Sirvi Autor "Tamme, Hannes" järgi
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Kirje Development of control and optimization methods for wood drying(Estonian University of Life Sciences, 2023) Tamme, Hannes; Muiste, Peeter (advisor); Tamme, Valdek (advisor); Institute of Forestry and Engineering; Spulle, Uldis (opponent)The purpose of wood drying is to obtain material with the desired final moisture content. During the process, it is necessary to find a balance between the quality of the wood and the energy and time spent. In order to find an optimal solution, it is important to know the condition of the material to be dried at a specific time. Often, the standard equipment of an industrial kiln is not enough when implementing a new drying schedule. In addition, there is a need for software that simulates wood drying, providing the initial drying regime, which can then be further optimized using the methodologies and sensors presented in this study. This work checks the occurrence of theoretically simulated moistening impulse response in experiments based on synchronous surface displacement, temperature and surface moisture sensors. For this purpose, it was necessary to develop specific sensors used for wood monitoring in the wood dryer climate. A physically justified measurement result is guaranteed when using sensors based on different working principles. When investigating the reliability of the sensors, typical issues and practically usable measurement ranges below and above the saturation point of the wood fiber were identified. The transition of the surface layer of wood from the first phase of drying to the second phase of drying was investigated. It was found that the transition of the surface layer to the second drying phase slows down the diffusion rate in the inner layers of the wood, which otherwise could still be in the first phase of drying due to their moisture content. In order to characterize the influence of the diffusion constant of the surface layer on the inner layers, the concept of critical diffusion constant was defined. In the process of wood drying, individually calibrated carbon fiber needle-electrodes were used to record the moisture content of wood at different depths from the surface of the board being dried. When creating an optimized drying plan taking into account the critical diffusion constant, it was possible to significantly shorten the drying time of a typical industrial drying plan at the same final moisture content. The optimized drying schedule was characterized by a higher drying strain, which can level down by a timed moistening pulse. In this thesis, the relative humidity value of the critical drying air corresponding to the critical diffusion constant for pine wood was found. It is easy for a timber company to use this information to modify its drying schedules on site. An electrical indicator of maximum wood drying stresses was also developed. Since the electrical resistance method is mostly used for wood drying monitoring in practice, the hardware and software of the patented polarization-type moisture meter prototype were improved. Galvanostatic charging mode and depolarization voltage monitoring capability was added.