Radio-Frequency Heating Kinetics of Softwood Logs

Abstract

The project assessed the radio-frequency (RF) heating characteristics of logs of two softwood species, namely, Engelmann spruce (Picea spp.) and subalpine fir (Abies lasiocarpa). Sixty logs, equally divided between the two species, were RF heated in two different circumstances—with or without bark—until the temperature sensor from a number of those scattered within each specimen with the lowest reading indicated 70°C. Both species heated in short periods of time (∼60 min), regardless of bark presence or absence, with relatively small energy requirements and without noticeable negative consequences on quality. The sapwood heated up faster, thus reaching higher temperatures because of its high moisture content and better complex permittivity values. Between the two tested species, fir is more prone to RF heating due to its higher ability to convert an electric field into heat.

Keywords:

• Dielectric heating
• Radio frequency
• Softwood logs

ACKNOWLEDGMENTS

This work was financially supported by a Strategic Grant from the Natural Sciences and Engineering Research Council of Canada.

Notes

^a Power and volume drop values were calculated as the difference between 100% and percentage ratios between individual and maximum values of each species class.

^a HR is the heating rate (°C/min) and P _D is the power density (kW/m³).