Single Water Research Articles

Mathematical Approach for Directly Solving Air–Water Interfaces in Water Emptying Processes

Emptying processes are operations frequently required in hydraulic installations by water utilities. These processes can result in drops to sub-atmospheric pressure pulses, which may lead to pipeline collapse depending on soil characteristics and the stiffness of a pipe class. One-dimensional mathematical models and 3D computational fluid dynamics (CFD) simulations have been employed to analyse the behaviour of the air–water interface during these events. The numerical resolution of these models is challenging, as 1D models necessitate solving a system of algebraic differential equations. At the same time, 3D CFD simulations can take months to complete depending on the characteristics of the pipeline. This presents a mathematical approach for directly solving air–water interactions in emptying processes involving entrapped air, providing a predictive tool for water utilities. The proposed mathematical approach enables water utilities to predict emptying operations in water pipelines without needing 2D/3D CFD simulations or the resolution of a differential algebraic equations system (1D model). A practical application is demonstrated in a case study of a 350 m long pipe with an internal diameter of 350 mm, investigating the influence of air pocket size, friction factor, polytropic coefficient, pipe diameter, resistance coefficient, and pipe slope. The mathematical approach is validated using an experimental facility that is 7.36 m long, comparing it with 1D mathematical models and 3D CFD simulations. The results confirm that the derived mathematical expression effectively predicts emptying operations in single water installations.

Effects of varied inundation characteristics on early life stages of a salt marsh plant

Tidal inundation is a major stress in salt marshes that regulates the patterns of plant distribution and the associated functions provided by vegetation communities. Usually, frequency is used to represent inundation intensity and can be estimated using elevation. However, frequency is only a statistical indicator of tidal inundation conditions during a given period, which ignores many details of tidal inundation characteristics based on a single tidal event. On the scale of a single tidal event, duration and water depth are important characteristics for describing inundation conditions, which vary along the elevation gradient. The frequency of tidal events of a specific duration and water depth also varied. To unravel the impact of varied inundation characteristics on the key life stages of a foundation plant, we designed an experiment with varied inundation treatments of different frequencies, durations, and depths. Our results showed that the frequency, duration, and depth of inundation events significantly influenced seed emergence, seedling survival, and growth. Stress can be strengthened by a higher frequency with a longer duration and larger depth. Among these factors, frequency had a dominant impact, followed by duration and water depth. Specifically, there is a trade-off between frequency, duration, and depth, suggesting that an inundation event with shallower depth and/or shorter duration would reduce the stress from higher frequency. The findings fill a gap in the loss of details of varied inundation characteristics on plant establishment on a fine scale. Further, it will help explicit inundation stress more accurately and clearly and provide important implications for stress relief solutions in coastal ecological restoration.

Releasing Preferentially Sequestered Na+ from Its Confinement by Beauvericin: A Single Water Molecule is the Accomplice.

Beauvericin (Bv) is a natural ionophore capable of transporting ions across biological membranes. Mass spectrometry and infrared spectroscopy show that Bv specifically captures sodium ions with a unique 6-fold coordination in its cavity, which illustrates how ions are carried through the membrane. But with no reports on how ions are released from Bv at the interface, a complete picture of the ion transport process has yet to be established. In this study, conformational changes of Bv complexes with alkali metal ions upon hydration were investigated using infrared spectroscopy and computational calculations. The addition of a single water molecule to Na+Bv pries the ion away from the 6-fold cavity to the amide face of the ionophore, evidence of the first step of ion release. In contrast, there is little impact on the other M+Bv complexes, with the ion bound to the three carbonyl groups on the amide face. Analysis of the carbonyl C═O and water OH stretching modes reveals the competition between ion-ionophore, ion-water, and water-ionophore interactions and demonstrates how water actively participates in ion transport by initiating ion release from the ionophore.

