Transient Moisture Distribution Research Articles

Encoder–Decoder Convolutional Neural Networks for Flow Modeling in Unsaturated Porous Media: Forward and Inverse Approaches

The computational cost of approximating the Richards equation for water flow in unsaturated porous media is a major challenge, especially for tasks that require repetitive simulations. Data-driven modeling offers a faster and more efficient way to estimate soil moisture dynamics, significantly reducing computational costs. Typically, data-driven models use one-dimensional vectors to represent soil moisture at specific points or as a time series. However, an alternative approach is to use images that capture the distribution of porous media characteristics as input, allowing for the estimation of the two-dimensional soil moisture distribution using a single model. This approach, known as image-to-image regression, provides a more explicit consideration of heterogeneity in the porous domain but faces challenges due to increased input–output dimensionality. Deep neural networks (DNNs) provide a solution to tackle the challenge of high dimensionality. Particularly, encoder–decoder convolutional neural networks (ED-CNNs) are highly suitable for addressing this problem. In this study, we aim to assess the precision of ED-CNNs in predicting soil moisture distribution based on porous media characteristics and also investigate their effectiveness as an optimizer for inverse modeling. The study introduces several novelties, including the application of ED-CNNs to forward and inverse modeling of water flow in unsaturated porous media, performance evaluation using numerical model-generated and laboratory experimental data, and the incorporation of image stacking to account for transient moisture distribution. A drainage experiment conducted on a sandbox flow tank filled with monodisperse quartz sand was employed as the test case. Monte Carlo simulation with a numerical model was employed to generate data for training and validation of the ED-CNN. Additionally, the ED-CNN optimizer was validated using images obtained through non-intrusive photographic imaging. The results show that the developed ED-CNN model provides accurate approximations, addressing the high-dimensionality problem of image-to-image regression. The data-driven model predicted soil moisture with an R2 score of over 91%, while the ED-CNN optimizer achieved an R2 score of over 89%. The study highlights the potential of ED-CNNs as reliable and efficient tools for both forward and inverse modeling in the analysis of unsaturated flow.

Simulation for Transient Moisture Distribution and Effects on the Electric Field in Stable Condition: 110 kV Oil-Immersed Insulation Paper Bushing

Oil-immersed insulation paper (OIP) bushing is one of the most important equipment in power transmission and distribution systems. Moisture is one of the most serious factors that affect the insulation status of OIP bushing. In this paper, the OIP bushing was assumed to be in a stable and simplicity condition, and then the transient moisture distribution of capacitor core and its effects on the electric field were studied. First, by dissecting a 110 kV OIP bushing, the specific sizes for modelling were obtained. Afterwards, a moisture diffusion model for OIP bushing was established based on COMSOL Multiphysics software, and it was also verified by moisture diffusion experiment. Then, the moisture distribution for different conditions were obtained and analyzed. Finally, a model for the electric field of OIP bushing was established, and then the effects of moisture on the electric field were studied.

The influence of hygrothermal effects on the cross-ply composite laminate with transverse cracking in transient mode

The stiffness reduction of symmetric hygrothermal cracked and aged cross-ply laminates is predicted by using two different models, shear-lag and variational approach. The material properties are considered to be dependent on temperature and transient moisture distribution in desorption case. This transient hygrothermal effect is taken into account to access the changes in the longitudinal modulus due to transverse cracking. The obtained results illustrate well the dependence of the stiffness degradation on the cracks density and transient environmental conditions, especially at high temperature. Through the presented study, we hope to contribute to the understanding of hygrothermal behaviour of cracked composite laminate.

Effect of fibre topology on hygro-mechanical response of polymer matrix composites

Diffusion of moisture through fibre reinforced polymers (FRP) is one of the main environmental causes of their deterioration and loss of service life. Moisture diffusion and the resulting stresses in a fibre–matrix system vary considerably with the topology of the fibres inside the polymer matrix. This paper reports a numerical study on stress build up in FRP due to moisture diffusion. The Fickian diffusion model is implemented. Stresses due to the transient moisture distribution have been estimated using a finite element model. Some fundamental topologies have been studied. Most important topological parameters have been identified. Utilising the results of fibre neighbourhood, interpretation of large microstructures has been discussed. Considerable interactions among neighbouring fibres can be observed in the stress build up. The results should help in designing moisture impeding microstructures for FRP and prolong their life.

