Water Concentration Distribution Research Articles

Modelling and Measurements of Temperature Distributions inside MEA and Its Effects on Water Transport

Polymer electrolyte fuel cell (PEFC) is one of the cleanest and most fuel saving energy conversion devices. For the optimal design of PEFC reaction layer, the understanding of coupled phenomena consists of heat and mass transport and electrochemical reaction is essential. For the understanding, the thin film micro sensor array has been developed and the temperature and water concentration distribution near reaction layer have been measured. Moreover, the multi-scale numerical simulation has been developed and conducted to realize the conjugated problem inside reaction layer of PEFC.

Distribution of dissolved water in magmatic glass records growth and resorption of bubbles

Volcanic eruptions are driven by the growth of gas bubbles in magma. Bubbles grow when dissolved volatile species, principally water, diffuse through the silicate melt and exsolve at the bubble wall. On rapid cooling, the melt quenches to glass, preserving the spatial distribution of water concentration around the bubbles (now vesicles), offering a window into pre-eruptive conditions. We measure the water distribution around vesicles in experimentally-vesiculated samples, with high spatial resolution. We find that, contrary to expectation, water concentration increases towards vesicles, indicating that water is resorbed from bubbles during cooling; textural evidence suggests that resorption occurs largely before the melt solidifies. Speciation data indicate that the molecular water distribution records resorption, whilst the hydroxyl distribution records earlier decompressive growth. Our results challenge the emerging paradigm that resorption indicates fluctuating pressure conditions, and lay the foundations for a new tool for reconstructing the eruptive history of natural volcanic products.

Combined measurement of concentration distribution and velocity field of two components in a micromixing process

A lot of production processes involve mixing steps. The understanding of fluid flows in mixing processes of liquid components is needed in order to develop appropriate mixers for the chemical and pharmaceutical industry. Especially mixing in microfluidic systems is a challenge due to the diffusion-based processes. A multi-lamination micromixer with chessboard outlet geometry is used to induce the mixing process. To get comprehensive information about the mixing process, the velocity profile of the fluid flow and the species concentration distribution during the mixing process should be measured. Thus, we have combined particle image velocimetry (PIV) and Raman scattering. To enable rapid detection, the Raman imaging mode is used to visualise the concentration distribution. By this setup light sheets along and orthogonal to the outlet of the micromixer are recorded and synchronized with PIV measurement. As a model system we have used water and ethanol/methanol, enabling a selective monitoring of the substances by choosing appropriate spectral areas. The PIV is recorded based on Mie scattering and fluorescence using microsphere tracers. In this study, we present a setup for determination of the velocity profile field and the spatial concentration distribution of water and ethanol/methanol in a micromixer.

Heat and mass transfer in conjugate food freezing/air natural convection

This work reports a study of the heat and mass transfer during the freezing of a block of beef in the freezer compartment of a household refrigerator. It takes into account the natural convection in air coupled to the heat conduction and water diffusion in the meat. The nonlinear partial differential equations describing mass conservation, linear momentum, energy and species concentration in two dimensions are solved with the SIMPLE algorithm and the finite volumes method. The results obtained include the unsteady state description of air movement as well as temperature and water concentration in the air, and temperature and water concentration distribution in the meat. The predicted weight loss of the food reaches a value of 1.5%.

Cryopreservation of Spin-Dried Mammalian Cells

This study reports an alternative approach to achieve vitrification where cells are pre-desiccated prior to cooling to cryogenic temperatures for storage. Chinese Hamster Ovary (CHO) cells suspended in a trehalose solution were rapidly and uniformly desiccated to a low moisture content (<0.12 g of water per g of dry weight) using a spin-drying technique. Trehalose was also introduced into the cells using a high-capacity trehalose transporter (TRET1). Fourier Transform Infrared Spectroscopy (FTIR) was used to examine the uniformity of water concentration distribution in the spin-dried samples. 62% of the cells were shown to survive spin-drying in the presence of trehalose following immediate rehydration. The spin-dried samples were stored in liquid nitrogen (LN2) at a vitrified state. It was shown that following re-warming to room temperature and re-hydration with a fully complemented cell culture medium, 51% of the spin-dried and vitrified cells survived and demonstrated normal growth characteristics. Spin-drying is a novel strategy that can be used to improve cryopreservation outcome by promoting rapid vitrification.