Chitosan supported hetero-metallic bio-nanocomposites for paracetamol removal from homogeneous solutions and heterogeneous mixtures with focused antibacterial studies

Biopolymers infused with bimetallic nanoparticles exhibit a wide range of functionalities necessary for efficiently eliminating diverse water contaminants. However, the protracted production process requires further exploration. As such, present study seeks to optimize microwave-assisted technique for the facile synthesis of cross-linked chitosan (CTS) supported bimetallic-oxide nanoparticles, specifically zinc oxide (ZnO) and iron-oxide (Fe3O4), denoted as CTS-TTP/Zn-Fe. The primary objective is to investigate the efficacy of these beads in the removal of Paracetamol (PCM) from single and complex water matrices while also assessing their antibacterial properties. Characterization includes chemical composition, surface structures, thermal stability, and magnetic properties. The experimental results demonstrated that CTS-TPP/Zn-Fe beads achieved a remarkable PCM removal efficiency of ~99 % (qm = 4.98 mg g−1), with a Zn:Fe mole ratio of 1:1. The experimental data showed good applicability with Freundlich isotherm and chemisorption-supported rate models (R2 > 0.9). To evaluate the long-term viability and practicality of these beads, three crucial field applicability tests were conducted. These encompassed competition studies with other pharmaceuticals, desorption investigations for repeated use, and efficiency evaluations in an ionic solution. Collectively, this research provides a comprehensive understanding, spanning from material design to practical applications, with potential relevance for large-scale wastewater treatment when coupled with appropriate flux control measures.

Accurate nuclear quantum statistics on machine-learned classical effective potentials.

The contribution of nuclear quantum effects (NQEs) to the properties of various hydrogen-bound systems, including biomolecules, is increasingly recognized. Despite the development of many acceleration techniques, the computational overhead of incorporating NQEs in complex systems is sizable, particularly at low temperatures. In this work, we leverage deep learning and multiscale coarse-graining techniques to mitigate the computational burden of path integral molecular dynamics (PIMD). In particular, we employ a machine-learned potential to accurately represent corrections to classical potentials, thereby significantly reducing the computational cost of simulating NQEs. We validate our approach using four distinct systems: Morse potential, Zundel cation, single water molecule, and bulk water. Our framework allows us to accurately compute position-dependent static properties, as demonstrated by the excellent agreement obtained between the machine-learned potential and computationally intensive PIMD calculations, even in the presence of strong NQEs. This approach opens the way to the development of transferable machine-learned potentials capable of accurately reproducing NQEs in a wide range of molecular systems.

Molecular Simulation of CH4 Adsorption Characteristics under the Coupling of Different Temperature and Water Content

The adsorption characteristics of CH4 have an important influence on gas content prediction, gas extraction, and hazard prevention. Therefore, we explored the mechanism of CH4 adsorption under the action of water and temperature to grasp the influence of water and temperature on the adsorption characteristics of CH4. In this paper, a giant, regular-system Monte Carlo method is used to simulate the CH4 adsorption behavior at the molecular level under different temperatures, water contents, and the coupling of both. The results indicate that an empirical formula for the coupling effect of temperature and water content on CH4 adsorption was obtained. The impact of different effects on CH4 adsorption is as follows: coupling effect > single temperature effect > single water content effect. The optimal combination is at a temperature of 363 K and a water content of 8.31%. Compared with the CH4 adsorption capacity without water at room temperature, the CH4 adsorption capacity is reduced by 68.04% under the coupling effect of the optimal combination. Temperature has a negative effect on the adsorption of CH4, and temperature changes the adsorption capacity by changing the average molecular kinetic energy of CH4. The reason why the increase in H2O reduces the adsorption capacity of CH4 is that the interaction between H2O and the oxygen-containing functional groups of coal is stronger than that of CH4. As the water content increases, the adsorption heat decreases, thereby inhibiting the adsorption of CH4. In addition, H2O has a smaller molecular dynamics radius as compared to CH4; the larger the free volume and surface area in the pore structure, the more adsorption pores it occupies, resulting in a more significant reduction in the adsorption of CH4.

