Liquid Transport Research Articles

(Invited) Leveraging Imaging Techniques to Accelerate the Advancement of Polymer Electrolyte Membrane Water Electrolyzers

Polymer electrolyte membrane water electrolyzers (PEMWEs) are critically needed to meaningfully incorporate clean renewable energy into our energy, transportation, and manufacturing sectors, for without this energy conversion mechanism, the intermittency of renewable energy will always pose a prohibitive cost barrier to practical use. However, in addition to overcoming the intermittency issue of renewable energy, energy storage also has the power to transform current energy infrastructure, particularly when plagued by older systems that lack modularity and flexibility. For example, electricity grids are often constrained to move electricity in and out of a jurisdiction with careful predictions based on past use and future needs. This comes at a cost when electricity must be sold at a loss to prevent a catastrophic surplus of electricity in the grid. While the potential for PEMWEs is tremendous, we must reduce their capital and operating costs in order to reach widespread adoption. In recent years, important work in the field has contributed to advancing PEMWEs in a variety of areas from new materials to flow field design; however, experimental validation, particularly spatially resolved, is necessary to take a fully informed approach to tailoring these materials and architectures.In this talk, I will discuss how we use X-ray and neutron imaging, both ex situ and operando, to provide high spatial and temporal resolution experimental performance and materials characterization for PEMWEs to inform our design process for new materials fabrication, new architectures, and operating parameters. We obtained nano-scale, 3D imaging of PEMWE catalyst layers to inform the stochastic simulations used to uncover the influence of pore size and ionomer distributions on electrical and ionic conductivities. We also used operando X-ray imaging to elucidate the influence of catalyst layer and porous transport layer interfacial conditions on liquid and gas transport behaviour. By applying neutron imaging, we elucidated the impact of temperature on the distribution heterogeneity of liquid water reactant at the catalyst layer. I will also discuss how we are using soft X-rays to perform synchrotron-based scanning transmission X-ray microscopy with absorption spectroscopy to uncover heterogeneity across performance and material characteristics for the PEMWE. Through these highly resolved techniques (in terms of time and space), we aim to advance our predictive models for designing next generation materials, interfaces, and flow configurations for high performance water electrolyzers.

Next Generation Fluorine-Free Proton Exchange Membranes for Electrochemical Energy Applications

Most commercially available proton exchange membrane (PEM)-based fuel cell and electrolyser systems currently employ perfluorinated sulfonic acid (PFSA)-based PEMs, e.g., Nafion. The use of these fluorinated polymers presents serious health and environmental concerns as their production, degradation, and disposal results in the release of hazardous perfluorinted compounds that have been shown to accumulate in the environment and are toxic to living organisms.[1] Developing non-toxic, safe-by-design hydrocarbon PEMs is therefore crucial to ensure that renewable technologies that rely on proton exchange membranes remain an environmentally friendly solution. Additional shortcomings of PFSA-based PEMs include their expensive synthetic cost, inherently high hydrogen crossover, and limited operating temperature range due to poor thermo-mechanical properties above 90 °C. Hydrocarbon (HC)-based membranes offer advantages over their perfluorinated counterparts in these specific areas, however, the main drawback of HC-PEMs is that they require a much greater density of sulfonic acid groups to achieve similar proton conductivities as PFSA-based polymers.[2] This leads to greater water uptake and excessive swelling which ultimately leads to reduced mechanical stability of HC membranes.More recently there has been an increasing number of reports exploring the use of block copolymer strategies to limit the water uptake and swelling properties of hydrocarbon PEMs while maintaining good ionic conductivity.[3] As the ion, liquid, and gas transport properties of the membrane are largely attributed to the hydrophilic blocks (i.e., with sulfonic acid groups) and the mechanical, chemical, and thermal stability of the resulting membrane is determined by the hydrophobic blocks (i.e., no sulfonic acid groups), it is postulated that the resulting membrane properties can be tuned by varying the fraction of hydrophilic/hydrophobic blocks.The overall goal of this project is to synthesise hydrocarbon block copolymer PEMs with reduced gas crossover and enhanced the mechanical properties while maintaining sufficiently high ionic conductivity, ultimately leading to higher performance and greater durability inelectrochemical energy conversion and storage systems, e.g., fuel cells and electrolysers. In this project we have compared the ex-situ properties of novel hydrocarbon block copolymers with PFSA-based Nafion membranes, e.g., water uptake and swelling, conductivity measurements, oxidative stability via Fenton's test, etc., as well as in-situ performance tests in single cell fuel cell and electroylzers.[1]Feng, M.; Wang, Z. et al. Sci. Rep. 2015, 5, 9859.[2]Holdcroft, S. Chem. Mater. 2014, 26, 381.[3]Guiver, M. et al. Chem. Rev. 2017, 117, 4759.