Hygrothermal Properties of Highly Toughened Epoxy Adhesives

The absorption and desorption of water in two different rubber-toughened epoxy adhesives was measured gravimetrically over a relatively wide range of temperature and relative humidity (RH). The data were fitted to a new diffusion model in which Fick's law was assumed to act in two sequential stages, each with its own diffusion coefficient and saturated water concentration. This “sequential dual Fickian” (SDF) model and a Langmuir-type diffusion model were both able to model the absorption behaviour. The dependence of the five SDF model parameters on temperature and RH was investigated in detail. The two diffusion coefficients were found to be largely independent of RH, while the fractional mass uptake values for each stage increased with RH. The absorption temperature only had a significant effect on the diffusion coefficient of the first stage and the fractional mass uptake of the second stage. Water desorption from the two epoxies was modeled accurately using Fick's law. A significant difference was observed between the amounts of retained water in the two adhesives after drying. The results can be used to predict the water concentration distribution in adhesive joints exposed to environments of changing temperature and RH.

On the Origins of Sudden Adhesion Loss at a Critical Relative Humidity: Examination of Bulk and Interfacial Contributions

The origins for abrupt adhesion loss at a critical relative humidity (RH) for polymeric adhesives bonded to inorganic surfaces have been explored using a model poly(methyl methacrylate) (PMMA) film on glass. The interfacial and bulk water concentrations within the polymer film as a function of D 2O partial pressure were quantified using neutron reflectivity. Adhesion strength of these PMMA/SiO 2 interfaces under the same conditions was quantified using a shaft loaded blister test. A drop in adhesion strength was observed at a critical RH, and at this same RH, a discontinuity in the bulk moisture concentration occurred. The moisture concentration near the interface was higher than that in the bulk PMMA, and at the critical RH, the breadth of the interfacial water concentration distribution as a function of distance from the SiO 2/PMMA interface increased dramatically. We propose a mechanism for loss of adhesion at a critical RH based upon the interplay between bulk swelling induced stress and weakening of the interfacial bond by moisture accumulation at the PMMA/SiO 2 interface.

Opto-thermal radiometry and condenser-chamber method for stratum corneum water concentration measurements

Opto-thermal radiometry and the condenser-chamber TEWL (trans-epidermal water loss) method are two novel technologies for in-vivo skin studies. In this paper, for the first time, we combine the measurement results of the two technologies, and study the stratum corneum water concentration distribution, water status in stratum corneum, stratum corneum thickness as well as its swelling effects, and stratum corneum water-holding capabilities. We present both the theoretical background and illustrative measurement results.

G114 燃料電池多孔質電極内物質輸送現象のLBM解析(一般セッション 燃料電池I)

Water vapor distribution in a cathode channel of polymer electrolyte fuel cell (PEFC) composed of gas supply channel and porous gas diffusion layer (GDL) is calculated by lattice Boltzmann method (LBM) in order to clarify effect of porous structure of GDL in PEFC on water distribution and dew point of supplied gas. It is shown that porosity of GDL affects maximum water concentration emerged in the GDL, resulting in increase of dew point with decrease of porosity. On the other hand, pore scale in the GDL is less influential on water concentration distribution and its resultant dew point of the supplied gas in the cathode of PEFC.

Surface-NMR relaxation and echo of aquifers in geomagnetic field

Macroscopic samples of near-surface water in pores or fractures of rocks down to 100 m and deeper are studied by the measurement of proton relaxation and echo in the Earth’s magnetic field. The excitation and reception of the surface nuclear magnetic resonance (SNMR) signal is accomplished with the help of an antenna, circle or 8-shaped (for the minimization of the outer electromagnetic jamming influence), placed at the surface. The frequency of magnetic resonance in the case considered amounts to several kilohertz, the dead time of the instrumentation to several milliseconds. Water in extremely small pores of water-resisting rocks (e.g., in argillaceous grounds), is chemically bound, crystallization or frozen water has smaller times of spin relaxation and is not registered. The distribution of water concentration with depth is determined by inversion of an integral equation, including the model and measured dependences of the SNMR signal against the intensity of excitation. The current state of the art of the SNMR sounding and perspectives of this method on the basis of free induction decay and spin echo detection and relaxation times measurement are presented. Free induction decayT 2 * equal to 60 ms, spin-echoT 2 equal to 220 ms, and inversion-recoveryT 1 equal to 700 ms relaxation times have been measured for medium-to coarse-grained sand aquifer. Microscopic characteristics of the aquifer — longitudinal relaxivity (7·10−3 cm/s), transverse relaxivity (3.5·10−2 cm/s), and local magnetic field gradient (2·10−2 G/cm) — have been estimated from experimental data. The importance of spin relaxation and echo measurements for obtaining the information about the microstructure of pores and fractures, as well as filtration, properties of aquifers and diamagnetic, paramagnetic and hydrocarbon contamination, is emphasized.

