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Electrodeposited cobalt phosphate has been reported in the literature as a robust alternative to noble metal-based electrocatalysts for the O2 evolution reaction. In parallel, atomic layer deposition (ALD) has been acknowledged as a key technology for the preparation of thin films for energy applications. With the present work, the authors have addressed the preparation of cobalt phosphate thin films by a plasma-assisted ALD process. The process developed consists of cobaltocene (step A) and trimethyl phosphate (step C) exposures alternated by O2 plasma (steps B and D) in an ABCD fashion. The process shows a linear growth with a growth per cycle of 1.12 ± 0.05 Å at 300 °C and no nucleation delay. The ALD saturation behavior has been demonstrated for each dosing step, and the process shows minimal inhomogeneity on 100 mm diameter wafers in terms of film thickness (

Oxidative coupling of methane (OCM) is a process to directly convert methane into ethylene. However, its ethylene yield is limited in conventional reactors by the nature of the reaction system. In this work, the integration of different membranes to increase the overall performance of the large-scale oxidative coupling of methane process has been investigated from a techno-economic point of view. A 1D membrane reactor model has been developed, and the results show that the OCM reactor yield is significantly improved when integrating either porous or dense membranes in packed bed reactors. These higher yields have a positive impact on the economics and performance of the downstream separation, resulting in a cost of ethylene production of 595−625 €/tonC2H4 depending on the type of membranes employed, 25−30% lower than the benchmark technology based on oil as feedstock (naphtha steam cracking). Despite the use of a cryogenic separation unit, the porous membranes configuration shows generally better results than dense ones because of the much larger membrane area required in the dense membranes case. In addition, the CO2 emissions of the OCM studied processes are also much lower than the benchmark technology (total CO2 emissions are reduced by 96% in the dense membranes case and by 88% in the porous membranes case, with respect to naphtha steam cracking), where the high direct CO2 emissions have a major impact on the process. However, the scalability and the issues associated with it seem to be the main constraints to the industrial application of the process, since experimental studies of these membrane reactor technologies have been carried out just on a very small scale.

The hydrogen flux degradation in hydrogen permeation tests of Pd/Nb30Ti35Co35 (at.%)/Pd composite membranes was experimentally investigated at temperatures from 400 to 650 °C. The hydrogen fluxes through the Pd/Nb30Ti35Co35/Pd membranes during isothermal long-term hydrogen permeation tests above 500 °C exhibit two hydrogen-flux-decline steps. The aggregation of the Pd-catalytic layer and the boundary layer formed between Pd and Nb30Ti35Co35 due to interdiffusion were experimentally confirmed contributing to the degradation of the hydrogen flux through the Pd/Nb30Ti35Co35/Pd membrane. Modelling work was carried out to reveal and validate the temperature-dependence of the two attributing factors to the degradation of hydrogen permeation flux.

A Diffuse Interface Model (DIM) is employed to model droplet impact on a heated solid surface. The DIM uses an especially constructed solid wall boundary condition which enables simulations with different wetting conditions of the solid surface. The model is also extended to include the effects of surface roughness on the behavior of the contact line dynamics. Multiple simulations are carried out to demonstrate the capabilities of the presented model. The simulation results demonstrate the influence of the wetting properties of the solid, with a higher cooling rate for hydrophilic than for hydrophobic wetting conditions. Surface roughness of the solid surface increases the cooling rate of the solid by enhancing the heat transfer between solid and fluid.

As buildings are a large energy user, it is important to not only reduce their consumption, but also have them generate their own electricity. Here, we describe a smart window that could reduce electricity consumption, normally used for air conditioning and lighting, by absorbing excess solar radiation with dichroic fluorescent dye molecules aligned in a switchable liquid crystal host and guiding the re-emitted light energy to the edges of the device, where it can be used to generate electricity via attached photovoltaic cells. The liquid crystals are responsive both to temperature changes and applied electrical fields. At higher temperatures, transmission decreases due to increased disorder in the liquid crystals, while the application of an electrical field increases transmission by effectively realigning the dyes for minimal absorption. Using alternative configurations, a window with a transparent rest state was also produced, in which transmission can be decreased by applying an electrical field, the thermal response remains identical.

In this paper a scaling method is proposed for scaling down the prohibitively large number of particles in CFD-DEM simulations for modeling large systems such as circulating fluidized beds. Both the gas and the particle properties are scaled in this method, and a detailed comparison among alternative mapping strategies is performed by scaling both the computational grid size and the riser depth. A series of CFD-DEM simulations has been performed for a pseudo-2D CFB riser to enable a detailed comparison with experimental data. By applying the scaling method, the hydrodynamic flow behavior could be well predicted and cluster characteristics, such as cluster velocity and cluster holdups agreed well with the experimental data. For a full validation of the scaling method, four mapping conditions with different ratios of the grid size and particle volume and of modified ratio of riser depth to particle size were analyzed. The results show that in addition to hydrodynamic scaling of the particle and fluid properties, scaling of the dimensions for the interphase mapping is also necessary. Keywords: Scaling method, CFB riser, CFD-DEM, Hydrodynamics, Clusters

Efficient CO2 reduction is predicted for CO2 microwave plasma by virtue of predominant excitation of the asymmetric stretch vibration. Although interpretation of ongoing research is generally based on this mechanism, direct measurement of the power partitioning to support the assumed preferential vibrational excitation in CO2 microwave plasma is currently lacking. Here, such measurements are performed on a 100 μs pulsed microwave CO2 discharge. The 2 microwave plasma albeit less predominant than often assumed.

