Solid electrolyte interphase (SEI) film resistance is an important parameter in the study of charge transfer kinetics of a Li-ion battery. The passive film affects diffusion process of Li-ions. As such, it becomes essential to include film resistance in battery modelling. However, the traditional method of estimating the SEI film resistance is costly and time consuming. An indirect approach based on Ohm’s law is thus presented in this paper. It relies on determining the interfacial polarisation from the difference of open-circuit voltage measured immediately after switching off the applied current and the equilibrium voltage. The technique is simple, easy to implement and can be used for a quick estimation of SEI film resistance with reasonable accuracy. For instance, average value of SEI film resistance for commercial LFP battery cell is measured as 0.004 Ohm · m 2 , which was found to be consistent with the values determined using the impedance spectroscopy techhnique in the published literature for lithium-carbon film electrodes.

One considers linear thermoelastic composite media, which consist of a homogeneous matrix containing a statistically homogeneous random set of aligned homogeneous heterogeneities of non-canonical (i.e. non-ellipsoidal) shape. The representations of the effective properties (effective moduli, thermal expansion, and stored energy) are expressed through the statistical averages of the interface polarization tensors (generalizing the initial concepts, see e.g. [1] and [2]) introduced apparently for the first time. The new general integral equations connecting the stress and strain fields in the point being considered with the stress and strain fields in the surrounding points are obtained for the random fields of heterogeneities. The method is based on a recently developed centering procedure where the notion of a perturbator is introduced in terms of boundary interface integrals estimated by the method of fundamental solution for a single inclusion inside the infinite matrix. This enables one to reconsider basic concepts of micromechanics such as effective field hypothesis, quasi-crystalline approximation, and the hypothesis of ellipsoidal symmetry. The results of this reconsideration are quantitatively estimated for some modeled composite reinforced by aligned homogeneous heterogeneities of non canonical shape. Some new effects are detected that are impossible in the framework of a classical background of micromechanics.

Aluminium based metal matrix composites (MMCs) have received considerable attention in the last decade for its potential industrial applications. One of the challenges encountered using Aluminium based MMCs is understanding the influence of the reinforcement particles on the corrosion resistance and mechanical properties. In this study the corrosion behaviour and mechanical properties of Al6063 reinforced with egg shell ash and rice husk ash were investigated. Waste Egg Shell Ash (ESA) and Rice Husk Ash (RHA) 212 μm in size were used to produce the composites with 10 wt% of reinforcements via stir casting technique. The RHA and ESA were added in the ratios of 10:0, 7.5:2.5, 5:5, 2.5:7.5, 0:10. Unreinforced Al6063 was used as baseline material. Immersion tests, potentiodynamic polarization techniques, tensile tests, optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the composites. The results showed that reinforcing with 7.5 wt% RHA + 2.5 wt% ESA provided the highest resistance to corrosion. Generally, a reduction in the corrosion rates were observed for the reinforced composites as the wt% of RHA increased. Porosity levels of the composites reduced with an increase in the percentage of ESA in the matrix. Microstructural characterization using SEM and OM revealed a distribution of pits on the composite surfaces which was more severe with increasing RHA percentage. The UTS (ultimate tensile stress) results revealed that the composite containing 10 wt% RHA had the maximum value of 161 MPa. The results demonstrate that rice husk ash and eggshell ash can be useful in producing low cost Aluminium composites with improved corrosion resistance and tensile properties.

The influence of surface pretreatment on the integrity of Tridecafloro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) coating on the substrate is presented. FOTS is a hydrophobic organic compound deposited on the SS 304 surface to enhance the corrosion protection of the metal. The surface was pretreated with silicon oxide, plasma oxide and both served as adhesions before the coating was deposited on the substrate by atomic layer deposition technique. The coatings were characterized by scanning electron microscope (morphology), atomic force microscope (surface roughness). The chemical composition and bonding structure were obtained by X-ray diffraction (XRD) and Attenuated-Fourier transform infrared (ATR-FTIR). The durability of the coating in corrosive media was investigated through electrochemical polarization and electrochemical impedance spectroscopy (EIS). The results obtained showed that silicon oxide pre-treated steel gave a better stability and improved properties to the coating than the plasma oxide pre-treated surface, and was distinctly discussed.

