Electrolyte Velocity Research Articles

Performance improvement of micro-fuel cell by manipulating the charged diffuse layer

A fuel cell device is presented based on a counter-flow microfluidic fuel cell (CFMFC) with nano-porous electrodes by developing an advection flux of ions within the electric double layer (EDL). Typically, in a microfluidic fuel cell, advection in the EDL is negligible because the near wall electrolyte velocity is zero. However, by using nano-pores, a non-negligible ion flux due to advection can be developed in the charged regions of the EDL which affects the structure of the EDL. In this article, we use a mathematical model to study how advection in the EDL affects the kinetic performance of fuel cells. Our model predicts that the peak power density can be increased by more than 2 fold in a CFMFC using this approach to kinetic enhancement.

The importance of key operational variables and electrolyte monitoring to the performance of an all vanadium redox flow battery

AbstractBACKGROUNDThe all vanadium redox flow battery (VRFB) has become the most common type of rfb, however, it is essential to improve our understanding of the importance of key operational variables, including electrode materials, electrolyte flow rate, current density and temperature, on the cell efficiency together with improved methods for cell monitoring.RESULTSSeveral carbon felts were characterized for their electrode activity. A commercially supplied electrolyte of unknown composition was analysed and was shown to contain a VO2+: V3+ ratio of 4.8:1 (total vanadium species = 1.5 mol dm−3) in 4 mol dm−3 H2SO4. A battery (100 cm2) was assembled using three‐dimensional carbon felts and planar carbon feeders as the electrodes with a Nafion® 115 proton exchange membrane. Performance was examined using electrolytes of varying vanadium ion concentration at volumetric flow rating from 0.5–3 mL min1. A suitable volumetric flow rate of electrolyte through each half‐cell was found to be in the range 1.5–2.0 mL min−1, corresponding to a mean linear electrolyte velocity of 1.0–10.1 cm s−1 through the carbon felt electrode. At a constant current charge and discharge current density of 100 mA cm−2 the typical voltage efficiencies were 65%. Charge‐discharge curves were then simulated using a detailed physical model, which generated good quantitative agreement with experimental cell performance.CONCLUSIONSThis study has quantified the effect of key process variables on cell efficiency. A mathematical model has been used successfully to describe charge‐discharge performance and the use of open‐circuit cell voltage has been shown to provide a simple and useful means of cell monitoring. Copyright © 2012 Society of Chemical Industry

Electrochemical Behavior of Selenium as Part of Composite Electrode in Sulfuric Acid Medium

The method of productiion of the composite selenium-graphitic electrodes based on organic polymer binder was proposed. Electrochemical behavior of the elementary selenium as content of composite electrode in sulfuric acid medium was assessed. A formation of hydrogen selenide during the cathode polarization, and formation of selenite and selenate ions was shown. An influence of potential spread velocity, acid concentration, and temperature of electrolyte were evaluated. Effective activation power for cathode process was estimated using the temperature-cathodic method.

전해질 유동 조건에 따른 아연공기전지 아연극 표면의 Zincate 이온 농도 예측을 위한 수치해석적 연구

수치해석을 이용하여 아연공기전지의 전기화학적 성능을 예측하였다. KOH 수계전해질 내부의 이동현상을 예측하기 위하여 Nernst-Planck식을 사용하였고, 전극 표면의 활성화손실을 모사하기 위해 아연극(음극)에는 Butler-Volmer식을, 공기극(양극)에는 Tafel식을 적용하였다. 정상상태해석을 통하여 아연/공기전지의 I-V곡선을 도출하였으며, 실험결과와의 I-V곡선 비교/분석을 통하여 수치 해석 모델의 타당성을 검증하였다. 전지반응 진행에 따른 전해질 내부의 이온 이동 및 분포 특성을 조사하기 위해 과도상태해석을 수행하였으며, 전극주변에서의 <TEX>${Zn(OH)_4}^{-2}$</TEX>, <TEX>$OH^-$</TEX>, <TEX>$K^+$</TEX> 이온들의 농도변화를 확인할 수 있었다. 또한, 다양한 전지전압조건 하에서 반응시간에 따라 아연극 표면에서의 <TEX>${ZnOH_4}^{2-}$</TEX>의 농도 변화를 해석한 결과, 반응진행시 아연극 표면에서 <TEX>${ZnOH_4}^{2-}$</TEX>의 농도가 최고성능을 나타내는 운전전압 0.63 V에서 약 1초 만에 포화농도에 도달하였으며, 일반적인 운전조건인 1.04 V에서는 약 13초 만에 포화농도에 접근하는 것으로 나타났다. In this work, the numerical analysis for the zincate behavior at a zinc electrode with an electrolyte flow was carried out for a ZAFC. The Nernst-Planck equation with a boundary condition of Butler-Volmer type was adopted to describe electrochemical effects of mass transfer, migration, kinetics of electrode. The Navier-Stokes equation, coupling to the Nernst-Planck equation, is also applied to describe the internal electrolyte flow fields. The validity of the numerical model is proved through the comparative analysis between numerical and experimental results. The concentration of zincate and the current density were also investigated at a zinc anode according to various electrolyte velocities. We have found the concentration of zincate decreased and the current density increased with an increase in the electrolyte velocity.