Dielectric frequency response of oil-paper composite insulation with transient moisture distribution

Because the temperature and load of transformer are variable, the moisture is usually inhomogeneous in oil-paper, especially for the traction transformer. In order to research the dielectric relaxation behavior of the oil-paper composite insulation with an inhomogeneous moisture distribution, it was proposed that a theoretical model for dielectric medium with an arbitrary distribution of conductivity and dielectric constant. The dielectric frequency response of oil-paper with transient moisture distribution was simulated by using the proposed model. The results show that transient moisture distribution caused the concentration polarization(CP), which enhanced the low-frequency relaxation. The model is validated against experimental data.

An algorithm to predict the transient moisture distribution for wall condensation under a steady flow field

The prediction and control of the indoor moisture distribution, especially for wall condensation, is very important for a healthy and energy-efficient environment. However, existing methods cannot accurately predict the transient indoor moisture distribution for wall condensation. In this study, the prediction of indoor transient moisture distribution is facilitated by using transient accessibility indices, which characterize the transport of the passive contaminants to describe boundary effects on the transient moisture distribution. An algebraic expression is obtained for the indoor moisture distribution, and a computational model is presented for the wall condensation problem. The model is validated by experiments and computational fluid dynamics (CFD) simulations, and the model is implemented for a wall condensation case study. The new model can easily predict the indoor moisture distribution under different boundary conditions and for a range of condensation time on the wall surfaces. This study provides an effective means of indoor moisture prediction and control, which may become an important tool for designing a non-uniform indoor environment.

Transient Moisture Distribution and Hygrothermal Stress Analysis of Composite Laminates Using Equivalent Diffusion Methods

It often takes several decades to reach moisture equilibrium state in composite laminates. Therefore, hourly varying fluctuating boundary moisture and temperature conditions require several millions of time steps to reach a state of equilibrium. A new transient analysis method is proposed to efficiently solve moisture distribution of composite laminates with rapidly fluctuating moisture and temperature boundary conditions. First, effective constant diffusivity and maximum moisture content were obtained by averaging transient temperature-dependent moisture diffusivity. In this way, a simple analytic solution can be effectively used to determine the transient moisture distribution under hourly fluctuating boundary conditions. Its efficiencies are demonstrated in three different conditions by comparing this method with a conventional finite difference method. Hygrothermal stress and material degradation were consequently discussed to demonstrate that we must avoid a simple knock-down factor or 40% devastating penalty and use more rational simulation and supporting data.

Two-dimensional hygrothermal transfer in porous building materials

A two-dimensional mathematical model for evaluating the simultaneous heat and moisture migration in porous building materials was proposed. Vapor content and temperature were chosen as the principal driving potentials. The numerical solution was based on the control volume finite difference technique with fully implicit scheme in time. Two validation experiments were developed in this study. The evolution of transient moisture distributions in both one-dimensional and two-dimensional cases was measured. A comparison between experimental results and those obtained by the numerical model proves that they are fully consistent with each other. The model can be easily integrated into a whole building heat, air and moisture transfer model. Another main advantage of the present numerical method lies in the fact that the required moisture transport properties are comparatively simple and easy to determine.

Experimental and theoretical investigation of non-isothermal transfer in hygroscopic building materials

In this paper a modified two-dimensional Luikov model for evaluating the non-isothermal moisture migration in porous building materials was proposed. The coupled heat and moisture transfer problem was modeled. Vapor content and temperature were chosen as the principal driving potentials. The coupled equations were solved by a numerical method, which consists of a finite difference technique with a fully implicit scheme in time. Two validation experiments were developed in this study. The evolution of transient moisture distributions in both one-dimensional and two-dimensional cases was measured. A comparison between experimental results and those obtained by the numerical model proves that they are fully consistent with each other. The modified model can be integrated into a whole building heat, air and moisture transfer model.

Development of an electrical time domain reflectometry (ETDR) distributed moisture measurement technique for porous media

In this paper, a novel electrical time domain reflectometry (ETDR) measurement technique capable of measuring moisture distribution profile in a porous medium is presented. A signal calibration algorithm to interpret the ETDR waveform based on an empirical relation between moisture content and differential impedance of the medium was developed. The transient distribution of the moisture content in a concrete block covered with fibre reinforced polymer laminate on one end surface was experimentally measured. The experimental results were then compared with the solution of a finite element analysis. Good agreement was shown for the trend of the transient moisture distribution profile. It was demonstrated that the ETDR distributed moisture sensor developed in the current study was capable of measuring the variation of the moisture content distribution in a porous medium.

