Capillary-porous Bodies Research Articles

Synthesis and magnetic relaxation properties of a porous glass magnetic microcarrier

The reaction of formation of magnetic iron oxide nanoparticles from aqueous solutions of Fe(+2,+3) salts was studied under homo- and heterophase conditions of capillary-porous bodies by the nuclear magnetic resonance relaxometry method. Magnetic composites based on Bio-Glas porous glasses were obtained by precipitation of iron oxide nanoparticles in pores ranging in size from 50 to 250 nm. The magnetic relaxation rate of water protons during the heterophase precipitation reaction was examined.

Numerical Simulation of Vacuum Drying by Luikov's Equations

A two-dimensional mathematical model was developed to simulate coupled heat and mass transfer in apple under vacuum drying. Luikov's equations are the governing equations in analyzing heat and mass diffusion problems for capillary-porous bodies. The model considers temperature- and moisture-dependent material properties. The aim of this study is to analyze the influence of some of the most important operating variables, in particular, pressure and temperature of drying air, on the drying of apple. The resulting system of unsteady-state partial differential equations has been solved by a commercial finite element method (FEM) package called FEMLAB (COMSOL AB, Stockholm, Sweden). Simulations, carried out in different drying conditions, showed that temperature is more effective than air pressure in determining the drying rate. A parametric study was also carried out to determine the effects of heat and mass transfer coefficients on temperature and moisture content distributions inside apple during vacuum drying. A comparison between the theoretical predictions and a set of experimental results reported in the literature showed very good agreement, especially during the first 4,200 s, when experimental data and theoretical predictions overlapped and relative errors never exceeded 2%.

Effect of structuring on the density of the liquid in colloidal capillary porous bodies

A method has been developed for calculating the density of the liquid in peat being dried, and liquid density data have been obtained for the first time for peat specimens differing in dispersity and for different drying temperatures. These data are at variance with the tabulated data for the corresponding structuring periods. Unprocessed and slightly processed peat specimens are characterized by smaller density values. High densities are observed for profoundly processed peat. The liquid density as a function of temperature passes through a maximum. At temperatures above the hydrogen bonding manifestation limit, the interaction between elements of the wet peat body is mainly due to the molecular van der Waals forces. The porosity of peat varies with temperature in both structuring periods. There is a discrepancy between the density data obtained using the conventional approach and those obtained by the method suggested here. The data coincide only for the first structuring period, when the moisture content is fairly high, because of the insignificant structuring effect of the solid phase.

Structural and mechanical properties of pelletized fine materials

The rheological aspect of pelletizing fine materials is considered. The elasticity modulus, yield strength and plastic viscosity of the capillary-porous bodies formed are determined. The defining effect of the viscosity of a porous dispersed medium of palletized fine materials on the structural and mechanical parameters of the granules formed is demonstrated.

Drying of Wheat Based on the Non-Equilibrium Thermodynamics: A Numerical Study

A new mathematical model to describe simultaneous heat and mass (liquid and vapor) transfer and shrinkage during drying of capillary-porous bodies with particular reference to prolate spheroid solid is presented. As an application, the methodology was used to predict drying of soft red winter wheat (Arthur). The mathematical model was based on the nonequilibrium thermodynamics considering variable transport coefficients and convective boundary conditions at the surface of the solid. All the partial differential equations presented in the model have been written in prolate spheroidal coordinates and solved numerically by a finite-volume method using implicit fully formulation. Results of the drying and heating kinetics and moisture content and temperature distributions in a wheat kernel during drying process are presented and analyzed. The methodology allows verification of the heat, liquid, and vapor fluxes, taking into account the thermal and hydrical gradients inside the grain.

