Non-uniform Moisture Distribution Research Articles

Potential water repellency influenced CO2 and CH4 release from moist soils: Experiments on water-repellent Japanese Andosols

Soil, the largest terrestrial carbon (C) pool on earth is an important source of greenhouse gasses. Soil water repellency (SWR), a moisture-dependent characteristic, is an important factor that affects microbial decomposition and gas release since it causes non-uniform moisture distributions in the soil matrix. It is not clear whether potential water repellency (PWR), measured on dried soils, can influence carbon dioxide (CO2) and methane (CH4) emissions under unsaturated moist conditions. This study aims to fill this knowledge gap using two water-repellent soils, and one non-repellent soil (NRS; control), under two temperature levels. Samples were collected from water-repellent Chamaecyparis obtusa (CYP) and Cryptomeria japonica (CED) forests, and the NRS was collected from Field Science Center in Ibaraki University, Ibaraki, Japan. Capillary-moistened samples were placed in closed chambers and separately exposed to 25 °C and 35 °C. Gas sampling was conducted in 1, 7, 14, 21, and 28 d. The PWR was measured with separate samples under the same conditions. CED soils showed significantly higher PWR compared with the NRS and CYP. The gas emission per g soil organic C (EGC; mg g−1 SOC h−1) was significantly low in CED soils compared with NRS and CYP, while NRS showed the highest emission. EGC of CO2 and CH4 showed significant strong negative correlations with PWR. The emission of CO2 and CH4 significantly increased with increasing temperature, and the Q10 was significantly high for CH4. Results indicated that the sensitivity to elevated PWR was higher for emission of CO2, whereas the sensitivity to the elevated temperature was higher for the emission of CH4. It was clear that PWR can influence moisture distribution in soil matrix in unsaturated moist soils and the processes that limit gaseous C emission. Further experiments are required on possible processes that enable PWR to influence gaseous C emission from moist soils.

Investigation of differential shrinkage stresses in a revolution shell structure due to the evolving parameters of concrete

Abstract The article focuses on the influence of differential shrinkage linked by drying at the early-age displacements and strain distribution of a concrete ring specimen. Depending on the gradient of dimension changes through the thickness, tensile stress occurs near the exposed surface where drying is greater and thus results in strain gradients development. An experimental design was carried out on a concrete ring cast in laboratory conditions in order to monitor strains and displacements. Subsequently, a finite element method was used to simulate the ring’s behaviour in drying conditions. The gradient development linked by a non-uniform moisture distribution in the thickness is established by solving the non-linear partial differential drying equation with Mensi’s diffusion law. The stress and displacement analysis was modeled by three nodes curved shell FEM (CSFE-sh) based on strain approximation with the shell theory. Finally, the ring’s behaviour includes both differential shrinkage resulting in the mechanical and physical properties of gradients development in the thickness and the influence of prestressing, in which the tensile creep effects have a great influence. The comparison of experimental results with numerical simulation shows that drying and tensile creep phenomena have the most important influence on the early-age stress development in the walled ring.

Effect of Samples Size on the Water Removal and Shrinkage of Eucalyptus urophylla × E. grandis Wood during Supercritical CO2 Dewatering

Eucalyptus urophydis E. grandis green wood with different lengths were dewatered using CO2 that was cyclically alternated between the supercritical fluid and gas phases. The results indicate that shorter specimens can be dewatered to below the fiber saturation point (FSP). There was no significant difference in the dewatering rate between the specimens of 20 and 50 mm in length. The dewatering was faster when the moisture content (MC) was over the FSP, leading to a greater gradient and a non-uniform distribution of moisture. The MC distributions in all specimens had no clear differences between in tangential and radial directions. Supercritical CO2 dewatering generated a different moisture gradient than conventional kiln drying. Most water was dewatered from the end-grain section of the wood along the fiber direction, but a small amount of water was also removed in the transverse directions. There was no deformation in the specimens when the MC was above the FSP.

