Interrelated Heat Research Articles

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.

Конвективная сушка пиломатериалов на основе управляемого влагообмена

Wood drying (in particular lumber drying), which almost entirely determines the quality of the wooden products, is one of the most complicated and energy-consuming processes in wood processing. Convective drying of lumber, in all its varieties, remains the most common by far. Computer modeling of wood drying processes is usually based on solving systems of differential heat and mass transfer equations. The methods for solving such systems, both analytical and numerical, are well researched and developed. However, the most important methodological issue is the correct formulation of the boundary conditions that determine the process of interrelated heat and mass transfer at the interface (wood – moist air). The convective drying has traditionally used the boundary conditions of type III by Academician A.V. Lykov, which are characterized by a sufficiently close correspondence between the mass flows moving from the wood depth and at the interface. This correspondence is described by the value of the so-called Bio mass transfer criterion. A computational experiment was carried out to verify these assumptions. It enabled to determine the possible controllability of the moisture removal during low-temperature convective drying of conventional lumber using modes of three-step and stepless structure. Besides this, the influence of the moisture removal on the dynamics of the internal stresses in wood was also studied. The results have shown that the stepless drying modes, on the one hand, offer a significant improvement in drying quality with practically no loss of drying capacity, and on the other hand, have better controllability. The results of the previously conducted and mentioned studies made it possible to propose general principles and then to patent a system for automatic control of moisture transfer during wood drying, which is fundamentally different from the previously known wood drying control systems. The system controls the drying process by adjusting the ratio of external to internal moisture transfer, rather than the value of the media parameters in the chamber. The moisture transfer control system for convective drying of lumber is of limited control: it cannot fully stabilize the values of the Bio mass transfer criterion. However, its use maintains a certain balance between internal and external moisture transfer, ensures the required drying quality and almost completely eliminates the occurrence of defects. For citation: Gorokhovsky A.G., Shishkina E.E., Agafonov A.S. Lumber Convective Drying Based on Controlled Moisture Transfer. Lesnoy Zhurnal [Russian Forestry Journal], 2022, no. 1, pp. 166–172. DOI: 10.37482/0536-1036-2022-1-166-172

ПРОГНОЗИРОВАНИЕ ДОЛГОВЕЧНОСТИ БЕТОННЫХ КОНСТРУКЦИЙ С УЧЕТОМ МАССОПЕРЕНОСА И КОЛЬМАТАЦИИ ПОР ПРИ КОРРОЗИИ

The object of research is the corrosion process of destruction of concrete and reinforced concrete structures in aggressive media. The purpose of the investigation is to establish a set of relationships and ratio between the characteristics of this process and various external and internal factors that affect the growth of corrosion. To solve the tasks set on the basis of the obtained experimental data, the method of mathematical modeling of corrosion processes was applied. The theories of physical and chemical transformations and heat and mass transfer laws suggest that different stages of corrosion can be simulated by differential equations of interrelated heat and mass transfer with boundary conditions. They are defined by arbitrary functions of initial transfer potentials and nonlinear boundary conditions of all known types. The possibilities of developed physical and mathematical models of mass transfer in the processes of studying corrosion of various types are demonstrated. They allow to evaluate the concentration of the transported component throughout the thickness of the concrete structure and in the biofilm itself at any time, as well as the concentration of "free" calcium hydroxide in the liquid phase. As a result, it is succeeded to predict the durability and reliability of concrete structures with a minimum error. The proposed author's model of the destruction of cement concretes, taking into account the colmatation of pores and capillaries, ensures the adequacy of judgments about the kinetics of mass transfer processes during corrosion of the II type.

Mathematical Model of Interrelated Heat and Mass Transfer with Account for the Two-Phase Lag

Mathematical Model of Interrelated Heat and Mass Transfer with Account for the Two-Phase Lag

Investigating regularities of gas hydrate ignition on a heated surface: Experiments and modelling

Interrelated heat transfer processes are numerically studied under conditions of chemical reactions and exothermic and endothermic phase transformations at methane gas hydrate ignition in the course of conductive heating. The dependences of the main characteristic of the process – the ignition delay time on the heating surface temperature, the sample heating rate, the activation energy of the fuel vapour oxidation reaction and the pre-exponential multiplier of the fuel vapour oxidation reaction are established. The limiting values of the main parameters of the energy source, under which the ignition conditions are implemented steadily, are revealed. It is shown that as the heater surface temperature increases, the ignition delay times decrease non-linearly. Self-preservation of the gas hydrate leads to an increase in the ignition delay time. The effect of self-preservation depends on the initial temperature of the heater.