Operando Identification of Temperature-Dependent Pore-Scale Gas Saturations in PEM Water Electrolyzers

Polymer electrolyte membrane (PEM) water electrolysis is a promising solution for the chemical storage of intermittent renewable energy in the form of clean hydrogen (1). For the widespread adoption of this technology, the efficiency of PEM electrolyzers must be improved through informed material design and tailored operating conditions to compete with incumbent carbon-emitting technologies (2). A main source of inefficiency is related to mass transport losses, where oxygen gas, a by-product of the anode reaction, accumulates in the anode porous transport layer (PTL) and hinders reactant liquid water delivery to reaction sites (3). Although extensive studies have explored this two-phase flow phenomenon, the consideration of operating temperature on gas accumulation in the PTL adds further complexity. A duality in temperature effects has been reported in the literature where increasing the operating temperature may encourage gas coverage which obstructs liquid water transport, but it may also enhance liquid water delivery due to favorable fluid property changes in viscosity and surface tension (4). Efforts have been made previously to reconcile these competing observations using 2D visualization methods (5), however a closer investigation using 3D visualization techniques will provide valuable pore-scale insights in the comprehensive understanding of the impact of operating temperature on gas transport in the PTL, and subsequently mass transport losses in the PEM electrolyzer.In this work, we employed operando X-ray computed tomography (CT) to visualize three-dimensional (3D) pore-scale gas saturations in the PTL at various industrially relevant operating conditions. Specifically, a custom in-house electrolyzer was imaged with synchrotron CT at five different temperatures (40°C, 50°C, 60°C, 70°C, 80°C) and current densities ranging from 0.5 A/cm² to 4.0 A/cm² with 0.5 A/cm² incremental steps. Electrochemical impedance spectroscopy and Tafel measurements were also acquired to characterize the relationship between gas distributions and corresponding mass transport overpotentials. Considering X-ray transparency, a model PTL made of carbon fibers was used to achieve sufficient contrast to quantify water and gas in the obtained images. Using precise volume registration and subtraction methods, pore-scale gas distributions in the PTL were quantified to reveal changes in bubble accumulation and coverage area at different operating temperatures and over operation time. The novel insights from this work will aid in our understanding of the complex relationship between operating temperature and multiphase flow phenomena in the PTL, which is vital for tailoring operating conditions of PEM electrolyzers to curtail the costs of green hydrogen production.

Open-Source and Multi-Fluid Numerical Modeling of Proton Exchange Membrane Fuel Cell

Numerical modeling is a powerful tool for the virtual design and optimization of the next-generation proton exchange membrane fuel cells (PEMFC). While almost all of them are not open-source, which causes inconvenience and limits. In this paper, a three-dimensional, multi-component, multi-fluid, open-source model developed in the commercial CFD package (CFX) is used to investigate the species’ transport in a proton exchange membrane fuel cell. The model includes a complete fuel cell with both the seven-layer membrane-electrode-assembly and the gas flow channels and bipolar plates, which account for all major transport phenomena. In the porous medium, liquid water transport is dominant by the capillary pressure gradient; momentum loss describes the Darcy equation; and mass transfer between phases by a nonequilibrium phase change model. Multi-component gas phases are governed by convection and diffusion. Moreover, diffusion is the predominant transport mechanism for dissolved water between the membrane and catalyst layers. Consequently, the code of this model is shared on GitHub to provide a starting point and inspire further development and optimization.