Time-dependent behavior of full-scale precast post-tensioned (PCPT) girders: Experimental and finite element analysis

Excessive volumetric changes associated with shrinkage and non-uniform moisture and heat distribution along long-span girders induce unwanted curvatures. This study aims at investigating both short- and long-term measurements of various quantities involving midspan deflections, tendon strains, longitudinal steel bar strains, concrete strains, and thermal changes in precast-post-tensioned (PCPT) girders. A total of 2 PCPT girders were cast in this study with symmetrical structural and geometrical details. Post-tensioning of the first and second girders was performed on the 28th and 120th days of their casting, respectively. Long-term measurement was performed on the first girder. It was observed that all measured parameters increased swiftly during post-tensioning. During the initial 30 days after post-tensioning, a gradual increase in all parameters was observed, whereas all measured parameters exhibited negligible increase beyond that. A Finite Element Model was generated using ATENA to estimate short-term deflections of PCPT girders during post-tensioning. In general, a good agreement between experimental and analytical midspan deflections was observed.

Spatial distribution and dynamics of cotton fine root under film-mulched drip irrigation

Fine roots distribution and dynamics (production, mortality, and longevity) significantly impact the crop soil ecosystems. However, the spatial distribution and dynamics of cotton (Gossypium hirsutum L.) fine roots under film-mulched drip irrigation are poorly understood. The present study aims to characterize these distributions and dynamics measured using a minirhizotron technique and the influence of soil conditions. The non-uniform distribution of soil moisture and salinity may lead to the differences of root length density (RLD) distribution. A clear decreased trend for the average RLD was observed in the shallow soil layer due to high localized salinity accumulated after brackish water irrigation. There existed a clear high soil moisture content strip at depth which may lead to a high RLD peak in the 95–100 cm soil layer. Average live root production was characterized by a very high rate during the initial growth stage followed by a decline after budding, which in turn was followed by a slight increase during boll opening. The average number of new roots was highest during the initial growth stages, decreasing after the budding stage. Thinner roots in the deep soil had shorter lifespans than those in shallow soil. Our study indicated that the minirhizotron technique can be used reliably as an in situ, non-destructive method for estimating cotton fine roots distribution and dynamics under film-mulched drip irrigation. To evaluate cotton fine root distribution and dynamics under film-mulched drip irrigation more accurately, a cotton root system architecture model could be parameterized in space and time based on the minirhizotron observations.

Intensify staple fibre drying by optimizing air distribution in multistage convective dryer using CFD

A non-uniform air distribution in the conveyor dryer contributes towards an uneven drying of material. In case of cellulosic fibre drying, portion of fibre bed, which is exposed to high air flow rate, dries faster compared to portion receiving lower air flow at the same temperature. Therefore, non-uniform moisture distribution is observed across the fibre bed. Along with on-field measurement, 3D Computational Fluid Dynamics (CFD) modeling was carried out to study air profile inside the convective dryer (capacity ∼x223C20 TPD). Validated model was used to design an optimum air distribution sieve to enhance the air uniformity which leads to uniform moisture across the dryer width. Five different air distribution sieves (Design – 1–5) were designed, and air velocity distribution were compared. Air distribution sieve with overall 17% opening (Design-4) shows 64% higher air uniformity from the base case which enhances production of premium grade (moisture range: 10.5–11.5%) fibres by 5% at the commercial scale. The robustness of the adopted design also shows its scalability from small (∼x223C20 TPD) to large scale dryer (capacity >100 TPD).

Experimental study on the effect of key mix design parameters on shrinkage and cracking resistance of dry-mix shotcrete

Shotcrete is used in a wide variety of repair applications that usually results in concrete elements having a large surface area. After curing, this large exposed surface area-to-volume ratio can lead to a non-uniform moisture distribution in the in-place shotcrete which will create differential drying shrinkage. The shrinkage and potential subsequent cracking depend on the selected material proportions and the curing regime. The three-fold focus of this study is to investigate (i) the possibility of improving the shrinkage performance of dry-mix shotcrete by optimizing the coarse aggregate and cement content, (ii) the influence of silica fume (SF) and a combined SF and fly ash (FA), (iii) and the influence of polymer, shrinkage-reducing admixture (SRA) and crack-reducing admixture (CRA) on shrinkage and cracking resistance of dry-mix shotcrete using a modified restrained shrinkage ring test. The results indicate that SF, FA, polymer, SRA, or CRA have the potential of reducing shotcrete rebound as well as improve their porosity and placement quality. The results also show that the effect of cement content on shrinkage is relatively small. The addition of SF or combined SF/FA increased the cracking potential of the dry-mix shotcrete mixtures while the addition of polymer, SRA, and CRA reduced the total free shrinkage and increased the cracking resistance of shotcrete. The results further indicate that shrinkage and cracking resistance of shotcrete are closely related to mixture parameters.