A three-dimensional model for negative half cell of the vanadium redox flow battery

A stationary, isothermal, three-dimensional model for negative half cell of the vanadium redox flow battery is developed, which is based on the comprehensive conservation laws, such as charge, mass and momentum, together with a kinetic model for reaction involving vanadium species. The model is validated against the results calculated by the available two-dimensional model. With the given geometry of the negative half cell, the distributions of velocity, concentration, overpotential and transfer current density in the sections that are perpendicular and parallel to the applied current are studied. It is shown that the distribution of the electrolyte velocity in the electrode has significant impact on the distribution of concentration, overpotential and transfer current density. The lower velocity in the electrode will cause the higher overpotential, further result in the side reaction and corrosion of key materials locally. The development of the design of the vanadium redox flow battery is discussed, and the further research is proposed.

Fundamental Experimental Study on Numerical-Control Electrochemical Finish Machining for Integral Impeller Blade

While the surface of integral impeller blade was electrochemically machined, cathode cannot rotate in accordance with other movement axes, which results in nonuniformity in velocity of electrolyte and normal direction of the machining blade surface, thereby causing inaccuracy in the machined blade surface. In order to solve this problem, the shaping law was studied in Electrochemical Finish Machining. Then relative positions between cathode slot and blade surface were analyzed during the process of Electrochemical Machining (ECM). Three parameters, namely feed direction, feed velocity and initial machining inter-electrode gap, were adjusted to conduct the fundamental experiments when direction of cathode slot was changed. Afterwards machining accuracy as well as surface quality of workpiece was analyzed. Finally according to experimental results, direction of cathode slot was determined practically in electrochemical machining process and the integral impeller blades meeting the requirement were electrochemically machined.

Perfusion electrodeposition of calcium phosphate on additive manufactured titanium scaffolds for bone engineering

A perfusion electrodeposition (P-ELD) system was reported to functionalize additive manufactured Ti6Al4 V scaffolds with a calcium phosphate (CaP) coating in a controlled and reproducible manner. The effects and interactions of four main process parameters – current density ( I), deposition time ( t), flow rate ( f) and process temperature ( T) – on the properties of the CaP coating were investigated. The results showed a direct relation between the parameters and the deposited CaP mass, with a significant effect for t ( P = 0.001) and t– f interaction ( P = 0.019). Computational fluid dynamic analysis showed a relatively low electrolyte velocity within the struts and a high velocity in the open areas within the P-ELD chamber, which were not influenced by a change in f. This is beneficial for promoting a controlled CaP deposition and hydrogen gas removal. Optimization studies showed that a minimum t of 6 h was needed to obtain complete coating of the scaffold regardless of I, and the thickness was increased by increasing I and t. Energy-dispersive X-ray and X-ray diffraction analysis confirmed the deposition of highly crystalline synthetic carbonated hydroxyapatite under all conditions (Ca/P ratio = 1.41). High cell viability and cell–material interactions were demonstrated by in vitro culture of human periosteum derived cells on coated scaffolds. This study showed that P-ELD provides a technological tool to functionalize complex scaffold structures with a biocompatible CaP layer that has controlled and reproducible physicochemical properties suitable for bone engineering.

