Moisture Content Field Research Articles

The Problem of Heat and Mass Transfer of a Half-Space with an Air Flow with Periodic Changes in Air Temperature

A system of differential equations, boundary and initial conditions for calculating temperature and moisture content fields in a homogeneous halfspace, the boundary of which is blown by an air flow, is formulated. The heat exchange of the boundary with the air medium occurs according to the Newtonian law, and mass transfer — according to the Dalton evaporation law. In the initial state, the air and the material have the same temperature, and water vapor, both near the surface of the material and outside the boundary layer, is in a saturation state, so there is no exchange of heat and moisture between the air and the material. At some point, the air temperature begins to produce small harmonic fluctuations near its initial value. For a mathematical model of heat and mass transfer, in which the movement of moisture to the surface is considered to be caused only by a drop in moisture content, i.e. the phenomenon of thermal diffusion is neglected, an asymptotic time view of the temperature and moisture content fields is obtained. The moisture content field has the form of a damped harmonic wave, and the temperature field is represented by the superposition of two waves of the same type, which have the same frequency, but different attenuation coefficients and phase velocities. The calculation of the basic wave parameters for a material with clay characteristics is carried out, and the results obtained are compared with experimental data. The constructed solution is a generalization of the Fourier formulas known in the literature, which are valid only in a situation when the material does not contain moisture, and according to the harmonic law, not the air temperature changes, but the surface temperature. The results obtained in the article will be used in geocryology as a theoretical tool in the study of seasonal fluctuations in the thermal and physical state of the soil, which is an important task in planning economic activities in the field of the distribution of frozen rocks.

Математическая модель процесса СВЧ и конвективной выпечки хлеба из сбивного теста

Whipped yeast-free bakery products require effective energy supply to dough in order to optimize energy consumption, baking time, and quality. This article introduces a verified mathematical model of microwave and convective baking for whipped bread based on heat and mass exchange equations.
 A full-scale experiment to verify the calculations involved dough samples with a humidity of 56 ± 1%. The samples underwent microwave and convective processing until the temperature in the crumb center reached 98 ± 1°C.
 The mathematical model was formalized as energy and mass conservation equations, which made it possible to consider baking as a non-stationary process of heat and mass transfer of moisture in an isotropic incompressible continuous medium in the diffusion approximation. The equation took into account the unstable phase transition boundary. The practical verification showed the mean error for microwave baking as 14.5% in temperature and 18.2% in moisture content. For convective baking, the results included 12.6% in temperature and 9.7% in moisture content. The mathematical model proved adequate to the real processes of heat and mass transfer. The error in calculating the temperature and moisture content fields was sufficient tooptimize the process.
 The physical and mathematical model of the baking process made it possible to evaluate the effect of technological variables on the temperature and moisture concentration fields in the dough samples. The mathematical model and the computational experiment can be used to identify static and dynamic characteristics of baking as an object of automatic control, i.e., to identify optimal control channels and actions, as well as to adjust the automatic control system to specific quality indicators.

Modeling heat and mass transfer in grain drying processes under the influence of electromagnetic field

Drying of grain materials by traditional convective methods typically involves significant energy consumption, primarily due to unproductive losses of thermal energy with the exhausted drying agent. Optimizing this process entails reducing the volume of drying agent used and compensating for reduced thermal energy through non-contact heat transfer methods such as microwave (MW) or infrared (IR) irradiation. However, mathematical modeling of these processes requires refinement as they differ from traditional convective heat drying processes. Grain drying is a complex thermophysical process, with heat and moisture transfer occurring within the capillary-porous material in a mutually dependent manner. To better understand these processes, it is necessary to establish mathematical models that account for the influence of the electromagnetic field. This article aims to theoretically investigate the drying process of plant raw materials under the influence of MW and IR electromagnetic fields based on analytical mathematical models. The conducted research indicates the potential of using electromagnetic fields to intensify the drying of plant raw materials, particularly through MW and IR irradiation, which allows for targeted heating of the moist zones of the material. The obtained analytical dependencies enable the calculation of temperature and moisture content fields in materials and determine the degree of influence of electromagnetic field parameters on heating and drying processes. These dependencies also help to more accurately identify heat and mass transfer model coefficients based on experiments. Such an analytical-empirical approach can be utilized to calculate rational processing regimes for grain raw materials under the influence of electromagnetic fields.

