Moisture Content Gradient Research Articles

Optimization of the plate drying process by electromagnetic radiation using the Green function method

An initial boundary value problem is formulated for calculating the heat-mass-energy fields in a homogeneous wet plate. To solve this problem, an original algorithm containing elements of analytical and numerical methods has been developed. In this method, solutions are written using the spatially one-dimensional Green function of the Neumann problem, which contains eigenvalues and eigenfunctions of the Sturm-Liouville boundary value problem. In comparison with the known numerical algorithms, the problems of the theory of electromagnetic drying for which its application can be effective are indicated. It is shown that the discrete supply of microwave energy significantly reduces the gradients of temperature, steam and moisture content, while reducing energy consumption by 11...12 %. The probability of an undesirable spontaneous temperature increase at the end of the drying cycle is significantly reduced, and the electrical and thermal conditions of the microwave energy source are improved.

The radial gradient of moisture content of silver birch wood in different seasons

Silver birch ( Roth) is classified in diffuse-porous wood category. In this case structure of wood tissue is quite similar across whole cross-sectional area. The aim of this study was to analyse cross-section variability of moisture content (MC) of growing silver birch wood, significant hardwood species in Polish forests. Investigations were performed on 120 model trees. In the trunk of each model tree, an increment core was collected at breast height. Samples were collected of 30 different trees in four different seasons. The greatest MC was observed during winter, lowest MC in summer. Differences in MC were statistically significant only between winter versus spring, summer, and autumn. Distribution of MC on cross-section was similar in each season. The greatest average value was observed close to pith, then it was decreasing in bark direction. The greatest difference between observed in spring – 19.51% (p < 0.05) and lowest in autumn – 4.66%. Distribution of green density (GD) on cross section was inverse proportional to MC value. Variations in GD and MC are relevant for log transport planning, weight-scaling systems, lumber drying and dynamic assessment of stiffness. Therefore, from an environmental loss perspective, it is important to determine changes in MC and GD across the year.Betula pendula

Functional traits indicate a continuum of tree drought strategies across a soil water availability gradient in a tropical dry forest

This study evaluates drought survival mechanisms of tropical dry forest (TDF) trees based on their functional traits (FTs). We addressed the following questions: (i) What are the dominant functional guilds (FGs) of tree species across a soil water availability gradient in TDF? (ii) What are the important FTs influencing tree species assemblage in different FGs? (iii) What is the functional composition of different FGs in the study sites, and how are they influencing biomass accumulation capacity (BAC) across the soil water availability gradient?We selected 12 FTs associated with plant water use strategies, viz., canopy cover intensity (CC), wood specific gravity (WSG), saturated stem water content (QWsat), leaf size or leaf area (LA), specific leaf area (SLA), relative water content (RWC), leaf dry matter content (LDMC), leaf nitrogen content (LNC), leaf phosphorus content (LPC), maximum saturated stomatal conductance (Gsmax), maximum saturated photosynthetic rate (Amax), and intrinsic water use efficiency (WUEi). By using these FTs, we classified 47 tree species by HCPC (hierarchical clustering on principal components) into three FGs, viz, drought avoiding (DAFG), drought resistant (DRFG), and drought tolerant (DTFG). For species grouping, QWsat was the most significant for DAFG, impacts of Amax, LPC, Gsmax and LNC were significant for DRFG, while LDMC and CC were significant for DTFG. Across the five forest fragments, along a soil moisture content (SMC) gradient, the three FGs exhibited significant differences in species richness, stem density, aboveground biomass, and biomass accumulation capacity (BAC). We observed increasing dominance of DAFG towards drier sites, while the abundance of DRFG and DTFG was higher towards moister sites. Among the three FGs, DTFG showed highest biomass and BAC in our study region. Strategies of DAFG were more associated with savanna habitats, while DRFG and DTFG exhibited strategies important for TDFs. Our findings could help forest managers in restoration and conservation of TDFs.

Non-Fickian Moisture Transport in Vegetable-Fiber-Reinforced Polymer Composites Using a Langmuir-Type Model.