In this work, using molecular dynamics simulations, we examine the effect of atomic charge delocalization on the pendant side chain of Nafion membrane on the structural and dynamical properties in various hydrated environments. The sulfur-sulfur radial distribution functions suggest that the sulfonate groups of the pendant side chain have closer geometric proximity with an increase in charge delocalization. However, the interactions of the sulfonate groups with water molecules/hydronium ions show a slight change with the charge delocalization. The average water cluster size decreases significantly with charge delocalization, though the diffusion coefficients of water molecules (at medium and higher water concentration) increase initially and then decreases slightly with excessive charge delocalization. The diffusion coefficients of hydronium ions do not follow any particular trend with charge delocalization. A complex interplay between sulfur-sulfur, sulfur-water/hydronium interactions, and water cluster distribution plays an essential role in the magnitude of the diffusion coefficient of water molecules and hydronium ions.

Metallic membranes have been studied by several research groups during the last 40 years. Most of the research has been focused on developing stable membranes able to achieve high flux and high permselectivity. The vast majority of proposed applications lie on hydrogen separation through Pd-based membrane. H2 separation is a very important process in the energy and chemical industry since several applications require H2 at different purity. Therefore, the integration of metallic membrane and membrane reactors has been widely studied and compared with the current technology form a technoeconomic point of view. Several application areas among industries can take benefit from the application of membrane, where energy and environmental sustainability, such as the reduction of CO2 emissions, still represent a major concern. This chapter aims to summarize some of the most relevant research works which have been published recently (2 separation. The analysis includes the use of different feedstocks, such as natural gas, coal, bio-based gas, and alcohol, as well as other chemicals.

A very interesting application of metallic membranes is their integration in multifunctional reactors called membrane reactors. This integration allows carrying out reaction and separation in a single device, which results in higher yields and milder conditions compared with conventional reactor systems. These results translate in lower CAPEX (because of reduction of reaction volume and circumventing downstream separations) and reduction of OPEX (because of milder conditions used in the reactor). This chapter introduces the concept of membrane reactors and gives an overview of the latest results achieved in membrane reactor performance and operation.

This chapter aims at providing an overall overview on the different approaches to modeling the hydrogen mass transport through Pd-based membranes, paying particular attention to the kinetic and transport phenomena occurring in nonideal conditions, which can be caused by several and, most of the times, concurrent occurrences, like sufficiently high hydrogen concentration, appreciable influence of adsorption and desorption, the presence of significant mass transfer resistance in the external gas phases and in the porous support, and the unwanted effect of inhibition phenomena due to the presence of certain species in mixture like CO and CO2. The motivation lies in the fact that a more precise membrane characterization including these phenomena is crucial in operating conditions close to those of interest for industrial applications.

Current Trends and Future Developments in (Bio-) Membranes: Recent Advances in Metallic Membranes presents recent developments in metallic membranes used in membrane reactors to save energy. It also offers a comprehensive review of the present state-of-the-art on the fabrication and design of metallic membranes and membrane reactors, considering various applications. This book focuses on the structure, preparation, characterization and applications of metallic membranes and membrane reactors, as well as transport mechanisms and simulation aspects. As recent research has focused on the development of metallic membranes and their applications, this book is an ideal reference on different production procedures and their use.

Metallic membranes and membrane reactors have become very popular tools for several process intensification strategies. This is being well recognized at European level, where several projects have been granted in the course of the last three Framework Programs on both membranes as separation tools and especially membrane reactors as process integration tools. This chapter, although not exhaustive (especially because of confidentiality issues), gives a good overview of the recent results of several EU-funded projects. It is worth noting that, apart from these projects, each country has also granted research projects on membrane reactors. These are not discussed in this chapter, although many results have already been reported in other chapters.

Reverse electrodialysis (RED) is a technology producing renewable energy from the mixing of river and seawater. In natural salinity gradients, multivalent ions are present, which lead to a reduced RED power output. Transport of multivalent ions against the concentration gradient and their trapping inside the membranes leads to a lower driving force and increased membrane resistance. The present work focuses on the effect of sulfate ions on anion exchange membranes in RED. A monovalent ion selective membrane ability to retain a higher open circuit voltage is offset by the higher resistance in the presence of sulfate, leading to losses in normalized power outputs (−25%) comparable to a standard grade membrane. Longer term experiments revealed that membrane resistance increases over time. This study highlights the need to address uphill transport, resistance increase, and decreased permselectivity of anion exchange membranes in presence of multivalent ions.

This chapter aims to provide an overview on techniques and developments about metal membranes for hydrogen production and purification. Such an overview covers membrane fabrication techniques and experimental methodologies. Finally a list of case studies of successful applications of metal membranes at a scale larger than the laboratory one is provided, giving the reader a nonexhaustive idea on the actual potentialities of these materials.

Hydrogenation, oxidation and alkylation are just some of the processes which are performed in bubble columns. One of the reasons to use a bubble column for these processes is the high interfacial mass transfer coefficients. Trying to simulate the mass transfer around the bubbles is however challenging due to the typically high Schmidt numbers of liquids, meaning that the mass boundary layer is very thin compared to the momentum boundary layer. To resolve this thin mass boundary layer, a subgrid scale model can be used. This work focuses on improving the subgrid scale model that we have embedded in our in-house front tracking framework of Claassen et al., AIChe J 2019. In the current implementation the unphysical numerical back diffusion at the grid into the bubble has been prevented with a staircase immersed boundary implementation. A verification has been performed by comparing the simulated, local and global Sherwood number with the analytical solution in creeping and potential flow regimes. Furthermore, the model was validated for 20 free rising bubbles of different shapes at industrial relevant Schmidt numbers (103-105). The model was able to correctly predict the Sherwood numbers.

