Diffusion Coefficient Of Water Research Articles

A Novel Numerical Model Considering Unsaturated Soil Properties and Computational Study on Heat and Moisture Transfer Characteristics of Helix Ground Heat Exchanger

Abstract A novel three-dimensional numerical simulation model for the helix ground heat exchanger was proposed in this paper, which takes into account unsaturated soil properties. This model is more suitable for real working conditions. To validate its accuracy, a miniature model heat transfer experimental platform was constructed. Additionally, the study conducted simulation research using three types of soil with significantly different thermal and moisture characteristics. Moreover, the comprehensive thermal conductivity and water diffusion coefficient of these three soil types were determined by relevant literature and experimental tests. The aim was to comprehensively explore the impact of different soil types on the heat and mass transfer of the helix ground heat exchanger. The results indicate that the numerical model developed in this paper accurately captures the heat and mass transfer characteristics of the helix ground heat exchanger to a certain extent. Increasing the comprehensive thermal conductivity and water diffusion coefficient of the soil can significantly enhance the heat exchange capacity of the exchanger. For instance, under sandy loam conditions, the heat exchange capacity is approximately 20.73% higher compared to clay loam conditions. The study also identifies two distinct areas around the helix ground heat exchanger: the severe change region and the soft change region. In the severe change region, there is a notable decrease in soil water content near the exchanger, which inevitably weakens the thermal conductivity of the soil. It is advised to minimize this effect through measures like active water spraying.

The distinctions of the interfacial nanostructures and properties between carbon fiber reinforced fast and conventional curing epoxy composites subjected to hydrothermal treatments

The vital role of the interphase in loading transfer in carbon fiber reinforced resin composites has received considerable critical attention. In this study, to quantitatively distinguish between the effects of hydrothermal aging on the interfacial nanostructures and properties of carbon fiber reinforced fast and conventional curing epoxy composites, peak force quantitative nano-mechanics (PF-QNM) technique by atomic force microscopy (AFM) was utilized to determine the interfacial modulus, adhesion and thickness. In addition, the shear behavior was studied by short-beam strength test, and the water uptake was investigated by water adsorption test. Based on the modulus contrast of the interphase in PF-QNM modulus image, the average interfacial thickness of the fast curing epoxy composites after 18 h of hydrothermal aging was 67 nm, increased 236 % when compared with the unaged composites. It was much higher than the rise of 70 % of the conventional curing epoxy composites after 18 h of hydrothermal aging while the interfacial thickness was 69 nm. Consistently, the average interfacial thickness of the fast and conventional curing epoxy composites determined by the adhesion were 68 nm (widened 247 %) and 68 nm (widened 67 %). In a word, the interfacial thickness of the fast curing epoxy composites was about 4 times than that of the conventional curing epoxy composites after 18 h of hydrothermal aging, because of the fast curing caused microcracks and flaws. Then, after 192 h of hydrothermal aging, the decreasing of short-beam strength of the fast curing epoxy composites were almost 1.6 times than that of the conventional curing epoxy composites, due to the faster growing of microcracks and delamination on the side surface of the fast curing epoxy composites short-beam samples during testing. Lastly, the maximum water absorption and diffusion coefficient of the fast curing epoxy composites were 1.2 % and 5.5 × 10−7 cm2/s respectively, which were both 1.3 times that of the conventional curing epoxy composites. Significantly, all the results proved that, attributing to the fast curing caused microcracks and flaws in the fast curing epoxy composites, through which water preferred to enter a composite along the fibers and interphase, the interphase in the fast curing epoxy composites were more sensitive to the hydrothermal aging than the conventional curing epoxy composites. Therefore, the water uptake, interfacial thickness and short-beam strength of the fast curing epoxy composites changed faster.