Using environmental DNA to assess the response of steelhead/Rainbow Trout and Coastrange Sculpin populations to postfire debris flows in coastal streams of Big Sur, California

AbstractObjectiveDebris flows are among the most extreme disturbances to streams and are predicted to become more frequent under climate change. We assessed the response of steelhead Oncorhynchus mykiss (anadromous Rainbow Trout)/Rainbow Trout (hereafter, collectively referred to as O. mykiss) and Coastrange Sculpin Cottus aleuticus populations to major postfire debris flows in two small coastal basins of California using noninvasive environmental DNA (eDNA) sampling.MethodsWe analyzed water samples from disturbed reaches for eDNA in the first two summers after debris flows. In Big Creek, all Coastrange Sculpin habitat was disturbed by debris flows, but a major tributary occupied by O. mykiss was not affected. In Mill Creek, all available habitat for both species was disturbed. We also sampled two unburned basins as undisturbed reference streams.ResultIn Big Creek, O. mykiss eDNA was detected in all water samples during both years, and concentrations in some samples approached the lowest concentrations in the reference streams. Coastrange Sculpin eDNA was detected only in a single water sample in the first year and was not detected in the second year. In Mill Creek, neither species was detected in the first year, but during the second year, O. mykiss eDNA was detected at very low concentrations in 40% of samples and Coastrange Sculpin eDNA was detected in a single sample.ConclusionOur results indicate that O. mykiss and Coastrange Sculpins either survived in or quickly reoccupied the disturbed reaches from within the basins. However, the detection rates for cases in which all habitat for a species in a basin was affected by debris flows indicate that abundances were very low, suggesting that persistence may be uncertain unless there is successful reproduction or immigration. Finally, eDNA appears to be effective for monitoring sensitive fish populations after a major disturbance; however, detection rates in individual samples may be low and require appropriate sampling designs to achieve the desired detection probability.

Estimating cation exchange capacity from hygroscopic water content change

AbstractThe existing models for estimating cation exchange capacity (CEC) from easy‐to‐measure hygroscopic water content (θh) were based on a single water activity (aw) value rather than on the processes that govern soil water vapor adsorption for a distinct aw range. Here, we present a new CEC estimation model based on θh data of 119 soils with different clay mineralogy (i.e., illitic [IL], montmorillonitic [ML], and kaolinitic [KA] samples) and organic carbon (OC) contents for the aw range from 0.23 to 0.57 (Δθ0.23–0.57) and validate its performance. Based on the hypothesis that multilayer adsorption exhibits a higher correlation with CEC than monolayer adsorption and capillary condensation, the aw range from 0.23 to 0.57 was chosen with CEC calculated as CEC = k × Δθ0.23–0.57. The performance of the new model is compared to the Arthur (2017) model and the Torrent (2015) model, which considers a single θh value. The average proportionality coefficient (k) varied with the dominant clay mineralogy of the investigated soils. For soils dominated by 2:1 clay minerals (i.e., IL and ML), the new model showed a good estimation accuracy (Nash‐Sutcliffe model efficiency [E] ≥ 0.85; root mean squared error [RMSE] ≤ 4.18 cmol(+) kg−1). The new model performed better for IL and ML samples than for KA samples, and yielded more accurate CEC estimations than the Arthur model and Torrent model for soils with 2:1 clay minerals. For soil with high OC content (>23.2 g kg−1), the new model slightly underestimated CEC (E = 0.66; RMSE = 5.87).

