Values Of Water Diffusion Coefficients Research Articles

Effect of manganese doping of corundum on the content and diffusion of water and other gases

The content of volatile gas-liquid impurities, degassing and diffusion characteristics of Mn-doped corundum synthesized in a supercritical water fluid were determined using the method of kinetic thermodesorption mass spectrometry. Water is the main volatile impurity in the crystals of Mn-doped corundum. An increase in the concentration of manganese in corundum increases the water content in the low-temperature form and affects the high-temperature water release by the diffusion mechanism in different ways: for MnCl2-precursor, the content of the high-temperature form increases, and for KMnO4 – decreases. The introduction of manganese into corundum significantly lowers the water content in the structure compared to undoped corundum, which is a favorable factor in the production of transparent ceramics. Carbonaceous impurities (CO2, CO, hydrocarbons CxHy) are the second largest group of volatile gas-liquid impurities. With an increase in the manganese content in corundum (for both Mn precursors), the release of hydrogen decreases while the release of oxygen increases. The reduction of hydroxyls to hydrogen and the oxidation of manganese ions are most effective when the concentration of hydroxyls in the corundum structure is significantly higher than the concentration of manganese ions. The diffusion coefficients of water in corundum with various manganese concentrations and with different Mn precursors were determined. The obtained values of water diffusion coefficients and their temperature dependencies make it possible to calculate the degassing time of the material to a certain degree at any temperature.

Mechanical properties and water absorption characteristics of composites reinforced with cotton fibres recovered from textile waste

The primary aim of this research is to develop thermoset composites reinforced with cotton fibres extracted from textile waste. These composites are mainly targeted to replace timber in its application for furniture items and in some visible and non-visible automotive components. The pre-consumer cotton textile wastes such as cutting waste, in garment manufacturing, and defective fabrics were converted into the fibrous form called ‘shoddy’, using rag-tearing technique. The fibrous web of shoddy was produced using the carding machine. This web was used for developing thermoset composites as a reinforcement material. The thermoset composites with four different fibre volume fraction values, namely 0.1, 0.2, 0.3 and 0.4 were developed using compression moulding technique. The developed composites were characterised by mechanical properties, dynamic mechanical properties, thermal degradation behaviour and water absorption behaviour. The mechanical properties of the composites were found comparable with that of commercial wood. These composites can be used to develop a dashboard panel. The composites developed in this research have shown low water diffusion coefficient values as compared with pine, oak and linden wood.

Characterisation of composite panels produced from lignin-glyoxal-resin reinforced by date palm petiole fibers

Different composites panels were prepared using two granulometrys of fibers from date palm petiole (PDPF) and bio-matrix from lignin-glyoxal-resin (LGR). The composites panels were manufactured at different PDPF percentages ranging from 10 to 70 wt%. Mechanical properties of the prepared samples were evaluated by measuring tensile strength, Young`s modulus and elongation. The obtained results showed that the sample made from fibers/thermo pressed resin 50/50 wt% has the best mechanical properties. The increase of the granulometry of the fibers from 250 to 500 µm results in an improvement of the tensile strength and Young`s modulus values. However, the LGR matrix reinforced with PDPF showed high values of water diffusion coefficient when compared to the unreinforced LGR.

Photoacoustic monitoring of water transport process in calcareous stone coated with biopolymers

Moisture is a critical control of chemical and physical processes leading to stone deterioration. These processes can be enhanced by microbial biofilms and associated exopolymers (EPS). There is limited current understanding of the water transport process across rocks covered by EPS. In the present work, we employed the photoacoustic technique to study the influence of three biopolymers (xanthan, microbactan and arabic gum) in the water transport process of two types of limestone rock of similar mineralogy but contrasting porosity. Both controls of RL (low porosity) and RP (high porosity) presented the higher values of water diffusion coefficient (D) than biopolymer-coated samples, indicating that biopolymer layers slowed down the transport of water. This trend was steeper for RP samples as water was transported seven times faster than in the more porous rock. Important differences of D values were observed among samples coated by different biopolymers. Scanning electron microscopy and optical microscopy showed that surface topography was different between both types of rocks; adherence of coatings was seen predominantly in the less porous rocks samples. FTIR and NMR analysis showed the presence of pyruvate and acetate in microbactan and xanthan gum, suggesting their participation on adherence to the calcareous surfaces, sealing surface pores. These results indicate that water transport at rock interfaces is dependent on the chemistry of biopolymer and surface porosity. The implications for reduced water transport in stone conservation under the influence of biopolymers include both enhanced and lower deterioration rates along with altered efficiency of biocide treatment of epilithic biofilms.