Kinetics model of crystal nucleation and growth in supercooled water for designing ice-templating soft matter scaffold

Ice-templating technology has recently attracted extensive attention to achieve programed structure-property relationships in porous soft matter scaffolds. However, there is a huge gap existed between theoretical understanding and practical applications of nucleation kinetics and growth of ice crystals in supercooled water. This paper establishes a nucleation kinetics model of crystal growth in supercooled water, for designing ice-templating soft matter scaffolds with programmable structure-property relationship. A phase transition model was firstly formulated to characterize liquid-liquid phase transition of supercooled water, based on a two-state model and free-volume theory. Effects of diffusion coefficient and density of the supercooled water on ice nucleation kinetics and crystal growth were investigated, based on the classic nucleation theory. Analytical results showed excellent agreement with experimental data, with correlation indices of R2=90.7 % for diffusion coefficients and R2=94.0 % for densities, respectively. The model predicted a nucleation rate of 31.7 m−3∙s−1 at 200 K and peak nucleation rate and crystal growth rates appearing at 183 K and 227 K. Constitutive relationships among mechanical behaviors, ice nucleus radius, nucleation ratio, and crystallization growth rate, were developed for the ice-templating scaffolds, based on the affine model theory and verified with finite element analysis results (R2= 99.9 %) and experimental results (R2 = 95.8 %). Finally, the prediction results using the proposed model were further verified using the experimental data reported in the literature. This study provides a new methodology to describe the nucleation kinetics and growth of ice crystals in supercooled water and programmable structure-property relationships in ice-templating soft matter scaffolds.

Changes of Temperature and Moisture Distribution over Time by Thermo-Hydro-Chemical (T-H-C)-Coupled Analysis in Buffer Material Focusing on Montmorillonite Content

Bentonite is used as a buffer material in engineered barriers for the geological disposal of high-level radioactive waste. The buffer material will be made of bentonite, a natural clay, mixed with silica sand. The buffer material is affected by decay heat from high-level radioactive waste, infiltration of groundwater, and swelling of the buffer material. The analysis of these factors requires coupled analysis of heat transfer, moisture transfer, and groundwater chemistry. The purpose of this study is to develop a model to evaluate bentonite types and silica sand content in a unified manner for thermo-hydro-chemical (T-H-C)-coupled analysis in buffer materials. We focused on the content of the clay mineral montmorillonite, which is the main component of bentonite, and developed a model to derive the moisture diffusion coefficient of liquid water and water vapor based on Philip and de Vries, and Kozeny–Carman. The evolutions of the temperature and moisture distribution in the buffer material were analyzed, and the validity of each distribution was confirmed by comparison with the measured data obtained from an in situ experiment at 350 m in depth at the Horonobe Underground Research Center, Hokkaido, Japan.

Measurement of the rotational relaxation time of intracellular water in dried yeast and Jurkat cells by near infrared spectroscopy

Molecular mobility of intracellular water is a crucial parameter in the study of the mechanism of desiccation tolerance. As one of the parameters that reflecting molecular mobility, the viscosity of intracellular water has been found intimately related with the protection of the phospholipid membrane because it quantifies the diffusion ability of water and mass in the intracellular environment. In this work we measured the intracellular water relaxation time, which can be translated into water viscosity, by using a previously established NIR-dielectric method to monitor the drying process of baker's yeast and Jurkat cells with different desiccation tolerance. We found that intracellular saccharide can significantly decrease the intracellular water viscosity. Also, the intracellular water diffusion coefficient obtained from this method were found in good agreement with other reports.

Intrinsic Water Transport in Moisture-Capturing Hydrogels.

Moisture-capturing hydrogels have emerged as attractive sorbent materials capable of converting ambient humidity into liquid water. Recent works have demonstrated exceptional water capture capabilities of hydrogels while simultaneously exploring different strategies to accelerate water capture and release. However, on the material level, an understanding of the intrinsic transport properties of moisture-capturing hydrogels is currently missing, which hinders their rational design. In this work, we combine absorption and desorption experiments of macroscopic hydrogel samples in pure vapor with models of water diffusion in the hydrogels to demonstrate the first measurements of the intrinsic water diffusion coefficient in hydrogel-salt composites. Based on these insights, we pattern hydrogels with micropores to significantly decrease the required absorption and desorption times by 19% and 72%, respectively, while reducing the total water capacity of the hydrogel by only 4%. Thereby, we provide an effective strategy toward hydrogel material optimization, with a particular significance in pure-vapor environments.