Теоретичне підґрунтя публічного управління у сфері водопостачання та водовідведення

The sphere of water supply and drainage is a critically important component of the socio-economic mechanism, which is characterized by numerous challenges that were actualized in wartime. Aim of this paper is to analyze the main theoretical approaches of public management in the field of water supply and drainage in order to identify the main principles and tools that affect the efficiency and sustainability of the field. The tools of strategic planning, operational management and emergency response are considered as key components of successful management in this area. Emphasis is placed on the special role of developing fair tariff policies and financial support for infrastructure investments. The importance of the legal framework that regulates the sphere, ensuring compliance with environmental standards and protection of consumer rights is highlighted. The environmental aspect of resource management in the field, which includes modern methods of wastewater treatment and minimizing the negative impact on natural water bodies, is considered. It was emphasized that state intervention is a key factor in ensuring equal access to clean water, which is a basic human right according to the United Nations. The problem of natural monopoly in the field is considered through the prism of high capital investments and low elasticity of demand, which limit market competition. Strategies to stimulate competition and improve service quality are explored, including regulating tariffs and encouraging innovation. The example of Scotland, where water supply management is centralized through the creation of a single national company Scottish Water, reveals the effectiveness of such an approach in improving infrastructure and ensuring high quality services with public participation. The importance of a multidisciplinary approach to management in the field is emphasized, with a special emphasis on the stability of the service in wartime. The research may be useful to researchers, state and local authorities, and international organizations. Further perspectives of research include the study of the peculiarities of the application of the theoretical base in the solution of scientific and practical problems in the field in Ukraine during the war.

Study of the Effect of Initial Plate Temperature in Jet Impingement Cooling Process

The microstructure characteristics and the properties of rolled steels are significantly affected by the heat transfer and boiling phenomena occurring during the jet impingement cooling on run‐out tables (ROT). In this study, experiments are conducted using a full industrial‐scale ROT facility with rectangular plates made of low‐carbon stainless steel (type 316L). The plate is heated up to a temperature ranging from to , then rapidly impinged using a single circular water jet, and the temperature drop is captured using an infrared thermal camera (FLIR A615 25°–50 Hz type). The dissipated heat flux, estimated experimentally using a 2D inverse heat conduction analysis, ranges from 6.1 to 3.4 MW m−2 across different zones along the plate surface. The impact of different initial plate temperature on the boiling behavior is studied by developing a 2D‐computational fluid dynamics (CFD) model, and the results are closely aligned with the experimental findings. The results reveal that when estimating the heat flux from CFD simulations, the best accuracy is obtained when considering fluid temperature at a point close to the plate surface (about 1 μm above the surface). Furthermore, the maximum extracted heat flux (MHF) is significantly influenced by the initial temperature of the plate. Increasing the initial plate temperature from 500 to 900 °C led to an increase of 82% in the MHF in stagnation zone, and 137% increase in the parallel‐flow region. The CFD model presented in this study and the full calculation of the boiling curves numerically will pave the road for investigating various practical parameters in jet impingement cooling.

Reconstruction of calcite (10.4) manifests itself in the tip-assisted diffusion of water

Calcite (calcium carbonate) is the most abundant carbonate in the Earth's crust. Due to its omnipresence it plays a prominent role in fields such as geochemistry, biomineralization and industrial processes. Moreover, the interaction of water with the most stable cleavage plane, calcite (10.4), has been studied intensively, elucidating atomic-scale details of water binding and structure formation on this surface. Interestingly, calcite (10.4) reconstructs under ultrahigh vacuum conditions, exhibiting a (2 × 1) surface unit cell. Although first indications of this reconstruction have been presented more than 20 years ago, a clear confirmation of the existence has been provided only very recently. Here, we study the tip-assisted diffusion of water molecules on calcite (10.4) under ultrahigh vacuum conditions. By recording images series using dynamic atomic force microscopy we follow the movement of water molecules on the surface kept at 140 K. Analyzing the change in consecutive images allows for elucidating details of the molecular movement on the surface. Most notably, the analysis reveals that water molecules occupy one type of adsorption position exclusively, while the other type is not adopted. Our analysis thus demonstrates that the (2 × 1) reconstruction manifests itself in the movement of single water molecules on this surface.