Solution of the Heat and Mass Transfer Problem for Soil Radiant Heating Conditions Using the Method of Finite Integral Fourier Transform

To achieve high agricultural yields, it is essential to predict the soil temperature and moisture regime, considering the heating technology employed. The research object is soil heated by a ceiling-mounted infrared emitter. The research subject encompasses one-dimensional unsteady fields of soil moisture content and temperature. The research goal is to forecast the soil temperature and moisture regime under radiant heating conditions. The research methods involve the analytical solution of heat and mass transfer differential equations using the method of finite integral Fourier transforms. Research results indicate that the top layer of milled peat, with an initial moisture content of 3.7 kg/kg, will reach a final moisture content of 1.0 kg/kg in approximately 6 hours during infrared drying. As a result of radiant heating, the soil temperature will rise from an initial 5 ℃ to a final 22.6 ℃ in approximately 3 hours. The analytical solution of the mass transfer differential equation can be utilized for theoretical studies of drying capillary-porous materials, such as determining the drying period or the thickness of the material layer that will dry to a specified final moisture content. The analytical solution of the heat transfer differential equation, accounting for both thermal conductivity and the Dufour effect, can be employed to manage the operation of the infrared radiation source, such as determining its operational and shutdown periods when the soil surface temperature reaches its maximum (critical) value. The mathematical solutions discussed in the article do not consider thermodiffusion processes in the soil layer (Soret effect), which presents a promising direction for further scientific research.

Решение краевой задачи тепломассопереноса методом конечного интегрального преобразования Фурье для условий лучистого обогрева почвы

The purpose of the research is to find, predict and regulate the temperature and humidity regime of the soil for the conditions of radiant heating of cultivation facilities using dark-type ceiling infrared radiators. In the work, without intermediate mathematical transformations, a generally accepted system of differential equations (both in dimensional and dimensionless forms) is presented, taking into account the main and cross processes of heat and mass transfer in dispersed media. For this system of equations, a particular analytical solution is considered, which takes into account not only the main phenomena of heat and mass transfer that occur independently of each other, but also the effect of water vapor transfer on the formation of the temperature field of the soil layer. Using the example of milling peat, the results of solving this problem are presented in the form of one-dimensional unsteady fields of temperature and moisture content. Taking into account the given unambiguity conditions (geometric, physical, initial and boundary conditions), it is established that the required values of moisture content and temperature will be reached in six hours. At the same time ,there is practically no change in moisture content during the time period under consideration on the coordinate segment z ∈[0;6,0] sm. The solution of the mathematical problem, implemented in a software environment, allows you to control the thermal and humidity conditions of the soil by regulating the heat flow on its surface (in the case of an obvious relationship between the magnitude of the heat flux and the intensity of evaporation from the soil surface). Due to the fact that the solution proposed in the article is a particular one and does not take into account thermal diffusion in the soil layer, i.e.the influence of temperature differences on moist ure transfer seems appropriate and of scientific interest to consider further the general solution of the system of differential equations of interrelated heat and mass transfer.

Solution of the Heat and Mass Transfer Problem for Soil Radiant Heating Conditions Using the Error Function

Achieving high yields of agricultural crops requires the ability to predict soil temperature and moisture regimes, taking into account soil heating technology. The object of study is soil heated by a ceiling infrared emitter. The subject of study is one-dimensional non-stationary fields of soil moisture content and temperature. The objective of the study is to predict soil temperature and moisture regimes under radiant heating conditions. Research methods: analytical methods for solving differential equations of heat and mass transfer using the error function. Research results: the top 5 mm layer of milled peat with an initial moisture content of 3.7 kg/kg will reach a final moisture content of 1.0 kg/kg in about 6 hours during infrared drying. As a result of radiant heating, the soil will heat up from an initial temperature of 5 ℃ to a final temperature of 20 ℃ in approximately 3 hours. The analytical solution of the mass transfer differential equation can be used for theoretical studies of drying of capillary-porous materials, for example, to determine the drying period or the thickness of the material layer that will dry to a given final moisture content. The analytical solution of the heat transfer differential equation can be used to control the operating mode of the infrared radiation source, for example, to determine the periods of its operation and switching off in case the soil surface temperature reaches the maximum (critical) value. The mathematical solutions considered in the article do not take into account the cross processes of heat and mass transfer, which is a promising direction for further scientific research.