The States, Diffusion, and Concentration Distribution of Water in Radiation‐Formed PVA/PVP Hydrogels

Hydrogels with various compositions of polyvinyl alcohol (PVA) and poly(1‐vinyl‐2‐ pyrrolidinone) (PVP) were prepared by irradiating mixtures of PVA and PVP in aqueous solutions with gamma‐rays from 60Co sources at room temperature. The states of water in the hydrogels were characterized using DSC and NMR T2 relaxation measurements and the kinetics of water diffusion in the hydrogels were studied by sorption experiments and NMR imaging. The DSC endothermic peaks in the temperature range −10 to +10°C implied that there are at least two kinds of freezable water present in the matrix. The difference between the total water content and the freezable water content was referred to as bound water, which is not freezable. The weight fraction of water at which only nonfreezable water is present in a hydrogel with FVP=0.19 has been estimated to be gH2O/gPolymer=0.375. From water sorption experiments, it was demonstrated that the early stage of the diffusion of water into the hydrogels was Fickian. A curve‐fit of the early‐stage experimental data to the Fickian model allowed determination of the water diffusion coefficient, which was found to lie between 1.5×10−11 m2 s−1 and 4.5×10−11 m2 s−1, depending on the polymer composition, the cross‐link density, and the temperature. It was also found that the energy barrier for diffusion of water molecules into PVA/PVP hydrogels was ≈24 kJ mol−1. Additionally, the diffusion coefficients determined from NMR imaging of the volumetric swelling of the gels agreed well with the results obtained by the mass sorption method.

Effects of rate-limited mass transfer on water sampling with partially penetrating wells.

Nonequilibrium concentration type curves are numerically developed and sensitivity analyses are performed to examine the relationships between effluent concentrations in partially penetrating monitoring/extraction wells, the vertical plume shape, and the mass transfer characteristics of the aquifer. The governing two-dimensional, axisymmetric nonequilibrium solute transport equation is solved in three stages using an operator-splitting approach. In the first two stages, the advection and dispersion terms are solved with the Eulerian-Lagrangian method, based on the backward method of characteristics for advection and the standard implicit Galerkin finite element method for dispersion. In the third step, the first-order, immobile-mobile domain mass transfer term is computed analytically for both two-site and lognormally distributed, multirate models. Effluent concentration variations with time and contour plots of the pore water concentration distribution in the aquifer are compared for a wide range of field- and laboratory-measured mass transfer rates, various plume shapes, and relevant physical/chemical parameter values, including pumping rate, vertical anisotropy ratio, retardation factor, and porosity. The simulation results show that rate-limited mass transfer can have a significant impact on sample and aquifer pore water concentrations during three-dimensional transport to a partially penetrating well. An alternative dimensionless form of the nonequilibrium solute transport equation is derived to illustrate the key parameter groupings that quantify rate-limited sorption effects and show the relative importance of individual parameters. A hypothetical field application example demonstrates the fitting of dimensional type curves to discrete-interval sampling data in order to evaluate the mass transfer characteristics of an aquifer and shows how type curve superposition can be used to model complex plume shapes.

電極多孔質構造を包含したカソード内水分移動の数値シミュレーション(テクニカルフォーラム1 水素の製造・輸送・貯蔵・利用)

The polymer electrolyte fuel cell (PEFC) is expected as one of the next power generation system. Although high-performance PEFC is expected, understanding of mass transfer is not enough due to the complex structure of PEFC. So it is very important to investigate the mass transfer inside the porous gas diffusion layer. We calculated the distribution of water concentration to simulate water transfer in PEFC cathode with porous gas diffusion layer. We used lattice Boltzmann method (LBM) to calculate the flow and water transfer in porous media, because LBM is easy to set boundary conditions. From these result, we suggest the way to estimate the conditions that PEFC works without flooding and concentration overvoltage.