Impacts of Adding Porous Media and Phase Change Material on Performance of Solar Water Distiller System Under Iraq Climatic Condition: An Experimental Study

ABSTRACTThis current investigation involves an experimental inspection of adding porous medium and phase change material (PCM) above the absorber surface to enhance the performance of a single slope and single basin solar water distiller system. To demonstrate the effectiveness of adding porous medium and PCM, the performance of the modified system and conventional system is compared under similar operating conditions. The system that uses porous medium and PCM is called MSS‐FPP, whereas the conventional system is called MSS‐F. Rectangular fins are fixed above the absorber plate for both models. For MSS‐FPP model, three different types of porous medium (stones, nuts, and black glass balls) are used in addition to paraffin wax filled inside circular tubes as a PCM. The data are collected in November and December 2023 in Mosul City, Iraq. The experiments are carried out under different water depths. The findings confirm that the performance of MSS‐FPP model is better than MSS‐F model by 41.32% (for water depth 3 cm) and 30.61% (for water depth 5 cm). The results also indicated that the water productivity of MSS‐FPP model is higher than MSS‐F model by 41.67% (for water depth 3 cm) and 30.65% (for water depth 5 cm). For MSS‐FPP model, the maximum water productivity and efficiency are obtained when using black glass balls as compared to nuts and stones types, where the highest water temperature and water productivity values are found equal 54°C and 1.01 kg/m2 for water depth 3 cm. The enhancement in the performance of modified solar water distiller system (MSS‐FPP) shows that using a porous medium and PCM has considerable impacts on the evaporation rate, heat exchange, and rate of heat transfer.

Development of multi droplet-based electricity generator system for energy harvesting improvement from a single droplet

Abstract Due to high output performance, the droplet-based electricity generator (DEG) is garnering attention as a promising alternative power source for small electronic devices. Accordingly, to utilize the DEG as a power source, the efforts to boost the output have focused on methods to modify material modification and introduce surface structure. However, the behavior feature that the reconfigured droplet falls after the DEG operation leaves room for one more droplet energy harvesting from a single droplet. Here, a multi DEG system (MDEG) constructed with multiple DEG units is proposed to harvest more energy from a single droplet. The continuous movement of a water droplet is realized through the inclined stair structure of the MDEG, resulting in electrical energy generation from a single water droplet as many times as it falls. In particular, 2-step MDEG consisting of two DEG units can have 45% higher performance than a single DEG. Therefore, this study implies a contribution to the development of DEGs by considering the droplet dynamics, which has been overlooked in existing DEG studies.

One dimensional water chain as a zipper in a new polymorph of trans [Cu(vanilin)2(H2O)2].2(H2O) crystal–A case of water induced polymorphism

A new polymorph [Cu(II)(vanillin)2(H2O)2].2(H2O) has been synthesized and characterized by single crystal X-ray structural studies. Two other crystals having same formula and coordination unit but differing supramolecular arrangement due to slightly different role played by water molecules have already been reported in the literature [B. Kozlevˇcar et al. Z. Naturforsch., B: Chem. Sci. 2005, 60, 1273][Kozlevčar et al. Acta Chim. Slov. 2005, 52, 40–43]. The current compound is another polymorph in this system which has arisen again due to a different supramolecular arrangement which is water induced. Hirshfeld surface and energy framework analysis have been employed to compare these three polymorphs by assessing the nature of intermolecular interactions. In the current compound strong OH···O hydrogen bonding interactions between coordinated water molecules and –OH group attached to vanillin ligand leads to parallel alignment of successive coordination units leading to a supramolecular ribbon topology that runs along the crystallographic a-axis. A zigzag chain of single file water chain is positioned in between successive ribbons which acts as a zipper giving rise to a 2D supramolecular arrangement of the molecular complexes. In two other reported polymorphs instead of a single file water chain a cyclic water motif has been observed. The electronic structure of the complex explored using DFT methodology. This set of three polymorphs is an interesting example of water induced polymorphism.