Computational fluid dynamics (CFD) simulations are conducted to study the transport phenomena in spiral wound membranes (SWM) within a Forward Osmosis (FO) module. The effect of the porous layer on the membrane performance is examined. Simulations are prepared for three different porous layer thicknesses by having the porous layer facing the draw channel, a mode known as AL-FS (active layer facing feed solution). In the current study, a Reynolds number range from 2 to 500 is considered. The Navier-Stokes and the mass transport equations are used to obtain the velocity, pressure and concentration fields in the flow channels. The local osmotic pressure and the membrane properties are used to calculate the water permeation over the membrane surface. The membrane is considered as a semipermeable functional surface of zero thickness. The effect of the porous layer is included in the flux model, but the flow and concentration fields in the porous layer are not resolved. The results suggest that increasing the streamwise velocity decreases the level of the external concentration polarization on both sides of the membrane which in turn leads to higher water flux through the membrane. Also, the existence of the porous layer reduced the membrane performance. The water flux didn’t improve much with increasing streamwise velocity at the same porous layer thickness. The suction velocity over the membrane starts at a high value at the inlet of the draw channel and decreases until reaching the outlet of the draw channel then it starts to increase slightly from the effect of the inlet of feed solution. Moreover, by increasing the net osmotic pressure difference, the water flux exhibited a non-linear increase.

This study investigates the effect of membrane properties — porosity, membrane thickness, and pore radius — on the performance of vacuum membrane distillation (VMD) process by achieving computational fluid dynamics (CFD) simulations on a three-dimensional domain of interest at fixed flow properties. The finite volume method (FVM) is adopted to solve momentum, solute mass transport, and energy equations in the feed channel. To accurately predict the rate of water vapor diffused through the membrane by Knudsen and viscous diffusion mechanism, local concentration, temperature, and flux are coupled at the membrane surfaces. In accordance with the flux, corresponding gradients for temperature and concentration are applied at the membrane boundaries. Since there is a strong coupling of flow properties at the membrane surface, the employed model is validated against an experimental study and further used to characterize the effect of PTFE membrane properties on permeate flux, temperature polarization, and concentration polarization. We found that different set of membrane design parameters substantially changes the total mass flux. The contribution of both viscous and Knudsen mechanism is comparable and, as such, prevents us neglecting neither of them. The temperature and concentration polarization are even more undesirable level for the larger pore sizes.

An exergy based analysis of the Environmental Control and Life Support System (ECLSS) aboard the International Space Station (ISS) is conducted to assess its overall performance. Exergy is chosen as a measure of performance because it accounts for both the first and second laws of thermodynamics. The exergy efficiency of a system is first defined as the total exergy destroyed by the system relative to the total exergy input to the system. To determine the ECLSS exergy efficiency, the system is divided into constituent subsystems which in turn are divided into assemblies and components. Based on this system decomposition, exergy balances are derived for each assembly or component. Exergy balances and supporting calculations are implemented in MATLAB ® code. The major subsystems of the ECLSS considered in this analysis include the Atmosphere Revitalization Subsystem (ARS), Atmosphere Control and Supply Subsystem (ACS), Temperature and Humidity Control Subsystem (THC), Water Recovery and Management Subsystem (WRM), and Waste Management Subsystem (WM). This paper focuses on the ARS and its constituent assemblies and components. Exergy efficiency of the ARS and its constituent assemblies and components is first presented. The Oxygen Generation Assembly (OGA), an assembly within the ARS, is then highlighted because the exergy destruction by the OGA is a large magnitude contributor to the overall exergy destruction of the ECLSS. The OGA produces oxygen to meet the crew’s metabolic demand via water electrolysis in a proton exchange membrane (PEM) electrolyzer. The exergy destruction of the OGA’s PEM electrolyzer is a function of the amount of oxygen produced, which determines the necessary current density and voltage drop across the PEM electrolyzer. In addition, oxygen production in the PEM electrolyzer requires deviation from the Nernst potential, presenting trade-offs between the exergy efficiency and critical life support functions. The results of parametric studies of PEM electrolyzer performance are presented with an emphasis on the impacts of polarization and operational conditions on exergy efficiency.