Developing a one-dimensional heat and mass transfer algorithm for describing the effect of green roofs on the built environment: Comparison with experimental results

This paper investigates the mathematical modelling of the effect of green roofs on mitigating raised urban temperatures. A dynamic, one-dimensional model is developed, describing heat and mass transfer in building materials, considered as capillary-porous bodies, the vegetated canopy, modelled as a combined plant–air canopy layer, the soil and the air. The model is validated with an experiment, conducted in the Welsh School of Architecture, in Cardiff, in summer 2004. The right choice of parameters that affect the accuracy of the model (such as the expression of the convective heat transfer coefficient and stomatal resistance) is discussed. Special attention is given to the comparison between the experimental results and the outputs of only heat transfer algorithms and heat and mass transfer expressions. Taking these comparisons into consideration, conclusions are drawn about developing an accurate algorithm describing the thermal effect of green roofs on the built microclimate.

Simultaneous estimation of the spacewise and timewise variations of mass and heat transfer coefficients in drying

In this article, the conjugate gradient method with adjoint problem is applied for the identification of the heat and mass transfer coefficients at the surface of drying capillary-porous bodies. The unknown functions are supposed to vary in time and along the surface open to the surrounding environment. The inverse problem is solved by considering either the heat or the mass transfer coefficients as unknown, as well as by considering simultaneously both functions as unknown. The effects of temperature and moisture content measurements on the inverse analysis are examined. A comparison of different versions of the conjugate gradient method is also presented as applied to the inverse problem under study.

The vapour–liquid interface and stresses in dried bodies

The paper presents a contribution to modelling the problem of vapour-liquid interface receding into dried body and stresses induced by drying of capillary-porous bodies. A complex algorithm comprising the specific mechanisms of drying in the first and second periods of drying is constructed. It enables calculation and drawing of the body temperature and drying curves for the whole drying process and identification of the vapour-liquid interface receding into the body. The drying induced stresses caused by the receding vapour-liquid interface and the non-uniform distribution of moisture content and/or temperature are analyzed. Numerical calculations of the temperature and drying curves and the drying induced stresses are carried out for the example of a finite dimensional kaolin cylinder dried convectively.

Influence of Moisture Evaporation from a Heated Surface on the Thermal Regime of a Capillary-Porous Body in the Initial Period of Drying

The results of experimental determination of a change in time of the intensity of moisture evaporation from the surface of a ceramic mass for soft-mud moulding in the initial period and in a portion of the first period of radiant drying are presented. Comparison between the theoretical solution obtained for the Fourier equation with the corresponding boundary conditions and experimental results has been made, which showed an agreement sufficient for practical purposes. Nomograms convenient for practical applications are presented.

Mathematical simulation of heat and mass transfer, phase conversions, and shrinkage for optimization of the process of drying of thermolabile materials

A mathematical model and a numerical method for calculation of the processes of heat and mass transfer, phase conversions, and shrinkage in drying of colloidal capillary-porous bodies are presented. The model and method allow one to conduct polyvariant calculation of the fields of temperature, volumetric concentration, and pressure in each of the components of the bound substance. A method of dehydration of thermolabile materials that makes it possible to minimize the time of drying and provide savings of energy and resources is presented.

Theoretical and technological aspects of removal of large amounts of organic liquids from capillary-porous bodies. III. Mathematical model of the process

A mathematical model of removal of large amounts of an organic liquid from a capillary-porous body in a superheated steam current is elaborated. The model can be used to determine the heat-transfer coefficients and the drying rate for all periods of the process and estimating the change in the composition of the liquid phase passing into the pores of the material in the first three periods for different process parameters.

Theoretical and technological aspects of removal of large amounts of organic liquids from capillary-porous bodies. II. Kinetics

The opinion expressed in [1] on the mechanism of removal of organic liquids from a capillary-porous body in a current of superheated steam was confirmed by direct kinetic experiments. It was found that during the first four periods of this process, the resistance of the boundary layer to transfer of matter is higher than the hydrodynamic resistance of the pore structure of the material, and removal of liquid mechanically bound with the porous body is limiting for the process as a whole. It is concluded that the efficiency and environmental safety of the process can be increased by implementing it in two different chambers, the first designed to remove the solvent with saturated steam, and the second for drying the material.

Theoretical and technological aspects of removal of large amounts of organic liquids from capillary-porous bodies. 1. Mechanism of the process

The basic concepts concerning the mechanism of removal of large amounts of organic liquids from capillary-porous materials in treating the materials with superheated steam are formulated. It is hypothesized that regardless of the level of thermodynamic affinity of the distilled solvent for the skeleton of the porous material, removal of liquid physically-mechanically bound, and not adsorption or osmotically bound with the material is limiting for the process as a whole.