Transitioning to a renewable energy economy requires the widespread integration of solar and wind power, which are intermittent, into the electricity grid. To this goal, it is paramount to develop cost-competitive, reliable, location-independence, and large-scale energy storage technologies. The hydrogen bromine flow battery (HBFB) is a promising technology given the abundant material availability and its high power density. Here, the aim is to perform a comprehensive techno-economic analysis of a 500 kW nominal power/5 MWh HBFB storage system, based on the levelized cost of storage approach. Then, we systematically analyze stack and system components costs for both the current base and a future scenario (2030). We find that, for the base case, HBFB capital investments are competitive to Li-ion battery technology, highlighting the potential of large-scale HBFB market introduction. Improving the stack performance and reducing the stack and system costs are expected to result in ~62% reduction potential in capital investments. The base-case levelized cost of storage, $0.074/kWh, is sufficiently low for a wind-solar storage system to compete with a fossil-based power plant, with potential for reduction to $0.034/kWh in the future scenario. Sensitivity analysis indicates that the levelized cost of storage is most sensitive towards the stack lifetime, which motivates research efforts into advanced electrocatalysts with higher durability and ion-exchange membranes with improved selectivity.

The purification of the α-olefins though challenging, is mandatory step for their use in the chemical industry. Since adsorptive separation using zeolites is one of the most promising alternatives for olefin/paraffin separation in terms of energy efficiency, we use a combination of experiments and molecular simulations to study the effect that the topology and chemical composition of the zeolite exert on the purification of olefins. To this aim we developed an effective potential for the cations with the double bond of the olefins. The potential parameters were validated with our experimental adsorption isotherms and isobars of propylene and 1-hexene. We performed an extensive study of propane/propylene separation in more than 200 all silica zeolites and several aluminosilicates. We also performed DFT and classical optimization of the structures, obtaining the minimum energy of a given chemical composition and topology, which is key factor for the adsorption mechanisms. DFT calculations also allowed the analysis of binding energies and binding geometries of propane and propylene in NaY and LTA5A. We discussed the effect exerted by the cations on the separation performance of the zeolites. Our study shows that aluminosilicates with calcium cations are the best candidates to separate olefins from paraffins, due to the stronger interaction of the double bond of olefins with these divalent cations., This work was supported by the Spanish Ministerio de Economía y Competitividad (CTQ2016-80206-P) and for the Ministerio de Ciencia, Innovación y Universidades (CTQ2017-92173-EXP). We thank C3UPO for the HPC support. A. Luna-Triguero and J. M. Vicent-Luna thank to Santander Universidades for their Beca Iberoamérica Santander Investigación. A. Sławek obtained financial resources as part of financing the doctoral scholarship from the National Science Center, Poland Grant No. 2018/28/T/ST5/00274.

The use of biogas as feedstock for hydrogen production was widely proposed in the literature in the last years as a strategy to reduce anthropogenic carbon emissions. However, its lower heating value compared to natural gas hampers the revamping of existing reforming plants. The use of composite carbon molecular sieve membranes for biogas upgrading (CO2 removal from biogas) was investigated experimentally in this work. In particular, ideal perm-selectivities and permeabilities above the Robeson plot for CO2/CH4 mixtures have been obtained. These membranes show better performances compared to polymeric membranes, which are nowadays commercialized for CO2 separation in natural gas streams. Compared to polymeric membranes, carbon membranes do not show deactivation by plasticization when exposed to CO2, and thus can find industrial application. This work was extended with a techno-economic analysis where carbon membranes are installed in a steam methane reforming plant. Results have been first validated with data from literature and show that the use of biogas increases the costs of hydrogen production to a value of 0.25 €/Nm3 compared to the benchmark technology (0.21 €/Nm3). On the other hand, the use of biogas leads to a decrease in carbon emissions up to 95%, thus the use of biogas for hydrogen production is foreseen as a very interesting alternative to conventional technologies in view of the reduction in the carbon footprint in the novel technologies that are to be installed in the near future.

In veel rapporten over waterelektrolyse wordt gezegd dat alkalische waterelektrolyse-technologie relatief inflexibel is ten opzichte van alternatieven zoals PEM elektrolyse, maar dit wordt zelden verder toegelicht. In het kader van het Alkaliflex project is de flexibiliteit van alkalische waterelektrolyse dieper onderzocht. Vier flexibiliteitslimiteringen zijn geïdentificeerd: gelijkrichters, gas zuiverheid, warmtemanagement en gas-vloeistofgedrag. Voor de meeste van deze limiteringen zijn oplossingen beschikbaar om de flexibiliteit te verhogen en alkalische technologie is dan ook niet inherent inflexibel. Wel is het zo dat de oplossingen om de flexibiliteitslimiteringen weg te nemen geld kosten en het per project bepaald zal moeten worden of dit aantrekkelijk is. Verder is het zeer de vraag of zeer flexibele elektrolyzers wel nodig zijn. De huidige behoefte aan zeer snelle flexibiliteit is namelijk beperkt en zeker op de lange termijn zal de waarde van korte termijn flexibiliteit waarschijnlijk afnemen door een toenemend flexaanbod. Daarentegen zal er door een toenemend aandeel van zonne- en windenergie wel meer behoefte komen aan flexibiliteit op uurbasis, maar hiervoor is zeer snel op- en afschakelen minder belangrijk. De minimale last waarop een elektrolyzer kan opereren blijft waarschijnlijk wel heel belangrijk. Het Alkaliflex project laat ook zien dat er kansen zijn voor de ontwikkeling van efficiëntere elektrolyzers op basis van betere elektrodestructuren en dunnere membranen. In het Alkaliflex project is een eerste prototype van een nieuwe laboratorium-elektrolyzer ontwikkeld op basis van 3D-print technieken, die al beter presteert dan een commercieel verkrijgbare laboratoriumelektrolyzer. Voor verdere ontwikkeling is er wel behoefte aan modellen die het complexe gas-vloeistof gedrag in elektrolyzers beter kunnen beschrijven. De huidige modellen hebben nog veel moeite om het gedrag in sterke elektrolieten en bij hoge gasfracties te beschrijven.