Kriging interpolation reconstruction of surrounding rock moisture content field

Kriging interpolation reconstruction of surrounding rock moisture content field

On the Problems of Monitoring Atmospheric Humidity Fields Using Satellite Microwave Radiometry Methods When Studying Cyclogenesis in the Tropical Atlantic

Some problems of microwave radiometric methods for monitoring fields of total atmospheric moisture content from satellites in areas of hurricane formation in the tropical regions of the Atlantic are considered. The possibilities of using polar-orbiting satellites (DMSP, EOS Aqua, GCOM-W1) for these tasks are analyzed a feature of which is the presence of gaps in satellite data (blind spots) resulting from divergence of scanning bands at lower latitudes. It is shown through a number of examples that the joint use of various satellites makes it possible to reduce the influence of this effect and obtain a clear picture of the evolution of atmospheric humidity fields in the tropical Atlantic and their connection with the evolution of tropical waves that initiate the formation of hurricanes.

Virtual test bench for computer-aided design of drum dryers based on kinetic laws of the drying process

The aim of the study is to create a virtual test bench, consisting of optimal design parameters that provide the maximum approximation of the real drying process to the experimental data.Method. Methods of modeling, formalized description, optimal design and management of technological processes and productions are applied. Result. A virtual test bench has been developed that allows real-time determination of the design parameters of drum-type dryers depending on the kinetic patterns of the drying process of various grain crops. As an object of study, the design of a two-section drum dryer was used, each section of which is equipped with a profile channel nozzle that provides a transverse supply of the drying agent through the pouring movable layer of the dispersed product to be dried. An algorithm for calculating the drying process is presented, which makes it possible to determine the fields of temperature and moisture content of grain in a wide range of regime parameters. With the use of CAD, a computer model of this installation was made with the possibility of autonomous rotation and movement of the drums relative to each other. A diagram of the synchronized operation of the moving elements of the installation under conditions of operational reconfiguration of its design in accordance with changes in the kinetic curves has been drawn up.Conclusion. The presented virtual test stand adequately and with high accuracy allows simulating the process of drying materials in a drum dryer; allows you to test the operation of a drum dryer at the development stage, conduct experiments with the highest possible accuracy, select the optimal drying modes for various materials with minimal energy consumption.

Решение краевой задачи тепломассопереноса методом источников для условий лучистого обогрева почвы

The purpose of the research is to find, predict and regulate the temperature and humidity regime of the soil for the conditions of radiant heating of cultivation facilities using dark-type ceiling infrared emitters. A system of differential equations (in dimensional and dimensionless forms) is presented, reflecting the relationship of thermal and mass transfer processes in colloidal capillary-porous bodies in the case of surface radiant heating. A partial analytical solution of this system of differential equations for a semi-bounded body is considered with the exclusion of the phenomenon of thermal and thermal conductivity and period diffusion processes. On the example of milling peat, taking into account the initial data, the solution of the boundary value problem of heat and mass transfer by the method of sources is obtained, which is one-dimensional non-stationary fields of moisture content and temperature. It is established that under the given initial and boundary conditions, as well as taking into account the thermophysical properties of milling peat, the required moisture content will be achieved in six hours, the temperature in three hours. By adjusting the thermal power of the infrared radiation source, and, therefore, the intensity of moisture evaporation from the soil surface into the environment, it is possible to control the rate of heating and drying of the layer (for example, to determine the time or frequency of watering the soil). To clarify the values of moisture content and soil temperature by coordinate and over time, it seems expedient to consider analytical solutions that took into account not only basic, but also conjugate processes of heat and mass diffusion

Accounting for among-sampler variability improves confidence in fuel moisture content field measurements