Ecological and morphological features of Rhodiola rosea L. in natural populations in the Altai Mountains 

AbstractThe paper presents the results of the comprehensive study of Rhodiola rosea L. in natural populations in the Altai Mountains. The phytocoenotic confinement, demographic structure, and morphological characters of coenopopulations of Rh. rosea were studied in different ecological and coenotic conditions in the Chemal and Kosh-Agach regions of the Republic of Altai. Correlation between the morphometric parameters and their calculated values for the shoot and sex of the studied individuals, as well as environmental factors, was revealed. Rhodiola rosea L. is a valuable medicinal plant used for functional diseases of the central nervous system. At present, the natural reserves and areas of natural growth of the golden root have decreased significantly. The species is included in the Red Data Book of the Russian Federation (2008) and many regional Red Data Books of Siberia. In the Altai Mountains, Rh. rosea is widespread throughout the highlands, where it has occupied a wide range of habitats. The study showed that the highest values of ecological and effective density are characteristic of coenopopulations which are part of various hygrophytic variants of alpine and subalpine miscellaneous herbs with a high total projective cover of the herbaceous layer (CP 1, 2, 3, 4). The lowest values were found for coenopopulations growing in communities with a scarce herbaceous layer or dense shrub layer, and on steep gravelly slopes with crumbling soil and nonuniform moisture distribution (CP 5, 6, 8, 9). The studied coenopopulations are normal, full-membered, or incomplete-membered (some of them lack postgenerative individuals). In terms of the ontogenetic spectra, they are mainly left-sided, with a predominance of young generative individuals (CP 4, 5, 7) or bimodal, with an additional peak for old generative individuals (CP 2, 3, 6, 8). Male and female individuals Rh. rosea differ in many morphometric characters of the generative shoots. In some coenopopulations (CP 2, 3, 6, 9), male and female individuals show multidirectional deviation of characters compared to the totality, which indicates that in different environmental conditions these characters are not only genetically determined but can also be related to the sex of individuals.

Electrical Capacitance Tomography to Measure Moisture Distribution of Polymer Foam in a Microwave Drying Process

Moisture distribution information is a critical element in drying processes. The drying of products by employing high-power microwave (MW) technology is widely used in the industry. Although microwaves allow volumetric and selective heating resulting in a significant reduction of processing time and energy consumption, there is always a risk of non-uniform moisture distribution in the final product. This paper investigates the capability of a designed electrical capacitance tomography (ECT) sensor to estimate the moisture distribution of polymer foams in a microwave drying process. The moisture distribution is estimated based on the non-intrusive contactless measurements of the electrical capacitances between the electrodes mounted on a frame around the target polymer foam. The obtained moisture information can be employed as feedback to a controller to adjust the power level of each microwave source in the microwave system to reduce or eliminate the non-homogeneity of the moisture distribution inside the polymer foam. In a series of experiments, we first examine the capability of the ECT sensor in estimating the moisture distribution in a stationary foam. We extend the tests to estimating the moisture distribution in a case where the foam is moving on a conveyor belt. Several study variables are taken, including the sample size, the sample location, the moisture percentage, the conveyor belt speed, and the microwave power. These experiments show that the sensor has a satisfactory accuracy in estimating the moisture distribution of the foam, and the ECT measurements can be further used in a closed-loop control system.