One considers a linear elastic random structure composite material (CM) with a homogeneous matrix. The idea of the effective field hypothesis (EFH, H1) dates back to Faraday, Poisson, Mossotti, Clausius, and Maxwell (1830–1870, see for references and details [1], [2]) who pioneered the introduction of the effective field concept as a local homogeneous field acting on the inclusions and differing from the applied macroscopic one. It is proved that a concept of the EFH (even if this term is not mentioned) is a (first) background of all four groups of analytical methods in physics and mechanics of heterogeneous media (model methods, perturbation methods, self-consistent methods, and variational ones, see for refs. [1]). New GIEs essentially define the new (second) background (which does not use the EFH) of multiscale analysis offering the opportunities for a fundamental jump in multiscale research of random heterogeneous media with drastically improved accuracy of local field estimations (with possible change of sign of predicted local fields). Estimates of the Hashin-Shtrikman (H-S) type are developed by extremizing of the classical variational functional involving either a classical GIE [1] or a new one. In the classical approach by Willis (1977), the H-S functional is extremized in the class of trial functions with a piece-wise constant polarisation tensors while in the current work we consider more general class of trial functions with a piece-wise constant effective fields. One demonstrates a better quality of proposed bounds, that is assessed from the difference between the upper and lower bounds for the concrete numerical examples.

Computational Fluid Dynamics (CFD) models allows the three-dimensional simulation of the complex electrochemical, fluid dynamics, and thermodynamic phenomena related to the temperature and pressure distribution in the channels and the porous media than occurs inside the fuel. This work presents a CFD Multiphysics simulation of a PEM Fuel Cell under different operational conditions in their inlet streams. The simulation was done by using COMSOL Multiphysics ® software, and it takes into account the mass transfer of gases in the channels, the porous media and the electrochemistry from reactions in a 5 cm 2 active area. From the electrochemical perspective, the relationship between the charge transfer and the overpotentials are taken into account by kinetic expressions. In addition, the ohm’s law is applied in conjunction with the charge transfer to describe the conduction of current in the electrodes and electrolytes. Gas diffusion layers (GDL) along with the catalyst layers are modeled as porous media restricting the electrochemical reaction. As the result of different simulation scenarios representing different operational conditions, the characteristic Polarization Curve of the fuel cell, the dependence between the voltage in the cell, and the demanded current by the load are obtained. A reduction in the electrical potential was evidenced due to the reaction activation potential, the ohmic losses due to the electrical resistance of the materials and the concentration losses as a result of deficiencies in the diffusion of the reactants through the porous medium. Currents distributions and water content are analyzed in order to understand the role of temperature, load, and humidity over the fuel cell performance.

This paper presents the results of theoretical study designed to measure the suitability of a dielectric elastomer as an actuator, from a group of acrylic and silicone elastomers. The micro molecular parameters of elastomers such as monomer type, monomer chain length and density were taken into consideration for analysis of actuation properties. Identification of monomer type of selected elastomers was done by using modified dielectric equations of polarization and stress induced due to applied electric field. The effect and the importance of electric field on the selected elastomers were also considered. To further understand the actuation potential of polymers, a comparison was done on the basis of their stress-electric field analysis. A conclusion was drawn on the basis of these comparisons and recommendations are given for an effective selection of polymers for use in actuator applications.

In this study, numerical simulations were performed to find the current-voltage distribution for a laminar flow-based membraneless fuel cell (LFFC). The system uses formic acid and oxygen as the fuel and oxidant, respectively, and has a Y-shaped geometry with two separate inlets that merge into a single channel. The main objective of this work is to analyze the impact of geometry and operating conditions on the performance of these devices. This is done by proposing a novel wavy-channel-based geometry for the side walls, along with planar top and bottom walls, and comparing the behavior of the corresponding system to that of LFFCs based on straight-channel walls. Special attention is placed on the effect of both the amplitude of the sinusoid and its wavelength on the performance of the device. The effect of flow rates — in the range of [200, 350] μL/min — is also studied. The mathematical model is formulated by considering the Navier-Stokes equations along with Butler-Volmer and Fick’s law. For each fuel-cell configuration, the governing equations are discretized and solved using finite elements, and the solutions given in terms of the polarization curves. The model was first verified using published numerical data for a straight-channel-based LFFC. The simulations show that the performance achieved by the device, based on the proposed wavy channel geometry, is slightly better than that of the LFFC with straight channel walls. On the other hand, higher flowrates significantly improve the power density of the device. Although the current mathematical model may be useful in a variety of applications, improvements on it are currently underway to account for the effects of potential distributions on ions within the flow channel, and results from it will be reported in the future.