Impact regimes of a single water droplet impacting a hot immiscible liquid surface

This paper studied the dynamic interaction process of a single water droplet impinging onto an immiscible target liquid, which was a follow-up study on a single water droplet impacting a miscible target liquid i.e. ethanol. Heptane was chosen as the impacted liquid, and the water droplet with a fixed diameter of 1.98 mm was used in the experiments. The droplet Weber number ranged from 30 to 762 by changing the height between the droplet and the impacted liquid surface. A high-speed digital camera at a speed of 2000 fps was used to capture the dynamic process. A comprehensive map We∼θ of typical impact phenomena including penetration, splashing, and bubble was plotted, considering both the cases of immiscible and miscible liquids. The critical Weber numbers of forming the typical phenomena were deduced. The critical Weber numbers for the transition from penetration to splashing and the transition from splashing to bubble could be approximately predicted by We=824.3−140.9e1.5θ and We=62.1+61.5θ, respectively. To clarify the formation mechanisms of typical phenomena, the energy conversions during the dynamic process were analyzed. The influences of pool temperature on energy conversion rates of the crater and jet formation could be predicted by χ=0.437θ+0.156 and φ=0.245θ+0.072, respectively.

Crop water stress index characterizes maize productivity under water and salt stress by using growth stage-specific non-water stress baselines

ContextThe use of non-destructive, continuous, and rapid canopy temperature (Tc) indices for crop stress diagnosis is of significant importance for improving crop water productivity (WP). However, the comprehensive applicability of the crop water stress index (CWSI), grounded in Tc, in diagnosing both single and combined water and salt stress, as well as characterizing physiological and growth traits, remains inadequately explored. ObjectiveWe aim to investigate the ability of CWSI to diagnose single and combined water and salt stress and to test whether a non-water stress baseline (NWSB) with or without growth stage and genotype differences influences CWSI to characterise maize leaf physiological and growth traits. MethodsHere, we measured the Tc using infrared radiation thermometers of two maize genotypes (XY335 and ZD958) under both single and combined water and salt stress over two growing seasons, compared the differences of NWSB in three growth stages, and established CWSI. Our analysis involved scrutinizing the differences in characterizing crop physiology and growth traits between CWSI calculated using NWSB with and without growth stage differentiations. ResultsOur findings indicated that Tc is modulated by an interplay of soil water content, VPD, and soil salinity. The NWSB exhibited variations with both growth stage (pslope < 0.001) and genotype (pslope or pintercept < 0.01). The CWSI can diagnose single and combined water and salt stress suffered by maize. Under no stress, and single and combined water and salt stress, CWSI was significantly correlated with stomatal conductance (R2 ≥ 0.31, p < 0.1) and net photosynthetic rate (R2 ≥ 0.38, p < 0.1), rather than with hydraulic traits. The mean CWSI across the entire growth period closely correlated with leaf area index (LAI), canopy photosynthetically active radiation interception, biomass, yield, and evapotranspiration across varying treatments (R2 ≥ 0.54, p < 0.1). Contrary to CWSI derived from NWSB without growth stage variations, utilizing CWSI with growth stage distinctions better characterized physiological traits, while the former was more suitable for delineating yield and WP. ImplicationsThis research underscores the efficacy of CWSI for stress diagnosis and the evaluation of gas exchange and productivity in maize under both single and combined soil water-salt stress. This investigation significantly propels forward the implementation of crop-centric irrigation strategies aimed at optimizing water utilization efficiency.

Observing one-divalent-metal-ion-dependent and histidine-promoted His-Me family I-PpoI nuclease catalysis in crystallo.