Computer-aided identification of the water diffusion coefficient for maize kernels dried in a thin layer

Abstract Uncertainties in mathematical modelling of water transport in cereal grain kernels during drying and storage are mainly due to implementing unreliable values of the water diffusion coefficient and simplifying the geometry of kernels. In the present study an attempt was made to reduce the uncertainties by developing a method for computer-aided identification of the water diffusion coefficient and more accurate 3D geometry modelling for individual kernels using original inverse finite element algorithms. The approach was exemplified by identifying the water diffusion coefficient for maize kernels subjected to drying. On the basis of the developed method, values of the water diffusion coefficient were estimated, 3D geometry of a maize kernel was represented by isoparametric finite elements, and the moisture content inside maize kernels dried in a thin layer was predicted. Validation of the results against experimental data showed significantly lower error values than in the case of results obtained for the water diffusion coefficient values available in the literature.

Specific ion effects on soil water movement

Soil water movement is closely related to soil tillage. However, the development of a solid understanding of the physical mechanism by which soil ionic composition influences soil water movement remains a challenge for the scientific community. In this study, the specific ion effects of Li+, Na+ and K+ on soil water movement in a permanently charged soil were examined, and the vertical infiltration experiment was employed. The results provided evidence of strong specific ion effects, for which cationic polarization appears to be responsible. The velocity of the wetting front in the presence of K+ was up to 18.0 and 1.52 times faster than that in the presence of Li+ and Na+, respectively; the water diffusion coefficient values in the presence of K+ were up to 2300 and 9.451 times higher than those in the presence of Li+ and Na+, respectively. At electrolyte concentrations ≤0.01molL−1, water could not infiltrate into the soil in the presence of Li+. Knowledge of the interaction forces of soil particles combined with the experimental results on soil water movement indicates that the specific ion effects can be explained by cationic polarization. We concluded that the different polarizabilities among the three cations resulted in different soil electric field strengths for a given soil under a given electrolyte concentration, which led to differences in soil pore and aggregate stability, and thus differences in the soil water movement. Our results imply that it may be possible to regulate soil water movement by adjusting ionic polarization in a soil.

Mathematical Modeling of Hot-Air Drying of Osmo-dehydrated Nectarines

Abstract The influence of osmotic pretreatment on nectarines with solutions of glucose syrup and sorbitol and subsequent dehydration at different temperatures (60 °C, 70 °C, or 80 °C) was evaluated. The kinetics of moisture loss during drying was obtained and mathematical models were adjusted to estimate the kinetic parameters. Effective diffusion coefficients were calculated using Fick’s second law. All drying kinetics exhibited only a falling-rate period during hot-air drying owing to moisture loss in the osmotic pretreatment. Moisture loss was favoured by the use of sorbitol, whereas the diffusivity of water increased when glucose was used as an osmotic agent. Logarithmic and Midilli et al. models best described the changes in moisture over time, whereas Fick’s second law estimated water diffusion coefficient values between 4.96×10−9 and 2.43×10−8 m2 s−1. These models may be employed to predict the optimum conditions for osmo-dehydrating nectarines under hot-air drying at the industrial level.

Experiment and model validation of water concentration jump of a composite coating on 2024 Al alloy

Water diffusion in a composite coating on 2024 Al alloy was experimentally studied using electrochemical impedance spectroscopy (EIS). The composite coating contained an inner silane film and an outer silicone-epoxy layer. The measured value of water diffusion coefficient of the composite coating by the EIS method was compared to the value predicted using a mathematical model. The results indicated the non-continuity of water concentration at the interface of silane film and silicone-epoxy layer. Considering water concentration jump on the silane film/silicone-epoxy boundary, the diffusion coefficient of the composite coating obtained by validation model was similar to that obtained from the experimental method.

Proton transport properties of sulphanilic acid tethered poly(methyl vinyl ether-alt-maleic anhydride)-PVA blend membranes

This work is an effort to demonstrate a simple approach to develop sulphonated hydrocarbon proton exchange membranes with randomly oriented and distributed pores that are suitable for separation and fuel cell applications. Sulphanilic acid (SA)-tethered poly(methyl vinyl ether-alt-maleic anhydride) (sPMVEMA) was synthesized and characterized using FTIR and 1H NMR. As the synthesized neat polymer lacked the membrane-forming property and was also water soluble, it was thought to physically blend the same with poly(vinyl alcohol) (PVA). The nanoporous proton exchange membranes were cross-linked with gluteraldehyde (GA). Further, ATR-FTIR spectra confirmed the cross-linking of the membranes. The TGA analysis showed the stability of blend membranes up to 300°C, suggesting a beneficial effect of PVA for ∼50°C. Likewise, analysis of the surface morphology using SEM, AFM and TEM images showed micro-level immiscibility between the polymers, sPMVEMA and PVA. This resulted in confirming nano-porosity in the membrane. The ion exchange capacity (IEC) and water uptake showed linear dependency on the weight fraction of sPMVEMA in blended membrane. The obtained water diffusion coefficient values increased with increase in weight fraction of the sPMVEMA in blend membranes. The membrane conductivity was measured at different proton concentrations and found to be 0.0045S/cm at 0.1M [H+] for 0.5 weight fraction of sPMVEMA with 75% SA modification. The diffusion coefficients were calculated using the iso-conductance method and found to be of the order of 10−10m2/s, compared to that of reported values in literature. Statistical evaluation was made to analyze and understand the obtained electro-chemical properties.

