Water Transport Model Research Articles

Nitrous oxide and nitrate as indicators of subsoil removal of N in pig slurry applied to Luvisols in Western Denmark

This one-year study examined effects of autumn- vs. spring- application of pig slurry, and the effect of a nitrification inhibitor (DMPP) for autumn-applied slurry, on transport and transformations of nitrogen in the soil profile. Duplicate field plots had ceramic suction cells at 50, 100, and 150 cm depths to calculate leaching for each treatment using NO3− concentrations and percolation simulated using a water transport model. Furthermore, soil moisture, soil texture and bulk density at 50, 100 and 150 cm depth, and water table level, were recorded. During campaigns, subsurface N2O concentrations at 20, 50, 100, and 150 cm depths, and N2O fluxes to the atmosphere, were monitored for indicators of denitrification activity. Autumn-applied pig slurry showed evidence for NO3− removal between 50 and 100 cm depth, and N2O concentration profiles indicated high denitrification activity around 50 cm depth. Autumn-applied slurry showed higher N2O emissions and lower crop yields compared to spring application, indicating losses occurred during winter. DMPP did not reduce average NO3− leaching, nor affect N2O emissions, but treatment effects were confounded by heterogeneity in compaction, clay content, and water table depth at plot level. The study showed that accounting for transport and transformations of N in the subsoil can contribute to understanding the environmental controls of N leaching, as well as direct and indirect N2O emissions.

Simulation of Heat and Water Transport on Different Tree Canopies: A Finite Element Approach

Heat and water transport modeling is a widely explored topic in micro-meteorology, agriculture, and forestry. One of the most popular models is the Simultaneous Heat and Water (SHAW) model, which includes partial differential equations (PDEs) for air-soil temperature and humidity, but with a priori discretized PDE for the foliage temperature in each canopy layer; it is solved using the finite difference method and the canopy shape is defined as a simple rule of proportionality of total quantities such as the total leaf area index. This work proposes a novel canopy shape characterization based on Weibull distribution, providing a continuous vertical shape function capable of fitting any tree species. This allows formulating a fully continuous SHAW-derived model, which is numerically solved by a finite element approach of P1 Lagrange type. For this novel approach, several numerical experiments were carried out to understand how the shape of well distinguishable canopies influences heat and water transport.

Enhanced Modeling of Water Diffusion in Natural Fibers: Application to Diss Fibers

ABSTRACT Water diffusion through natural fibers represents an important aspect with regard to the integrity of biocomposites. Usually, diffusion model is defined assuming circular fiber cross-sections, while microscopic analysis findings revealed other geometries. This was found to affect the modeling of water transport through fibers and provide a gap versus experimental data. This work aims to present a numerical approach using finite element method to overcome the limits of use of analytical approaches relating to the morphological shape of vegetal fibers. The cross-section of the Diss fibers was observed by an optical microscope and simulated at an ellipsoidal shape after processing the images. Then, the average morphological parameters were determined. A numerical finite element model was implemented based on the observed geometry in order to determine the diffusion coefficient by an inverse approach compared to experimental results. The results showed that the numerical approach made it possible to raise the effect of fiber morphology, often assumed to be circular for plant fibers in analytical approaches, on the diffusion coefficient value, which was defined by a unique diffusion coefficient.

Water transport in recycled aggregate concrete under sustained compressive loading: Experimental investigation and mesoscale numerical modelling