Metal-ion-dependent nucleases play crucial roles in cellular defense and biotechnological applications. Time-resolved crystallography has resolved catalytic details of metal-ion-dependent DNA hydrolysis and synthesis, uncovering the essential roles of multiple metal ions during catalysis. The histidine-metal (His-Me) superfamily nucleases are renowned for binding one divalent metal ion and requiring a conserved histidine to promote catalysis. Many His-Me family nucleases, including homing endonucleases and Cas9 nuclease, have been adapted for biotechnological and biomedical applications. However, it remains unclear how the single metal ion in His-Me nucleases, together with the histidine, promotes water deprotonation, nucleophilic attack, and phosphodiester bond breakage. By observing DNA hydrolysis in crystallo with His-Me I-PpoI nuclease as a model system, we proved that only one divalent metal ion is required during its catalysis. Moreover, we uncovered several possible deprotonation pathways for the nucleophilic water. Interestingly, binding of the single metal ion and water deprotonation are concerted during catalysis. Our results reveal catalytic details of His-Me nucleases, which is distinct from multi-metal-ion-dependent DNA polymerases and nucleases.

Observing one-divalent-metal-ion-dependent and histidine-promoted His-Me family I-PpoI nuclease catalysis in crystallo

Metal-ion-dependent nucleases play crucial roles in cellular defense and biotechnological applications. Time-resolved crystallography has resolved catalytic details of metal-ion-dependent DNA hydrolysis and synthesis, uncovering the essential roles of multiple metal ions during catalysis. The histidine-metal (His-Me) superfamily nucleases are renowned for binding one divalent metal ion and requiring a conserved histidine to promote catalysis. Many His-Me family nucleases, including homing endonucleases and Cas9 nuclease, have been adapted for biotechnological and biomedical applications. However, it remains unclear how the single metal ion in His-Me nucleases, together with the histidine, promotes water deprotonation, nucleophilic attack, and phosphodiester bond breakage. By observing DNA hydrolysis in crystallo with His-Me I-PpoI nuclease as a model system, we proved that only one divalent metal ion is required during its catalysis. Moreover, we uncovered several possible deprotonation pathways for the nucleophilic water. Interestingly, binding of the single metal ion and water deprotonation are concerted during catalysis. Our results reveal catalytic details of His-Me nucleases, which is distinct from multi-metal-ion-dependent DNA polymerases and nucleases.

Flow-Engineered 3-D Printed Electrodes for Alkaline Water Electrolysis

Initially, industrial alkaline electrolyzers had 2-D bipolar plates as electrodes in a configuration in which there is an important physical gap between the electrodes (e.g., 2 mm). This setup presented a high ohmic resistance and is commonly limited to a current density in the order of 0.5 A·cm-2 due to gas screening, i.e., the produced gases form a non-conductive layer over the entire electrode surface, limiting current density. The more advanced designs of today include the use of a zero-gap cell where the interelectrode distance is limited to the thickness of the separator (hundreds of micrometers for diaphragms and tens of micrometers for membranes). Commonly, 2-D electrodes such as perforated plates or an expanded metal mesh are used. As the electrode is pressed against the separator, the gases are forced to be evacuated at the backside of the electrode, avoiding the screening effect. As a consequence, much higher current densities can be achieved. More recently, there has been an increasing interest in the integration of 3-D electrodes in the zero-gap configuration, as they present higher surface areas than their counterpart 2-D electrodes. Nevertheless, bubbles can get trapped inside the intricate 3-D electrode structures. Several strategies are used to mitigate bubble entrapment, including the use of a forced electrolyte flow.The current study aims to investigate the possible electrochemical performance improvement of a single alkaline water electrolysis cell by using 3-D printed electrodes with graded structures, engineered to enhance bubble removal under the effect of a forced electrolyte flow. As the majority of the current is concentrated near the separator, the tailored 3-D printed electrodes present low strut distances and, consequently, a high surface area in this region. Further away from the separator, the distance between the struts gradually increases, decreasing flow-related energy dissipation and avoiding bubble entrapment. This tailored laterally graded structure promotes a difference in pressure along the direction perpendicular to the separator, allowing to extract bubbles from the region near the separator and to evacuate them towards the region with higher strut distances more efficiently. Furthermore, our flow cell was designed to promote a homogeneous upstream flow at the entrance of the electrode. Based on previous findings [1], a Schwarz triply periodic minimum surface was chosen as electrode geometry, as this geometry can channel the flow and reduce bubble-induced ohmic resistance. This geometry is defined by the following mathematical equation: t = sin(2·π·z/L)·sin(2·π·x/L) - 0.4·sin(2.4·π·y/L)·cos(2·π·z/L)·cos(2·π·x/L)with L the periodicity (e.g., an L = 1 mm means that the structure repeats itself in the space at each 1 mm), and t relates to void fraction.Different electrodes with a Schwarz geometry were analyzed in a combined experimental and simulation approach. Electrodes were 3-D printed using selective laser melting, and a strut in the order of 500 μm was achieved. Explicit computational fluid dynamics simulations were performed to estimate bubble residence time and path. Experimental analyses were conducted in a flow-through setup operating under industrial standard conditions of 30 wt% KOH electrolyte at 70°C to elucidate the performance disparities between these structures. Our findings indicate that such tailored 3-D printed electrodes are capable of significantly outperforming previously reported performances in the literature using more stochastic 3-D electrodes like foams. Furthermore, results show that the printed structures are more sensitive to electrolyte flow, presenting an important overvoltage reduction with increase in electrolyte flow rate. We also identified the most critical structural parameters controlling bubble evacuation, thereby significantly reducing the cell's ohmic resistance. Ultimately, this study also emphasizes the critical role of efficient gas evacuation for high-rate alkaline electrolysers using a zero-gap design.[1] Rocha F, Delmelle R, Georgiadis C, Proost J. Electrochemical Performance Enhancement of 3D Printed Electrodes Tailored for Enhanced Gas Evacuation during Alkaline Water Electrolysis. Advanced Energy Materials 2022;13:2203087.

