Behavior Of Liquid Water Research Articles

Phase diagram and critical properties of a two-dimensional associating lattice gas.

We revisit the associating lattice gas (ALG) introduced by Henriques etal. [Phys. Rev. E 71, 031504 (2005)PLEEE81539-375510.1103/PhysRevE.71.031504] in its symmetric version. In this model, defined on the triangular lattice, interaction between molecules occupying nearest-neighbor sites depends on their relative orientation, mimicking the formation of hydrogen bonds in network-forming fluids. Although all previous studies of this model agree that it has a disordered fluid (DF), a low-density liquid (LDL), and a high-density liquid (HDL) phase, quite different forms have been reported for its phase diagram. Here, we present a thorough investigation of its phase behavior using both transfer matrix calculations and Monte Carlo (MC) simulations, along with finite-size scaling extrapolations. Results in striking agreement are found using these methods. The critical point associated with the DF-HDL transition at full occupancy, identified by Furlan et al. [Phys. Rev. E 100, 022109 (2019)2470-004510.1103/PhysRevE.100.022109] is shown to be one terminus of a critical line separating these phases. In opposition to previous simulation studies, we find that the transition between the DF and LDL phases is always discontinuous, similar to the LDL-HDL transition. The associated coexistence lines meet at the point where the DF-HDL critical line ends, making it a critical-end-point. Overall, the form of the phase diagram observed in our simulations is very similar to that found in the exact solution of the model on a Husimi lattice. Our results confirm that, despite the existence of some waterlike anomalies in this model, it is unable to reproduce key features of the phase behavior of liquid water.

Soft X-Ray Imaging of Polymer Electrolyte Fuel Cells Using Different Support Materials for Catalyst Layers

The polymer electrolyte fuel cell (PEFC) is a highly efficient and environmentally friendly energy device that has been developed for fuel cell vehicles and other applications due to its low operating temperature and compact size. The PEFC is assembled by putting a membrane electrode assembly (MEA), which consists of the polymer electrolyte membrane with the catalyst layers and the gas diffusion layers on both sides, between separators. Pt nanoparticle catalysts supported on carbon black (Pt/C) are usually used for catalyst layers because of their large surface area and high electrical conductivity. However, carbon supports are oxidized and corroded during operation, resulting in performance degradation. Therefore, research has been conducted using Pt supported on tin oxide (Pt/Nb-SnO2), which has high durability and a porous structure similar to that of carbon supports, as an alternative material for the catalyst layers [1]. Tin oxide supports have material properties such as wettability that differ greatly from carbon supports, and the effect of these material properties on liquid water behavior during power generation has not been clarified. It is essential to understand the liquid water transport in PEFCs for the improvement of performance, because excessive liquid water accumulation (flooding) at the cathode hinders the transport of the reaction gas and causes concentration overvoltage.In this study, in order to clarify the effect of the catalyst layer support material on the liquid water transport, we made catalyst layers using carbon and tin oxide supports respectively, and investigated the liquid water behavior in the MEAs under fuel cell operation using high-resolution soft X-ray radiography.PEFCs with a reaction area of 5×8 mm2 were constructed using carbon support catalyst layers and tin oxide support catalyst layers, respectively. The same components were used except for the catalyst layer. The PEFCs were set in a soft X-ray imaging system (TUX-9000D, Mars-Tohken X-ray Inspection). This system can observe PEFCs and take images at a spatial resolution of about 1.0 µm. Hydrogen was supplied to the anode and air to the cathode, and the power generation tests were conducted in the high current density region where flooding is likely to occur. The voltage drop during power generation of the PEFC with Pt/SnO2 catalyst layer was larger than that of the PEFC with Pt/C catalyst layer. In-situ observation of the liquid water behavior in the PEFC was performed by taking images in the MEA cross-sectional direction at the same time as power generation. The images were taken at the position where both the area under the rib and the area under the channel could be observed. The soft X-ray radiograph of the MEA before power generation is shown in Figure 1 (a). The generated water during the power generation was identified by image processing that subtracted the image taken after operation from the image taken under open-circuit voltage conditions. Figure 1 (b) and (c) show the soft X-ray radiographs of liquid water after 20 minutes of power generation under the current density of 0.8 A/cm2. After the cell startup, the amount of water retention increases on the cathode side of the PEFC and the difference in the amount of water retention under the rib and under the channel was observed. It was also shown that the distribution of liquid water in the porous material was different between the carbon support and tin oxide support catalyst layers attributed to support materials and structures of the catalyst layers properties.AcknowledgmentsThe catalyst with Tin oxide support material used in this study was provided by NEDO ECCEED'30. The authors would like to acknowledge their assistance in assembling PEFCs for visualization study.[1] Y. Chino et al, J Electrochem Soc., 162-7 (2015), F736. Figure 1