The durability properties of load-induced damaged concrete incorporating recycled concrete aggregates (RCAs) have previously been reported, but the investigation on water transport in recycled aggregate concrete (RAC) subjected to sustained loading remains to be limited, especially involving both numerical simulation and experimental aspects. This paper presents a comprehensive exploration on capillary water absorption in RAC under various sustained compressive stress levels (λc = 0, 0.1, 0.3, 0.5, 0.7). An improved experimental set-up was self-designed for realizing the coupled action of sustained compressive loading and water absorption by RAC, and then a series of water absorption tests for specimens with different replacement ratios of RCAs (0, 30%, 50%, 100%) were experimentally conducted. The coupled effects of sustained stress level and replacement ratio on the sorptivity of RAC were further discussed. The quantitative correlation between the sorptivity and stress level was obtained to derive the formula of hydraulic diffusivity. Based on the unsaturated flow theory and Mazar's damage variable, the prediction model of water transport in load-induced damaged concrete was established. A mesoscopic model of RAC modelled as a five-phase composite material by considering the old and new interfacial transition zones (ITZs) as interphases was developed and employed to numerically simulate the process of water transport in load-damaged concrete. The mechanical and hydraulic parameters for multiple ITZs of RAC were determined by summarizing the previous studies. The visual numerical results indicate that the distribution of water content and wetting front of penetration depth were remarkably affected by the stress level and the content of RCAs. The comparison of cumulative amount of water absorption indicates that the numerical results agreed well with the obtained experimental measurements, fairly validating the feasibility and accuracy of the developed models. It further illustrates the mesoscopic numerical modelling can be practically adopted to simulate water transport process coupled with sustained loading and also visually exhibit the wetting front of water penetration in RAC.

A new quasi-3-D model with a dual iterative coupling scheme for simulating unsaturated-saturated water flow and solute transport at a regional scale

Soil water in an unsaturated zone is the major source of groundwater recharge, and likewise soil contaminants are the major source of groundwater contamination. It is thus essential to jointly consider soil water movement and solute transport together with groundwater movement and solute transport, which is particularly important when addressing regional-scale problems. This study developed a new quasi-3-D model for simulating regional-scale saturated–unsaturated water movement and solute transport in arid and semi-arid agricultural areas. The unsaturated soil water movement and solute transport processes are simulated by a 1-D soil water and solute transport model referred to as UBMOD, and the saturated groundwater movement and solute transport are simulated by MODFLOW and MT3DMS. In the quasi-3-D model, the soil water movement and groundwater movement modules are iteratively coupled and the soil solute transport and groundwater solute transport modules are iteratively couple. This is referred to as a dual iterative coupling scheme. Strength and weakness of the quasi-3-D model and the coupling scheme were evaluated with two synthetic cases and a real-world application. Results indicate satisfactory performance of the model, which demonstrates the reliability of the dual iterative coupling scheme. Besides, the impacts of spatial and temporal discretization and stress period on model stability and accuracy has been evaluated. And the model is more computationally efficient than the fully numerical methods based on Richards’ equation when the problem is a 2D/3D problem with a scale larger than 10 m. Moreover, the application to the Hetao Irrigation District indicates that the developed model is effective and efficient for the real-world regional-scale agricultural problems. Above all, it is concluded that the new model is more suitable than existing models for simulating regional-scale unsaturated–saturated soil water movement and solute transport in arid and semi-arid agricultural areas.

All-condition economy evaluation method for fuel cell systems: System efficiency contour map

For fuel cell research, fuel economy evaluation methods for fuel cell systems are the basic tools; however, current fuel economy evaluation methods do not meet the demand for comprehensive analyses of the economy of fuel cell systems. In this study, we propose an all-condition economy evaluation method for fuel cell systems. To estimate the all-condition state of fuel cell systems, we developed a 1-D water transport model and an air compressor model for all operating conditions. Inspired by the knowledge of internal combustion engines, we developed an innovative fuel cell system efficiency contour map for evaluating all operating conditions. This method decouples the economy evaluation from test operating conditions and control strategy and demonstrates the fundamental characteristics of fuel cell systems. Based on the fuel cell system efficiency contour map, we propose an optimized control strategy for fuel cell hybrid vehicles, which reduces fuel consumption by 1.45%–13.14%. • Based on the system efficiency contour map, an all-condition economy evaluation method of fuel cell system has been proposed. • A fuel economy analysis simulation model of the fuel cell system has been established. • The one-dimensional water transport regulation and the power consumption of air compressor have been considered. • An optimized control strategy for a fuel cell vehicle has been proposed, which can reduce 1.45%–13.14% fuel consumption.