During the presentation I will discuss the development of two diagnostics to increase our current level of understanding of the vibrational kinetics within CO2 discharges, with the intention to ultimately contribute to a controlled and efficient dissociation process. The diagnostic techniques are (1) time resolved in situ Fourier transform infrared (FTIR) spectroscopy and (2) spatiotemporally resolved in situ rotational Raman spectroscopy. Both techniques are used to obtain information about the rovibrational density distributions in the electronic ground state of CO2 in a pulsed glow discharge. During the active part of the plasma pulse a clear non-equilibrium is observed between the rotational and the ν3, and the (ν1, ν2) and ν3 vibrational density distributions. The results provide ample experimental foundation to expand our knowledge on CO2 vibrations and dissociation, especially through comparison with numerical models. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 813393

Scope is enhancement of scalar transport (heat, chemical species) in engineered flow systems by reorientations of a laminar base flow. Practical applications include mixing in inline heat exchangers by downstream reorientation of baffles, stirring in bio-reactors by cyclic repositioning of impellers, and subsurface chemicals distribution for in situ minerals mining by unsteady pumping schemes. Conventional reorientation schemes consist of a periodic reorientation (in space or time) of the flow designed to accomplish efficient fluid mixing. However, whether this approach indeed yields optimal scalar transport for significant diffusion and/or chemical reactions is unclear. The present study explores an alternative approach: adaptive reorientation of the flow by interval-wise selection of the reorientation that is predicted to yield optimal scalar transport for a future time horizon. Key enabler for fast predictions is a compact model based on the spectral decomposition of the scalar evolution in the baseflow. The adaptive reorientation scheme is investigated for a representative problem: enhanced heating of a cold fluid in a 2D circular domain by an unsteady flow driven by step-wise activation of moving boundary segments. This reveals that the adaptive reorientation scheme can substantially acceleratethe heating compared to conventional time-periodic reorientation designed for efficient mixing and thus demonstrates its potential for attaining optimal scalar transport in reoriented flows.

This work addresses plasma chemistry in the core of a vortex-stabilized microwave discharge for CO2 conversion numerically, focusing on the pressure-dependent contraction dynamics of this plasma. A zero-dimensional model is presented for experimental conditions in a pressure range between 60 and 300 mbar and a temperature range between 3000 and 6500 K. Monte Carlo flux (MCF) simulations, which describe electron kinetics, are self-consistently coupled to the plasma chemistry model. The simulation results show that an increase in pressure is accompanied by a transition in neutral composition in the plasma core: from a significant amount of CO2 and O2 at low pressures to a O/CO/C mixture at high pressures, the composition being determined mostly by thermal equilibrium and by transport processes. The change of temperature and composition with pressure lead to higher ionisation coefficient and more atomic ion composition in the plasma core. These changes result in an increase in ionisation degree in the plasma core from 10−5 to 10−4. These factors are shown to be fundamental to drive contraction in the CO2 microwave discharge.

In this paper, a hybrid computational technique for the Direct Numerical Simulation of hydrodynamics and (convective) mixing in complex two-phase systems is presented. The hybrid Immersed Boundary and Volume of Fluid method is based upon a single-fluid approach in combination with Henry’s law for the concentration jump. The convective species fluxes are evaluated using PLIC-based geometrical advection, which is consistent with the advection of the local fluid volume fractions. Complex geometries can be accounted for and are treated with the Immersed Boundary method. Following the verification for single phase and two-phase systems, the model was used to investigate the influence of the container geometry on the mixing of a tracer due to tilting of the container. For both cylindrical and rectangular containers, an increasing tilting angle enhances the convective motion and consequently the mixing efficiency. The cylindrical geometry was found to possess a better mixing efficiency than the rectangular geometry. Keywords: Direct numerical simulation, Volume of fluid method, Immersed boundary method, Mass transfer, Henry’s law, Contact line dynamics

In this study, an efficient ghost cell‐based immersed boundary method is used to perform direct numerical simulations of mass‐transfer processes in bidisperse arrays. Stationary spherical particles, with a size ratio of 1.5, are homogeneously distributed in a periodic domain in the spanwise directions. Simulations are performed over a range of solids volume fractions, volume fraction ratios of small‐to‐large particles, and Reynolds numbers. Through our studies, we find that large particles have a negative influence on the overall mass‐transfer performance; however, the performance of individual particle species is independent on the relative volume fraction ratios. We propose two correlations: (a) a refitted Gunn correlation for a better description of the interfacial transfer performance based on individual particle species; (b) a fractional calculation for a simple estimation of the overall performance in bidisperse systems using characteristics of individual particle species. We also investigate how well the overall mass‐transfer coefficient can be predicted by defining an appropriate equivalent diameter.

This paper reports on recent research advances in supervisor synthesis, as well as industrial applications and future research challenges, especially in the context of a research project funded by Rijkswaterstaat, responsible for the construction and maintenance of infrastructure in the Netherlands.