(Invited) Utilization of Bio-CO2 and Bio-Methane for Fuel Production: Integration Solid Oxide Electrolyzer, Low Energy Plasma Reformer with Fischer-Tropsch Synthesis

Transition to renewable energy is essential to achieve climate protection objectives. Besides storing electricity for later use, fuel production using renewable energy is an essential part of reducing fossil dependance. Hydrogen production is receiving the greatest attention as a carbon free energy carrier with the potential to fuel future fleets of hydrogen fuel cell vehicles, to store grid electricity to accommodate asynchronous generation and load, and to a lesser extent to displace heating fuels. However, the highest value application in current markets is the production of liquid transportation fuels such as sustainable aviation fuels (SAF) and low (fossil) carbon diesel fuel. However, liquid hydrocarbon fuels only achieve the decarbonization goals if they displace fossil fuels and are produced from sustainable, ideally biogenic carbon resources.Solid oxide electrolysis cell (SOEC) stack developed by OxEon team for MOXIE, the Mars OXygen ISRU Experiment has demonstrated the use of CO2 as an electrolysis feedstock aboard the Perseverance rover which as of this writing has operated thirteen times on Mars, splitting the Mars atmosphere CO2 to carbon monoxide and oxygen, as the first ever demonstration of In Situ Resource Utilization (ISRU) on another planet. The technology is applicable to efficient resource utilization on this world and OxEon is actively developing power to fuels technology to maximize the conversion of biogenic carbon to high value, energy dense, liquid transportation fuels that are needed by an existing vehicle fleet that will be on the road and in the air decades to come.OxEon’s technologies are being applied to bridge the electrical and materials energy sectors. In this project OxEon processes the bio-CO2 through an SOEC and the bio-CH4 through a low energy plasma reformer. The combined synthesis gas is supplied to a Fischer-Tropsch reactor. The combination offers several advantages: the yield of biofuel nearly doubles by use of the bio-CO2 compared to the bio-methane alone, cooling the FT reactor generates all the steam needed in the SOEC system reducing the effective operating voltage (accounting for raising steam) from > 1.5 V/cell to < 1.3 V/cell, oxygen by-product from the SOEC is used in the autothermal reformer, as is some of the FT produced water. The product fuel is all bio-carbon, but it also embodies renewable electric energy in a high-value, storable and transportable liquid hydrocarbon that will be usable in the current air and ground fleets.

Microfluidics-Based Blood Typing Devices: An In-Depth Overview.

Identification of correct blood types holds paramount importance in understanding the pathophysiological parameters of patients, therapeutic interventions, and blood transfusion. Considering the wide applications of blood typing, the requirement of centralized laboratory facilities is not well suited on many occasions. In this context, there has been a significant development of such blood typing devices on different microfluidic platforms. The advantages of these microfluidic devices offer easy, rapid test protocols, which could potentially be adapted in resource-limited settings and thereby can truly lead to the decentralization of testing facilities. The advantages of pump-free liquid transport (i.e., low power consumption) and biodegradability of paper substrates (e.g., reduction in medical wastes) make it a more preferred platform in comparison to other microfluidic devices. However, these devices are often coupled with some inherent challenges, which limit their potential to be used on a mass commercial scale. In this context, our Review offers a succinct summary of the recent development, especially to understand the importance of underlying facets for long-term sustainability. Our Review also delineates the role of integration with digital technologies to minimize errors in interpreting the readouts.

Methane fermentation to methanol (biological gas‐to‐liquid process) usingMethylotuvimicrobium buryatense5GB1C