A dynamic, convenient and accurate method for assessing the flood risk of people and vehicle

With the increase of extreme rainstorm caused by climate change, and the development of urbanization and the improvement of people's living standard, there is an urgent need to draw a dynamic, convenient and accurate flood risk map for different disaster bearing bodies, so as to protect people's lives and properties, as well as improve people's risk awareness and facilitate people's lives. This study mainly researched a method of drawing a dynamic, convenient and accurate flood risk map for people and vehicle. In this study, the surface runoff is simulated by GPU (Graphics Processing Unit) Accelerated Surface Water Flow and Transport model (GAST model), meanwhile, the flood risk of people and vehicle is graded base on the incipient velocity formulas, the most unfavorable principle and grading method, finally, the method is applied in two application cases. The following results are obtained: (1) this method could assess the flood risk of people and vehicle dynamically, conveniently and accurately; (2) the flood risk of people is less than that of vehicle, for the same flood hazard, time and place; (3) the adverse effect of water depth on flood risk for vehicle is greater than that for people. This method of assessing the flood risk map of people and vehicle is of great significance, for flood risk management, land use plan and emergency management department to reduce flood disaster risk.

Evaluation of a novel mechanistic approach to predict transport of water and ions through shale

Prediction of transport parameters is an important issue in shale formations. A unique and novel to address this subject is the Revil model (Revil et al. 2011) which has been updated here for multivalent salts. The updated model for water and ion transport through shale has been evaluated against a range of experimental data sets. The updated Revil model only needs a few number of shale properties such as cation exchange capacity (CEC), porosity, and grain density which can be readily measured in laboratory. Also in the present work three parameters (f_Q,β_((+))^S,ν) have been considered as calibration parameters in the dynamic mode.In addition to updating Revil model for multivalent salts, we derived equations to calculate water and ion uptake in shale sample, a simplified equation to estimate IS and a proof for the conjecture that IS correlates with ME.The results show that in static mode, the model predicted the trend of data, however, the effect of semipermeable nature of shale on water uptake and alteration of ionic concentration in pore space was found negligible because of high salt concentrations (i.e. Cf>0.5M). In dynamic mode, by adjusting calibration parameters for each of test data, a complete matching could be obtained. In case of adjusting all experiments with only three common calibration parameters the prediction was not satisfactory, however, the results of intact-anion method was more accurate than Donnan method. When multiple sets of ME data in a broader range of concentration including low concentrations were plotted along with high-concentration data, correlativity was significant (R2>0.9). The present study for the first time in petroleum engineering research, suggested and implemented the updated Revil model as an applied tool for investigating static and dynamic behavior of semipermeable shales.

The transcriptome of anal papillae of Aedes aegypti reveals their importance in xenobiotic detoxification and adds significant knowledge on ion, water and ammonia transport mechanisms

The anal papillae of mosquito larvae are osmoregulatory organs in direct contact with the external aquatic environment that actively sequester ions and take up water in dilute freshwater. In the disease vector Aedes aegypti mechanisms of ion, water and ammonia transport have only been partially resolved. Furthermore, A. aegypti larvae are known to reside in high ammonia sewage and high salt brackish waters, and understanding of anal papillae function in these conditions is in its infancy. The objective of this study was to identify the complement of ion and water transport genes expressed by the anal papillae of freshwater larvae by sequencing their transcriptome, and comparing their expression in anal papillae of larvae abruptly transferred to brackish water for 24 h. Results identified a number of ion and water transport proteins, ammonia detoxifying enzymes, a full suite of xenobiotic detoxifying enzymes and transporters, and G-protein coupled receptors of specific hormones. We identified a marked increase in transcript and protein abundance of aquaporin AaAQP2 in the anal papillae with abrupt transfer to brackish water. We present an updated and more comprehensive model for ion and water transport with additional putative transporters for Na+ and Cl- uptake in the anal papillae. These are organs which are actively engaged in Na+, Cl- and water uptake and regulation when the aquatic larvae encounter fluctuating salinities over the course of their development. Furthermore the transcriptome of the anal papillae includes a full set of xenobiotic detoxification genes suggesting that these are important detoxification organs which is particularly important when larvae reside in polluted water.

Drying model of a high salt content cementitious waste form: Effect of capillary forces and salt solution

A water transport model coupling capillary liquid flow with vapor diffusion is developed to describe the drying process for a cementitious waste form with high salinity porewater. Vapor-liquid equilibrium is formulated as the driving force for vapor diffusion and the model accounts for pore capillary and high salinity effects on water thermodynamic activity. Pore filling and porewater surface tension as a function of pore size distribution and water saturation have been quantified for the material. Geochemical speciation modeling is used to simulate porewater activity as a function of composition over the range of saturation. The theoretical relationship between relative humidity and water saturation generally agrees with experimental measurement, and the developed model is capable of predicting drying rates under various external relative humidity conditions. The model was developed to be incorporated into reactive transport models considering the effects of drying such as salt redistribution and efflorescence.