Scanning beam interference lithography (SBIL) technology is applied to produce large-area grating with nanoscale phase accuracy. One of the greatest challenges of SBIL is locking interference fringe to a moving substrate with nanometer spatial phase error, which requires measuring the fringe phase with subnanometer precision. We are developing a novel homodyne phase-locking interferometer (HPLI) to meet the harsh measurement requirements. The HPLI offers high precision phase measurements as well as the direction recognition of the interference fringe drift with a four-orthogonal detection system. However, nonlinearity error impacts the phase measurement accuracy of HPLI with nanometer scale, which is mainly due to polarization mixing. In this paper, we present a method to estimate and compensate nonlinearity error in real time by applying an extended Kalman filter algorithm. The simulation results show that the method can effectively eliminate the nonlinearity error.

This paper studies the vibration of Zinc oxide (ZnO) nanowires in electric field via molecular dynamics (MD) simulation and continuum beam models. First, the size effects of the equivalent Young’s modulus and piezoelectric constant of ZnO nanowires are obtained by MD simulation and characterized by core-shell model. The piezoelectric constants of ZnO nanowires decrease with the rising of the size of cross section. The equivalent tensile and bending Young’s modulus of ZnO nanowires in polarization direction increases with the increasing of the cross section size. The equivalent tensile and bending Young’s modulus in polarization direction predicted by core-shell model is in good agreement with MD simulation. Then, the vibration of the cantilevered ZnO nanobeam is simulated by MD. When the cross section size becomes larger, the vibration frequencies predicted by continuum theory coincide with those obtained by MD simulation better. Finally, the effect of electric field on vibration frequency of a ZnO nanowire is studied by MD simulation and continuum beam models. It is found that the natural frequencies rise with the increasing of electric field for the case of positive electric field in polarization direction. But the natural frequencies will decrease with the increasing of negative electric field when the intensity of the electric field is relatively weak. The natural frequency is hard to be obtained when the phase transition is occurring in relatively strong negative electric field. The vibration frequencies of the cantilevered Timoshenko beam with axial force due to the effects of electric field are obtained. The frequencies obtained by Timoshenko beam model agree with MD results very well. The vibration frequencies of the continuum theory agree with MD results better when the size of the cross section increases. The vibration frequencies of the ZnO nanowire keep constant when the direction of electric field is perpendicular to the polarization direction.

Improvement in power generation performance of PEFC (Polymer Electrolyte Fuel Cell) is required for its market supremacy in automotive applications. In particular, it is important to suppress concentration overpotential in high current density operation. The microstructure of CCL (cathode catalyst layer) is known to have a great effect on the power generation performance of PEFC. Also, the requirement for the species transport characteristics should vary with the thickness-wise position in CCL. Therefore, the purpose of this study is to design the microstructure of CCL by using multi-layered cathode catalyst layer and to evaluate oxygen transport properties. In this research, we fabricated three kinds of multi-layered CCLs which have the difference in I/C (ionomer to carbon) ratio of GDL (gas diffusion layer)-side layer (0.3, 0.5, 0.9). And, we investigated oxygen transport-reaction phenomena by evaluating polarization characteristics, ECA (electrochemical surface area) and R CL (oxygen transport resistance in the CCL) using limiting current measurements. As I/C ratio is decreased from 0.9 to 0.5, R CL is decreased 49%. On the contrary, as I/C ratio is decreased from 0.5 to 0.3, R CL is slightly increased. ECA is monotonically decreased as I/C ratio is decreased from 0.9 to 0.3. These results show that the species transport characteristics alone have optimum condition in the GDL-side CCL at around I/C = 0.50. In addition, we fabricated four kinds of multi-layered CCLs which have the difference in I/C ratio of GDL-side layer (0.5, 0.9) and mass fraction of platinum (10 wt%, 46 wt%.) Oxygen transport resistance is evaluated in CCL by separating the resistance to two components, R macro (by Knudsen diffusion) and R local (by dissolution diffusion in ionomer,) by applying the ladder resistance model in CCL. As I/C ratio is decreased from 0.9 to 0.5, R macro is decreased and R local is increased regardless of mass fraction of Pt. These results show that the ionomer amount of micropore in CCL is decreased, the micropore diameter is increased, and dissolution surface area near platinum is decreased as I/C ratio is decreased 0.9 to 0.5. These results strongly suggest that there is an optimization strategy of I/C ratio of GDL-side layer in CCL.