The purpose of this article was to theoretically study the non-Fickian moisture absorption process in vegetable-fiber-reinforced polymer composites using a Langmuir-type model. Here, the focus was on evaluating the effect of the water layer thickness that surrounds the composite during the water migration process. The solutions of the governing equations were obtained using the finite volume method, considering constant thermophysical properties and non-deformable material. The results for the local and average moisture content and concentration, gradient values, and the transient rates of the free and bound (water) molecules in the process were presented and analyzed. It was observed that the water layer thickness strongly influenced the water absorption kinetics, the moisture content gradient values, and the equilibrium moisture content inside the material. It is envisaged that this new approach will contribute to better interpretation of experimental data and a better understanding of the physical phenomenon of water absorption, which directly affects the properties of composite materials.

Effect of Supercritical CO2 Drying on Moisture Transfer and Wood Property of Eucalyptus urophydis

Wood dried using supercritical CO2 has unique properties because water is removed directly from the cell lumens through the cycling between supercritical and gas phases. Eucalyptus urophydis green wood was dried by supercritical CO2 at 50 °C and pressure of 10, 20, and 30 MPa; the effect of supercritical CO2 drying on moisture content distribution and transfer, as well as the permeability and extractive content of the wood, was investigated. The results showed that the supercritical CO2 drying rate was high, showing the highest drying rate at 20 MPa and the lowest at 10 MPa. Drying rate increased with pressure below 20 MPa in this study; drying rate represented no positive relation to pressure over 20 Mpa. Moisture content distribution was more uneven in the low-pressure drying conditions and in the middle transverse section of the specimens. The moisture content gradient in tangential was greater than that in longitudinal, especially for the drying of 10 MPa, indicating that water was removed mainly in the former direction of wood. More extractives were removed from wood at higher pressure during supercritical CO2 drying. Bordered pits were broken up more at higher pressure conditions. The decreased extract yields and increased amount of opened bordered pits increased the permeability of the wood after supercritical CO2 drying.

Remote Sensing, Archaeological, and Geophysical Data to Study the Terramare Settlements: The Case Study of Fondo Paviani (Northern Italy)

During the Middle and Recent Bronze Age, the Po Plain and, more broadly Northern Italy were populated by the so-called “Terramare”, embanked settlements, surrounded by a moat. The buried remains of these archaeological settlements are characterized by the presence of a system of palaeo-environments and a consequent natural gradient in soil moisture content. These differences in the soil are often firstly detectable on the surface during the seasonal variations, with aerial, satellite, and Laser Imaging Detection and Ranging (LIDAR) images, without any information on the lateral and in-depth extension of the related buried structures. The variation in the moisture content of soils is directly related to their differences in electrical conductivity. Electrical resistivity tomography (ERT) and frequency domain electromagnetic (FDEM), also known as electromagnetic induction (EMI) measurements, provide non-direct measurements of electrical conductivity in the soils, helping in the reconstruction of the geometry of different buried structures. This study presents the results of the multidisciplinary approach adopted to the study of the Terramare settlement of Fondo Paviani in Northern Italy. Remote sensing and archaeological data, collected over about 10 years, combined with more recent ERT and FDEM measurements, contributed to the analysis of this particular, not yet wholly investigated, archaeological site. The results obtained by the integrated multidisciplinary study here adopted, provide new useful, interesting information for the archaeologists also suggesting future strategies for new studies still to be conducted around this important settlement.

Isothermal diffusion of water vapor in unsaturated soils based on Fick’s second law

In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mechanism of water vapor in unsaturated soil, a water vapor migration test device was developed to conduct the water vapor migration indoor test. The test results demonstrate that the characteristics of water vapor diffusion in unsaturated soil conformed to Fick’s second law. A mathematical model for water vapor diffusion under isothermal conditions in unsaturated soil was established based on Fick’s law. Factors including the initial moisture content gradient, initial moisture content distribution, soil type and temperature that affect the water vapor diffusion coefficient were analyzed. The results show that there was good agreement between the moisture content calculated by the mathematical model and obtained by the indoor experiment. The vapor diffusion coefficient increased with increasing initial moisture content gradient and temperature. When the initial moisture content gradient is constant, the vapor diffusion coefficient increases with the increase of matrix suction ratio in dry and wet soil section. The effect of soil type on the water vapor diffusion coefficient was complex, as both the moisture content and soil particle sizes affected the water vapor diffusion.