A Simple Model to Predict Hydraulic Conductivity in Medium to Dry Soil From the Water Retention Curve

AbstractThe mathematical representation of the soil hydraulic properties is of central importance for modeling water, solute and energy transport in soils. The established models of the water retention and hydraulic conductivity curves account for capillary water retention and conductivity, but neglect water adsorption and water flow in films and pore corners. They are therefore suited for modeling flow and transport processes in the medium to wet moisture range, but are susceptible to failure in dry soil. The model system developed by Peters (2013, https://doi.org/10.1002/wrcr.20548; 2014, https://doi.org/10.1002/2014wr016107) and Iden and Durner (2014, https://doi.org/10.1002/2014wr015937) (PDI in the following) is a simple parametric framework that overcomes these structural shortcomings. However, it requires one additional parameter to scale the hydraulic conductivity curve in the moisture range where non‐capillary flow dominates. Measured conductivity data are required to determine this scaling parameter and to compute the hydraulic conductivity over the complete moisture range. In this contribution, we first show that the original PDI model is in close agreement with a comprehensive model for film conductivity in porous media. We then derive a physically‐based approach to predict the film conductivity from the water retention curve. This improved PDI model has the same number of parameters as established models and provides a complete prediction of the hydraulic conductivity curve including non‐capillary flow if water retention data and the saturated conductivity are known. Application to literature data covering a broad range of textures shows an improvement of the conductivity prediction by the factor five if compared to the van Genuchten/Mualem model.

Influences of thermal damage on water transport in heat-treated cement mortar: Experimental and theoretical analyses

Water transport in the heat-damaged cement mortar is closely related to the evaluation of durability for structures exposed to fire and the recycling of thermally damaged cement-based materials. In this study, the influence of microstructure on water transport in unsaturated and saturated heat-treated cement mortar was analyzed based on experimental results from neutron radiography, water permeability, mercury intrusion porosimetry (MIP) and X-ray computed tomography (CT) tests. Neutron radiography was employed to track the dynamic wetting front in real time during water imbibition in the heat-treated mortar specimens exposed to a series of temperatures (105°C, 200°C, 400°C, 600°C, 800°C). The evolution of the wetting front was analyzed according to the square root of time based on neutron images. A deviation from the standard t1/2 pattern of the wetting front was found when water imbibition in the cement mortar specimens treated by a temperature ≥400°C. The absorptivities of different imbibition stages were determined for heat-damaged cement mortar. Mechanisms for the change of typical absorptivities with the evolution of thermal damage were discussed from the perspective of microstructure. In addition, causes for the occurrence of anomalous water absorption were explored by considering the role of thermal cracks and potential physicochemical reactions. Methods were proposed to estimate the effective tortuosity of water channels in the cement mortar damaged by different temperatures. The representative size of water channels was estimated with the calculated tortuosity. The estimated water channels size was compared with the pore aperture determined by MIP. At last, the estimated water channels size and tortuosity from imbibition data were utilized to predict the water permeability of the heat-treated mortar using a capillary model. By comparing the predicted and measured permeabilities, the correlation and difference between unsaturated and saturated water transport in the heat-treated cement mortar were analysed. Future work for modeling water transport in heat-damaged cement mortar was discussed.

Improved pseudopotential lattice Boltzmann model for liquid water transport inside gas diffusion layers

Liquid water transport inside the gas diffusion layers (GDLs) plays a vital role in water management of proton exchange membrane fuel cells (PEMFCs). In this study, an improved pseudopotential multiphase lattice Boltzmann model is firstly developed to realize the actual density and viscosity ratios in porous media. The proposed model is based on a non-orthogonal multiple-relaxation-time (MRT) LB model and a new improved wettability boundary condition. In terms of the relationship between capillary pressure Pc and saturation s, the proposed model shows a good agreement with the experimental data. Using the validated model, the effects of capillary pressures and contact angles of mixed wettability on the liquid water invasion process for Toray-090 GDLs with two Polytetrafluoroethylene (PTFE) contents (10 wt% and 20 wt%) are studied. It is found that the liquid water shows capillary fingering behaviors and the liquid water saturation profiles along the through-plane direction of the GDLs become more non-uniform with increasing contact angle of PTFE.

