Stefan Jan Kowalski

Theory of thermodiffusion for solids

Abstract The aim of this work is the derivation of a complete set of differential equations of thermodiffusion in solids, accounting, at the same time, for simultaneous action of the mechanical, temperature and concentration fields. The analysis is based on the thermodynamics of irreversible processes with the usual assumptions made in the theory of thermoelasticity and an additional assumption that there is no chemical reaction and that the local temperatures of the matrix and the diffusive substance are the same. Generalized laws of heat and mass flow are also introduced in the paper. Such a theory can be used to describe, for example, the thermochemical treatment of metals.

Moisture transport, thermodynamics, and boundary conditions in porous materials in presence of mechanical stresses

Abstract General equations for simultaneous heat and mass transfer with free enthalpy taken as a universal potential for both the moisture transport and the phase transitions have been proposed in this paper. Detailed discussion of these equations is given for boundary conditions characteristic of convective drying of capillary-porous materials.

A plasticity theory for fluid-saturated porous solids

Abstract A theory of plastic flow is developed for an elastic-perfectly plastic porous solid with its intercommunicating void spaces filled with a viscous fluid. The constitutive equations are established where full use is made of the thermodynamical equations. The final result of the paper is the complete set of equations of the theory and the boundary conditions for the medium in question.

The response of dried materials to drying conditions

Abstract The response of dried materials to a variation in drying conditions is studied in this paper. The aim of the study is to establish an appropriate system of control of drying processes to avoid destruction of the dried materials. The development of methods of control allows one to design optimal drying processes. We conclude in this paper that the optimal control of drying processes has a wide range of possibilities

Drying stress formation by inhomogeneous moisture and temperature distribution

The field of moisture concentration and the field of temperature are the two factors that induce stresses in dried materials. The main aim of this paper is to estimate the influence of these two factors on the formation of drying-induced stresses. The considerations are based on the model elaborated by the authors and the analysis of the drying-induced stresses is carried out on a convectively dried prismatic bar.

THERMOMECHANICS OF THE DRYING PROCESS OF FLUID-SATURATED POROUS MEDIA

ABSTRACT Aspects of the thermomechanics of fluid-saturated porous solids relating to the drying process of materials are discussed in the paper. From the balance equations and the principles of thermodynamics of irreversible processes, the differential equations describing the drying body deformations and induced stresses, the temperature, and the moisture content distributions are developed. The porous body is assumed to be elastically deformed and the pore space is filled with an immiscible liquid-gas mixture-the moisture. The phase transitions of liquid into gas are taken into account

Drying processes involving permanent deformations of dried materials

Abstract A system of differential equations describing the mechanical behaviour of fluid saturated capillary-porous bodies with permanent deformations caused by drying processes is presented in the paper. Three variants of deformations of the matrix material were considered: elastic, viscoelastic and elasto-plastic. A general form of physical relations was established as well as the equations describing the heat and mass transfer were developed. The paper also discusses a procedure of formulation of boundary conditions.

Thermodynamics of fluid-saturated porous media with a phase change

SummaryIn the present paper some aspects of the thermodynamics of a fluid-saturated porous solid, taking into account the phase change of liquid into gas, are discussed. Based on the principles of the thermodynamics of irreversible processes, restrictions for the constitutive equations of the constituents are developed, in particular for the phase transition. The porous body is assumed to be incompressible and elastically deformed, and the pore space is filled with an immiscible liquid-gas mixture (moisture). The theory presented here provides some background that can be found suitable, e.g., for drying aspects.

Mathematical Modelling of Shrinkage During Drying

ABSTRACT Main aim of this paper is to present a mathematical model describing the shrinkage phenomenon of materials undergoing drying processes. The model was constructed using the methods of continuum mechanics and the principles of thermodynamics of irreversible processes.it considers the similtaneous deformation of the dried body accompanying the heat and moisture changes and the drying induced stresses

Natural convective flow between an array of vertical cylinders

Abstract The natural-convectioe flow of a viscous and heat-conducting fluid in systems of cylinders, arranged vertically in regular patterns, is studied. The aim of the study is to determine the conditions of stability of the fluid when heated from below and cooled from above. In particular, the influence of geometry and thermal properties of the system on the free stationary convection are studied. A new way of calculating the free convection threshold is proposed. The final results are analytical formulas for determining the critical Rayleigh numbers for the studied forms of flow and graphs, showing the dependency of these numbers on the geometrical parameters of arrays.