Experimental Study of Combustion Characteristics of Micron-Sized Aluminum Particles and Liquid Water

Experiments have been performed to explore the combustion behaviors of spherical micron-sized aluminum (Al) particles and liquid water for Al particle sizes in the range of . The ignition of quasi-homogeneous Al/water mixtures was successfully implemented by employing a novel ignition method, and self-sustained flame propagation was obtained in the mixtures over a broad range of fuel-equivalence ratio . The burning rates, flammability limits, and thermal structure of the propagating flame were determined. The combustion products were also analyzed. For the particle sizes considered, the burning rates were found to first increase and then decrease as increased, with the maximum values occurring at and substantially lower than nano- mixtures. The dependence of the burning rate on particle size follows a power law, , indicating that the reaction process of and water is kinetically controlled. Base on the experimental observations, a simplified flame propagation model was developed to provide insight into the effects of particle size and equivalence ratio. Combustion product analyses revealed that Al residues increased as was further increased from 0.7, and the combustion efficiency of aluminum decreased accordingly.

3D Visualization of Liquid Water Penetration from MPL to Substrate Layer in PEFC Using in-Situ X-Ray Tomographic Microscopy

X-ray tomographic microscopy (XTM) is used to clarify liquid water behavior in polymer electrolyte fuel cell (PEFC). It was difficult to acquire 3D image of liquid water in gas diffusion layer (GDL) by using laboratory-based XTM because the intensity of laboratory-based X-ray is lower than that of synchrotron-based X-ray. By improving the cell, 3D visualization of liquid water in substrate layer and cracks of micro porous layer (MPL) is achieved. It is also shown that liquid water in substrate layer tends to remain in the bigger pore diameter.

Soft X-Ray Imaging of Polymer Electrolyte Fuel Cells Using Different Support Materials for Catalyst Layers

Water management in polymer electrolyte fuel cells (PEFC) is an important factor for improving cell performance. It is necessary to understand the liquid water behavior in the porous layer during power generation. In this study, we prepared PEFCs using carbon and tin oxide as the support materials for the catalyst layer, respectively. Although tin oxide supports have high durability, their wettability differs greatly from that of carbon supports, and there is concern that flooding is likely to occur. Liquid water in the two types of PEFCs during power generation was observed by soft X-ray radiography. It was shown that the distribution of liquid water in the porous media was different between the carbon support and tin oxide support catalyst layers due to the differences in support materials and structures of the catalyst layers.

The influences of electric field intensity and driving force on the slip behaviour of water flow in a nanochannel.

In the present work, non-equilibrium molecular dynamics (MD) simulations are used to investigate the flow of liquid water between two metallic solid atomistic smooth walls. The present work focuses on the combined effect of external electric field and driving force on the slip behaviour and structure of liquid water at the solid-water interface. The upper wall of the set model is positively charged, and the lower wall of the model is negatively charged. The simulation results show that as the driving force increases, the slip length also increases. At a given driving force, no matter how the electric field intensity changes, there is almost no change in the slip length, so the slip length is independent of the electric field strength. In addition, the results found that there is a linear relationship between the slip length and the normalised main peak of the static structure factor under different driving forces.