Research on Flow Field Simulation and Experiment of Numerical Control Electrochemical Machining

To design the flow field of inner-spraying ball-end cathode in NC-ECM, the numerical model was bulit according to the physical model of the cathode flow channal, and the computational fluid dynamics (CFD) method was applied to slove the numerical model. The velocity and pressure distributations were obtained. The influences of the cathode internal structure and the outlet shape on the velocity of electrolyte were analyzed on the basis of the numerical simulation. The relatively good simulation results were obtained by means of the optimization design of the cathode. Based on the experiment results, the accuracy of simulation was verified, and the correction number of the design of the flow field was reduced in NC-ECM. It is indicated that the computational fluid dynamics (CFD) method can be applied to simulate the flow field, and the optimization design of the cathode can be guided according to the results of simulation.

Zinc morphology in zinc–nickel flow assisted batteries and impact on performance

The zinc morphology on repeated charging and discharging in flow-assisted zinc–nickel oxide cells was studied. The results show that higher charge rates cause more dendritic growth of zinc deposition on charging and tend to cause deterioration of battery cells. However, when the electrolyte velocity is higher than 15 cm s −1, the direction of dendrites was distorted toward the flow direction and the internal short circuit was suppressed. Good cycle life was obtained – 1500 cycles at 100% depth of discharge and C/2 charge and discharge rate. Also, the battery was scaled up to a 100 Wh prismatic cell, and more than 200 cycles were obtained.

Charge–Discharge Performance of a Novel Undivided Redox Flow Battery for Renewable Energy Storage

The redox flow battery is ideal for utility-scale renewable energy storage applications. In this work, a novel undivided battery employing porous flow through electrodes is investigated. Because of low charge–discharge efficiencies reported in previous work employing high superficial electrolyte velocities and current densities, three electrolyte systems are investigated here at two concentrations (0.02 and 0.1 M) employing low-current densities and superficial velocities: [Ru(acac)3] in acetonitrile, [Fe(bpy)3(ClO4)2] in acetonitrile, and VOSO4 in aqueous sulphuric acid (all-vanadium system). The highest energy efficiencies are obtained with the all-vanadium system: 13.4% for 0.02 M electrolyte and 12.0% for 0.1 M electrolyte.

Optimization of Predicted Cell Voltage & Caustic Current Efficiency in a Chlor-Alkali Membrane Cell with Application of Genetic Algorithm

This paper presents the development of hybrid neural-genetic algorithm model for the prediction of cell voltage and caustic current efficiency (CCE) versus various operating parameters in a lab scale chlor-alkali membrane cell. Each of six process parameters including anolyte pH (2-5), operating temperature (25-90 oC), electrolyte velocity (1.3-5.9 cm/s), brine concentration (200-300 g/L), current density (1-4 kA/m2), and run time (up to 150 min) were thoroughly studied at four levels for low caustic concentrations (5 g/L). According to the obtained results, the predicted cell voltages and current efficiencies using GA modeling were found to be very close to the measured values with an average deviation of about 2.82% & 1.77% for test validation data, respectively. It was also found that the developed model is not only capable to predict the voltage and current efficiency but also to reflect the impacts of the other process parameters on the same functions.

Development and comparison of non-parameter regression methods for prediction of cell voltage and current efficiency in a lab scale chlor-alkali membrane cell

This article presents the development & comparison of Non-parameter Regression Methods such as Artificial neural network (ANN), Genetic algorithm optimization (GA) and Support vectormachine (SVM) models for the prediction of cell voltage and caustic current efficiency (CCE) versus different operating parameters in a lab scale chlor-alkali membrane cell. In order to validate the model predictions, the effects of various operating parameters on the cell voltage and CCE of the membrane cell were experimentally investigated. Each of six process parameters including anolyte pH (2–5), operating temperature (25–90°C), electrolyte velocity (1.3–5.9 cm/s), brine concentration (200–300 g/L), current density (1–4 kA/m2), and run time (up to 150 min) were thoroughly studied. The new models yielded the accurate prediction of experimental data with the lowest standard deviation error (SD). It was found that the developed models are not only capable to predict the voltage and CCE but also to reflect the impacts of process parameters on the same functions. According to the obtained results, SVM model is suitable for the prediction of CCE with an average deviation of 1.53% while GA & ANN models are more accurate than SVM model for predicting the voltage with an AD of 1.21% & 1.27%, respectively.