An IGBA Algorithm-Based Curve Reconstruction Method of Frequency-Domain Dielectric Spectroscopy for OIP Bushing With Nonuniform Moisture Distribution

Oil-impregnated paper (OIP) bushing is essential equipment in traction power supply systems, and its moisture status is directly related to the power transmission of high-speed railway. Also, the moisture distribution in the OIP bushing insulation is usually nonuniform. The frequency-domain dielectric spectroscopy (FDS) method is now widely accepted as the most potential method for evaluating the moisture status of the OIP traction bushing with nonuniform moisture distribution. However, as far as the FDS curve reconstruction of field bushing is concerned, it remains a challenge. In this article, based on the extended Debye model, a new curve reconstruction method (including equivalent circuit and mathematical models) of the bushing dielectric response is proposed. Then, the reconstruction method is converted into a mathematical problem of programming optimization. Based on the advantages of metaheuristic algorithms such as simplicity, flexibility, derivative-free mechanism, and local optimal avoidance, an improved metaheuristic algorithm was used to address the optimization problem. Finally, the proposed method was tested on bushing samples and real bushings. The research shows that the proposed method of curve reconstruction can well characterize the FDS curves of the traction bushing insulation with the nonuniform moisture distribution.

An improved ring test to assess cracking resistance of concrete under restrained shrinkage

Self-restraint caused by differential shrinkage along the radius of a concrete ring has great driving effect on the restrained cracking in the traditional ring test. In order to estimate cracking potential of concrete under restrained shrinkage, i.e. steel ring restraint effect, an improved circular/elliptical ring test was proposed by pre-setting a 6 mm long real crack at the inner circumference of the concrete specimen. Meanwhile, a numerical study based on fracture theory was conducted to investigate the cracking mechanism of the improved ring test. By introducing the fictitious crack model, the crack initiation age and propagation process in the ring specimen were simulated using the initial fracture toughness-based cracking criterion. The driving forces of the shrinkage cracking, provided by self-restraint and steel ring restraint, were analyzed and the influence of the pre-set crack length on the cracking age was discussed. The results indicated that, different from the traditional ring test, the shrinkage crack firstly initiated from the pre-set crack and then unstably propagated toward the outer circumference of the concrete in the improved method. In the crack propagation process, the self-restraint provided cracking insistence rather than driving force on the shrinkage cracking due to the bending effect along the radial direction caused by non-uniform moisture distribution in concrete. Therefore, the driving force of the shrinkage cracking was totally provided by the steel ring restraint and would overcome the cracking resistances from concrete material and non-uniform shrinkage. Furthermore, the advantage of the elliptical geometry in increasing the restraining level was still available for the improved ring test with a pre-set crack, which could make the shrinkage cracking occur in advance and enhance the steel ring restraint.

A High-Precision Diagnosis Method for Damp Status of OIP Bushing

An accurate assessment of the damp status of oil-impregnated paper (OIP) bushings is crucial for the power industry to make informed decisions on the maintenance and replacement schedule of bushings. This article proposes a hybrid of the convolutional neural network (CNN) and the hidden Markov model (HMM) for estimating the damp status (i.e., moisture level and moisture source) of bushings especially when nonuniform moisture distribution exhibits in the bushing. First, simulation models of moisture diffusion and frequency-domain spectroscopy (FDS) of the OIP bushing were constructed using the finite element modeling (FEM) approach. Then, CNN was employed to extract informative features from FDS results of the OIP bushing, which is sensitive to both concentrations and sources of moisture. Finally, HMMs were further utilized as a strong stability tool to recognize the damp status of OIP bushings. The proposed method was implemented to identify the bushing damp status using both simulation data and real-life measurements. Identification results demonstrate that the proposed method has high accuracy in determining the moisture level and moisture source of the OIP bushing insulation.

Artifacts in electrical measurements on wood caused by non-uniform moisture distributions

Abstract This paper examines how the moisture conditioning method affects the electrical conductance of wood. A widely used dataset was acquired by Stamm in 1929 who used a method of conditioning where water-saturated wood specimens were partially dried, sealed and left for a period of time for moisture to be redistributed before the electrical conductance was measured. However, more recent measurements combined conditioning above saturated salt solutions and pressure plate/pressure membrane techniques to obtain equilibrium moisture contents at constant relative humidity levels in the full moisture range. In this paper, the electrical conductance as a function of moisture content was compared for these two conditioning methods. When the specimens were conditioned to constant relative humidity levels, the data obeyed a percolation model better than when the conditioning procedure by Stamm was used. This was attributed to that Stamm’s method gives moisture gradients through the specimen because of sorption hysteresis effects, even though the wood is conditioned to a steady-state moisture content. Equilibration to constant relative humidity levels thus provided more well-defined moisture states and that the data followed a percolation model indicates that the mechanism of electrical conduction in wood does not change, even at high moisture contents.

