Influence of frequency on electromagnetic field distribution in a wood pile when drying in a vacuum-dielectric chamber

Abstract

Due to its properties as strength, hardness, wear resistance and good appearance, wood is widely used in furniture production, construction, and in manufacture of musical instruments, etc. The technology of vacuum-dielectric drying of wood is the combined use of high-frequency dielectric heating which has proven itself in electrical technology, including for drying wood in vacuum. The technological advantages of vacuum dielectric chambers (VDC) compared to traditional drying methods provide not only an increase in the drying speed of wood, but also the elimination of fires, because the process takes place at temperatures below 70°C. At the initial stage of the study, the analysis of the technical characteristics of high-frequency generators produced by domestic and foreign industry was carried out. To select the optimal current frequency, a problem was solved aimed at identifying patterns of distribution of electric field strength along horizontal and vertical coordinates along the cross section of a pile of dried wood (oak, larch, spruce and pine) depending on the frequency of the HF generator current. The study of the VDC - wood pile system was carried out in the licensed software environment “ELCUT”. It was found that the research results presented in relative units for a pile formed from larch, spruce and pine coincided by 98-100% with the results obtained for an oak pile. Thus, a standard frequency of 13.56 MHz may be recommended for powering the VDC regardless of the type of wood being dried. This statement was confirmed by the results obtained by using well-known engineering calculation methods to calculate and select the optimal frequency of the HF generator current. Based on the research findings, the following conclusions may be drawn: the frequency of 13.56 MHz is the optimal frequency for drying wood of various species in an air-conditioning chamber; the specified frequency ensures high uniformity of the distribution of electric and temperature fields across the cross-section of the pile being dried and, as a consequence, the required category of drying quality.