Mechanism and Kinetics of Water Absorption of Plantain Fibre Reinforced Bio-Composites

Mechanical characteristics, dimensional stability, and bonding strength are all impacted by water sorption in polymer filler materials. The diffusion coefficient (D) of water through polymer composite, should be determined to understand the impact of the deterioration on service life and micro-leakage. In this study, the kinetics and properties of water absorption by short-term immersion in room-temperature plantain fibre reinforced epoxy bio-composites (PFRC), were studied. 5, 10, 20, and 30 percent, plantain fiber (PF) volume fractions of bio-composite specimens were made. Due to the high cellulose content of natural fibers (NF), the percentage of moisture absorption grew as the PF volume fraction increased. The mechanism and kinetics of PFRC's water absorption were found to follow the Fickian diffusion mode and had the propensity to behave in the Fickian mode.

Dynamic modeling of the occurrence, sources, and environmental behavior of polybrominated diphenyl ethers in Zhelin Bay, China

This study analyzed polybrominated diphenyl ethers (PBDEs) in Zhelin Bay, China, investigating their occurrence, sources, and environmental behavior. PBDE congeners were detected in all sampled media. The Σ13PBDE concentrations in the dissolved phase ranged from 1.04 to 41.40 ng/L, while the concentrations ranged in suspended particulate matter from 0.02 to 12.56 ng/L. In sediments, PBDE concentrations ranged from 1.41 to 8.57 ng/g. The higher proportion of PBDEs in the dissolved phase in the bay than in the estuary is attributable to the type of PBDE products used in the aquacultural process in Zhelin Bay. Moreover, correlation analysis between PBDE concentrations and environmental parameters showed that the primary factor influencing PBDE concentrations in Zhelin Bay sediments may shift from riverine inputs to aquaculture. Principal component analysis and positive matrix factorization revealed that PBDEs in the water of Zhelin Bay primarily originated from the degradation of octa-BDE, deca-BDE, and penta-BDE products employed in aquaculture. In contrast, the PBDEs in Zhelin Bay sediments mainly originated from riverine inputs. In addition, a level IV dynamic fugacity-based multimedia model was used to simulate the temporal variation of PBDE concentrations in Zhelin Bay. Modeled short-term trends showed a relatively swift transport of PBDE congeners in the water column to the atmosphere and sediments. Over the long term, sediment concentrations gradually decreased, in contrast to the less rapid declines observed in the atmosphere and water. Furthermore, this study revealed that the transport and transformation processes of PBDEs in the Zhelin Bay environment were considerably influenced by the diffusion coefficient in water, the water-side mass transfer coefficient at the water–sediment interface, the sediment resuspension rate, and the organic carbon–water partition coefficient.

Impact of water absorption on the creep performance of epoxy/microcrystalline cellulose composites

AbstractRecently, considerable effort has been made to study cellulose/epoxy composites. However, there is a gap when it comes to understanding the post‐conditioning anomalous effect of moisture uptake on their mechanical and dynamic‐mechanical properties, and on their creep behavior. In this work, up to 10.0 wt% microcrystalline cellulose (MCC) was incorporated into epoxy resin by simple mixing and sonication. Epoxy/MCC composites were fabricated by casting in rubber silicone molds, and rectangular and dog‐bone test specimens were produced. The moisture uptake, dynamic mechanical, chemical, tensile, and creep behavior were evaluated. The incorporation of MCC increased the water diffusion coefficient. The changes in storage modulus and glass transition temperature, combined with Fourier‐transform infrared spectroscopy analysis, evidenced that water sorption in epoxies causes both plasticization and additional resin crosslinking, although the latter is prevented by the addition of MCC. The creep strain of the composites increased by 60% after conditioning, indicating that plasticization induced by water sorption plays an important role in the long‐term properties of the composites.