Protective Lines for Suppressing the Combustion Front of Forest Fuels: Experimental Research

The article presents the results of experimental research, determining the conditions for suppressing the combustion front of forest fuels (FF) with the use of a protective water line. Integral parameters, velocities and other characteristics of the main interrelated heat and mass transfer processes, phase transformations and chemical reactions are studied. The conditions for suppressing the combustion front of typical forest fuels (needles; leaves; a mixture of needles, leaves and branches) are established. The experimental conditions are designed to be the utmost close to those of ground forest fires and parameters of fire lines: in terms of temperature, wind velocity, the forest fuel layer thickness, the size of water droplets, etc. The rational dimensions (width, length, depth) of the protective water lines, the density of water irrigation of the material surface, the volume of liquid, the time of spraying are determined. It is shown that effective conditions for forest burning localization can be achieved at almost complete thermal decomposition of a small layer of FF near the barrier line. It is established that necessary and sufficient conditions of FF combustion localization can be reliably predicted using the obtained dependences of specific water flow rate on FF volume.

Mathematical simulation of the ignition of coal particles in airflow

A numerical study of interrelated heat and mass transfer processes with consideration for the thermal reaction of the organic matter of fuel on the gas-phase ignition of coal particles with sizes from 50 to 500 μm in airflow was performed. Minimum air temperatures at which the ignition of volatile substances occurs in an oxidizing atmosphere were determined. The calculated values are lower than the level of maximum permissible temperatures in the individual sections of systems for the preparation of pulverized coal at coal-burning power plants.

Electric field control of NOx formation in the flame channel flows

The present studies aimed to obtain clean fuel combustion and get detailed information about the processes that determine the electric field effect on NOx formation in flame channel flows. The experimental studies demonstrate that the interaction between the radial electric field and the flame initiates the field-forced drift motion of positive radical ions in a field direction. The energy exchange between ions and gas particles produces interrelated heat and mass transfer to the negatively biased channel walls. Hence, by varying the applied voltage, a field-enhanced reducing of a flame temperature is obtained, thereby lowering thermal NOx formation during the fuel combustion up to 30-80%.

On the Problem of Nonisothermal Mass Transfer in Porous Media

We propose a model of nonstationary processes of interrelated heat and mass transfer in porous media that takes into account the mutual influence of vapor and liquid pressures determined by the contribution of the capillary and surface forces and temperature on the interphase mass‐transfer intensity, the thermocapillary flows, and the mechanical and dynamic equilibrium conditions of thin layers of liquids on curved interfaces. The results of the numerical solution of the system of equations of heat and mass transfer in capillary‐porous bodies in discrete and continuous heating as well as with allowance for the effect of nonequilibrium of phase transformations have been analyzed.

Calculation of Heat and Mass Transfer Processes in Binary Two-Phase Systems Used in Absorption Thermotransformers

Processes of interrelated heat and mass transfer in a film of the solution running off the surface and absorbing steam which is in contact with the film are studied. The models allowing for heat liberation in absorption that leads to a change in equilibrium values of temperature and concentration on the phase interface are suggested for description of interrelated processes of transfer in these systems. On the basis of the solutions obtained a technique is developed for calculation of combined heat and mass transfer in absorption in the case of film running-off along the bundle of horizontal tubes.

Simulation of thermal and moisture-content conditions on the upper layer of peat soils

The problem of two-dimensional interrelated heat- and moisture-transfer in the upper layer of soil is formulated taking into account exchange by heat and moisture with the ground-level air layer. On its basis a difference scheme was constructed and algorithms and a program were developed to calculate the processes of heat and moisture transfer. We evaluated the effect of various meteorological and hydrological factors and the composition of organogenic rocks on the change in the temperature and moisture-content conditions of peat deposits and soils.

A Method for Estimating Heat-Shielding Properties of Mineral Wool Insulation Based on Silicate Fibrous Materials

A method for estimation of the heat-shielding properties of gas-filled mineral wool insulators is considered, which takes into account the mechanism of interrelated heat and mass transfer processes and their intensities, depending on the service conditions, design specifics, and technological parameters of the insulating material.

Application of numerical methods in solving problems of interrelated heat and mass transfer and transformation of structure in easily deformable natural systems

The article considers processes of heat and mass transfer with transformation of structure in easily deformable natural disperse systems. A numerical method is used to solve such problems. With this method as a basis, a computational experiment is carried out making it possible to describe the behavior of these systems in a first approximation.

Modeling of two-dimensional interrelated heat and mass transfer problems and structure transformation

A numerical method to solve interrelated heat and mass transfer problems with structure transformation for easily deformable disperse capillary-porous media is suggested. Structure transformations of bodies of various shape, composition, and capability of cracking during drying are analyzed.