Because of the impracticality of long life time testing of hydrogen bromine flow batteries (HBFBs) under real, cyclic operating conditions, we utilized a high-frequency cycling load accelerated lifetime test (ALT) to evaluate the membrane electrode assembly performance in HBFBs. Four different membrane chemistries were tested to assess the relative long-term performance and durability of the corresponding HBFBs and to understand the main long-term failure mechanism in HBFB technology. The high-frequency cycling load ALT is a highly valuable method to assess long-term HBFB (components) stability and to understand the degradation/failure mechanism. The results showed that the utilization of long side chain perfluorosulfonic acid (LSC PFSA, i.e. Nafion®) membranes result in stable HBFB operation until a sudden cell failure at the end of the cycle life. The use of a more selective (lower bromine species crossover) reinforced LSC PFSA membrane results in approx. five times longer life times. In contrast, the use of a grafted polyvinylidene fluoride (SPVDF) membrane results in a slow incremental performance decrease (or area resistance increase) during the ALT and, again, a sudden cell failure at the end of the cycle life. After the ALT, the LSC PFSA membrane still shows high chemical stability. On the other hand, the grafted SPVDF and SPE membranes show clear membrane degradation visible as a strong decrease in IEC and an increase in ohmic AR. Gradual Pt catalyst degradation-dissolution, that results in insufficient Pt catalyst loading and subsequently low hydrogen reaction kinetics, is the main failure mechanism of the HBFBs. The membrane bromine species crossover rate is directly related to the rate of Pt catalyst degradation-dissolution and scales almost linearly with the cell total ampere-hours. As long as the catalyst loading is sufficient and does not reach a minimum value, this observed Pt degradation-dissolution rate does not significantly impact the cell performance.

In this work, we perform simulations of particle laden flow in a wide and long narrow channel in a Newtonian fluid. Simulations are performed for mono-sized and equal density spheres with varying Archimedes and Reynolds number. In the simulations, different phases of particle transport - rolling, saltation and suspension are observed. During simulations the average bed height is monitored and its steady state value is used for proposing a correlation between solids volume fraction (ϕ), shear Reynolds number (Res) and Archimedes number (Ar). This correlation is used to predict the critical shear Reynolds number for particle lift-off and a condition at which particles would occupy the whole channel at a given Archimedes number. The value of this critical Reynolds number is compared with the critical Reynolds number for single particle lift-off.

Gas–liquid bubble column reactors are often used in industry because of their favorable mass transfer characteristics. The bubble mass boundary layer in these systems is generally one order of magnitude thinner than the momentum boundary. To resolve it in simulations, a subgrid scale model will account for the sharp concentration variation in the vicinity of the interface. In this work, the subgrid scale model of Aboulhasanzadeh et al., Chem Eng Sci, 2012, 75:456–467 embedded in our in‐house front tracking framework, has been improved to prevent numerical mass transfer due to remeshing operations. Furthermore, two different approximations of the mass distribution in the boundary layer have been tested. The local and global predicted Sherwood number has been verified for mass transfer from bubbles in the creeping and potential flow regimes. In addition, the correct Sherwood number has been predicted for free rising bubbles at several Eötvös and Morton numbers with industrial relevant Schmidt numbers (103–105).

In this article, gain errors in current sensing for highly dynamic three-phase drives with three current sensor measurements are compensated without the aid of the machine plant model. As three current sensors are used, redundant information from the neutral current measurement is extracted by constructing its mathematical relation with the measured time-varying dq current. The proposed method compensates for non-symmetrical current sensor gain errors even in the presence of offset errors. A Recursive Sliding Window Least Square method is proposed to minimize the computation effort such that the method is suitable to be applied online. It does not incorporate a low-pass filter or averaging method based on electrical speed, making it suitable for highly dynamic applications. It is able to be applied in any three-phase AC machine, as the machine plant is not considered. Analysis, simulation and experimental results obtained from the hardware prototype by mimicking the actual application of high-precision mechatronics demonstrate the validity of the proposed method.

Forward osmosis (FO) is an emerging process to dewater whey streams energy efficiently. The driving force for the process is the concentration gradient between the feed (FS) and the concentrated draw (DS) solution. Here we investigate not only the effect of the DS concentration on the performance, but also that of the FS is varied to maintain equal driving force at different absolute concentrations. Experiments with clean water as feed reveal a flux increase at higher osmotic pressure. When high product purities and thus low reverse salt fluxes are required, operation at lower DS concentrations is preferred. Whey as FS induces severe initial flux decline due to instantaneous protein fouling of the membrane. This is mostly due to reversible fouling, and to a smaller extent to irreversible fouling. Concentration factors in the range of 1.2–1.3 are obtained. When 0.5 M NaCl is added to whey as FS, clearly lower fluxes are obtained due to more severe concentration polarization. Multiple runs over longer times show though that irreversible fouling is fully suppressed due to salting in/out effects and flux decline is the result of reversible fouling only.

The formation of a stagnant cap on a bubble attached to a microelectrode is studied by means of numerical simulation including both thermo- and solutocapillary effects. Recently, strong Marangoni flow in an electrolyte around electrogenerated bubbles was observed by Yang et al. [1] and Massing et al. [2]. High local current density above the electrode led to Ohmic heating of the electrolyte near the bubble foot and resulted in thermocapillary convection. However, the experimentally observed Marangoni convection can be predicted better if a stagnant cap of surfactants on the top of the bubble is assumed. The present work provides evidence that supports this hypothesis and simulates the stagnant cap utilizing two methods. In the first method, a critical stagnation angle θ s , which marks the border of the stagnant cap, is specified. At the top of the bubble above the stagnation θ s the interface motion is suppressed whereas at the bottom of the bubble below the stagnation θ s the thermocapillary effect dominates. In the more extensive second method, a transport equation for the surfactant concentration on the bubble interface is included. In this method, the thermo- and solutocapillary effects compete along the entire interface of the bubble. As a result, the top part of the bubble interface will stagnate. We quantify the rigidity of the bubble interface by a dimensionless number, the elasticity number. This elasticity number is the ratio of the solutocapillary stress due to surfactant variation to the thermocapillary stress due to temperature variation. The relevant temperature variation is due to Ohmic heating and is observed to scale with the square of the potential difference. As a consequence, the Marangoni velocity is also found to scale with the square of the potential difference. Additionally, the forces acting on the bubble before detachment are analysed. Special attention is given to the Marangoni force that is more dominant than reported previously because we included the force caused by the uneven pressure distribution along the bubble interface. The pressure distribution is uneven due to a secondary Marangoni vortex in the wedge between the bubble and the electrode. Furthermore, a general framework for Marangoni numbers is introduced to quantify the effect of each specific source of surface stress variation upon the spatial distribution of each variable governed by a convection-diffusion equation.