Background Direct fuel moisture content measurements are critical for characterising spatio-temporal variations in fuel flammability and for informing fire danger assessments. However, among-sampler variability (systematic differences in measurements between samplers) likely contributes to fuel moisture measurement variability in most field campaigns. Aims We assessed the magnitude of among-sampler variability in plot-scale Calluna vulgaris fuel moisture measurements. Methods Seventeen individuals collected samples from six fuel layers hourly from 10:00 hours to 18:00 hours. We developed mixed effects models to estimate the among-sampler variability. Key results Fuel moisture measurements were highly variable between individuals sampling within the same plot, fuel layer, and time of day. The importance of among-sampler variability in explaining total measured fuel moisture variance was fuel layer dependent. Among-sampler variability explained the greatest amount of measurement variation in litter (58%) and moss (45%) and was more important for live (19%) than dead (4%) Calluna. Conclusions Both consideration of samplers within the experimental design and incorporation of sampler metadata during statistical analysis will improve understanding of spatio-temporal fuel moisture dynamics obtained from field-based studies. Implications Accounting for among-sampler variability in fuel moisture campaigns opens opportunities to utilise sampling teams and citizen science research to examine fuel moisture dynamics over large spatio-temporal scales.

Lateral terrestrial water fluxes in the LSM of WRF‐Hydro: Benefits of a 2D groundwater representation

AbstractThe interactions between the atmosphere and the land surface are characterized by complex, non‐linear processes on varying time scales. The Noah‐MP is a medium complexity land‐surface model (LSM), which was recently selected as the new default LSM for the hydrologically enhanced Weather Research and Forecasting modelling system (WRF‐Hydro). Compared to its predecessor, several parameterizations were considerably improved and new ones added, inter alia more sophisticated groundwater descriptions, which aim to replace the traditional free‐drainage lower boundary condition. This study investigates the benefits that can be obtained from a two‐dimensional groundwater representation within the WRF‐Hydro modelling system by performing two offline simulations for the upper Danube river basin. In comparison to the free‐drainage reference simulation, the lateral routing of groundwater and the two‐way interaction with the water table greatly enhances small scale variability in simulated fields of soil moisture content and evapotranspiration (ET). The representation of upward fluxes from the aquifer helps to maintain higher soil moisture contents and thus ET during prolonged dry periods. These differences are rather small though (<2%) and explained by the fact that the study region is considered to be limited by radiative energy and not water availability. The most striking difference however is the performance gap in simulating streamflow. WRF‐Hydro with 2d groundwater scheme clearly outperforms the reference simulation in terms of performance metrics. A comparison with hourly streamflow observations for the water year of 2016 yields average Kling‐Gupta efficiencies of 0.79 versus 0.57 for the reference. Given that both model configurations were not calibrated beforehand, we conclude that the two‐dimensional groundwater option is especially beneficial for applications in poorly or even ungauged catchments. Furthermore, the inclusion of a so far missing compartment of the water cycle in the WRF‐Hydro modelling system allows for a more holistic representation of interactions between atmosphere land surface and subsurface, which will be advantageous in feedback studies with the fully coupled WRF‐Hydro.

Numerical assessment of wood moisture content-based assignments to service classes in EC 5 and a prediction concept for moisture-induced stresses solely using relative humidity data

Moisture content (MC) fields in wood are in strong interplay with the surrounding climate, leading to dimensional changes in wooden elements as well as variation of their material behavior. In the European standard for the design of timber structures (EC5) these effects are considered by assigning wood members to service classes which are solely based on environmental conditions, but independent of the cross-sectional dimensions. Moisture-induced stresses resulting from dimensional changes are not directly considered. In this paper, we compare the EC5 assignment of service classes to an assignment based on the actual MCs, determined by simulations. Further, we present an approach to assign the service class for solid and glued laminated timber cross sections, depending on the dimensions of the cross section and based on realistic climate simulations for one location. With the proposed approach, the influence of moisture on serviceability design can be taken into account more appropriately, which is important when computing deflections and performing simulations based on 2nd order theory. In addition, a method to estimate MC distributions for larger cross sections solely based on relative humidities is proposed. With these, also moisture-induced stresses and dimensional changes can easily be considered in a static analysis.