Cracking the code: real-time monitoring of wood drying and the occurrence of cracks

Predicting kiln-drying schedules for a given wood species is not yet possible, despite many research efforts. This is mainly due to insufficiently considering important spatio-temporal variables such as moisture and temperature gradients, and wood anatomical features during drying in the predictive modelling framework. To understand the influence of aforementioned variables, an experimental measurement set-up was developed consisting of heat-resistant load cells mounted in an oven to record the weight of the wood specimens dried at 100 °C. A camera was mounted outside the oven to acquire images of the end grain through the transparent door of the oven, as such enabling to monitor the occurrence of cracks. Furthermore, custom-made electrodes were inserted as well at different depths in the specimen to measure the electrical resistance, which relates to the moisture content. Specimens were also equipped with thermistors to record the temperature in the specimens at different depths from the surface. Heat-resistant wires from load cells, electrodes and thermistors were connected with data loggers outside the oven. Three specimens of basralocus (Dicorynia guianensis) were selected, measuring 50 mm wide, 50 mm thick and 120 mm long. The results show that it is possible to real-time monitor average moisture loss, local moisture content gradient represented by the electrical resistance gradient and wood temperature gradient as a function of time. These temporally resolved gradients can be related to the occurrence of cracks. This methodology enables to unveil interrelationships between the measured variables and changes of the wood anatomical structure, of utmost importance for the fine-tuning of kiln-drying schedules.

Study of the dielectric gradient values of reinforced concrete sample by considering radar measurements in an inverse problem

ABSTRACT The goal of this study is to develop a tool that will evaluate the moisture content gradient in the depth of reinforced concretes in the context of building safety. The monitoring of ageing phenomena, such as the corrosion of steel reinforcements, depends on the amount of water and on its gradient as they are directly related to the dielectric values of the concrete. In this paper, to obtain these values, we propose to solve an inverse problem for reinforced concrete. First, an experimental device based on radar measurements is proposed with its 3D numerical model. Next, we describe an inverse process to determine a dielectric profile according to the depth and validate it on measured data obtained for control samples.

Application of the Response Surface Methodology for Designing Oscillation Drying of Beech Timber

Oscillation drying is one of the possible approaches for reducing drying time and limiting drying defects of hardwood timber. This study aimed to design oscillation-drying schedules for beech (Fagus sylvatica L.) timber using the response surface methodology (RSM) and to develop an empirical model describing relationships between drying time, drying rate, moisture content gradient after drying, and the parameters of oscillation drying, i.e., dry-bulb temperature increase, equilibrium moisture content (EMC) decrease, and the duration of phase #1 in the drying schedule. The design employed 8 unique drying schedules for which early stage of drying was studied. The Gompertz model was used to describe the change in moisture flux as a function of moisture content, with estimated parameters of the model used to determine relations between the maximum flux at the initial moisture content, the maximum rate of flux change, and the critical moisture content for the maximum rate of flux change for each oscillation-drying schedule. Analysis of variance (ANOVA) revealed that the decrease in EMC was the only factor significantly influencing oscillation drying. For the most intense oscillation-drying schedule, maximum moisture flow was ca. 75% higher compared with the control drying schedule. Drying processes that accounted for a decrease of EMC from 15% to 12% were characterized by significantly shorter drying time (by 35.8%), 52.6% higher drying intensity, and ca. two times larger moisture content gradient. These results confirm theoretical findings relating the increase of oscillation-drying intensity with the difference in wet-bulb temperature between phases of the drying processes.

