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Thermomechanics of drying processes. (English) Zbl 1038.74002
Lecture Notes in Applied and Computational Mechanics 8. Berlin: Springer (ISBN 3-540-00412-2/hbk). 365 p. (2003).
The book affords a very extensive insight in many aspects of drying. It is written in the first instance for engineers but, according to the author, “without any loss of its scientific character”. Originally, the subject “drying” which refers to the process of moisture removal from saturated materials, is of the highest interest in chemical engineering. In practice (for example wood processing, paper industry, food industry or dewatering of sludge) one is anxious to find drying procedures which consume as few energy as possible and which excite only non-destructive deformations of the material. As a matter of course, also the theoretical investigation of the subject is very interesting. Former studies concentrated mainly on heat and mass transport processes without exhaustive analysis of the mechanical effects occuring in dried materials. The dried material has usually been assumed to be rigid. In contrast, in the book at hand a theory is presented which describes multiphase transport in deformable saturated capillary-porous media, based on balance equations and the principles of irreversible thermodynamics. The theory enables the prediction of temperature and moisture content distributions and their evolution in time, as well as a description of deformations and the evaluation of drying induced stresses in dried bodies.
The moist material which may be, e.g. ceramics, wood, foams, etc. can be thought of as being composed of solid particles separated from one another by water coatings. Diminishing the coating dimension during drying involves reduction of the material volume (shrinkage) and causes a stonger attraction between skeleton particles due to atomic interaction. As a consequence, one observes an increase in strength of the material during the drying course. The shrinkage phenomenon involves consolidation of the material. A non-uniform shrinkage, which occurs, e.g., during a high drying rate, may pose a non-uniform consolidation and undesired deformations resulting in warping or fissure of the dried products. These mechanical phenomena that accompany drying processes can only be accounted for explicity on the basis of thermomechanics of fluid-saturated porous solids. The dried material is characterized by alterable physical and mechanical properties due to the continuous change of moisture content. The material may change its properties during the drying process from plastic through viscoelastic and elastic to brittle. Furthermore, the material coefficients in general depend on the moisture content, which makes the theory generally non-linear.
The book is composed as follows: After two short chapters on properties of dried materials and characterization of drying processes, the balance equations are introduced. The following chapters deal with the thermodynamics, rheological properties and constitutive relations for elastic, viscoelastic, plastic and brittle materials. Boundary conditions for the different periods of drying are presented. An introduction to the numerical analysis of drying processes follows, i.e. Galerkin’s formulation of the problem and the numerical time integration. Some examples are thus solved and discussed. One of the chapters deals with a very important property of dried materials, namely the anisotropic structure. This feature is shown considering wood as example. The book ends with a chapter on experimental studies.
In spite of a unique contribution on an important subject, the book is not always well balanced in the presentation. Some issues, such as thermodynamical potentials, Langmuir theory etc. are not elaborated clearly enough for unexperienced readers. Some basic issues, for example, balance equations or numerical introduction are presented comparatively in detail. Nevertheless, all in all, the book is valuable reading for people working on modeling of drying processes.

MSC:
74-02 Research exposition (monographs, survey articles) pertaining to mechanics of deformable solids
74F10 Fluid-solid interactions (including aero- and hydro-elasticity, porosity, etc.)
76S05 Flows in porous media; filtration; seepage
74A15 Thermodynamics in solid mechanics
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