok-Ki
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.18 no.6
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    • pp.569-576
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    • 2012
  • In general, aluminum alloys forms the passive film($Al_2O_3$, $Al_2O_3{\cdot}3H_2O$) in neutral solution. However, the passive film created on the surface will be destroyed by chloride ions contained in sea water so the corrosion will occur. In this study, in order to solve the problem of corrosion under a seawater environment, potentiostatic protection techniques were applied to Al-4.5%Mg-0.6%Mn aluminum alloy in seawater. At polarization experiments, active state were observed at anodic polarization and concentration polarization by reduction of dissolves oxygen and activation polarization were found at anodic polarization. As a results of potentiostatic experiment, calcareous deposit were created much more as applying time increase from the turning point of the concentration polarization and activation polarization and crevice corrosion was partially observed between calcareous deposit and surface of base metal. Overall potentiostatic anodic polarization experiment was difficult to apply potentiostatic corrosion protection technology by occurrence of active state, whereas potentiostatic cathodic polarization experiment examined optimum corrosion protection condition of -1.1 V~-0.75 V within the range of concentration polarization considered various applying time.

Permeation Behavior of Surfactant through Membrane (계면활성제의 분리막에 대한 투과거동)

  • Ahn, Soon-Cheol;Lee, Kwang-Rae;Kim, Ki-Chang
    • Journal of Industrial Technology
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    • v.18
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    • pp.259-265
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    • 1998
  • The molecular weights of surfactant SDS(M.W. 288) and SLS(M.W. 420) are smaller than the molecular weigh cut-off of cellulose acetate membrane used in this study. However, 20% of SDS and 67% of SLS were rejected by cellulose aectate membrane. The higher rejection rate of SLS than that of SDS is due to the longer hydrophobic chain and greater molecular weight. There was no resistance to permeation rate by membrane fouling. Most of permeation resistance was due to the concentration polarization. Permeation rate was declined with operating time and with increase in concentration of surfactant due to concentration polarization.

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A Study on the Concentration Polarization Layer Resistance in Ultrafiltration of Macromolecular Solutions (고분자 용액의 한외여과에서 농도분극층 저항에 관한 연구)

  • 염경호
    • Membrane Journal
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    • v.2 no.1
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    • pp.59-66
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    • 1992
  • The experimental studies were carried out on ultrafiltration of PEG #6000 and dextran 70T macromole¬cules. using an asymmetric cellulose acetate membrane in a cross flow plane type cell. Effects of pressure difference. feed concentration were studied on permeate flux and observed rejection for both the macromole¬cules. and the concentration polarization layer resistance $R_{b1}$ on permeate flux was analysed. The concentration polarization layer resistance $R_{b1}$ was correlated with the average macromolecule concen¬tration $C_{b1}$ in polarization layer. The resulting dimensionless correlation was expressed as : $\frac{R_{b1}}{{R_m}}=\alpha[\frac{\rho_{b1}}{C_{b1}}]^\beta$

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Evaluation of water permeability of forward osmosis membranes using osmotically driven membrane test (랩스케일 정삼투실험을 통한 정삼투막의 수투과도 평가)

  • Lee, Junseo;Kim, Suhan
    • Journal of Korean Society of Water and Wastewater
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    • v.30 no.4
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    • pp.417-425
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    • 2016
  • Desalination is a key technology to overcome water shortage problem in a near future. High energy consumption is an Achilles' heel in desalination technology. Osmotically driven membrane processes like forward osmosis(FO) was introduced to address this energy issue. Characterizing membrane properties such as water permeability(A), salt permeability(B), and the resistance to salt diffusion within the support layer($K_{ICP}$) are very important to predict the performance of scaled-up FO processes. Currently, most of researches reported that the water permeability of FO membrane was measured by reverse osmosis(RO) type test. Permeating direction of RO and FO are different and RO test needs hydraulic pressure so that several problems can be occurred(i.e. membrane deformation, compaction and effect of concentration polarization). This study focuses on measuring water permeability of FO membrane by FO type test results in various experimental conditions. A statistical approach was developed to evaluate the three FO membrane properties(A, B, and $K_{ICP}$) and it predicted test result by the internal and external concentration polarization model.

Evaluation of Concentration Polarization at Feed in the Permeation of VOCs/$N_2$ mixtures through PDMS membrane (VOCs/질소 혼합물 증기투과시 공급액부 경계층에서의 농도분극 분석을 위한 모델식 확립)

  • 염충균;이상학;최정환;이정민
    • Membrane Journal
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    • v.11 no.2
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    • pp.74-82
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    • 2001
  • By using a phenomenological approach, model equations incorporating the resistance-in¬series concept were established to evaluate quantitatively concentration polarization in the boundary layer in feed adjacent to the membrane surface in the vapor permeation and separation of volatile organic compounds (VOCS)/$N_2$ mixture through po]y(dimethylsiloxane) (PDMS) membrane. The vapor permeations of various VOCS/$N_2$ mixtures through PDMS membrane were carried out at various feed flow rates. Chlorinated hydrocarbons, such as, methylene chloride, chlorofonn, 1,2-clichloroethane and 1,1,2-trichloroethane were used as organic vapor. By fitting the model equations to the experimental penneation data. the model parameters were detennined. respectively. Both the mass transfer coefficient of VOC across tbe boundary layer and concentration polarization modulus as a measure of the extent of concentration polarization were eitimated Quantitatively by the mooe1 equations with the determined model parameters. From the analysis on the detennined model parameters, the boundary layer resistance due to the concentration polarization of VOCs component was found to be more significant when the condensability of voe was greater. This study seeks to emphasize the importance of the boundary resistance on the vapor penneation of the vapor/gas mixtures with high permeability and high selectivity towards the minor component VOC.

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