Modeling of thermal processes in the technologies for wood processing | Modelirovanije teplovych processov v technologijach obrabotki drevesiny

The current monography is the result of the cooperation under a scientific-research project with the topic Thermal processes in the technologies for wood processing between the Faculty of Forest Industry at the University of Forestry in Sofia, Bulgaria and the Faculty of Wood Sciences at the Technical University in Zvolen, Slovakia supervised by the authors between 2008 and 2010. The project has been funded by the Scientific-research sector at the University of Forestry in Bulgaria and by the Cultural and Teaching Grant Agency of the Ministry of Education in Slovakia (KEGA SR). The work that the authors have done on the given problems over more than three decades has been described briefly in the monography. The prevailing portion of the processed wood is subjected to thermal and or thermal-humidity influences, as a result of which it is transformed from a raw material into an industrial product with desired or given properties. The knowledge and analysis of the thermal and moisture-transferring processes in the technologies for wood processing creates a theoretical base for the constant improvement of the technologies themselves and of the equipments, in which they are carried out. This allows for the understanding of the essence of the specific technologies and for the development of science-based measures for the increase of the quality of the production, the decrease of energy consumption, etc. In each particular case of thermal processing, the following problems need to be sorved: the most economically viable regime needs to be determined (temperatures and duration of processing), the necessity for thermal energy needs to be calculated and the automatic carrying out of the optimal regime needs to be ensured. The monography is dedicated to the solution of these important for both the science and practice problems using mathematicai modeling of the processes of thermal processing of wood lumber in the technologies for production of veneer, plywood, parquet, and parts for the furniture industry. The thermal processing of wood materials is carried out by treating them with saturated or humid steam or with hot water, as a result of which main plasticizing or ennoblement of the wood is achieved. The materials are subjected to thermal processing with the aim of plastification in the production of veneer, as well as with the aim to receive bent parts in the production of chairs and sporting equipment. This is determined by the circumstance that the heated humid wood has an increased deformation capability and is susceptible to cutting and spatial configuration. A significant portion of beech, acacia, walnut and other lumber is subjected to thermal processing with the aim of ennoblement of the wood. Parquet and important, dimension-stable parts for the furniture industry are then produced from the ennobled wood. A main goal for the development and optimization of the contemporary technologies for thermal processing of wood materials is the science-based determination of the temperature in separate points of their volume at each moment of the heating. An inseparable part of this process is the conditioning in the air medium of the heated plastificated materials with the aim of homogenization of the temperature fields in their volume before the consequent bending or cutting of the veneer. The correct and effective control of this process is possible only when its physics and the weight of the influence of each of the few dozens factors are well understood. The non-defective carrying out of the process of thermal treatment depends on the dimensions, initial temperature, and the function of the wood materiais, on the build and themicrostructure specifics of the wood species, on the anisotropy of the wood, and on the content and aggregate condition of the water in it. Other important factors are the law for the change in the values of the temperature of the processing mediums, the manufacture parameters of the equipment, the thermo-physical characteristics of the material of the corpus and insulation layer of the equipment, of the surrounding air, the degree of loading of the equipment with wood materiais, etc. The influence of so many factors is covered and adequately reflected in the described in the monography 1 D, 2D and 3D non-linear mathematical models of the processes of heating of prismatic and cylindrical materials with different functions during the time of their thermal processing and consequent conditioning, as well as in the models of specific energy consumption, necessary for the carrying out of this processing. The models can be used for the calculation and visualization of the non-stationary distribution of the temperature fields of materials containing or not containing ice during their thermal processing and conditioning. The calculation of the change in the temperature field in the volume of materials containing ice in the beginning of their thermal processing is interconnected for the periods of the melting of the ice and after that, taking into account the flexible boundary of the melting ice. Based on the calculations it can be determined when the moment of reaching in the entire volume of the heated wood has occurred for the necessary optimal temperatures needed for bending of the parts or for cutting the veneer, as well as the stage of the ennoblement of the wood desired by the clients. The models can also be used for the calculation of the non-stationary change in separate components of the thermal balance of the equipments for thermal processing (specific energy consumption for 1D, 2D and 3D heating of the wood itself, for the heating of the equipment, for thermal emission from it, etc.).