Soil biogeochemistry of the capillary fringe in laboratory mesocosms with contrasting soil textures

AbstractThe capillary fringe is a poorly defined, tension‐saturated region with important influences on soil biogeochemistry. The goal of this research was to evaluate the effects of the capillary fringe moisture gradient on biogeochemical processes and to assess whether these processes are more similar to those of unsaturated or saturated zones. Effects were documented during 118 d using two soils with contrasting textures in laboratory mesocosms. A water table was maintained at a constant height, and the parameters measured included soil moisture, inorganic N, decomposition, and reduction changes. Moisture levels suggest that capillary rise occurred ≥22.5 cm above the water table in both soils. Although limited by experimental methods, including using homogenized and sieved soil materials, biogeochemical trends for all measured parameters were seen by depth and between soils and seem to be influenced by water content and O2 diffusion. Nitrate concentrations increased above the water table. Decomposition was lowest in and immediately above the saturated water table and greatest where moisture and O2 were balanced. Reducing conditions existed ≥10 cm above the water table in the sandy soil and ≥5 cm in the loamy soil, indicating that these regions share characteristics with the saturated zone. The sandy soil showed reduction higher above the water table than the loamy soil, possibly due to structural and O2 diffusion differences due to experimental methods. Specific heights of capillary fringe were not identified; instead, the data support a model of a continuous moisture content gradient in the capillary fringe between the water table and soil surface.

Combined single-stage tempering and microwave vacuum drying of the edible mushroom Agrocybe chaxingu: Effects on drying characteristics and physical-chemical qualities

To reduce the moisture content gradient during drying, a single-stage tempering treatment based on parameters including intermediate moisture content (M), tempering temperature, tempering time and relative humidity was used to assist microwave vacuum drying (MVD) of the edible mushroom Agrocybe chaxingu. The influences of these parameters on product quality were analyzed by response surface methodology. The tempering treatments led to the increased effective moisture diffusivity and shortened effective drying time when compared with continuous MVD. Analysis of variance results showed M has the most significant impact on the quality parameters of A. chaxingu including the rehydration ratio, polysaccharide content, free amino acid content (FAA), and color, while the other three parameters only had a small but significant effect on some of those characteristics. Compared to continuous MVD, the total FAA content of tempering treatments enhanced by 10.81%–32.08%, especially aspartic, glutamic acid, isoleucine, leucine and valine. Overall, tempering-assisted MVD was found to be a potential drying of A. chaxingu, as it offers a more efficient drying process with better quality.

Temperature-driven migration of heavy metal Pb2+ along with moisture movement in unsaturated soils

Nonlinear coupled heat-moisture-contaminant transport equations are established to analyze the temperature-driven movement of moisture and migration of heavy metal Pb2+ in unsaturated soils. A new soil–water characteristic curve (SWCC) with hysteretic effects is constructed, which can directly give the scanning curve equations starting from any point on the boundary curves without introducing a new equation or new parameters. The theoretical results demonstrate good agreement with the results of laboratory tests in a soil column and satisfactorily verify the hysteretic effects of moisture movement induced by thermal cycling. Due to the obvious driving effect of the temperature gradient, the moisture in the soil column gradually moves to a distant point and develops a nonuniform distribution. Finally, the driving potential of the temperature gradient and the driving potential of the moisture content gradient reach a new equilibrium. In addition to the flow of liquid water, the movement of moisture also includes the transformation of liquid water to water vapor. With the movement of moisture, the migration distance of heavy metal Pb2+increases with increasing initial moisture content. Generally, kaolin clay with a high adsorption capacity has an obvious retardation effect on the migration of heavy metal contaminants.

Effects of hygrothermal environment on the buckling and postbuckling performances of stiffened composite panels under axial compression

Effects of hygrothermal environment on the buckling and postbuckling performances of stiffened composite panels under axial compression were investigated experimentally and numerically in this paper. Hygrothermal aging experiment on stiffened composite panels was conducted in 70 °C distilled water and the moisture uptake was analyzed every 24 h until to moisture saturation. Moisture uptake process and moisture content distribution along the thickness direction were analyzed by using finite element (FE) method. Thin region and thick region of stiffened composite panels were defined and classified respectively according to moisture uptake process. Then the axial compressive experiments were performed on the hygrothermal aged specimens, with comparison of compression on virgin specimens. Strains, loads, out-of-plane displacements, shortening and failure modes were analyzed comparatively. The results indicate the hygrothermal environment impose much negative effects on the stability and carrying ability of specimens. In the end, a new approach for simulating the dynamic properties of unsaturated specimens was proposed, which considered the gradient of moisture content. Effects of various moisture content on buckling and postbuckling performances were determined.