In this Letter, the counterintuitive and largely unknown Raman activity of oxygen atoms is evaluated for its capacity to determine absolute densities in gases with significant O-density. The study involves C O 2 microwave plasma to generate a self-calibrating mixture and establish accurate cross sections for the 3 P 2 ↔ 3 P 1 and 3 P 2 ↔ 3 P 0 transitions. The approach requires conservation of stoichiometry, confirmed within experimental uncertainty by a 1D fluid model. The measurements yield σ J = 2 → 1 = 5.27 ± s y s : 0.53 r a n d : 0.17 × 10 − 31 c m 2 / s r and σ J = 2 → 0 = 2.11 ± s y s : 0.21 r a n d : 0.06 × 10 − 31 c m 2 / s r , and the detection limit is estimated to be 1 × 10 15 c m − 3 for systems without other scattering species.

Funding Information: This work is part of the research program HTSM with Project No. 15352, which is (partly) financed by the Netherlands Organization for Scientific Research (NWO). R.L.P. acknowledges funding from Academy of Finland, ALDI project, decision no. 331082. VTT Technical Research Centre of Finland Ltd. and Dr. M. Utriainen are acknowledged for supplying the PillarHall LHAR3 and LHAR4 conformality test structures. Lam Research Corp. is acknowledged for providing vertical trench nanostructures. Solliance and the Dutch province of Noord Brabant are acknowledged for funding the TEM facility. Finally, the authors thank Dr. M.A. Verheijen for the TEM imaging, Dr. B. Barcones Campo for the FIB preparation of the TEM sample, and C. van Helvoirt for the technical support. Publisher Copyright: © 2021 The Authors. Published by American Chemical Society. Copyright: Copyright 2021 Elsevier B.V., All rights reserved. Atomic layer deposition (ALD) can provide nanometer-thin films with excellent conformality on demanding three-dimensional (3D) substrates. This also holds for plasma-assisted ALD, provided that the loss of reactive radicals through surface recombination is sufficiently low. In this work, we determine the surface recombination probability r of oxygen radicals during plasma ALD of SiO2 and TiO2 for substrate temperatures from 100 to ∼240 °C and plasma pressures from 12 to 130 mTorr (for SiO2). For both processes, the determined values of r are very low, i.e., ∼10-4 or lower, and decrease with temperature and pressure down to ∼10-5 within the studied ranges. Accordingly, deposition on trench structures with aspect ratios (ARs) of

A numerical model based on the fundamental continuum transport equations is developed to simulate the Fischer-Tropsch synthesis in a slender packed column. Internal and external mass transport limitations are considered in a fully resolved manner where a two-way coupling between mass and heat transport is accounted for. A Langmuir-Hinshelwood type kinetic model is used for the reaction rate in the catalyst phase which is then intrinsically coupled to the fluid phase transport by enforcing the appropriate boundary condition using the Immersed Boundary Method. The fixed bed reactor consists of 220 particles packed in a random manner using the Discrete Element Method where cooling from the wall to the bed is also considered. The influence of temperature and concentration on conversion and selectivity is investigated. The Direct Numerical Simulation of the Fischer-Tropsch reactor is then compared with an equivalent 1-D heterogeneous reactor model which employs empirical closures.

Zeolitic imidazolate frameworks (ZIFs), a subclass of metal–organic frameworks (MOFs), have been widely investigated as additive in mixed matrix membranes (MMMs), but systematic studies to identify critical intrinsic ZIF-type parameters that determine the MMM performance are lacking. Therefore, three isoreticular gmelinite (GME) ZIFs, i.e., ZIF-68, 69 and 78 that are distinct by their partial different imidazolate linkers, were incorporated in Matrimid matrices to systematically elucidate the effects of the varying pore aperture, pore diameter, pore volume and functionality of the ZIFs on the CO2/N2 and CO2/CH4 MMM mixed gas permeability. The incorporation of the ZIFs in Matrimid increases the CO2 permeability for all MMMs for both CO2/N2 and CO2/CH4 feed mixtures without compromising the selectivity. The highest increase in CO2 permeability is observed for the 20 wt% ZIF-68 MMM, with an increase in CO2 permeability of 116% for CO2/N2 feed and 122% for CO2/CH4 feed relative to Matrimid was achieved and surpassed the permeability of conventional ZIF-8/Matrimid MMMs. Regarding the isoreticular ZIF series, the results showed that for a higher permeability a larger pore aperture, diameter and volume of the ZIFs in the MMMs are more beneficial than a more polar functionality with smaller pore size, aperture and volume.