AbstractMethanol is a potential alternate liquid transportation fuel for blending with gasoline. Biochemical conversion of methane to methanol is a green process for methanol production. This paper reports biochemical methanol production using type I γ‐proteobacteriaMethylotuvimicrobium buryatense, which has particular importance from the viewpoint of scalable biological gas to liquid processes for industrial application. A statistical design of experiments (at the serum bottle level) was used to optimize fermentation parameters. Enhancement in methanol accumulation was attempted using methanol dehydrogenase inhibitors. This was followed by a validation experiment run in a bioreactor at optimum conditions. At optimum conditions (pH = 7, phosphate concentration = 140 mM, temperature = 25°C) and optical density (600 nm) of 0.3, a methanol titer of 8.54 mM was achieved in 24 h (methane conversion = 20.8%). The addition of a methanol dehydrogenase inhibitor (0.5 mM Ethylenediaminetetraacetic acid) enhanced the methanol concentration to 10.37 mM. Experiments in a 3.7 L bioreactor using 1.68 bar headspace pressure and optical density (600 nm) of 0.1 yielded 23.7 mM methanol in 24 h (methane conversion = 47.8%). The methanol titers obtained usingM. buryatense5GB1C in 24 h fermentation are significantly higher than several previously reported methanotrophs. These results demonstrate the potential ofM. buryatense5GB1C for the biochemical synthesis of methanol.

Hall anomalies of the doped Mott insulator

The Hall coefficient of the strongly interacting square lattice Hubbard model is calculated for temperatures between the antiferromagnetic interaction and the Mott gap scales. The leading order thermodynamic formula is evaluated for all doping concentrations. Second-order corrections of the thermodynamic formula are calculated and found to be negligible. The Hall coefficient diverges toward the Mott insulator. Below 45% doping the Hall sign is reversed relative to band structure-based Boltzmann’s equation. These results elucidate the effects of the Mott insulator on the charge carriers and their non-Fermi liquid transport.

Quantification of powder phase transient accumulation behaviour in gas–powder–liquid flow through a packed bed with the cohesive zone of a blast furnace

Lower regions of industrial reactors, such as blast furnace, are complex multiphase system in which, gas, powder, and liquid flow co-, counter-, and cross-currently. Laboratory-scale experimental models are yet to consider this multiphase transport, even under chemically inert, cold conditions. In the iron-making blast furnace, the presence of fused metal and non-wetting nature of liquid iron towards coke bed challenges the simultaneous transport of gas, powder and liquid. Adverse conditions results in powder accumulation and liquid hold-up which decrease the coke bed’s permeability, and consequently, the furnace’s productivity. An experimental investigation on the aforementioned system is conducted for various flow conditions. Greater gas pressure drop, increase in raceway size, localized flooding of liquid, and distinct powder accumulation characteristics are observed as phases are introduced into the bed. Exploratory data analysis yields steady-state and transient correlations for powder hold-ups. The validity and functionality of these correlations are demonstrated.

Anti-gravity drop motion and co-solute transport of hexamethyldisilane - tetrahydrofuran binary mixture on glass surface

Surface wettability modulation have garnered significant research interest due to diverse applications across fields ranging from microfluidics to biomedical devices. Surface wettability determined by factors like chemical composition and surface topography, influences a surface’s ability to attract or repel liquids. An essential phenomenon within surface wettability is the ability of droplets to move against gravity, known as uphill motion. This motion is particularly important in microfluidic devices requiring precise droplet control. Creating a surface with tuneable wettability supporting uphill motion is critical for optimizing device design. In this work, we proposed a simple and effective way to achieve tetrahydrofuran droplet self-running horizontally and sliding uphill without any other external force. We have used a complete wetting glass surface onto which binary non-aqueous THF drop containing hexamethyldisilane (HMDS) demonstrated uphill drop motion with tilted angle of ∼ 10°. This binary drop mixture of volatile THF and HMDS with various concentrations demonstrated self-propulsion on both the horizontal and tilted surfaces. We also examined the transport of an additional solute utilizing the binary mixture of HMDS-THF. The droplet motion against the gravity was achieved by gradient in solute concentration-based Marangoni stress. The potential applications of droplet motion against gravity on tilted surfaces span various domains. It can be harnessed for self-cleaning surfaces, microfluidic designs, and controlled liquid transport systems.