Investigation of effects of hydrophilic micro-porous layer on liquid water behavior by X-ray imaging

In this study, X-ray imaging and electrochemical measurements were simultaneously performed to clarify the effects of the properties of micro-porous layers (MPLs) on the i-V performance and the liquid water behavior (LWB) of polymer electrolyte fuel cells (PEFCs) operating at a cell temperature of 50 ∘ C and relative humidity of 80 %. To evaluate the effects of wettability, structure and thickness of MPLs, four types of MPLs were tested. The results demonstrate that LW accumulation (LWA) in the substrate part decreased in hydrophilic MPLs by a mechanism that sucks up liquid water and evaporates it. Moreover, MPLs using carbon fiber (CF) material demonstrated less LWA than those using carbon black (CB). Furthermore, the difference in MPL thickness significantly affects the cell performance and LWB, indicating that the MPL thickness optimization is necessary. These results indicates that hydrophilic MPLs effectively suppress LWA and enhance the oxygen transport. • The effects of hydrophilic MPLs are studied using in-situ X-ray visualization. • Hydrophilic MPL wicks liquid water from accumulated water in the substrate layer. • Carbon fiber MPL case demonstrates higher performance than carbon black MPL case. • Thicker MPL reduced liquid water accumulation compared to thinner MPL.

Numerically investigating two-phase reactive transport in multiple gas channels of proton exchange membrane fuel cells

Understanding the coupled mechanisms between two-phase flow and reactive transport in proton exchange membrane fuel cells is important for improving cell performance. In this study, a one-dimensional + three-dimensional model is developed to simulate the air–water two-phase flow, mass transport and electrochemical reaction in the cathode side of proton exchange membrane fuel cells. Dynamic water behaviors affected by several forces in three channels are well captured by the volume of fluid method. Effects of liquid water behaviors on pressure drop, mass flow rate, oxygen concentration distribution, current density and especially the distribution characteristics among different channels are discussed. It is found that the current density increases under certain flow patterns such as droplet detachment and water film on the top wall. Compared with single-phase flow, the two-phase flow magnifies the flow maldistribution in different channels, and such maldistribution in turn leads to different water detachment sequence in the three channels. The change of the mass flow rate in the second channel is more sensitive to that in the third channel. Effects of the gas channel wall wettability and channel structures are also investigated. The results show that changing the gas channel as hydrophobic will lead to higher pressure drop, lower current density and poorer flow distribution among different channels, which thus is not desirable in application. Modified structures of rectangle channel and tapered channel are finally explored. Compared with the base case, the tapered channel results in increased flow uniformity and averaged current density by 65.9% and 1.5%, respectively.

Investigation of liquid water behaviors inside a PEMFC cathode with a leaf-like biomimetic flow field design based on Murray’s Law

ABSTRACT Water management is the key to further improvement in the performance and durability of proton electrolyte membrane fuel cells (PEMFCs). The flow field inside the bipolar plates has a major role in managing the flooding process. Biomimetic flow field designs have been capturing the attention of researchers for their promising characteristics including uniform flow distribution and low pressure drop. Therefore, this study investigates liquid water behaviors inside a leaf-like biomimetic flow field design based on Murray’s Law using at the cathode of a PEMFC. The investigation is conducted using a computational simulation method utilizing the commercial software Ansys Fluent, in which the volume of fluid method is implemented for the three-dimensional, two-phase, unsteady flow simulation with the application of a dynamic contact angle model. The results are the general water transport process, the velocity, and pressure distribution inside the leaf-like biomimetic flow field design based on Murray’s Law.

Visualization of dynamic behavior of liquid water in the microporous layer of polymer electrolyte fuel cell during water injection by time-resolved X-ray computed tomography

Liquid water behavior in the microporous layer (MPL) of a polymer electrolyte fuel cell (PEFC) was investigated using time-resolved X-ray computed micro-tomography (CT) to elucidate the unsteady flow during flooding. The water was injected into an MPL laminated on top of the substrate of a gas diffusion layer (GDL) to simulate the cathode in an operating PEFC. A CT scan time as high as 4.2 s was achieved, which enabled capture of the water motion in MPL pores with sizes of ca. 30 and 100 μm. Dynamic water transport from a hydrophobic MPL pore to the hydrophilic carbonaceous binder that bonds the substrate fibers was observed.