Capillary penetration in fibrous matrices studied by dynamic spiral magnetic resonance imaging

The dynamic spiral nuclear magnetic resonance (NMR) imaging technique was used to investigate the water imbibition into cellulose fiber matrices. The advancing water boundary, water concentration distribution, and swelling degree within the fiber matrix samples were monitored as a function of time over the entire absorption process. A combined image that shows the time evolution of the absorbed water concentration distribution within the fiber matrix was synthesized from the dynamically acquired NMR image data set. The NMR imaging data clearly demonstrated that water imbibition into a fiber matrix consists of two different processes: water penetration into capillaries between fibers and water diffusion into the cellulose fibers. The advancing liquid front is primarily determined by the water capillary flow and can be quantitatively described by Washburn equation. The slower water diffusion process in fibers is mainly responsible for the fiber swelling. The time evolution of the absorbed water concentration distribution can be qualitatively interpreted in terms of steady capillary flow and concentration-gradient-driven diffusion into fibers with a constant permeability. The effects of pore morphology, tortuosity, and surface heterogeneity to the water absorption process are also discussed.

Computational Method to Assess Concentration of Water in Crude Oil Downstream of a Mixing Section

This paper describes a method for predicting the concentration distribution of water in crude oil in a pipe section downstream of a region of mixing and droplet break-up. The complexity of the problem and the necessary simplifications are described. The method with its approximations is justified on grounds of possible savings in financial outlay. Details of governing equations, computational method and boundary conditions lead on to the link between forces on the droplet and the velocity of the droplet relative to the bulk liquid. The model incorporates turbulence enhancement and decay, and secondary velocities likely to approximate to those following a T-piece or bend or swirl-creating element. The computer program was tested against data provided by BP and the results suggest that if the predictions indicate adequate mixing then they are likely to underestimate the uniformity of the mixture. The predictions may be used to assess the suitability for sampling based on Case 1 of the draft ISO Standard (1) but must not be used to assess the suitability for sampling based on Case 2 of the draft standard unless fall-out has been allowed for in the program. The paper reviews the assumptions and approximations involved in this model. Further work in these areas is needed to allow the model to be used with greater confidence.

THE MECHANISM OF DEUTERATION OF NYLON 4 WITH HEAVY WATER

The mechanism of deuteration of nylon 4 membranes by D2O vapor has been investigated in relation to the sorption of water.The degree of deuteration of nylon 4 at 25°C was saturated at 17.5, 25 and 31% by cumulative contact with D2O vapor for 5, 30 and 60min a time, respectively, and equilibrated at the value of 38% by a long contact.On the other hand, the reduced sorption curve for water showed a sigmoidal one at 25°C. To these experimental results, Long's diffusion theory based on the time dependence of surface concentration of penetrant was applied under an assumption of a proportional relation of the degree of deuteration to the quantity of sorbed water. Long's parameters were obtained as β=1.6×10-2min-1 and DL=1.25×10-6cm2/min. By use of these parameters, water concentration distribution curves were calculated.These results suggest that water molecules diffuse instantaneously into the center of membrane, and the quantity of sorbed water and the degree of deuteration increase uniformly throughout the membrane with gradual relaxation of hydrogen bonding of nylon 4 caused by water (D2O) sorbed in the earlier contact period.

Theoretical study of the inactivation of phosphatase during spray drying of skim-milk

A theoretical calculation is presented of the drying history of skim-milk droplets under spray drying conditions. From the unsteady state diffusion equation the water concentration distribution is calculated as a function of time; simultaneously the thermal degradation of the enzyme alkaline phosphatase is calculated and integrated over the particle. Effects accounted for are the temperature and concentration dependence of the water diffusion coefficient and of the degradation rate constant, and the shrinkage due to water loss. Droplet geometries considered are the “solid sphere” model (fully liquid droplets) and the “hollow sphere” model (with air bubble in the centre). The effect on final phosphatase retention of the following process variables was investigated: dissolved solids content of the feed, air temperature, particle size, and gas bubble size.