Moisture distribution in drying ordinary and high performance concrete cured in a simulated hot dry climate

Adequate moisture is very important during early age of portland cement concrete. The Single Point Magnetic Resonance Imaging technique was used to study the effects of various lengths of moist curing, and the use of curing compound, on the amount and distribution of evaporable water during drying of ordinary and high performance concrete. The specimens subjected to six different curing regimes, were cast in triplicate for a total of 72. After moist curing at 38°C, the specimens were subjected to uniaxial drying in an environmental chamber at 38°C and 40% relative humidity that simulated hot dry climate conditions. As the specimens were drying, Magnetic Resonance Imaging was used to study the evaporable water distribution, non-destructively and with millimetric resolution. The Magnetic Resonance Imaging profiles indicated a reduced moisture loss with increasing length of moist curing. Extended moist curing was especially beneficial for the two self-compacting concrete mixtures, particularly for the cover concrete. In all mixtures the use of curing compound was only marginally better than one day moist curing, but was significantly better than air curing, particularly for the cover concrete. The moisture diffusivity was evaluated from the transient moisture distribution profiles using the Boltzmann transformation method. The results indicated a strong dependence of the moisture diffusivity on the moisture content when above 80% saturation, whereas below this value it remains almost constant. The moisture diffusivity is significantly reduced with increased moist curing period.

Evaluation of Soybean Seedcoat Cracking During Drying:PART II. Using MRI

ABSTRACT MRI techniques were developed and employed for non-destructive and noninvasive study of seedcoat cracking in low moisture soybean kernels during heated air drying. Proton density image and transient moisture distribution profile of a single soybean kernel can be obtained using MRI. These MRI techniques proved to be particularly useful for the continuous observation of initiation and propagation of seedcoat cracking during the entire period of drying process without interruption. The proton density images of soybean kernels showed that seedcoat cracking was initiated perpendicular to the long axis of the kernel near the hilum. The transient moisture distribution profiles in soybean kernels during drying indicate that moisture gradient developed during drying was higher in the seedcoat than in the cotyledon. Drying temperature and initial average moisture content were positively correlated with the soyhean seedcoat crackig. The location of the

Moisture Diffusivity of Cellulose Insulation

Test specimens of blown cellulose insulation were placed in contact with water to initiate an isothermal moisture intake process in which liquid water was allowed to enter freely against gravity into the specimens. The transient moisture distribution in the specimens was determined using the gamma-ray attenuation method over a period of 10 days. The results indicate that, as with most porous systems, the specimens first establish a characteristic water retention curve and then undergo a unique secondary moisture transport process. This paper presents the experimental data from the investigation. The data were used to derive information on the moisture diffusivity of cellulose insulation, in relation to the secondary mois ture transport process undergone by the test specimens.

Experimental and Analytical Investigations of Simultaneous Heat and Moisture Transport through Glass Fiber Insulation

Glass fiber insulation is one of the most commonly used building materials in residential wall cavities. In the normal conditions under which buildings operate, the moisture content in this insulation may locally vary from that of a very dry to a fully saturated state. This gives rise to many mechanisms for moisture trans port in the insulation. This article looks at all the possible mechanisms through which moisture is transported. This is done through two series of experiments and detailed numerical analysis The experiments include investigations on water vapour transport in the presence of thermal gradients and drying of fully saturated speci mens through evaporation. Physical quantities measured include history of heat flux, boundary temperatures and relative humidities and transient moisture distributions. The simultaneous heat and moisture transport processes are mathematically described through a pair of conservation equations In a finite difference method, these equations are used for detailed numerical analysis of the processes. The numeri cal analysis makes use of the experimental data to derive consistent values for a set of moisture transport properties, representative of a sample of medium density glass fiber insulation. The properties include thermal conductivity as a function of mois turc content, vapour permeability as a function of temperature, moisture diffusivity as a function of moisture content and temperature, heat capacity and hydraulic con ductivity as functions of moisture content and sorption isotherm. A sensitivity anal ysis and an independent experiment on the drying of a randomly wet specimen sup port the results obtained from the numerical analysis

AN EXPERIMENTAL STUDY OF MOISTURE AND TEMPERATURE DISTRIBUTIONS DURING FREEZE‐DRYING

SUMMARY– Measurements of the moisture and temperature distributions were made during freeze‐drying beef at a pressure of 1 torr. The transient moisture distributions measured with gamma ray techniques indicate that the phase change region would have a thickness less than 3/16 in., that no drying takes place until the phase change region reaches a given position, and that no additional drying occurs after the phase change passes a given position. A careful study of the data showed that the drying rate was influenced by heat transfer through the frozen region to the phase change position.