Liquid water transport in PEMFC cathode with symmetrical biomimetic flow field design based on Murray's law

Water management in the flow field as well as the flooding process in the gas diffusion and catalyst layers enormously influence proton exchange membrane fuel cells (PEMFCs) performance and reliability. Researchers have developed many different designs for flow channels that can be used to distribute fuel or oxidant in PEMFCs (proton exchange membrane fuel cells). Among these designs, novel biomimetic designs have captured special attentions from researchers due to their capability of distributing fluids effectively. This study presents an investigation of the liquid water transport within a porous layer and a symmetrical biomimetic flow field based on Murray's law. The volume of fluid (VOF) method is employed, and the dynamic contact angle (DCA) effects are also considered for better prediction of water distribution. The water transport process and water distribution inside the porous layer and flow field are obtained from the simulation results. Recommendations are given for this type of flow field design based on the behaviors of liquid water in the porous layer and flow field.

Using Attenuated Total Reflection (ATR) Apparatus to Investigate the Temperature Dependent Dielectric Properties of Water, Ice, and Tissue-Representative Fats

A novel method of investigating the temperature dependent variation of aspects of the complex refractive index n* in samples in the THz range using continuous, non-polarised, synchrotron radiation is presented. The method relies on the use of ATR apparatus, and retains the advantage of minimal sample preparation, which is a feature of ATR techniques. The method demonstrates a “proof of concept” of monitoring temperature reflectance whilst continuously heating or cooling samples by using a temperature variable Thermal Sample Stage. The method remains useful when the refractive index of the sample precludes attenuated total reflection study. This is demonstrated with the water reflectance experiments. The temperature dependent ATR reflectance of tissue-representative fats (lard and Lurpak® butter) was investigated with the novel approach. Both are within the ATR range of the diamond crystal in a “true” ATR mode. Lard showed no clear temperature variation between −15 °C and 24 °C at 0.7 to 1.15 THz or 1.70 to 2.25 THz. Lard can be regarded as having invariable, constant, dielectric properties within mixtures when biological substances are being assessed for temperature dependent dielectric variation within the stated THz ranges. Lurpak® butter (water content 14.7%) displayed temperature dependent reflected signal intensity features with a steady decline in reflectivity with increasing temperature. This is in line with the temperature-dependent behaviour of liquid water. There is no rapid change in reflected signal intensity even at −20 °C, suggesting that emulsified water retains liquid-water-like THz properties at freezing temperatures.

Pore-scale numerical study of multiphase reactive transport processes in cathode catalyst layers of proton exchange membrane fuel cells

understanding interactions between multiphase flow and reactive transport processes in catalyst layers (CL) of proton exchange membrane fuel cells is crucial for obtaining better performance and lower cost. In this study, a pore-scale model is developed to simulate coupled processes occurring in CLs, including oxygen diffusion, electrochemical reaction, and air-liquid two phase flow. Simulation conducted in an idealized local CL structures shows that the pore-scale model successfully captures dynamic behaviors of liquid water including generation, growth and subsequent migration, as well as the interaction between multiphase flow and reactive transport. Pore-scale simulation is then conducted in hydrophobic CLs with complicated structures where carbon, platinum, ionomer and pores are resolved. It is found that filling modes of the liquid water in the CLs are different. Before forming the continuous flow paths in CLs, liquid water presents as tiny droplets in pores surrounding relative large pores. After the continuous flow paths are formed, liquid water dynamic behaviors follow the capillary fingering mechanism. The multiphase flow and reactive transport processes are closely coupled with each other, and as liquid water saturation increases the reaction rate decreases. Increasing the hydrophobicity can alleviate the water flooding, accelerate the water breakthrough, and facilitate the water evaporation.