Due to the requirement for developing more sustainable constructions, natural fibers from agricultural wastes, such as coir fibers, have been increasingly used as an alternative in concrete composites. However, the influence of coir fibers on the hydration and shrinkage of cement-based materials is not clear. In addition, limited information about the reinforcing mechanisms of coir fibers in concrete can be found. The goal of this research is to investigate the effects of coir fibers on the hydration reaction, microstructure, shrinkages, and mechanical properties of cement-based light-weight aggregate concrete (LWAC). Treatments on coir fibers, namely Ca(OH)2 and nano-silica impregnation, are applied to further improve LWAC. Results show that leachates from fibers acting as a delayed accelerator promote cement hydration, and entrained water by fibers facilitates cement hydration during the whole process. The drying shrinkage of LWAC is increased by adding fibers, while the autogenous shrinkage decreases. The strength and toughness of LWAC are enhanced with fibers. Finally, three reinforcement mechanisms of coir fibers in cement composites are discussed.

Competitive adsorption of water is an important issue in the adsorption-based industrial processes of bio- and flue gases separation. The dehumidification of gases prior to separation would increase process complexity and lower its economic interest. In this work, large-scale computational screening was applied to identify Metal-Organic Frameworks (MOFs) structures which exhibit high CO2/CH4 selectivity and total loading higher than 0.5 mol/kg (in the presence of water). High-throughput Grand Canonical Monte Carlo (GCMC) screening of nearly 3000 existing MOF materials was carried out. Initial selection assumed fixed values of pore limiting diameter (PLD) and Henry's constant for water and allowed one to preselect 764 structures. After GCMC simulations carried for 50/50 CO2/CH4 mixture, at ambient conditions (p = 1 bar, T = 298 K), and variable gas humidity (0%, 5%, 30% and 40%) the final selection revealed 13 most promising MOFs structures. We focused on analysis of the correlations between the properties of the selected MOFs and the separation selectivity. We show that the selectivity is a complex function of the porous materials characteristics and finding selective sorbent, performing well in dry and wet conditions requires careful analysis of available MOFs.

The hydrodynamic properties of gas–liquid flows in water electrolyzers are of great practical interest since the local distribution of gas influences the amount of electrical energy required to produce hydrogen. We used the Euler-Euler model to simulate the multiphase flow in a water electrolyzer and compared the results to existing experimental data, for a range of current densities. Our study shows that if only the drag force and buoyancy force are incorporated in the model, the spreading of the gas layers formed at the electrodes is not accurately predicted. By adding the turbulence dispersion force to the model, reasonable agreement with the experimental data could be obtained for the higher current densities. The turbulence dispersion had to be implemented via user-defined functions, in order to obtain results that satisfied the momentum balance. In addition the effect of different turbulence models on the turbulent dispersion was investigated.

The chemistry of the interface between the metal halide perovskite absorber and the charge transport layer affects the performance and stability of metal halide perovskite solar cells (PSCs). The literature provides several examples of poor PSC conversion efficiency values, when electron transport layers (ETLs), such as SnO2 and TiO2, are processed by atomic layer deposition (ALD) directly on the perovskite absorber. In the present work, we shed light on the chemical modifications occurring at the perovskite surface, during ALD processing of SnO2 and TiO2, in parallel with the evaluation of the PSC cell performance. The ALD processes are carried out on a (Cs,FA)Pb(I,Br)3 perovskite by adopting tetrakis(dimethylamino)tin(IV) and tetrakis(dimethylamino)titanium(IV) as metal precursors and H2O as the coreactant for SnO2 and TiO2, respectively. Perovskite surface modification occurs in the form of an ultrathin PbBr2 layer. Furthermore, in the case of SnO2, halogen molecules are detected at the interface, in parallel with the initial growth of an oxygen-deficient SnO2. Subgap defect states just above the valence band maximum of SnO2 are also detected. These states act as hole traps at the perovskite/SnO2 interface, subsequently promoting charge recombination and deteriorating the performance of the cell. We hypothesize that a redox reaction between the perovskite, or its decomposition products, and the Sn metal center of the ALD precursor takes place: I− and Br− are oxidized to I2 and Br2, respectively, and Sn(IV) is reduced to Sn(II). In contrast, the Ti(IV) metal center does not undergo any redox process, and, as a result, a promising 11% power conversion efficiency is measured with TiO2 as the ETL. This result strongly suggests that TiO2 may be a more suitable ETL, when processed directly on the perovskite absorber.

Gas-liquid systems involving dispersed bubbly flows are often encountered in industry due to their favourable heat and mass transport characteristics. A key element of such systems involving interfacial mass transfer are the thin mass boundary layers prevailing at the phase boundaries. Resolving these thin boundary layers in numerical simulations is very challenging because of the need for very fine grids. Such grids often over-resolve the hydrodynamics which accounts for most of the CPU time. In this paper, we propose a multiple resolution approach that resolves the momentum boundary layers on a coarse (fixed) Cartesian grid and the mass boundary layers on a finer (adaptive) grid. The methodology proposed in Panda et al. (2019) for static rigid particles is extended to deformable moving interfaces and applied to single rising bubbles where the computed Sherwood number is compared with empirical correlations and numerical simulations available in literature.

