Heating characteristics of western hemlock (Tsuga heterophylla) in a high frequency field

Abstract

The research aimed to establish whether dielectric heating of wood at high frequency could be accomplished fast, without excessive temperature fluctuations and no wood degrade. The intention was to develop optimized dielectric heating schedules in order to effectively pasteurize green timbers and logs for export-an eco-friendly substitute to currently used toxic chemical method. Data analysis revealed that the electric field distribution within the specimen was a strong function of its dielectric properties. Specifically, homogeneous moisture contents generated constant electric field values while heterogeneous distributions generated sudden drops and raises of the electric field strength with heating uniformly dispersed due to a fast redistribution from hot to colder areas. Convection losses through air contact may reduce the average heating rate of the timber shell by about 50%. Verhalten von Western Hemlock (Tsuga heterophylla) bei HochfrequenzerhitzungZusammenfassung In dieser Studie wurde untersucht, ob Hochfrequenzerhitzung von Holz schnell und ohne über-mäßige Temperaturschwankungen und ohne Beeinträchti-gung der Holzqualität durchgeführt werden kann. Ziel war es, ein optimiertes Erhitzungsprogramm zur effektiven phytosanitären Behandlung von für den Export bestimmtem Schnitt-und Rundholz zu entwickeln -als umweltfreundliche Alternative zu den gegenwärtig verwendeten toxischen chemischen Verfahren. Die Versuchsergebnisse zeigten, dass die Verteilung des elektrischen Feldes im Prüfkör-C. Lazarescu · S. Avramidis ( )

Wood sanitization protocol for export packaging of Pinus radiata wood using a radiofrequency heat treatment

“…In wood with high moisture content (MC), the loss factor is high and varies little, which favors the RF heating process (Huang et al 2013). When they compared the sanitization process of two species of conifers (Pinus contorta and Thuja plicata), Lăzărescu et al (2012) showed that heating rates were not correlated to the MC of materials, as the T. plicata heated up faster than the P. contorta at the same MC. Therefore, the species used has a greater effect on dielectric properties than MC, although is important to clarify that the changes in MC change the mass of wood that is going to be heated during the process to up to 11 % (Esquivel-Reyes 2017).…”

Numerical Study of Focusing Effects of Microwaves inside Wood Due to Timber Ring Structure

“…A review of different microwave wood testing techniques is given in [1] and these include propagation modelling, measurement techniques, hardware implementation, and determination of wood properties. According to [2,3], microwave heating, for example, offers several advantages over other drying methods and chemical procedures because its technique is eco-friendlier and causes less damage in the timber sample compared to employing toxic chemicals. Besides, microwave heating method is faster and gentler in comparison to live steam.…”

Chemical‐Free Pest Control by Dielectric Heating with Radio Waves and Microwaves: Thermal Effects

“…In Germany, the damage caused by dry rot fungus ( Serpula lacrymans ) alone adds up to 200 million € a −1 . State‐of‐the‐art pest control focuses on chemical as well as physical methods . However, in recent years the application of chemical wood preservatives in living and working areas has been declining to avoid the contamination of indoor air.…”