Prediction of mass transport profiles in a laboratory filter-press electrolyser by computational fluid dynamics modelling

A commercial computational fluid dynamics code (Fluent) has been used to analyze the performance of a unit cell laboratory; the filter-press reactor (FM01-LC) operating with characteristic linear flow velocities between 0.024 m s −1 and 0.110 m s −1. The electrolyte flow through the reactor channel was numerically simulated using a finite volume approach to the solution of the Navier–Stokes equations. The flow patterns in the reactor were obtained and the mean linear electrolyte velocity was evaluated and substituted into a general mass transport correlation to calculate the mass transport coefficients. In the region of 150 < Re < 550, mass transport coefficients were obtained with a relative error between 5% and 29% respect to the experimental k m values. The differences between theoretical and experimental values are discussed.

Static research of flow in rotor channels of the regenerator

One demonstrates here the results of static experiments which suggest the pulsating flow in rotating channels of the rotor of heat regenerators occurs. Electrolytic technique was used to measure distribution of the mass transfer coefficient for one of many straight, round, radial ducts of the rotor for different angle positions at mean Reynolds number as a parameter. The use of the Chilton–Colburn analogy made it possible to state the angle-distribution of flow-velocity. The Reynolds number deviation was about ±30% in comparison with its mean value which suggests that the phenomenon should be taken into account in formulating the models of rotary heat exchangers. An equality – approximately – of the mean velocity of an out-gassed electrolyte in the opposite ducts of the rotor of the model, working in a closed hydraulic system, was stated which was justified theoretically for one-dimensional flow.

Design of a Recycle Process for Color Filters Using an Arc-Form Tool

A new process of electrochemical machining (ECM) using an arc-form electrode is investigated for the removal of ITO from thin film transistor liquid crystal display (TFT-LCD) color filters. This study uses a fifth generation TFT-LCD as a test case. A smaller arc-form tool thickness and end radius provides an effective current density and a larger discharge space, enhancing the ITO removal process. A high-flow electrolyte velocity elevates the discharge mobility and improves the ITO removal effect. A color filter, combined with a fast feed rate, has enough electric power for highly effective ITO removal.

Effects of process conditions on cell voltage, current efficiency and voltage balance of a chlor-alkali membrane cell

The effects of various operating parameters on the cell voltage and current efficiency of a laboratory-scale chloralkali (CA) membrane cell were studied at low caustic concentrations (5–22 g/L). Five process parameters studied include anolyte pH (2–5), cell temperature (25–90°C), electrolyte velocity (2.2–8.4 cm/s), brine concentration (200–300 g/L) and current density (1–4 kA/m 2), which were determined at four levels using DSA/Cl 2 as anode, nickel as cathode and Flemion® 892 as the membrane. Taguchi and ANOVA techniques were employed for experimental design and data analysis, respectively. Current density and cell temperature were found to be the most striking parameters on the cell voltage with contribution percentage ( P value) of 70% and 23%, respectively. However, in case of current efficiency, the highest P value is due to brine concentration (33%) while the lowest one corresponds to the cell temperature (13%). The caustic current efficiency was between 97%–99%. The results from voltage balance analysis revealed that the main contributors to the CA cell voltage at low caustic concentration are voltage drop due to the membrane, nickel cathode and the catholyte. The impact of other cell resistance components is minor. The measured and estimated cell voltages were found to come close at higher current densities.

Prediction of cell voltage and current efficiency in a lab scale chlor-alkali membrane cell based on support vector machines

The main aim of this study is to investigate the impacts of operating parameters on the cell performance and predicting the same by SVM technique. This paper though introduces support vector machines (SVMs), a relatively new powerful machine learning method based on statistical learning theory (SLT), into cell voltage and current efficiency forecasting. In order to validate the model predictions, the effects of various operating parameters on the cell voltage and current efficiency of the membrane cell were experimentally investigated. The membrane cell included a standard DSA/Cl2 electrode as the anode, a nickel electrode as the cathode and a Flemion 892 polymer film as the membrane. Each of six process parameters counting anolyte pH (2–5), operating temperature (25–90 °C), electrolyte velocity (2.2–5.9 cm/s), brine concentration (200–300 g/L), current density (1–4 kA/m2), and run time were thoroughly studied at four levels for low caustic concentrations (5–22 g/L). The developed SVM model is not only capable to predict the cell voltage and caustic current efficiency (CCE) but also to reflect the impacts of process parameters on the same functions. The predicted cell voltages and current efficiencies using SVM modelling were found to be very close to the measured values, particularly at higher current densities.