Neural closure models have recently been proposed as a method for efficiently approximating small scales in multiscale systems with neural networks. The choice of loss function and associated training procedure has a large effect on the accuracy and stability of the resulting neural closure model. In this work, we systematically compare three distinct procedures: "derivative fitting", "trajectory fitting" with discretise-then-optimise, and "trajectory fitting" with optimise-then-discretise. Derivative fitting is conceptually the simplest and computationally the most efficient approach and is found to perform reasonably well on one of the test problems (Kuramoto-Sivashinsky) but poorly on the other (Burgers). Trajectory fitting is computationally more expensive but is more robust and is therefore the preferred approach. Of the two trajectory fitting procedures, the discretise-then-optimise approach produces more accurate models than the optimise-then-discretise approach. While the optimise-then-discretise approach can still produce accurate models, care must be taken in choosing the length of the trajectories used for training, in order to train the models on long-term behaviour while still producing reasonably accurate gradients during training. Two existing theorems are interpreted in a novel way that gives insight into the long-term accuracy of a neural closure model based on how accurate it is in the short term., Comment: 24 pages and 9 figures. Submitted to Computers and Mathematics with Applications. For associated code, see https://github.com/HugoMelchers/neural-closure-models

Physical dynamic networks most commonly consist of interconnections of physical components that can be described by diffusive couplings. These diffusive couplings imply that the cause-effect relationships in the interconnections are symmetric, and therefore, physical dynamic networks can be represented by undirected graphs. This article shows how prediction error identification methods developed for linear time-invariant systems in polynomial form can be configured to consistently identify the parameters and the interconnection structure of diffusively coupled networks. Furthermore, a multistep least squares convex optimization algorithm is developed to solve the nonconvex optimization problem that results from the identification method.

Homogeneous nucleation of water is investigated in argon and in nitrogen at about 240 K and 0.1 MPa, 1 MPa, and 2 MPa by means of a pulse expansion wave tube. The surface tension reduction at high pressure qualitatively explains the observed enhancement of the nucleation rate of water in argon as well as in nitrogen. The differences in nucleation rates for the two mixtures at high pressure are consistent with the differences in adsorption behavior of the different carrier gas molecules. At low pressure, there is not enough carrier gas available to ensure the growing clusters are adequately thermalized by collisions with carrier gas molecules so that the nucleation rate is lower than under isothermal conditions. This reduction depends on the carrier gas, pressure, and temperature. A qualitative agreement between experiments and theory is found for argon and nitrogen as carrier gases. As expected, the reduction in the nucleation rates is more pronounced at higher temperatures. For helium as the carrier gas, non-isothermal effects appear to be substantially stronger than predicted by theory. The critical cluster sizes are determined experimentally and theoretically according to the Gibbs-Thomson equation, showing a reasonable agreement as documented in the literature. Finally, we propose an empirical correction of the classical nucleation theory for the nucleation rate calculation. The empirical expression is in agreement with the experimental data for the analyzed mixtures (water-helium, water-argon, and water-nitrogen) and thermodynamic conditions (0.06 MPa-2 MPa and 220 K-260 K).

Nanofabrication techniques with atomic level precision are needed for advancement to smaller technology nodes in the semiconductor industry. Thermal atomic layer etching (ALE) is currently being developed to isotropically etch material for future applications. In this Letter, an alternative plasma-based ALE process for isotropic etching of Al2O3 is introduced involving SF6 plasma and trimethylaluminium [TMA, Al(CH3)3] pulses, providing higher etch rates and lower processing temperatures than conventional thermal ALE. This process illustrates that a fluorine-containing plasma can serve as a viable reactant for ALE and that plasmas—besides their conventional use in anisotropic ALE—can be employed for isotropic ALE. In situ spectroscopic ellipsometry measurements confirmed saturation of both SF6 plasma and TMA half-cycles, which results in an etch per cycle (EPC) of 3.1 ± 0.1 A at 260 °C. The isotropic nature of the plasma ALE process was demonstrated by transmission electron microscopy analysis of Al2O3-coated 3D trench structures after performing ALE cycles. A mechanism of fluorination by F radicals and ligand exchange reactions involving TMA is proposed for this plasma ALE process based on observations from infrared spectroscopy, which are supported by reactant synergy analysis. This work establishes the benefits that a plasma can deliver for isotropic ALE.

Energy consumption for seawater desalination by multistage electrodialysis (ED) is lowered last decade from 6.6 kWh/m3 to 3.6 kWh/m3. In multistage ED the driving force can be adapted to the conditions of that specific desalination stage. In this study however, we varied the membrane area, the residence time, and the membrane properties in the different stages to investigate the transport mechanisms of salt and osmotic water to improve the desalination performance of multistage ED even further. Residence time affects both salt fluxes and osmotic transport. We showed that a longer residence time is beneficial in the first stages, in combination with a shorter residence time in the later stages. The gradient in the later stages between the diluate and concentrate compartments is large, and a short residence time decreases the undesired osmotic flow, resulting in lower product (diluate) loss. Moreover, the use of membranes with lower water permeability in the last three stages results in state-of-the-art energy consumptions of 2.2 kWh/m3 for the desalination of 510 mM NaCl to 5.4 mM NaCl using multistage ED. This obtained diluate salinity more than meets the WHO standard for drinking water of 8.5 mM NaCl.

In order to mitigate the effects of salt water intrusion at sea locks, bubble screens are installed which act as a barrier between the dense sea water and the fresh water inland. In order to optimize the design of the bubble screen, in this study a state-of-the-art numerical model is developed based on the Euler-Lagrange CFD method which is expanded with a simple salt balance and concentration-density coupling. The model has been validated by means of experimental results on a laboratory-scale bubble screen. The liquid circulation and entrainment have been investigated for two types of bubble injection methods. It is found that the bubble screen is successful as a separator of salt and fresh water in an initial period of τ s e p = 30 seconds but acts more as a mixer at later times due to the swaying of the screen. The rate of the mixing increases with the air flow rate. Two mechanisms of salt intrusion are distinguished; a delayed density current along the bottom and entrained liquid being circulated through the domain back to the screen. An optimum in air flow rate is found at a Froude air number F r a i r = 0.91 . Bubble screen behaviour is also checked at the lock-scale using lock-scale geometry and simulations. The amount of salt transmitted agrees well with the large-scale field tests up until the reported Frair numbers but Frair > > 1 need to be tested to check for the optimum as found in the lab-scale tests.