Influence of stefan flow on heat and mass transfer and kinetics of chemical reactions of a carbon particle in air

With account taken of Stefan flow, an analysis of the interrelated heat and mass transfer of a carbon particle in parallel reactions on its surface is performed.

Impacts of spatially and temporally varying snowmelt on subsurface flow in a mountainous watershed: 1. Snowmelt simulation

Abstract The dominant source of streamflow in many mountainous watersheds is snowmelt recharge through shallow groundwater systems. The hydrological response of these watersheds is controlled by basin structure and spatially distributed snowmelt. The purpose of this series of two papers is to simulate spatially varying snowmelt and groundwater response in a small mountainous watershed. This paper examines the spatially and temporally variable snowmelt to be used as input to the groundwater flow modelling described in the second paper. Snowmelt simulation by the Simultaneous Heat and Water (SHAW) model (a detailed process model of the interrelated heat, water and solute movement through vegetative cover, snow, residue and soil) was validated by applying the model to two years of data at three sites ranging from shallow transient snow cover on a west-facing slope to a deep snow drift on a north-facing slope. The simulated energy balances for several melt periods are presented. Snow depth, density, and the m...

SENSITIVITY OF SOIL FREEZING SIMULATED BY THE SHAW MODEL

ABSTRACT Sensitivity analyses conducted on hydrologic models are useful for understanding the complicated interactions of hydrologic processes and for demonstrating the potential errors resulting from incorrect estimation of input parameters. The effects of typical changes (measurement errors or natural variability) in input parameters on soil freezing as simulated by the Simultaneous Heat and Water (SHAW) model were investigated. The SHAW model simulates the interrelated heat and water transfer within snow, residue, and soil using estimated or measured weather data. Simulated frost depth was found to be very sensitive to small changes in air temperature (1° C) and initial snow depth (10 cm). Simulated frost depth was also potentially sensitive to the specified soil temperature for the lower boundary depending on the proximity of frost depth to the depth of the simulated profile. Site, residue soil characteristics having the greatest impact on simulated frost were slope, thickness of the residue layer, thermal conductivity of soil particles, soil bulk density, and a surface roughness parameter. Soil hydraulic parameters had little effect on frost depth, but had a large impact on water movement toward the zone of freezing and ice content of the frozen soil.

Simultaneous Heat and Water Model of a Freezing Snow-Residue-Soil System II. Field Verification

ABSTRACT Frozen soil has a major effect in many hydrologic and erosion situations, but it is very difficult to predict, especially on tilled agricultural soils with crop residue and intermittent show cover. A Simultaneous Heat And Water (SHAW) model to provide this predictability by simulating the interrelated heat, water and solute transfer through snow, crop residue and soil was presented in a companion paper (Part I). Detailed climatic, soil temperature, water content and frost depth data were collected for six diverse tillage-residue conditions during two winters to verify the model predictions. When compared to measured values, simulated soil temperatures were excellent, simulated frost depths were quite good, and simulated soil water profiles were good. Minimal calibration was necessary because the model uses fundamental equations for heat and water transfer with readily definable site parameters.

Simultaneous Heat and Water Model of a Freezing Snow-Residue-Soil System I. Theory and Development

ABSTRACT Frozen soil is a major cause of runoff and erosion on many watersheds. Tillage and crop residue management greatly affect soil freezing but their effects have been nearly impossible to predict. A detailed, physically-based model is presented which integrates detailed representations for the interrelated heat, water and solute transfer through snow, crop residue and soil. Measured or estimated hourly weather data are used to predict soil freezing depths, evaporation and profiles of temperature, moisture, ice and solutes.

Estimating the Performance of Gas Turbine Heat-Recovery Boilers Off-Design

In installations where a gas turbine is coupled to a steam prime mover through an exhaust heat steam generator, the need may arise to estimate the behaviour of the latter away from its specified design conditions. For example, the performance of the steam generator when the gas turbine is operating away from its design conditions may be of fundamental importance in relation to the economics of a proposed coupled installation. In particular, it determines inter alia the extent to which supplementary firing may be required. A question closely related to that of the off-design performance of a given exhaust heat steam generator is that of evaluating the comparative merits as regards thermal performance of designs differing in the layout and configuration of the heat-transfer surfaces when tendered for the same specified duty. (The need for such assessments frequently arises in the examination of competitive tenders.) The paper discusses briefly procedures allowing the influences of the interrelated heat balances of the heat-transfer surfaces, of the heat-transfer surface geometry and of the steam and gas physical properties to be analysed separately and integrated into a computational procedure permitting their combined effect on performance to be determined with sufficient accuracy.