Daughter oil droplet entrainment by oil-coated bubble bursting

Compound bubbles with a liquid coating in another continuous immiscible bulk phase are ubiquitous in a wide range of natural and industrial processes. Their formation, rise and ultimate bursting at the air–liquid interface play crucial roles in the transport and fate of natural organic matter and contaminants. However, the dynamics of compound bubbles has not received considerable attention until recently. Here, inspired by our previous work (Yang et al., Nat. Phys., vol. 19, 2023, pp. 884–890), we investigate the entrainment of daughter oil droplets in bulk water produced by a bursting oil-coated bubble. We document that the size of the entrained daughter oil droplet is affected by the oil coating fraction and the bulk liquid properties. We rationalize this observation by balancing the viscous force exerted by the extensional flow produced by bubble bursting with the capillary force resisting the deformation of the oil coating, and considering the subsequent end-pinching process which finally entrains the daughter oil droplets. We propose a scaling analysis for the daughter oil droplet size that well captures the experimental results for a wide range of oil coating fractions and Ohnesorge numbers of the bulk liquid. In addition, we discuss the non-monotonic variation of daughter droplet size with the Ohnesorge number, and show the eventual absence of daughter droplets because of the strong viscous effect in the high-Ohnesorge-number regime. Our findings may advance the fundamental understanding of compound bubble bursting and provide guidance and modelling constraints for bubble-mediated contaminant transport in liquids.

A paper-based microfluidic aluminum–Air battery with intrinsic migration of electrolyte

The aluminum-air battery is one of the most promising candidates for next-generation miniaturized energy storage devices due to its high theoretical energy and capacity density. However, anodic self-corrosion and bulky liquid transportation systems have severely limited its practical energy density, hindering its usage for miniaturized applications. Here, we developed a microfluidic aluminum-air battery with zinc oxide (ZnO) as the inhibitor to overcome the abovementioned hurdles. The ZnO embedded alkaline electrolyte and microfluidic structure gain a maximum power density of 18.94 mW/cm2, an open circuit voltage of over 1.6 V, and a specific capacity of 2335.25 mAh/g (at 20 mA/cm2), while maintaining a low self-corrosion rate of 0.3043 mL/(cm2 min). In addition, the microfluidic design and ZnO embedment support the batteries to continuously work at 20 mA/cm2 for 120 min, 6.0 times the non-microfluidic ones and 1.18 times the microfluidic ones without ZnO. The performance of the battery can be improved by series connection or enlargement of the geometric active area. The design and method analogy proposed in this work can be readily migrated to the construction of miniaturized aluminum-air cell as reliable power sources.

Review of directional liquid transport on surfaces with different structures

Directional liquid transport has many cutting-edge applications, such as fog collection, agricultural drip irrigation, biochemical microreactors, water harvesting, non-powered micro-drug delivery, thin-film lubrication etc. There are many surfaces or linear structures in the natural systems can occur directional transport of water. In this paper, two bionic structures inspired by natural structures and two artificially fabricated surface structures are presented and their flow laws and mechanical mechanisms are described. Thereby, it is analysed that surface-driven external forces, such as the gradient of surface energy and the gradient of Laplace pressure, and surface pinning in other directions are the key points to drive the directional flow of liquids.

Influence of deposited liquid structures on the separation efficiency of thin oleophilic fiber layers of mist filters

The presence of oil mists constitutes a significant hazard to both, human health and the environment. In industrial applications, the effective separation of these mists typically relies on the utilization of multi-layer nonwoven coalescence filters. The underlying mechanisms governing droplet deposition, liquid transport within the filter matrix, and the evolution of the overall differential pressure have been extensively documented in the existing literature. However, limited and contradictory information is currently available regarding the impact of deposited liquid structures under varying saturation levels on the separation efficiency of coalescence filters.In this study, the influence of an increased liquid saturation at different filtration velocities on the fractional and total separation efficiency of thin porous non-woven fiber layers comparable to the first fiber layers of the first filter layer of commercially utilized coalescence filters are evaluated. As the oil load increases to a saturation of S≤ 0.4, the total separation efficiency (number-based) decreases, for all investigated filtration velocities. In addition, a shift of the most penetrating particle size (MPPS) to smaller droplet sizes and a decrease of the MPPS efficiency is observed. This decrease is attributed to a higher interstitial velocity resulting from the accumulation of liquid within the filter matrix, leading to a lower fractional separation efficiency in the diffusion regime. However, at saturation levels S≥ 0.6, the separation efficiency (meaning both, fractional and total separation efficiency) begins to increase due to the formation of partial oil films, leading to a blockage of void space. These films significantly enhance inertial separation. At the highest investigated saturations (S=0.8), the highest separation efficiencies due to a nearly complete coverage of the filter layers by an oil film are observed. The film formation is confirmed through backlit images of the oil-loaded filter material. Furthermore, an increase of the MPPS efficiency for a saturation of S=0.8 with increasing filtration velocity due to increased diffusional separation is recorded, which cannot yet conclusively answered by the authors. Additionally, the differential pressure across the fiber sheets is presented, revealing a more pronounced influence of the oil film on the differential pressure at increasing filtration velocities.