Mathematical modelling of wheat kernel drying with input from moisture movement studies using magnetic resonance imaging (MRI), Part I: Model development and comparison with MRI observations

A three-dimensional (3D) simultaneous heat and moisture transfer drying model for a single wheat kernel was developed. The model was based on the information obtained from magnetic resonance imaging (MRI) of wheat drying. The model assumed a non-uniform initial moisture distribution and two different values of water diffusion coefficients in the germ and endosperm of a wheat kernel. The model was theoretically developed using finite element method and then solved using COMSOL® Multiphysics™, a commercial finite element software package. Model simulations were performed on the actual shaped 3D geometric objects obtained from the MR images of wheat kernels using image processing algorithms. Model-predicted moisture data were compared with the results obtained from MR images under similar drying conditions. Activation energies of the water removal process in the endosperm and germ were calculated to be 26.5 and 13.8 kJ mol−1, respectively, based on the range of drying temperatures under study.

Mathematical modelling of wheat kernel drying with input from moisture movement studies using magnetic resonance imaging (MRI), Part II: Model comparison with published studies

The predicted moisture data, using the three-dimensional (3D) single wheat drying model (Part I) considering actual kernel geometry, were compared with two published semi-empirical thin-layer wheat drying models, and one published axisymmetric heat and mass transfer model for a single wheat kernel. The published axisymmetric model assumed a uniform initial moisture distribution within the whole kernel of ellipsoidal geometry and a single value of the water diffusion coefficient. Our model predictions agreed well with the observations obtained from the published models. Further, our model can predict the moisture distribution pattern within individual wheat components with drying time. Moisture and temperature distributions inside the wheat kernel and the effect of drying temperature on wheat quality were explained by calculating the Biot and Lewis numbers. High Biot numbers for moisture transfer (0.89×106–3.04×106 for endosperm and 1.98×106–3.37×106 for germ) indicated that moisture transfer inside the wheat structural components was governed by high internal resistance, whereas low Biot numbers for heat transfer (0.12–0.20 for endosperm and 0.02–0.10 for germ) indicated that heat transfer was controlled by external resistance and, hence, temperature within the wheat kernels was uniform at any given time during drying. Lewis numbers indicated that the rate of heat transfer was very high compared to moisture transfer in both the endosperm and the germ. Sensitivity analysis was performed for selecting proper model parameters which indicated that values of water diffusion coefficients in the germ and endosperm are the most sensitive parameters for a grain drying process.

Optical Measurement Technique of Water Contents in Polymer Membrane for PEFCs

The feasibility of an optical technique is examined for the measurement of the membrane water content in polymer electrolyte fuel cells (PEFCs). Transmission of the infrared light of 1.92 μm wavelength is used to measure the water content in the polymer electrolyte membrane. A calibration procedure is examined, and the technique is applied for the transient measurement of a Nafion membrane that gives the value of water diffusion coefficient, consistent with previous reports. The technique is then applied to an operating PEFC to show its applicability for in situ measurement.

Combined effect of gamma-irradiation and osmotic treatment on mass transfer during rehydration of carrots

The exposure to irradiation pretreatment results in increase in cell wall permeabilization, leading to softening of tissue and the loss of turgor pressure, thereby affecting the reconstitution properties. Rehydration kinetics of gamma-irradiated (3.0–9.0 kGy) and water (0° Brix) or osmotic pretreated (up to 50° Brix) carrot samples were studied. The diffusion coefficient for water infusion and solute loss during rehydration of irradiated and osmotically pretreated and finally dried samples were estimated considering Fickian diffusion. The results shows that as increase in doses of gamma irradiation resulted in decrease in water and increase in solute diffusion coefficient. The pretreatment with water (0° Brix) resulted in increased water gain and reduced solute loss during rehydration for irradiated samples. The samples pretreated with osmotic solution of 10° Brix (concentration more than the natural cell water concentration) could not absorb more water in comparison with control because of cell permeabilization caused by the osmotic treatment due to osmotic stress. The water diffusion coefficient values decreased and solute diffusion coefficient increased with an increase in dose rates. The equilibrium moisture as well as equilibrium solid content were dependent on the treatment conditions.

Sorption and Transport of Water Vapor in Amphiphilic Block Copolymer Films

Water vapor sorption in films consisting of poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) amphiphilic block copolymers has been measured gravimetrically at air relative humidity in the range 38–94% at 24°C. The water sorption isotherm was obtained and compared to data for water vapor desorption (drying) for the same system. The kinetics of water vapor sorption were determined. The percentage of water gain is initially a linear function of square root of time, indicating Fickian diffusion in the block copolymer films. Diffusion models were used to fit the experimental results and to extract water diffusion coefficient values in the block copolymer film, the internal structure of which was initially semicrystalline (due to PEO) and, above ∼12% water, lamellar lyotropic liquid crystalline.