Numerical simulation of irrigation scheduling using fractional Richards equation

A method of soil moisture content prediction is presented using fractional differential generalization of one-dimensional Richards equation for the purposes of decision support in irrigation. We propose to use water head dynamics data gathered in the beginning of growth season to perform a calibration of the model by the meta-heuristic particle swarm algorithm. Van Genuchten model is used to describe water retention curve. The cases of the known values of its coefficients along with their identification from water head dynamics data are considered. The paper presents the results of model verification for both classical Richards equation and its fractional differential generalization. For the conditions of sprinkling irrigation in the south of Ukraine, we estimate the accuracy of modelling the water head dynamics measured by the Watermark sensors and the accuracy of seasonal irrigation rate assessment. The obtained results show that the use of water transport model that take soil fractality into consideration has no effect on assessing seasonal irrigation rate but gives up to 7% increase in accuracy while predicting the time and rate of next irrigation application.

Prediction of soil hydraulic properties by Gaussian process regression algorithm in arid and semiarid zones in Iran

The soil water retention curve (SWRC) is one of the principal soil hydraulic properties that is needed as input data in modeling water and solute transport through unsaturated soils. Field or laboratory measurement of SWRC is labor-intensive, expensive and time-consuming. Pedotransfer functions (PTFs) have been developed as an indirect method to predict soil hydraulic properties (e.g. SWRC) from more easily measured soil data by data mining tools. The novelty of the present study is the application of Gaussian process regression (GPR) algorithm as a data mining technique, to predict the SWRC, and comparing its performance with that of the multiple linear regression (MLR) and Rosetta methods, which has not been conducted so far. In this study 15 GPR and MLR-based PTFs were developed to predict the parameters of the van Genuchten model from different combinations of readily available properties of 223 soil samples that were taken from six provinces of Iran. The k-fold (k = 20) cross validation approach was utilized to obtain training and testing data sets for each PTF. The predictions of the GPR and MLR-based PTFs were evaluated by different criteria. The GPR-based PTFs had greater accuracy and reliability than MLR method in predicting SWRC according to integral root mean square error (IRMSE) criterion. However, the differences were not significant (P > 0.05) in the testing step, but the reliability of both methods were significantly (P < 0.05) better than Rosetta-based PTFs. The covariance functions of GPR method can be effectively fitted by kernels with different features for modeling complex relationships. The GPR method can be considered as a competitive alternative to develop parametric-PTFs.

Understanding water and solute transport in thin film nanocomposite membranes by resistance-in-series theory combined with Monte Carlo simulation

The lack of mechanistic insights into the water and solute transport in the thin film nanocomposite (TFN) membrane active layer posed a major challenge in the fundamental understandings and performance optimization of such membranes in water treatment. In this work, we develop a novel water and solute transport model to qualitatively and quantitatively study the influence of intrinsic permeabilities and geometric parameters of the NPs and the NPs-polymer intermediate layer on the widely observed flux enhancement of TFN membranes based on the resistance-in-series theory and Monte Carlo simulation. The simulation results demonstrate a small amount of porous or even non-porous NPs addition would result in a significant flux increase due to either high NP permeability, high intermediate layer permeability, or the combined effects of the abovementioned factors. Besides, we find that an optimized combination of NPs mass loading and NPs size, thicker intermediate layer and TFN membrane with minimized NPs aggregation are preferred to achieve high permeate flux. This simulation can be used to predict TFN membrane performance and provide guidance on engineering the next-generation TFN membranes with high flux as well as improved rejections, to tackle with the widely acknowledged problem of flux and rejection trade-off.