The desalination process using reverse osmosis membrane is used around the globe to produce fresh water. In the present paper, simulations are conducted to examine steady and transient nature of the flow inside a three dimensional desalination module containing cylindrical spacers. Navier-Stokes and mass transport equations are solved to determine the flow and concentration field in the feed channel for Reynolds number of 800. The spiral wound membrane is treated as a functional surface where the solution-diffusion model is applied. The flow and the concentration field are strongly three dimensional and transient in nature. The present authors demonstrated that the momentum mixing induced by the presence of spacers enhances the flux performance of the membrane. It is also shown that transient effects and the secondary flows induced by three dimensional flow transitions are mitigating the concentration polarization and fouling/scaling that occurs along the surface of the membrane.

Membrane filtration systems are used in a variety of processing industries where their performance meet and exceed the requirements in cost and quality. However, it is a challenge to design a small pore-size membrane system that treats very concentrated, large-volume streams within a reasonable time period. In the processing industries, several membrane technologies are used to separate various fluid streams where the concentrate or filtrate contains high-value products. Nevertheless, pore blocking is one of the major factors determining the applicability, efficiency and performance of the membrane filtration and separation system. Inside and outside membrane pore blockages lead to concentration polarization and cake buildup that reduces the flux rate and increases losses in system efficiency. There are four pore blocking mechanisms identified and modeled (complete, standard, intermediate and cake). Several experimental and theoretical works exist that describe the pore flow and blocking process. Depending on the processing fluid and membrane characteristics, all or some of the blocking mechanisms will be exhibited during the filtration process. Understanding the fluid and membrane size and characteristics in addition to pore blocking mechanisms is very important to designing effective membrane filtration systems that overcome the drawbacks associated with membrane performance. Furthermore, developing a membrane filtration system with a target cleaning process that controls membrane performance declines and maintains a reasonable flux for an extended period of time requires understanding and identifying the cause of membrane blocking. In this study, the membrane blocking during the filtration process was investigated experimentally. The experiment was designed to simulate the characteristics of a fluid stream encountered in food processing. The higher concentration was selected to manage the experiment time as well as to address worst-case scenarios, while the lower concentrations were selected to manage the filter area reduction. Dead-end filtration of two yeast solution concentrations were filtered through two different filter areas. In addition, the dynamic tests were conducted with shear generated using an impeller operated at various rotational speeds. Several tests were performed and the filtrate volume, time, pressure and agitation rate were recorded. The volume was measured with a graduated cylinder and the time measured in seconds. The results show the membrane blocking process is significantly affected by the membrane and fluid characteristics. The plots of pore blocking models and the experimental membrane filtrate data show the dominant pore blocking observed for both filters and flow process is cake filtration. The side-by-side comparison also indicates that the dominant pore blocking mechanisms depend on time. Thus, the initial and final pore blocking may not be attributed to the same pore blocking mechanism. Although it cannot be clearly shown from the current study, some part of the experimental flux profile may also be shaped by the combined pore blocking effects.