Short high-accuracy tritium data time series for assessing groundwater mean transit times in the vadose and saturated zones of the Luxembourg Sandstone aquifer

Abstract. Among the manifold of environmental tracers at hand, tritium is the only one that can give information on groundwater age within the timescale of 100 years for the entire flow system, i.e., unsaturated and saturated. However, while in the Southern Hemisphere, a single water sample is sufficient for tritium-based young groundwater dating, several tritium measurements spanning multiple years are still needed in the Northern Hemisphere to disentangle the natural cosmogenic tritium input from that caused by the atmospheric thermonuclear weapons tests mainly carried out in the early 1960s. Although it is advised to focus tritium dating on sites where long chronicles of tritium data are available, in this study we tested the potential for short high-accuracy tritium data series (∼4 years) to date groundwater from 35 springs draining the Luxembourg Sandstone aquifer (central western Europe). We determined groundwater mean transit times using the lumped-parameter model approach in a Monte Carlo uncertainty estimation framework to provide uncertainty ranges inherent to the low number of tritium data at hand and their related analytical errors. Our results show that unambiguous groundwater mean transit time assessments cannot be determined solely based on such recent short tritium time series, given that several ranges of mean transit times appeared theoretically possible. Nonetheless we succeeded in discriminating groundwater mean transit times in the vadose and saturated zones of the aquifer through a stepwise decision process guided with several supplementary data. The mean transit time required for water to cross the vadose zone was estimated to be between 0.5±0.5 and 8.1±1.2 years depending on the spring, while for water to flow through the saturated zone, it varied from 5.7±2.4 to 18.9±4.6 years (median ± half of the 5–95 percentile range). Our findings are consistent with both the tritium measurements of individual springs and the hydrogeological context of the study area. We specifically corroborated the dating results using the known hydrogeological properties of the Luxembourg Sandstone aquifer, the hydrochemistry of the studied springs, and their discharge dynamics. When translated into water velocities (which average ∼12 and ∼170 m yr−1 for the vadose and the saturated zones, respectively), the tritium dating results mirrored the horizontal–vertical anisotropy of the aquifer's hydraulic properties caused by the bedded character of the Luxembourg Sandstone. In addition to improving our understanding of water transit times in the Luxembourg Sandstone aquifer, this study demonstrates how it is currently possible to use short tritium time series to date young groundwater bodies at new sites in central Europe.