Long-term uplift of high-speed railway subgrade caused by swelling effect of red-bed mudstone: case study in Southwest China

A high-speed railway must support fast-moving vehicles and have strict low-deformation requirements. However, many high-speed railways encounter the problem of abnormal subgrade deformation caused by expansive rocks. In this study, the Neijiangbei station of the Chengdu-Chongqing high-speed railway in Southwest China, where the subgrade has undergone continuous and stable uplift during the construction and operation periods, was considered as an example. The Jurassic red-bed mudstone widely distributed in this area is a typical expansive rock, and its swelling effect is the main cause behind the uplift of the subgrade. Results of water-absorption tests, disintegration tests, and expansion tests indicate that the red-bed mudstone is characterized by easy disintegration, slow water absorption, and long-term swelling. A decoupling analysis method for the seepage and swelling of red-bed mudstone was proposed to simulate the water infiltration through the fissures and the temporal and spatial changes in the swelling. Using monitoring data, an inversion analysis of the high-speed railway subgrade uplift was conducted, and the subgrade deformation was predicted. The results suggest that the main changed area of the moisture-content field in the rock formation was a small area near the fissure layer. The moisture content of the mudstone increased rapidly in the first few years of infiltration and increased slowly over subsequent decades. Correspondingly, the subgrade uplift increased rapidly in the first few years after excavation owing to the swelling of the mudstone; thereafter, the growth rate decreased, but the subgrade uplift maintained long-term continuous growth for several decades.

A Critical Review of Current Imaging Techniques to Investigate Water Transfers in Wood and Biosourced Materials

This review paper proposes a critical overview of experimental techniques and innovative experimental methods to observe and deeply understand the migration of water inside wood and biosourced materials. The state of the art of the knowledge of water transfer phenomena are first presented, namely liquid and bound water migration, together with shrinkage/swelling. Then, the papers presenting the 3D imaging techniques at high resolution offered by recent technologies, such as magnetic resonance imaging, X-ray tomography, and in situ tomography-mechanical tests. They enable visualization and analysis of water transfer mechanisms in eco-responsible materials such as natural fiber-concretes, wood, and biobased insulating materials. The 2D and 3D images processed with specific software packages allow for an overview of the distribution and orientation of the material components, as well as the moisture-content field which affects most properties of the materials such as mechanical properties (compression and tensile strength), hygro-thermal performance, as well as durability. Finally, the Digital Volume Correlation method allows for the observation and evaluation of deformation, cracks and failure mechanisms resulting from either a mechanical or hydric loading. The paper intends to help the reader to acquire a deep understanding of water imbibition and drying mechanisms in such materials.

Solution of the Problem of Plate Drying by Electromagnetic Radiation by Green's Function Method

An initial-boundary value problem for calculating heat and mass transfer fields in a homogeneous wet plate blown by an air flow and exposed to electromagnetic radiation is formulated. To solve this problem, we developed an original algorithm containing elements of analytical and numerical methods. It is based on the procedure of splitting the process by physical factors. This procedure is used to replace related problems for the temperature and moisture content fields with separate initial-boundary value problems for these fields on successive layers of the difference grid that are separated by small time intervals. Their solutions, in turn, can be constructed by the method of variable separation, which was impossible to apply to the original problem. 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. The ad-vantages of the new computational algorithm in comparison with the known numerical algorithms are considered, and the problems of the theory of electromagnetic drying for which its application can be effective are indicated.

Intensification of the Foam Technology by the Energy of Electrohydrothermal Force Fields. Part 3. Investigation of the Processes of Heat and Mass Transfer in a Foam System under the Action of EHTFF

As a result of thermal expansion of the gas phase of a foam mass playing the role of compacting component in a closed volume, we observe the appearance of excess internal pressure accompanied by the formation of the fields of pressure, temperature, and moisture content. The partial flows of liquid caused by these fields are directed from the center toward the perforated walls of the form and go further leaving the form. Under the action of electrohydrothermal force fields, we observe the appearance of three partial flows of moisture combined into a single flow in the mass. Thus, the phenomenon of self-compaction is accompanied by the processes of heat and mass transfer. At low temperatures, moisture moves in the material in the form of a fluid. At the same time, at high temperatures, it has the form of vapor. The density of the total flow of moisture can be represented as the sum of densities of the partial flows. The analytic investigation of the mechanism of heat-and-mass transfer flows enables us to study the behavior of the foam mass in the course of heat-and-force treatment and to choose the best conditions for this treatment.