Characterization of Water Absorption, Thickness Swelling and Diffusion Coefficient of Natural Fiber/Epoxy Bio-Composites for Applications in Aquatic Environment

The aim of this work was to study the suitability of wood flour, fluted pumpkin stem and rice husk flour/epoxy bio-composites for application in aquatic environment. The water absorption, thickness swelling and diffusion coefficient of wood flour, fluted pumpkin stem flour, rice husk flour/epoxy bio-composites were investigated. Composites were prepared by the hand layup method at varying weight percentages of filler reinforcement (10, 20 & 30%). The increase in the addition of the fillers enhanced the water absorption, thickness swelling and diffusion coefficient of the composites. However, after 14 days of immersion, all the composites attained an equilibrium state. It was observed that with 30wt% filler loading, the fluted pumpkin stem flour epoxy composites showed the highest water absorption of 40.5%, diffusion coefficient of 10.80x10-8m2/s, followed by the wood flour epoxy composite with water absorption of 35.3%, diffusion coefficient of 8.17x10-8m2/s, while rice husk flour epoxy composites had the lowest water absorption of 16.5%, diffusion coefficient of 6.12x10-8m2/s. The same trend was observed for the composites with 20 and 10 wt% filler loading. In terms of thickness swelling, the wood flour composite showed 1.62%, followed by fluted pumpkin stem flour composite 1.40% and rice husk flour composite 0.35% with 30wt% filler loading. A similar trend was observed for the composites with 20 and 10wt% filler loading. This study can be useful to comprehend the effect of water absorption on the performance of natural fiber composites and help in creating designer compositions for use in building, construction and automotive.

Pore‐Scale Modeling of Water and Ion Diffusion in Partially Saturated Clays

AbstractAn accurate mechanistic understanding of solute diffusion in partially saturated clays is critical for assessing the safety of deep geological repositories for radioactive waste. In this study, a pore‐scale numerical framework is developed to simulate water and ion diffusion in partially saturated clays. First, the two‐phase Shan‐Chen Lattice Boltzmann method is employed to establish the liquid‐gas distribution in a reconstructed three‐dimensional pore geometry of a clay. An equivalent solute method is also developed and validated to improve the numerical stability of the solution at the liquid/gas interface corresponding to steep variations of the concentration and diffusion coefficient of the water tracer. By using a mobility‐distance relationship from molecular simulations, Fick's law is numerically solved to simulate water diffusion in nanopores, while the coupled Poisson‐Boltzmann‐Nernst‐Planck equations are solved to simulate ion diffusion under the influence of the electrical double layer (EDL). Our model reveals that the decrease of relative effective diffusion coefficients during the desaturation is more pronounced for ions than for water, due to the additional transport pathway of water tracers in the gas phase. The obtained effective diffusion coefficients of tritiated water and ions agree well with reported data from compacted sedimentary rocks. By comparing the local electric potential and the distribution of ion concentrations in single pores, the simulation results suggest that the EDL in unsaturated clays has a more complex influence on ion distribution than under fully water‐saturated conditions. This study provides critical insights into the coupled transport processes of solutes in partially saturated clays.

ReaxFF molecular dynamics of graphene oxide/NaCl aqueous solution interfaces.

In this work, the interaction of NaCl aqueous solution with graphene (G), graphene oxide (GO), and graphite oxide (GTO) is studied using the ReaxFF module of Amsterdam Modeling Suite (AMS) software. We consider four models using the NaCl aqueous solution, containing a graphene sheet (G), a single sheet of GO with epoxide and hydroxyl groups on its surface, 4 layers of GO to model GTO, and a bulk NaCl solution as a reference. The structural and dynamical properties of G, GO, and GTO were quantified by analyzing the functional groups, radial distribution functions, density profiles and diffusivities of water and ions. Due to the reactive force field, the systems underwent spontaneous modification of surface functional groups during the first 750 ps after which the structure stabilizes (the energy stabilizes in less than 400 ps). Pristine graphene in contact with the NaCl solution formed hydroxyl groups on the edges, i.e., converted to partially reduced graphene oxide. The epoxy groups (Oe) on the initial GO were rather unstable, leading to a reduction of their number, however, there was an increase in the number of hydroxyl groups (Oh), mainly at the edges. The interactions of NaCl with the carbon-based sheets are rather weak, including GO and GTO which are decorated with numerous functional groups. Diffusion coefficients of water agree with the available data, but discrepancies in Na+ and Cl- diffusivity compared to other references underscore the need for further development in the dynamic parameters of the reactive force field used. In essence, our research provides specific data previously unreported, laying a foundation for advancing water desalination system design. The study's novelty lies in its realistic approach to graphene/graphene oxide modification, comprehensive characterization, and the application of the reactive force field to explore the graphene oxide-NaCl aqueous interface, contributing to the development of a practical membrane system for water desalination.

