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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

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The problem of lumber drying is considered. The relevance of the research is due to the need to improve the system of automated control of the technological process of drying lumber on the basis of modern information technologies, reducing the energy-intensity of these technologies, which is enshrined in the program documents of forest industry development at the governmental level. It is shown that the most effective solution will be the use of fuzzy modeling. In this case, the characteristics of the uncertainty of the input parameters and the influencing factors will be taken into account. The functional purpose of the automated control system is to provide a given level of moisture content of wood with the required quality of wood (exclusion of damage). It is extremely difficult to obtain such a functional dependence on the heating temperature in the drying chamber and equilibrium air humidity by traditional statistical methods due to the uncertainty of the parameters, therefore, the apparatus of the theory of fuzzy sets should be used for this task. The purpose of this work was to analyze researches in the field of lumber drying and substantiate the meaningful formulation of the problem of moisture content and lumber drying time modeling. The methodological basis of theoretical studies were: the drying theory, wood science, apparatus of mathematical and fuzzy modeling. The result of the research is the substantiation of the meaningful formulation of tasks of fuzzy modeling of the humidity and lumber drying time. The scientific novelty of research follows from the proposed theoretical approach to estimating the parameters of moisture content and drying time of lumber on the basis of fuzzy modeling. The practical applicability of the results lies in the possibility of using the developed problem statement for fuzzy inference of the functional dependence of the control of drying of materials.

The paper considers the relevant issue of improving wood drying, reducing the energy intensity of these technologies , primarily by means of automated process control systems based on modern information technologies. To take into account the uncertainties of the input parameters and the influencing factors the apparatus of fuzzy modeling was used. To complete the work, it was necessary to obtain the missing functional dependences of the wood moisture content and time of drying on the heating temperature and the equilibrium air humidity in the drying chamber based on fuzzy output, which was the purpose of this work. Methodologically, the work is based on the drying theory, wood science, the regulation of mathematical and fuzzy modeling, and in terms of checking the adequacy of the proposed fuzzy model, the methods of mathematical statistics and the theory of experiment were used. The results of the research are the obtained dependences of drying time and wood moisture content on the heating temperature and the equilibrium air humidity in the drying chamber, the synthesis of which is performed by means of Fuzzy Logic Toolbox of the Matlab application. The scientific novelty of research can be seen in the development of models of drying process based on fuzzy modeling. The practical applicability of the results is the possibility of creating an intelligent system of automatic control of the drying process of lumber.