Simultaneous estimation of spatially-dependent mass and heat transfer coefficients of drying bodies

In this article, the conjugate gradient method with adjoint problem is applied for the identification of the heat and mass transfer coefficients at the surface of drying capillary-porous bodies. The unknown functions are supposed to vary along the surface open to the surrounding environment. The effects of temperature and moisture content measurements on the inverse analysis are examined. The inverse problem is solved by considering either the heat or the mass transfer coefficients as unknown, as well as by considering simultaneously both functions as unknown.

Description of Heat and Mass Transfer in Film Boiling of Superfluid Helium in Microgravity in a Capillary-Porous Body

Description of Heat and Mass Transfer in Film Boiling of Superfluid Helium in Microgravity in a Capillary-Porous Body

CORRECTION OF TEMPERATURE AND MOISTURE DISTRIBUTIONS IN WOOD DRYING

A procedure is proposed to improve the numerical solutions of the Luikov equations of heat and mass transfer in capillary-porous bodies based on the measured temperature and moisture data. The main idea of the procedure can be summarized as a modeling technique with online correction ability. The procedure is demonstrated by a one-dimensional problem of heat and mass transfer in spruce sample. Numerical simulation shows that the accuracy of the solutions for the heat and mass transfer can be improved significantly by using the proposed method.

Kinetics of Moisture and Heat Transfer between a Capillary Porous Body and an Aerosol

The kinetics of moisture and heat transfer between a capillary porous body and a gas–vapor–liquid medium with a dispersed liquid phase (aerosol) is described theoretically.

Solution of a Heat Equation of Hyperbolic Type with Mixed Boundary Conditions on the Surface of an Isotropic Half-Space

INTRODUCTION The phenomenological theory of heat conduction assumes that the heat propagation velocity is infinitely large, which is justified by computations of temperature fields in bodies under ordinary conditions observed in practice. However, for rarefied media and nonstationary processes of high intensity, one should take account of the fact that heat propagates at a finite velocity. Lykov [1, p. 21] suggested a theory of finite heat and particle propagation velocities in capillary-porous bodies, which implies that wr = √ λ/ (cγτr), where wr is the heat propagation velocity, τr is the time constant of the thermal flow, λ is the thermal conductivity, c is the specific heat, and γ is the material density. As a rule, wr ∼= 150− 300 m/sec and τr ∼= 10−9 − 10−15 sec for gases, and the effect of the finite heat propagation velocity on the heat transfer becomes observable in the case of a supersonic flow. Then the heat equation has the form [1, p. 21]

Non-linear model for wood saturation

The paper presents a non-linear model of saturation with fluid of anisotropic capillary porous bodies and the results of experimental investigations of wood saturation with methacrylate. The obtained experimental curves illustrating the distribution of methacrylate in wood samples allow the estimation of material coefficients and verification of the theoretical model. The theoretical model is developed based on the balance equations of mass, momentum, and energy, and the thermodynamics of irreversible processes. The non-linear differential equation, describing the distribution of methacrylate content in wood and its evolution during the saturation is solved numerically. The theoretical curves obtained on the basis of both linear and non-linear models are compared with the experimental data and better agreement between them for the non-linear model is stated.

Superfluidity of Aqueous Solutions of Mechanically Activated Quartz in Capillary Porous Bodies

Water permeation through porous beds of ground quartz is not explicable in terms of the classical filtration theory: as the filtration rate is reduced, the water permeability of these beds grows monotonically to a doubled value, while the theory predicts that it must be invariable in the range of filtration rates examined. This phenomenon is a direct consequence of the mechanical activation (solubilization) of quartz during grinding. The superfluidity phenomenon is also observed with specially prepared aqueous solutions of mechanically activated quartz and porous bodies formed from chemically inactive powders. It is demonstrated that the superfluidity of water in beds of mechanically activated powders is due to the formation of such solutions during filtration.