The Effect of Inner Layer Fiber Diameter and Fabric Structure on Transplanar Water Absorption and Transfer of Double-layered Knitted Fabrics

It is a prerequisite of sportswear fabrics to not only absorb plenty of water, but also transfer it to the environment as fast as it is possible. The present study examines water absorption and transfer of double-layered polyester/cotton fabrics. It intends to determine the simultaneous effect of fiber diameter and fabric structure of inner layer (polyester layer) on water management properties of these fabrics. The controversial effect of fiber fineness on water absorption capacity is critically discussed. The results revealed the key role of stitch type on the liquid water behavior; Fabrics with miss stitch in their inner layer had the least absorption capacity (mass of absorbed water into a known area of fabric) and the highest evaporation rate which are two determining factors in comfort sensation. Decreasing the inner layer fiber diameter decreased the rate of evaporation significantly. Comparing the initial rate of absorption suggests faster transfer of liquid through fabrics with coarser fibers. However, the effect of fiber fineness on the absorption capacity was found dependent on the structure of the fabric which should be considered for interpretation of the results. Overall, S3PC was the most comfortable fabric among the samples examined in this study.

Shock Hugoniot Data for Water up to 5 Mbar Obtained with Quartz Standard at High-Energy Laser Facilities

In this work, we present experimental results on the behavior of liquid water at megabar pressure. The experiment was performed using the HIPER (High-Intensity Plasma Experimental Research) laser facility, a uniaxial irradiation chamber of GEKKO XII (GXII) at the Institute of Laser Engineering (ILE), and the PHELIX at GSI (GSI Helmholtz Centre for Heavy Ion Research), a single-beam high-power laser facility, to launch a planar shock into solid multilayered water samples. Equation-of-state data of water (H2O are obtained in the pressure range 0.50–4.6 Mbar by tuning the laser-drive parameters. The Hugoniot parameters (pressure, density, etc.) and the shock temperature were simultaneously determined by using VISAR and SOP as diagnostic tools and quartz as the standard material for impedance mismatch experiments. Finally, our experimental results are compared with hydrodynamic simulations tested with different equations of state, showing good compatibility with tabulated SESAME tables for water.

Macroscopic Modeling of Liquid Water in Channel of Jari Cell Based on Detailed Two-Phase CFD

In this work, we modeled liquid water behavior in channels based on detailed two-phase CFD for application on Full-Cell scale multiphysics simulation. In our work, in order to execute efficient simulations in full-cell scale, all relevant transport phenomena in PEFC (mass, chemical species, and heat) are considered macroscopic, where the phenomena are coupled with electrochemical reactions. In order to apply this method for conditions in which liquid water is important, two-phase fluid models should be constructed properly.In order to model two-phase flow in channels, we evaluated the relationship between liquid water volume fraction, pressure drop, and liquid water velocity in macroscopic control volume with detailed CFD using OpenFOAM. The calculation target is the JARI cell channel and mesh size is 50 micrometer order. We used the interIsoFoam for the solver, which uses the VOF method for two-phase flow and geometric surface reconstruction method for surface capturing. The relationship is expressed by the table data that shows the relationship between the liquid phase volume fraction and liquid phase velocity or pressure loss multiplier. The table data shows a good representation of the below. Dependency of pressure drop on the water volume fractionDependency of drainage droplet size on the gas flow rateDehydration speed In order to evaluate the obtained models, we calculated PEFC simulations with the models and validated the calculations.In our simulator, in order to estimate the performance of PEFC cells taking all relevant transport phenomena (mass, chemical species, and heat) is solved on the coarse-grained mesh, coupled with electrochemical reactions. The mass transport equation is solved by Darcy’s law, using the distribution of the equivalent hydraulic parameter in flow channels estimated by detailed gas phase CFD. Here mass transport is coupled with heat and chemical species transport equations. Those all transport phenomena are coupled with electrochemical reactions in the MEA. Transport of chemical species and water through the MEA is also considered. Many engineering models are employed in order to consider various transport phenomena, like water up-take into electrolytes and effective transport of oxygen from the gas phase to reaction sites in catalyst layers, etc. Electrochemical reactions are modeled by the Butler-Volmer equation, in the manner of lumped parameter models.The calculation using the derived two-phase model well reproduce the below phenomena. Various Overpotentials difference between drive conditionsDrainage speed difference depending on gas flow ratesLiquid water difference between under the rib and the channelOxygen depletion depending on stoichiometry and liquid water distribution