Development of an artificial neural network model for prediction of cell voltage and current efficiency in a chlor-alkali membrane cell

This paper presents the development of an artificial neural network (ANN) model for the prediction of cell voltage and caustic current efficiency (CCE) versus various operating parameters in a lab scale chlor-alkali membrane cell. In order to validate the model predictions, the effects of various operating parameters on the cell voltage and current efficiency of the membrane cell were experimentally studied. The membrane cell incorporated a standard DSA/Cl 2 electrode as the anode, a nickel electrode as the cathode and a Flemion 892 polymer film as the membrane. Each of the six process parameters including anolyte pH (2–5), operating temperature (25–90 °C), electrolyte velocity (2.2–5.9 cm/s), brine concentration (200–300 g/L), current density (1–4 kA/m 2), and run time were thoroughly studied at four levels and low caustic concentrations (5–22 g/L). The predictions of ANN model as well as those from other statistical methods were evaluated versus the measured values of cell voltages. The developed ANN model is not only capable to predict the cell voltage and caustic current efficiency but also to reflect the impacts of process parameters on the same functions. The predicted cell voltages and current efficiencies using ANN modeling were found to be close to the measured values, particularly at higher current densities.

Numerical Simulation of Electrolyte Two-Phase Flow Induced by Anode Bubbles in an Aluminum Reduction Cell

In the production process of aluminium reduction cells, the anode bubble laden layer has several important influences on the performance of the aluminium reduction cells. Especially for a "drained cathode cell", without the agitating of movement of the melted metal, the bath flow field could be more important. In this paper, the electrolyte two-phase flow fields were studied by using numerically simulation method based on a two-phase turbulence model combining the k - ? model and the Discrete Random Walk model. The results show that: the motion of the bubbles mostly exists within a thin layer under the anode, which results in inducing local electrolyte to flow around the anode in various circulation flows; the flow field in the anode-cathode space can be divided into three regions with different characters; the results also show the Driving action of bubbles is closely related to the current density, inclination of anode and the anode-cathode distance. In general, the increasing in the current density increases the electrolyte velocity and the turbulent kinetic energy. The decrease in ACD significantly enhances the uniformity of the electrolyte flow field in the anode-cathode space. The increase in anode inclination angle increases the velocity of the electrolyte in the anode-cathode space, which would be beneficial to improving the diffusion and dissolution of the alumina and reducing the resistance between the anode and cathode.

Liquid-wall mass transfer in three phase fluidized beds with cross-flow of electrolyte

Liquid-wall mass transfer coefficients were computed in a gas–liquid fluidized bed from the limiting current data obtained at the outer surface of different cross electrodes for both the cases of oxidation of ferrocyanide and reduction of ferricyanide ion. Particles of different sizes and densities were used as bed material and electrodes of five different diameters of length 44.5 mm were used. The fluid electrolyte velocities were varied from minimum fluidization velocities to well below the terminal velocities of the particles before the gas phase enters the test section. The liquid-wall mass transfer coefficient increased with increasing superficial gas velocity at a constant superficial liquid velocity upto a certain extent and reached a plateau. At constant superficial gas velocity, k L increased with increasing superficial liquid velocity. k L decreased with increase in electrode diameter. The effect of particle size on k L was found to segregate into two regions, one for d p > 4 mm and the other for d p < 4 mm. k L increased with increase in ɛ , reached a maximum and beyond an ɛ value of 0.85 showed a declining trend. The liquid-wall mass transfer coefficient data for both oxidation and reduction were correlated in terms of Coulburn factor j D , void fraction ɛ , Reynolds number based on electrode diameter Re , Froude number based on gas velocity Fr g and gas to liquid mass velocity ratio G mr .