Numerically scheduling plant water deficit index-based smart irrigation to optimize crop yield and water use efficiency

Knowledge-driven "smart" irrigation proposes to achieve explicitly targeted crop yield and/or irrigation water use efficiency (WUE). A coupled crop growth and soil water transport model was established and applied to schedule irrigation for drip-irrigated and film-mulched maize through numerical simulation. By designing various scenarios with either a constant or variable threshold of plant water deficit index (PWDI) to initiate irrigation, the quantitative relationship between PWDI threshold and the corresponding yield and WUE was investigated with acceptable errors between the measured and simulated values (R2 > 0.85). The model allowed determination of PWDI thresholds designed to reach specific combinations of yield and WUE to consider actual conditions such as availability and cost of water resources. Regulated deficit irrigation with a variable threshold, considering variability of physiological response to water stress, was superior to a constant PWDI threshold in improving WUE. A constant PWDI threshold of 0.54 and 45 threshold combinations among various growth stages were suggested to obtain same relative values of yield and WUE. Numerical simulation has the potential to provide reliable dynamic information regarding soil water and crop growth, necessary for smart irrigation scheduling, due to its ability in integrating the effects of environmental conditions and economic considerations and, as such, should be further studied to enhance simulation accuracy and subsequently to optimize irrigation scheduling under complex situations.

On the Efficacy of Water Transport in Leaves. A Coupled Xylem-Phloem Model of Water and Solute Transport

In this paper, we present and use a coupled xylem/phloem mathematical model of passive water and solute transport through a reticulated vascular system of an angiosperm leaf. We evaluate the effect of leaf width-to-length proportion and orientation of second-order veins on the indexes of water transport into the leaves and sucrose transport from the leaves. We found that the most important factor affecting the steady-state pattern of hydraulic pressure distribution in the xylem and solute concentration in the phloem was leaf shape: narrower/longer leaves are less efficient in convecting xylem water and phloem solutes than wider/shorter leaves under all conditions studied. The degree of efficiency of transport is greatly influenced by the orientation of second-order veins relative to the main vein for all leaf proportions considered; the dependence is non-monotonic with efficiency maximized when the angle is approximately 45° to the main vein, although the angle of peak efficiency depends on other conditions. The sensitivity of transport efficiency to vein orientation increases with increasing vein conductivity. The vein angle at which efficiency is maximum tended to be smaller (relative to the main vein direction) in narrower leaves. The results may help to explain, or at least contribute to our understanding of, the evolution of parallel vein systems in monocot leaves.

An undiscovered facet of hydraulic redistribution driven by evaporation-a study from a Populus tomentosa plantation.

Maintaining the activity and function of the shallow root system of plants is essential for withstanding drought stress, but the associated mechanism is poorly understood. By investigating sap flow in 14 lateral roots (LRs) randomly selected from trees of a Chinese white poplar (Populus tomentosa) plantation receiving three levels of irrigation, an unknown root water transport mode of simultaneous daytime bi-directional water flow was discovered. This mode existed in five LRs confined to the surface soil without attached sinker roots. In the longer term, the bi-directional water flow was correlated with the soil water content. However, within the day, it was associated with transpiration. Our data demonstrated that bi-directional root sap flow occurred during the day, and was driven by evaporative demand, further suggesting the existence of circumferential water movement in the LR xylem. We named this phenomenon evaporation-driven hydraulic redistribution (EDHR). A soil-root water transport model was proposed to encapsulate this water movement mode. EDHR may be a crucial drought-tolerance mechanism that allows plants to maintain shallow root survival and activity by promoting root water recharge under extremely dry conditions.

Numerical Modeling of Water and Gas Transport in Compacted GMZ Bentonite under Constant Volume Condition

During deep geological disposal of high-level and long-lived radioactive waste, underground water erosion into buffer materials, such as bentonite, and gas production around the canister are unavoidable. Therefore, understanding water and gas migration into buffer materials is important when it comes to determining the sealing ability of engineered barriers in deep geological repositories. The main aim of our study is to provide insights into the water/gas transport in a compacted bentonite sample under constant volume conditions. The results of our study indicate that water saturation is obtained after 450 hours, which is similar to experimental results. Gas migration testing shows that the degree of water saturation in the samples is very sensitive to the gas pressure. As soon as 2 MPa or higher gas pressure was applied, the water saturation degree decreased quickly. Laboratory experiments indicate that gas breakthrough occurs at 4 MPa, with water being expelled from the downstream side. This indicates that gas pressure has a significant effect on the sealing ability of Gaomizozi (GMZ) bentonite.