Finely tuned water structure and transport in functionalized carbon nanotube membranes during desalination.

Molecular dynamics simulations were performed to tune the transport of water molecules in nanostructured membrane in a desalination process. Four armchair-type (7,7), (8,8), (9,9) and (10,10) carbon nanotubes (CNTs) with pore diameters around 1 nm were chosen, their interior surfaces were modified with -OH, -CH3 and -F groups. Simulation results show that water transport in nanochannel depends on confined water structures which could be regulated by precisely controlled channel diameter and chemical functionalization. Increasing CNT diameter changes water structures from single-file-like to be square and hexagonal-like, then into a disordered pattern, resulting in a concave-shaped trend of water permeance. The -OH functional groups promote structural ordering of water molecules in (7,7) CNT, but disrupt water structures in (8,8) and (9,9) CNTs, and reduce the order degree of water molecules in (10,10) CNT, moreover, exert an attraction to enhance surface friction inside channel. The -CH3 groups induce more strictly single-file movement of water molecules in (7,7) CNT, turning water structures in (8,8) and (9,9) CNTs into two and triangular column arrangements, improving water transport, however, causing again square-like water structure in (10,10) CNT. Fluorinations of CNT make water structure more disordered in (7,7), (9,9) and (10,10) CNTs, while enhance the square water structure in (8,8) CNT with a lower water permeance. Through changing channel diameter and functionalization, the low tetrahedral order corresponds to a more single-file-like water structure, associated with rapid water diffusion and high permeability; an increase in tetrahedrality results in more ice-like water structures, lower water diffusion coefficients, and permeability. The results of this study demonstrate that water transport could be finely regulated via a functionalized CNT membrane.

Assessment of calcium alginate gels as wall materials for encapsulation systems.

Calcium alginate gels are widely used to encapsulate active compounds. Some characteristic parameters of these gels are necessary to describe the release of active compounds through mechanistic mathematical models. In this work, transport and kinetics properties of calcium alginate gels were determined through simple experimental techniques. The weight-average molecular weight ( = 192 × 103 Da) and the fraction of residues of α-l-guluronic acid ( = 0.356) of sodium alginate were determined by capillary viscometry and 1 H-nuclear magnetic resonance at 25 °C, respectively. Considering the half egg-box model, both values were used to estimate the molecular weight of calcium alginate as = 2.02 × 105 Da. An effective diffusion coefficient of water ( = 2.256 × 10-9 m2 s-1 ) in calcium alginate was determined using a diffusion cell at 37 °C. Finally, a kinetics constant of depolymerization ( = 9.72 × 10-9 m3 mol-1 s-1 ) of calcium alginate was obtained considering dissolution of calcium to a medium under intestinal conditions. The experimental techniques used are simple and easily reproducible. The obtained values may be useful in the design, production, and optimization of the alginate-based delivery systems that require specific release kinetics of the encapsulated active compounds. © 2023 Society of Chemical Industry.

Water Effective Diffusion Coefficient in Dairy Powder Calculated by Digital Image Processing and through Machine Learning Algorithms of CLSM Micrographs.