NON-STATIONARY HEAT AND MOISTURE TRANSFER INTERCONNECTED PROCESSES IN PLANT MATERIALS MODELING IN CONDITION OF MILLIMETER-WAVE ELECNROMAGNETIC FIELDS IMPULSE INFLUENCE

On the basis of the theory of interconnected heat and mass transfer during phase transformations, as developed by A.V. Lykov (together with his students) with the help of methods of thermodynamics of irreversible processes, a system of differential equations in partial derivatives (for one-dimensional case)was proposed, which has a hyperbolic mass transfer equation taking into account the final value of mass transfer rate. In this paper, heat transfer is described by the equation, which adequately simulates the mentioned process within the quasi-stationary temperature fields. This approach is fair for modeling the processes of heat and mass transfer in plant materials under conditions of combined supply of energy under the action of constant and pulsed fields of millimeter range (the so-called extremely high-frequency range (EHF-band) with the carrier frequency GHz), as processed by short wave pulses. The non-stationary fields of moisture content (mass transfer) excited by video pulses in these media (bodies) and materials are presented analytically due to accurate periodic and non-stationary solutions of the heat-and-mass transfer equations obtained directly in the time domain outside the Fourier series, by analogy with the known results of A.B. Schwarzburg. The results obtained in this work can be further used to improve and refine engineering methods for calculating the parameters of diagnostic equipment, which is used to determine the characteristics of the vegetation cover of fields for agricultural purposes, when designing highways and overpasses in a rugged terrain, as well as while developping such devices and during exploitation of such equipment.

Intensification of foam technology by the energy of the electrohydrothermal power field. Part 3. Investigation of the processes of heat and mass transfer in the foam system under the influence of EHTPF

As a result of thermal expansion in the foam mass of the gas phase, which acts as a sealing component in a closed volume, excessive internal pressure is generated and fields of pressure, temperature, and moisture content are formed. Particular flows of liquid arising from these fields are directed from the center to the perforated walls of the form with a distance beyond it. In EHTPF, there are three partial flows of moisture that make up a single flow in the mass. Thus, self-compaction is accompanied by heat and mass transfer processes. At low temperatures, moisture moves in the material in the form of a liquid, and at high temperatures, in the form of vapor. The density of the total moisture flow can be represented as the sum of the densities of private flows. An analytical study of the mechanism of heat and mass transfer flows allows one to analyze the behavior of the foam mass during heatpower treatment and to choose the best conditions for it.

Immersion Freezing of a Scots Pine Single Seed in a Water-Saturated Dispersion Medium: Mathematical Modelling

Forest owners will be able to solve the problem of protecting small forest seeds from mechanical and atmospheric influences during aerial sowing, as well as the problem of manufacturing capsules in the field, saving financial, time and material resources. The process of creating a capsule by freezing the seed in a water-saturated dispersed system—immersion freezing—allows you to organize the technological properties of forest seeds depending on the initial requirements. In most cases, the quality of the seed capsule is determined by the thermophysical and mechanical properties of the components. The technological process of obtaining seed capsules for aerial seeding and the choice of freezing modes is based on a priori mathematical modeling of heat-and-mass transfer processes. The main purpose of the study is to predict the duration of the seed freezing process in a capsule with a water-saturated dispersed medium, depending on the external temperature conditions, the geometric parameters of the capsule and the seed. The cooling agent is carbon dioxide. The research is based on the use of numerical modeling methods on the platform COMSOL Multiphysics. A mathematical model is proposed that allows us to obtain the dynamics of the distribution of temperature and moisture content fields in the dispersed system and seed depending on a complex of geometric and thermophysical factors. The time of immersion freezing of the capsule with the common pine seed for the conditions considered should be in the range of 150 to 250 s.