Investigations of Water Transport in Shale Reservoir with Dual-Wettability by Using Monte Carlo Method.

How liquids transport in the shale system has been the focus because of fracturing fluid loss. In this study, a single-nanopore model is established for liquid transport in shale while considering the slip effect and effective viscosity of confined fluids. Then, the fractal Monte Carlo (FMC) model is proposed to upscale the single-pore model into shale porous media. The effects of different transport mechanisms, shale wettability, and pore characteristic parameters on confined liquid flow in shale rock are investigated. Results show that FMC permeabilities are 2-3 orders of magnitude larger than intrinsic and slip-corrected permeabilities in organic matter. However, the slip effect and effective viscosity have little influence on water flow in inorganic matter. With the contact angle of organic pore (θom) increasing and contact angle of inorganic pore (θin) decreasing, the effective permeability of the whole shale matrix grows in number. The enhancement factor in the situation of θom = 170° and θin = 20° is 4 orders of magnitude larger than the case of θom = 130° and θin = 40°, although the close effective macroscopic contact angle (θeff = 80°) occurs in these two cases, which indicates that shale microscopic wettability has a significant impact on the confined liquid transport. Moreover, with the increase of porosity and maximum pore diameters, shale permeability increases rapidly, but the enhancement factor has the opposite trend. Compared with the tiny impact of the variance of minimum inorganic pore diameters, minimum organic pore diameters have more significant impacts on liquid flow in shale systems, and the enhancement factor also rapidly increases up to 30 times for the case of 0.5 nm because of the strong slip effect.

Heterogeneous-elasticity theory of instantaneous normal modes in liquids

Since decades, the concept of vibrational density of states in glasses has been mirrored in liquids by the instantaneous-normal-mode spectrum. In glasses instantaneous configurations are believed to be situated close to minima of the potential-energy hypersurface and all eigenvalues of the associated Hessian matrix are positive. In liquids this is no longer true, and modes corresponding to both positive and negative eigenvalues exist. The instantaneous-normal-mode spectrum has been numerically investigated in the past, and it has been demonstrated to bring important information on the liquid dynamics and transport properties. A systematic deeper theoretical understanding is now needed. Heterogeneous-elasticity theory has proven to be particularly successful in explaining many details of the low-frequency excitations in glasses, ranging from the thoroughly studied boson peak, to other anomalies related to the crossover between wave-like and random-matrix-like excitations. Here we present an extension of heterogeneous-elasticity theory to the liquid state, and show that the outcome of the theory agrees well to the results of extensive molecular-dynamics simulations of a model liquid at different temperatures. We find that the spectrum of eigenvalues ρ(λ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\rho (\\lambda )$$\\end{document} has a sharp maximum close to (but not at) λ=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda =0$$\\end{document}, and decreases monotonically with |λ|\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$|\\lambda |$$\\end{document} on both its stable and unstable side. We show that the spectral shape strongly depends on temperature, being symmetric at high temperatures and becoming rather asymmetric at low temperatures, close to the dynamical critical temperature. Most importantly, we demonstrate that the theory naturally reproduces a surprising phenomenon, a zero-energy spectral singularity with a cusp-like character developing in the vibrational spectra upon cooling. This feature, known from a few previous numerical studies, has been generally overlooked in the past due to a misleading representation of the data. We provide a thorough analysis of this issue, based on both very accurate predictions of our theory, and computational studies of model liquid systems with extended size.