Characterization of moisture states and transport in MUF resin-impregnated poplar wood using low field nuclear magnetic resonance

In this study, the spin–spin relaxation time (T2) distributions of free water and bound water, as well as the moisture content (MC) profiles of MUF resin-impregnated poplar wood (Populous tomentosa) sample (RI) were investigated by low-field nuclear magnetic resonance, with the aim of providing insights into how MUF resin impregnation affects the moisture states and moisture transport in modified poplar wood during drying. The T2 curves demonstrated that the resin treatment did not increase the number of peaks in the T2 distributions, but affected the T2 value as compared to the control. Above the fiber saturation point (FSP), the T22 (corresponds to the free water in wood rays and wood fibers) of the RI sample exhibited an increase compared to the control, while the T23 (corresponds to the free water in the vessels) was almost unchanged. Below the FSP, a shorter T21 (corresponding to the bound water) of the RI sample was observed compared to the control. The drying curves and MC profiles indicated a significant difference in the moisture transport in the RI sample as compared to the control. The gradually cured resin system in the wood surface layer during drying provided a barrier for the transfer of water in the center layer toward to the surface, causing the resin curing reactions in the surface and core layers to be out of sync. Therefore, a more significant MC gradient was observed for the resin-impregnated sample.

In-situ monitoring of moisture diffusion process for wood with terahertz time-domain spectroscopy

The moisture diffusion process in balsa wood was monitored using the terahertz time-domain spectroscopy (THz-TDS) technique. The reflective THz signals were measured during the drying and the absorption phase of the moisture in the balsa wood. Measurements were conducted along the direction of the wood grain (longitudinal) and perpendicular to the direction of the wood grain (tangential). From the results, the relationship between the pulse intensity of the THz signal and moisture content was quantitatively investigated. Further, an image of the moisture concentration gradient was constructed through the THz intensity analysis. From the study, it was possible to monitor the variation of diffusion coefficient depending on the moisture content gradient from the THz measurement. Moreover, using the measured concentration gradient, the moisture diffusion coefficient could be derived regardless of complicated boundary conditions of diffusion. Consequently, the degree of moisture diffusion can be successfully measured using the THz-TDS technique. This can then be utilized for the determination of the moisture diffusion coefficient in various industrial structures.

Study on Runoff and Infiltration for Expansive Soil Slopes in Simulated Rainfall

In order to understand the hydrological process of expansive soil slopes, simulated rainfall experiments were conducted to study the effects of slope gradient and initial soil moisture content on runoff and infiltration for expansive soil slopes located in south China. The field program consisted of four neighboring slopes (70%, 47%, 32%, and 21%) instrumented by a runoff collection system and moisture content sensors (EC-5). Results from the monitored tests indicate that there was delay in the response of surface runoff. The runoff initiation time decreased with initial soil water content and increasing slope gradient. After the generation of runoff, the cumulative runoff per unit area and the runoff rate increased linearly and logarithmically with time, respectively. The greater the initial soil moisture content was, the smaller the influence of slope gradient on runoff. A rainfall may contribute from 39% to about 100% of its total rainfall as infiltration, indicating that infiltration remained an important component of the rainwater falling on the slope, despite the high initial soil water content. The larger the initial sealing degree of slope surface was the smaller the cumulative infiltration per unit area of the slope. However, the soil moisture reaction was more obvious. The influence of inclination is no longer discernible at high initial moisture levels. The greater the initial soil moisture content and the smaller the slope gradient, the weaker was the change of soil water content caused by simulated rainfall. The influence of initial soil moisture content and slope gradient on the processes of flow and changes of soil water content identified in this study may be helpful in the surface water control for expansive soil slopes.