Moisture profile analysis of food models undergoing glass transition during air-drying

Moisture profiles evolution of a cellular food product (potato) and two non-cellular food models made with maltodextrins (DE19 and DE36) were investigated during air-drying at two different temperatures, 25 °C and 55 °C. MRI results of suggested a non-uniform moisture distribution within potato, whilst the non-cellular food models had a more uniform profile. As expected, temperature had an impact on the drying kinetics and on the pore formation. While temperature had no impact on dry layer development for potato, it had a major impact on dry layer development for non-cellular food models. The fact that the two non-cellular food models used in this study have different glass transition temperatures but presented the same dry layer development curve does not support the hypothesis that glass transition is the driver mechanism for dry layer formation. The applicability of Fick's law was assessed by fitting experimental moisture profile data to quadratic polynomials. Fick's law provided a fairly accurate estimation of the water profiles of materials having different glass transition temperatures only when the dry layer at the surface was not taken into account, and more specifically during the middle stages of drying.

Theoretical and experimental investigation into the moisture migration characteristics of coal during oscillatory motion

It is a common occurrence that the moisture migrates during coal handling, such as storage, conveying and shipping. This results in a non-uniform moisture distribution giving rise to problems in handling. Current theories and mathematical models are mainly focused on static moisture migration, which is not suitable for dynamic moisture migration scenarios. To find out how moisture migrates in coal during oscillatory like motion, a theoretical model is established based on the Green-Ampt equation. The theoretical model assumes that hydraulic conductivity is an average value and water can be drained from the bottom. An oscillation factor is introduced to the hydraulic conductivity to suit the oscillation condition and a water-voids ratio is added to suit the model in an unsaturated drainage. These factors, including water based particle density, free drained saturation (FDS) moisture content, particle size distribution, are obtained through experiments. The predicted value of drained water from the theoretical model is validated by shipping log data of drained water from coal, which proves the model is practicable for calculating the mass of drained water of coal during oscillatory like motion.

Freezing of partially saturated air-entrained concrete: A multiphase description of the hygro-thermo-mechanical behaviour

Even though air-entrained concrete is usually used for concrete structures located in cold climates that are exposed to wet environments, frost damage is frequently detected during inspections. However, it is often hard to assess the extent and severity of the damage and, thus, there is a need for better tools and aids that can complement already established assessment methods. Several studies have successfully shown that models based on poromechanics and a multiphase approach can be used to describe the freezing behaviour of air-entrained concrete. However, these models are often limited to the scale of the air pore system and, hence, hard to use in applications involving real structures. This study proposes a hygro-thermo-mechanical multiphase model which describes the freezing behaviour of partially saturated air-entrained concrete on the structural scale. The model is implemented in a general FE-code and two numerical examples are presented to validate and show the capabilities of the model. The first concerns a series of experimental tests of air-entrained cement pastes, whereas the second aims to show the capability of the model to account for an initial non-uniform distribution of moisture. While the model predictions underestimate the magnitude of the measured strains, the results still show that the model can capture the general freezing behaviour observed in the experimental tests on the structural scale. Furthermore, the results demonstrate that the model is capable of describing freezing induced deformations caused by non-uniform moisture distributions.

Effect of Vertical Distribution of Soil Water on N<sub>2</sub>O Emission under Drip Irrigation

N2O emission has obvious water effect, but the current research is not deep enough. The soil wetting mode of drip irrigation technology is obviously different from that of conventional irrigation. Using the method of soil box indoor simulation, the N2O emission under different soil vertical water content was analyzed. Hydrus Software was used to simulate the soil wetting body under different drip irrigation technical parameters, the relationship between the combination of drip irrigation technical parameters and soil vertical water content was studied, and then the relationship between the N2O emission and the combination of drip irrigation technical parameters was proposed. The results showed that soil N2O emission flux increased with the increase of soil moisture, and the maximum emission flux was three times as much as the minimum emission flux. Under the condition of uniform distribution of soil moisture, soil N2O emission flux was smaller than that under non-uniform distribution of soil moisture. Hydrus software simulation results show that drip flow rate is 2.0 L/h, the irrigation period is 5 days, the irrigation quota is 12 mm, and the soil N2O emission flux is the largest. Adjusting the combination of technical parameters of drip irrigation can reduce soil N2O emission flux.