One of the most notable methods for improving microflows is the design of an orthogonal electrode pair that accentuates the non-uniformity in the electric field and, as a result produces stronger net flows at lower voltages. Orthogonal electrodes also have been reported to produce high velocity fluid flow when excited by AC signals, showing potential for micro-pumping applications. Breaking the symmetry of electric fields in the electrode pair produces a unidirectional flow [1] which is salubrious for pumping. As many research groups believe that the Manipulation of microfluidics and particles can be effectively done by AC electrokinetic (ACEK) technique, the current research work in our lab involves in designing a multifunctional system to manipulate the particles to improve the binding process and the fluid flow. This research also explicates the AC electrokinetic processes such as capacitive electrode polarization, Faradic polarization and the AC electrothermal effect, to better explain the directional flow patterns and their role in manipulating the microfluidics. Different flow patterns were obtained by varying the level and frequency of AC potential.

Properties of ferroelectric films are highly influenced by inevitable defects, such as hydrogen impurity. This study is focused on theoretical and numerical studies to probe effects of hydrogen contamination on ferroelectric stability in PbTiO 3 (PTO) films using the first-principles effective Hamiltonian. First-principles calculations are performed to determine the possible position, formation energy, and mobility of hydrogen impurity atom, and the calculated results are used as inputs to molecular dynamics (MD) simulations in a large system. The hydrogen atom is able to move along the polarization with small energy barriers. The energy difference between a hydrogen contaminated PTO and a pure PTO is considered as an energy penalty term induced by hydrogen contamination and has been added to the effective Hamiltonian. Then, the MD effective Hamiltonian with the energy penalty is employed in MD simulations to investigate the effects of hydrogen contamination on the ferroelectric responses of PTO films with various thicknesses and temperatures. The hysteresis loops are presented and analyzed for PTO films with various concentrations of hydrogen impurities and thicknesses. Hydrogen contamination reduces the remnant polarization, especially for thin films. As the concentration of hydrogen impurities increases, the critical thickness increases. By analyzing the vertical cross section snapshots, it has been found that the hydrogen impurity atoms near interfaces affect the polarization throughout the entire PTO films.

One considers a linear heterogeneous media (e.g. filtration in porous media, composite materials, CMs, nanocomposites, peristatic CMs, and rough contacted surfaces). The idea of the effective field hypothesis (EFH, H1, see for references and details [1], [2]) dates back to Mossotti (1850) who pioneered the introduction of the effective field concept as a local homogeneous field acting on the inclusions and differing from the applied macroscopic one. It is proved that a concept of the EFH (even if this term is not mentioned) is a (first) background of all four groups of analytical methods in physics and mechanics of heterogeneous media (model methods, perturbation methods, self-consistent methods, and variational ones, see for refs. [1]). An operator form of the general integral equations (GIEs) is obtained which connects the driving fields and fluxes in a point being considered. Either the volume integral equations or boundary ones are used for these GIEs, new concept of the interface polarisation tensors are introduced. New GIEs present in fact the new (second) background (which does not use the EFH) of multi-scale analysis offering the opportunities for a fundamental jump in multiscale research of random heterogeneous media with drastically improved accuracy of local field estimations (with possible change of sign of predicted local fields).

In contrast to the classical local and nonlocal theories, the peridynamic equation of motion introduced by Silling (J. Mech. Phys. Solids 2000; 48: 175–209) is free of any spatial derivatives of displacement. The new general integral equations (GIE) connecting the displacement fields in the point being considered and the surrounding points of random structure composite materials (CMs) is proposed. For statistically homogeneous thermoperistatic media subjected to homogeneous volumetric boundary loading, one proved that the effective behaviour of this media is governing by conventional effective constitutive equation which is intrinsic to the local thermoelasticity theory. It was made by the most exploitation of the popular tools and concepts used in conventional thermoelasticity of CMs and adapted to thermoperistatics. A generalization of the Hills equality to peri-static composites is proved. The classical representations of effective elastic moduli through the mechanical influence functions for elastic CMs are generalized to the case of peristatics, and the energetic definition of effective elastic moduli is proposed. The general results establishing the links between the effective properties (effective elastic moduli, effective thermal expansion) and the corresponding mechanical and transformation influence functions are obtained by the use of the decomposition of local fields into load and residual fields. Effective properties of thermoperistatic CM are expressed through the introduced local stress polarization tensor averaged over the extended inclusion phase. This similarity opens a way for straightforward expansion of analytical micromechanics tools for locally elastic CMs to the new area of random structure peri-dynamic CMs. Detailed numerical examples for 1D case are considered.