Classification and simplified design rules concerning the moisture performance of capillary active insulation materials

Conventional interior insulation systems protect the wall from condensation in winter by the help of vapor barriers or vapor retarding insulation materials. However, these solutions also reduce the drying potential of the walls towards the inside. This can be a disadvantage if wetting from the outside due to rain or other influences takes place and the drying potential to the outside is not sufficient. In such cases, so called capillary active materials can be an alternative, because they provide additional drying potential to the inside in summer thanks to a rather low vapor diffusion resistance. In winter they work without vapor retarders because they can store and wick water away from the condensation plane back towards the interior by capillary action. In practice, there are currently many different materials under the label "capillary active" with a correspondingly wide range in terms of moisture storage, liquid transport and vapor diffusion resistance and it is difficult to decide, whether material is suitable for an application or not. There is still missing a common definition of the performance of such materials. While for most other materials already simplified design and application rules for the application as interior insulation are available, capillary active interior insulation materials still require an individual design, normally by the help of hygrothermal simulation. In order to simplify also their practice application, a classification of the moisture performance of capillary active interior insulation, considering the influencing parameters of relevance on the moisture level at the critical interface between wall and interior insulation was developed. On this basis, also a simplified verification process as well as design rules for the main practical application fields become possible, which allows designers to choose an appropriate system for the specific situation.

Effects of Hydrophobic Treatment on Performance and Water Management of Titanium Felt GDLs in PEMFCs

This work follows our recent study of titanium fibre felts applied as a cathode gas diffusion layer (GDL) in a proton exchange membrane fuel cell. Here, an in-house hydrophobic treatment of PTFE (0−20 wt%) is applied to these felts and the effects on cell performance, gas diffusion, and water transport are studied with comparison to conventional commercial carbon GDLs. The titanium fibre felt with a low PTFE loading of 5 wt% consistently outperformed the untreated substrate and all carbon GDLs tested across all six sets of operating conditions. This loading is shown to improve flooding resistance due to the increased hydrophobicity while not majorly reducing porosity, gas permeability, or ohmic resistance. The low loading also maintains a fraction of hydrophilic pathways within the substrate which has been shown to contribute to improved liquid water transport under wetter operating conditions. An increase in PTFE loading to 10 wt% and higher results in reduced porosity and permeability, and saturation of the internal structure of the substrate with PTFE resulting in poorer performance. Finally, the full range of treated and untreated felts are shown to exhibit a good balance between water retention, water rejection, and hydrophobicity based on oxygen transport resistance.

АНАЛИЗ ПРОЧНОСТИ КОНТЕЙНЕРОВ-ЦИСТЕРН ПРИ УДАРНЫХ ВОЗДЕЙСТВИЯХ НА ОСНОВЕ КОМПЬЮТЕРНОГО МОДЕЛИРОВАНИЯ

The paper presents the strength analysis results for a tank-container designed for liquid cargo transportation by rail, automobile and water transport based on computer modeling. The most severe in terms of loads and extreme operation mode of tank-containers is chosen as the conditions for the computer experiment, implying an impact in the longitudinal direction when railway cars collide during their dismantling from the hill at marshalling stations. Calculations are performed using the static analysis module Static Structural of the ANSYS Workbench engineering software package for two loading options for a transport tank: a standard one, corresponding to GOST 33211-2014, and a refined loading option for the tank-container shell. Based on the numerical solution of the differential equations system for the liquid cargo movement, the analysis of which is performed using the finite volume method in the CFX module of the ANSYS Workbench engineering software package, the obtained values of hydrodynamic pressures in the tank are accepted as the initial data for the refined computer simulation. Conclusions are drawn on the influence of taking into account the distribution of hydrodynamic pressure inside the transport tank on the stress-strain state of the tank-container. The distributions of normal, equivalent von Mises stresses, as well as deformations for two loading schemes are obtained. Using the Fatigue Tool of the Static Structural static analysis module, the number of cycles that the structure can withstand is determined, taking into account the equivalent stresses concentration areas. The conclusions are formulated based on the computational results, and the recommendations are offered to improve transportation safety and ensure the safety of cargo using tank-containers.

Peristome-mimetic surfaces using three-dimensional microcavities for unidirectional liquid transport

Peristome-mimetic surfaces using three-dimensional microcavities for unidirectional liquid transport