Simulation of Stresses Induced by Heat and Mass Transfer in Drying Process of Clay-like Material

Drying represents one of the oldest unit operations employed in industrial processes. Drying is viewed as a process of simultaneous heat and mass transfer. Porous Clay-like material undergoes stresses due to non-uniform distribution of temperature and moisture induced by heat and mass transfer respectively. The aim of this work is to simulate the stresses induced by heat and mass transfer during drying. A mathematical model to simulate the convective drying of a porous material like clay has been developed. The problem investigated involves highly coupled equations considering heat, mass, and mechanical aspects. The particularity of the model is that it takes into account the strong coupling between mass transport, heat transport and mechanical behavior of the material. The variables of coupling are the solid deformation, moisture content and temperature of porous medium. A numerical solution is sought to foresee the variation of moisture content, temperature, shrinkage, heat transfer induced stresses and mass transfer induced stresses during drying. The solution developed as a model is capable of predicting the quality of the product through a failure criterion. The model is validated through the comparison of simulated and experimental data. Simulation results show that the heat transfer induced stresses are significantly less important in compression with the mass transfer induced stresses and can be neglected in modeling of drying process.

FDS analysis for multilayer insulation paper with different aging status in traction transformer of high-speed railway

The traction transformer of a high-speed railway is long-term subjected to the effects of impulse traction loads, such that the aging status of a multilayer insulation paper between high and low voltage windings is non-uniformly distributed due to the non­uniform distribution of temperature. To enhance the use of the frequency domain dielectric spectroscopy (FDS) method in engineering, this paper studies the effects of non-uniform thermal aging on the frequency domain dielectric spectrum of multilayer insulation paper. Based on the experimental designs and preparation of experimental materials, the frequency domain dielectric spectrum of a multilayer insulation paper with uniform and non-uniform thermal aging distribution was tested. Afterwards, the effects of non-uniform thermal aging on the frequency domain dielectric spectrum of multilayer insulation paper were discussed and analyzed based on the tested results. The results show that: 1) The effects of the non-uniform distribution of DP (cellulose structure) can be ignored. The non-uniform distribution of the aging byproducts (except moisture) has limited effects on the tested results, which is far less than the effects of moisture. The non-uniform distribution of moisture is the dominant factor and affects the results. 2) In terms of insulation paper with a defined aging status, its order in the multilayer insulation paper does not affect the tested results. 3) The tested results of the insulation samples with a non-uniform aging distribution can no longer reflect the moisture content of the wettest section, and the evaluated moisture content is slightly higher than the average moisture content of the multilayer insulation paper.

Partial wetting irrigation resulted in non-uniformly low nitrous oxide emissions from soil

Partial wetting irrigation influences soil moisture distribution, which potentially changes soil nitrous oxide (N2O) emission. Incubation experiments were conducted to reveal the impact of non-uniform moisture distribution on soil N2O emissions under subsurface-drip-irrigation (SDI), with surface-irrigation (SI) as a control. Results indicated that soil N2O emission from different subregions of SDI soil varied synchronized to soil moisture. The wetting-drying process in different soil subregions under SDI incurred pulse N2O emissions unexceptionally, but the pulse magnitudes and timing of the occurrence varied among subregions. The pulse N2O emission magnitudes positively correlated to the match degree of soil moisture to the optimal soil moisture level for peak N2O emissions. The soil water-filled-porosity WFPS ranges for peak N2O fluxes, the determine coefficient of the exponential functions between N2O flux and soil WFPS and its average slopes, decreased gradually from the central to periphery SDI soil subregions. Both peak and cumulative N2O fluxes were much lower from the periphery subregions than from central subregions. On the whole, SDI reduced the cumulative N2O emissions by 77.3–86.7% compared to SI, with periphery suberegions of R3 and R4 contributing for more than 76%. The partial wetting SDI irrigation can significantly reduce soil N2O emissions and is a promising strategy for soil N2O emission mitigation. Further research should be conducted on how to design SDI properly to balance the soil moisture uniformity/efficiency and soil N2O emission reduction.