Rehydration of dairy powders is a complex and essential process. A relatively new quantitative mechanism for monitoring powders' rehydration process uses the effective diffusion coefficient. This research focused on modifying a previously used labor-intensive method that will be able to automatically measure the real-time water diffusion coefficient in dairy powders based on confocal microscopy techniques. Furthermore, morphological characteristics and local hydration of individual particles were identified using an imaging analysis procedure written in Matlab©-R2023b and image analysis through machine learning algorithms written in Python™-3.11. The first model includes segmentation into binary images and labeling particles during water diffusion. The second model includes the expansion of data set selection, neural network training and particle markup. For both models, the effective diffusion follows Fick's second law for spherical geometry. The effective diffusion coefficient on each particle was computed from the dye intensity during the rehydration process. The results showed that effective diffusion coefficients for water increased linearly with increasing powder particle size and are in agreement with previously used methods. In summary, the models provide two independent machine measurements of effective diffusion coefficient based on the same set of micrographs and may be useful in a wide variety of high-protein powders.

Simulation study on the coupled heat and mass transfer of CO2 in a heavy oil-water liquid system based on an improved lattice Boltzmann (LB) method

This study investigates the heat and mass transfer when low-temperature CO2 diffuses in a heavy oil–water liquid system based on an improved Lattice Boltzmann (LB) method. First, we determine the CO2 diffusion coefficients in heavy oil and water and the heat transfer coefficients of heavy oil and water using the pressure drop (DP) method and the laser flash (LF) method, respectively. Then, a numerical model that couples the heat and mass transfer in the system is established based on the improved LB method. The effect of low-temperature CO2 on the temperature field of the system and the effect of changes in the temperature field on CO2 diffusion are investigated. Finally, we develop a micro-model reproducing the heat and mass transfer of CO2 in water and heavy oil-saturated porous media to validate the accuracy of the numerical model. The results demonstrate that the CO2 diffusion coefficients in heavy oil and water linearly increase with the temperature increases. The heat transfer coefficients of heavy oil and water are insensitive to the changes in temperature. The heat transfer process has a great impact on the mass transfer of CO2 in the liquid system. The CO2 diffusion velocity slows down as the system temperature decreases because of the heat transfer (from 400 K to 300 K), leading to a reduction percentage of 300 % in the CO2 front movement velocity. Compared to the scenarios neglecting heat transfer, CO2 diffusion distance and amount decrease by 38 % and 50 %, respectively because of the changes in the temperature field of the system.

Hydrothermal aging of glass fiber epoxy‐carbon nanocomposites and its service life predictions based on tensile strength

AbstractThis paper investigates the hydrothermal aging of pultruded glass‐fiber reinforced epoxy nanocomposite rods with carbon nanofillers. The nanocomposites developed in this study are proposed for the core of high‐tension low‐sag conductors in power transmission. Nanocomposites were fabricated with a nanomodified matrix containing 0.2 wt.% of multi‐walled carbon nanotubes and 0.6 wt.% of graphene nanoplatelets. The epoxy nanocomposites tensile strength and life predictions were determined under different water aging conditions. Objective of the study is to evaluate the water absorption kinetics and its impact on tensile strength, microstructure and to compute the service life under hydrothermal aging by predictive techniques. Nanocomposites were aged in water at 30, 50, and 80°C for a duration of 3000 h, and the microstructure and chemical composition were investigated. Based on Arrhenius's theory, a service life prediction model based on the tensile‐strength of the nanocomposite is established for hydrothermal aging. The results have shown that the addition of carbon nanofillers to the epoxy matrix improves the hydrophobicity and reduces the water diffusion coefficient. Water absorptions of the nanocomposites are observed to follow Fick's law, and its influence on the mechanical properties of the nanocomposite is evident and is more significant in epoxy composites without carbon nanofillers. After 3000 h of immersion at 50 and 80°C, the tensile strength retention is above 85%. The hydrothermal environment accelerates the development of micro‐voids and cracks, which are initially formed and observed to be the primary reason for the degradation in mechanical strength under service conditions, in addition to debonding of the fibers.Highlights Carbon nanocomposites were aged at different temperatures and durations. Service life prediction model established based on Arrhenius's theory. Addition of carbon nanofillers enhances hydrophobicity and reduces water diffusion. Tensile strength retention above 85% after 3000 h of aging. Hydrothermal aging accelerates aging contributing to strength degradation.