Molecular interpretation of the non-Newtonian viscoelastic behavior of liquid water at high frequencies

Using classical as well as ab-initio molecular dynamics simulations, we calculate the frequency-dependent shear viscosity of pure water and water-glycerol mixtures. In agreement with recent experiments, we find deviations from Newtonian-fluid behavior in the THz regime. Based on an extension of the Maxwell model, we introduce a viscoelastic model to describe the observed viscosity spectrum of pure water. We find four relaxation modes in the spectrum which we attribute to i) hydrogen-bond network topology changes, ii) hydrogen-bond stretch vibrations of water pairs, iii) collective vibrations of water molecule triplets, and iv) librational excitations of individual water molecules. Our model quantitatively describes the viscoelastic response of liquid water on short timescales, where the hydrodynamic description via a Newtonian-fluid model breaks down.

Observation of Liquid Water Behavior in a Self-Supporting MPL of PEFC

Observation of Liquid Water Behavior in a Self-Supporting MPL of PEFC

Numerical simulation of water droplet transport characteristics in cathode channel of proton exchange membrane fuel cell with tapered slope structures

In proton exchange membrane fuel cells (PEMFC), the design of the cathode flow field is very important, because an excellent flow channel design can not only accelerate the transmission rate of liquid water, but also affect the distribution of electrode reactants and electrode products which influence the electrochemical performance of the fuel cell. This study presents three new channels (models 1,2 and 3), which were created using two unilateral slopes and a bilateral slope structure with tapered tube lengths of 0.4, 1.2 and 0.8 mm, respectively. The dynamic behavior of liquid water under the three design schemes is numerically studied based on the volume of fluid method. And the influence on the performance of fuel cell was analyzed synthetically. The results indicate that the introduction of a tapered and sloping structure can improve the transmission efficiency of the droplets in the flow channel, and the maximum droplet removal time of the new channel can be reduced by 24.4%compare with standard conventional flow channel. The slope structure guides the flow path of water droplet and reduces the occurrence of droplet spatter. Influenced by the slope and tapered structures, the turbulence of airflow near the bottom surface (gas diffusion layer)of the flow channel is enhanced and Oxygen concentration in the cathode is raised, which improves the mass transfer capacity and average current density of reactive surface. In conclusion, the new type of channel with a tapered and sloping structure has a potential to improve the performance of water management in the cathode channel of PEMFC.

Effect of gas diffusion layer thickness on liquid water transport characteristics in polymer electrolyte membrane fuel cells

Researchers worldwide endeavor to develop the thinner gas diffusion layers (GDLs), which are enabling to achieve high power-density polymer electrolyte membrane fuel cells (PEMFCs). A number of experiments have attempted to understand the underlying mechanisms in the GDL that are responsible for water management and performance improvement. Here, we investigate the effect of GDL thickness on the dynamic behavior of liquid water using a multiphase lattice Boltzmann method. Various GDL configurations are simulated aiming on the fundamental understanding of multiphase flow phenomena. We report results of water saturation, water distribution and relative pressure distribution inside the GDL to elucidate the impact of GDL thickness on the water transport behavior. Water breakthrough and water creeping that determine the water behavior are deeply studied. In addition, we investigate the influence of channel-rib (CR) structure on a thin GDL. Optimum CR width is pursued for the effective water removal from a thin GDL. The results and findings here are expected to lead to more reliable water management and related high-power technologies of PEMFCs.