Continuous microwave drying of germinated brown rice: Effects of drying conditions on fissure and color, and modeling of moisture content and stress inside kernel

Suitable fissures in kernels and the golden yellow color are the desired visual quality to evaluate germinated brown rice (GBR) subjected to drying processing. To improve the visual quality of GBR dried in a continuous microwave dryer, the effects of microwave intensity (1–5 W/g), air velocity (0–2 m/s), drying duration for per drying pass (2–10 min), and material layer thickness (4–12 mm) on the formation of visual quality of GBR in terms of fissure and color were investigated by using bench experiments and numerical modeling. The results showed that temperature and moisture content of the final dried GBR had high uniformity in the continuous microwave dryer, and most of the dried GBR kernels were in a “mild” (1–2 fissures in kernels) and “moderate” (3–4 fissures in kernels) fissure degree at the microwave intensity of 2–3 W/g. The increasing air velocity may weaken the effects of interior stress caused by moisture content gradients on fissures in GBR kernel. The chroma b*, representing the golden yellow color index of GBR, significantly (P < 0.05) increased with the microwave intensity and the drying duration for per drying pass of 4–6 min. The material layer thickness lower than 10 mm was suitable for the formation of golden yellow color appearance of GBR. The simulation results confirmed that microwave intensity had a positive effect on the formation of fissures for GBR in a continuous microwave dryer due to the rising stress along the short-axis direction of GBR kernel. The distribution of moisture content inside GBR kernel was relatively uniform under the microwave intensity lower than 3 W/g, and the higher moisture content gradients aggravated the evolution of fissures in kernels. Considering the desired visual quality of the final GBR, the appropriate microwave drying conditions of GBR were developed as microwave intensity of 2 W/g, air velocity of 1.0–1.5 m/s, drying duration of 6 min for per drying pass and 8 mm material layer thickness, which induced the generation of suitable fissures and the formation of golden yellow color for GBR under the continuous microwave dryer. This study may provide a preference for the industrial application of microwave drying of cereal materials such as GBR.

Mathematical description of super-high frequencies drying process of free-running food media in device with combined energy input

At the present time the maim quantity of free-running food products, including grains, are dried in units with convective method of heat input. To intensify convective drying, general attention is paid to improving the method of moving and mixing the product with drying agent, to guarantee fast and quality drying. The use of high and super-high frequency allows can significantly intensify the drying processes, because the phenomenon of super-high frequencies energy into heat conversion throughout the processed material volume contributes to the most uniform heating of the product, compared to other heat input methods. The optimal solution for drying free-running food products is a combination of convective and high-frequency heat input methods. This combination allows controlling gradients of moisture content and temperature, changing its directions, which significantly affects quality of the resulting dry product. In this regard, combined approach to drying process modeling is of practical interest: on the one hand, there are used analytical solutions, based on physical laws application or phenomenological equations, and, on the other hand, experimentally established a relationship between temperature and moisture content of media, which is considered as a heat and mass transfer characteristic for each material.

Drying characteristics of wood of invasive tree species growing in an urban environment

Non-native tree species are increasingly growing in urban environments, where they are exposed to cultivation and pruning measures, and in many cases their growth becomes uncontrolled, even invasive. In such cases the structure of the wood is more heterogeneous, with more tyloses, discolorations and decay, and higher moisture content. The drying of such wood is more demanding and cannot rely on the standard drying schedules. Therefore, the drying kinetics of the boards (thickness 22 mm, 28 mm and 46 mm) of three wood species (black locust – Robinia pseudoacacia; box elder – Acer negundo and horse chestnut – Aesculus hippocastanum) were analysed at 20 °C and 40 °C. Additionally, the drying quality was assessed by determining the moisture content gradient, drying stresses and presence of typical drying defects. In the drying tests the moisture content gradients were relatively low in all species, so no high drying stresses were generated. Due to the expected high risk of collapse, careful drying of green maple was needed, to prevent board twisting when a pronounced number of knots and greater fibre deviation occurred. Half-drying times indicated the longer drying of thicker black locust boards, and very careful drying of maple. We confirmed the usability of the half-drying time to compare the drying kinetics of different wood species and assortments.