Evaluation of water diffusion, water vapor permeability coefficients, physicochemical and antimicrobial properties of thin films of nopal mucilage, orange essential oil, and orange pectin

There is a growing interest in the development of biodegradable, safe materials to extend the shelf life of food and replace non-biodegradable plastics. Several materials have been investigated that can be used as edible coatings to extend the shelf life of fruit and vegetable products. In the present work, the design and characterization of different films of nopal mucilage, orange pectin, and orange essential oil were investigated for their potential use as edible coatings. It was found that the pectin concentration had a significant effect (p<0.05) on the thickness, color, and transparency of the edible films. According to the results, the formulation 0.5% mucilage-0.25 % pectin-0.25 % essential orange oil was chosen. Infrared spectroscopy showed no changes in the chemical compounds of the film formulation. The XRD pattern showed that this thin film is amorphous and contains calcium oxalate of nopal mucilage and oleic acid. In the water vapor permeability tests, the films containing orange essential oil in their formulation showed a higher effective water diffusion and water permeability coefficients as compared to the other formulations. In addition, the concentration of orange essential oil has an antimicrobial effect (p<0.05) on some bacteria of interest for food safety. This work demonstrates a new methodology and measurement technique to determine the effective water diffusion and water permeability coefficients for edible thin films based on the photoacoustic effect.

Effect of Sonication and Edible Coating on Total Phenolic Content, Antioxidant Capacity, and Physical Characteristics of Infrared-Dried Sweet Cherries

This research studied the influence of combined ultrasonic (40 kHz, 150 W, for 3 min) and 0.2% xanthan gum (XG), guar gum (GG), and wild sage seed gum (WG) coating pretreatments on total phenolic content, antioxidant activity, drying time, effective water diffusivity coefficient ( D eff ), rehydration ratio (RR), total color difference ( Δ E ), and surface shrinkage (SS) of infrared-dried sweet cherries. The ultrasonic pretreatment increased the water transfer rate and water diffusivity during infrared drying and decreased the drying time of fresh sweet cherries. The edible coating enhanced the total phenolic content, antioxidant activity, dehydration time, and RR and decreased the D eff , Δ E , and SS values of infrared-dried sweet cherries. The highest value of total phenolic content (3469.7 μg galic acid/g dry) was recorded for pretreated sweet cherry samples by GG. The mean antioxidant activities for uncoated, XG-coated, GG-coated, and WG-coated sweet cherries were 35.64, 59.88, 54.38, and 61.19%, respectively. In this study, the sweet cherry D eff varied from 2.23 × 10 − 9 m2/s (for untreated cherries) to 5.00 × 10 − 9 m2/s (for sonicated and uncoated cherries). The experimental data for the drying curves were fitted to various single-layer equations, and the Page equation using the experimental constants best described the drying rate of sweet cherries. The mean Δ E values for uncoated, XG-coated, GG-coated, and WG-coated sweet cherries were 15.11, 9.91, 8.74, and 10.69, respectively.

Impact of water diffusion on electrical properties of epoxy nanocomposites

This study investigates the effects of water ageing at 80 °C on glass fibre hybrid epoxy nanocomposites with multi-walled carbon nanotubes and graphene nanoplatelets. Effect of water uptake in the epoxy matrix is mitigated by the inclusion of carbon nanofillers, leading to improved hydrophobic nature. A comparative study is performed on the water uptake of the epoxy-amine matrix cured with aliphatic amine, with 0.4 weight percent of MWCNT and 0.6 weight percent of graphene nanoplatelets (GNPs). Gravimetric assessment and electrical impedance measurements are carried out over a period of 3000 h to assess water diffusion coefficients and water saturation. Water absorption is measured until saturation, and results show that the water diffusion coefficient of the hybrid nanocomposites is increased from 2.51 × 10−8 (m2 s−1) at 27 °C to 3.32 × 10−8 (m2 s−1) at 80 °C and it is higher than that of the base epoxy composites. Cole–Cole diagrams have revealed heterogeneity of the composites studied. Water diffusion results in the plasticization of the matrix, and it manifests in the broadening of the tanδ peak observed in water-aged epoxy composites. With the inclusion of hybrid MWCNT and GNP nanofillers.,the water diffusion coefficient is reduced to half, and saturation is increased by four times.