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European Journal of Wood and Wood Products

, Volume 69, Issue 2, pp 295–301 | Cite as

Softwood heating in radio frequency fields

  • Ken Watanabe
  • Alhassan Abubakari
  • Ciprian Lazarescu
  • Stavros AvramidisEmail author
Originals Originalarbeiten

Abstract

The aim of this study was to investigate the heating rate of lodgepole pine (Pinus contorta) and western red cedar (Thuja plicata) during radio frequency (RF) heating. Wood specimens (40 × 150 × 1000 mm3) with various moisture content and power density were heated using a laboratory size RF dryer at a frequency of 40.7 MHz, until shell temperature reached 56 °C that is approved as a lethal temperature for phytosanitation. Heating rate was positively correlated with power density and negatively correlated with moisture content. The ratio of heating rate to power density had a negative correlation with moisture content and density in both pine and cedar. The regression lines for moisture content had good coefficient of determination (R 2) values of 0.63 and 0.61 °C m3/min kW (pine), 0.50 and 0.55 °C m3/min kW (red cedar) in both shell and core, respectively. The results demonstrate that the ratio of heating rate to power density is a useful parameter to estimate heating rate. The derived empirical equations made possible the calculation of the heating rate within test conditions applied to this study. The initial temperature rise in shell and core allowed a rather accurate determination of local power density. One dimensional mathematical model to describe the heating rate of wood during RF heating that was derived from the governing heat transfer equation combined with internal heat generation was developed and verified. The model using local power density had high R 2 of 0.71 and 0.93 in both shell and core, respectively, indicating that the model was able to predict heating rate of wood with various moisture content under the known power density distribution.

Keywords

Power Density Radio Frequency Fiber Saturation Point Dielectric Loss Factor Pinus Contorta 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Erhitzung von Nadelholz in Hochfrequenzfeldern

Zusammenfassung

Ziel dieser Studie war es, die Aufheizrate von Lodgepole Kiefer (Pinus contorta) und Western Red Cedar (Thuja plicata) bei Hochfrequenzerwärmung (RF) zu untersuchen. Holzprüfkörper (40×150×1000 mm3) mit unterschiedlicher Holzfeuchte und Leistungsdichte wurden mit einem Labor-Hochfrequenztrockner bei einer Frequenz von 40,7 MHz erwärmt, bis die Oberflächentemperatur 56 °C erreicht hatte. Diese gilt im phytosanitären Bereich als letale Temperatur. Die Aufheizrate korrelierte positiv mit der Leistungsdichte und negativ mit der Holzfeuchte. Das Verhältnis von Aufheizrate zu Leistungsdichte korrelierte sowohl bei Kiefer als auch bei Western Red Cedar negativ mit der Holzfeuchte und der Dichte. Die Regressionsgeraden mit der Holzfeuchte wiesen gute Bestimmtheitsmaße (R 2) von 0,63 und 0,61 °C m3/min kW für Kiefer und 0,50 und 0,55 °C m3/min kW für Red Cedar an der Oberfläche bzw. im inneren Querschnittsbereich auf. Die Ergebnisse zeigen, dass das Verhältnis von Aufheizrate zu Leistungsdichte ein nützlicher Parameter zur Schätzung der Aufheizrate ist. Die hergeleiteten empirischen Gleichungen ermöglichten die Berechnung der Aufheizrate unter den in dieser Studie gewählten Versuchsbedingungen. Der anfängliche Temperaturanstieg im äußeren und inneren Querschnittsbereich erlaubte eine ziemlich genaue Bestimmung der örtlichen Leistungsdichte. Ein eindimensionales mathematisches Modell zur Beschreibung der Aufheizrate von Holz während der Hochfrequenzerwärmung, hergeleitet auf Basis der geltenden Wärmeübergangsgleichung in Verbindung mit der internen Wärmeentwicklung, wurde entwickelt und verifiziert. Das Modell, das die lokale Leistungsdichte verwendet, ergab hohe R 2-Werte von 0,71 und 0,93 im äußeren bzw. inneren Querschnittsbereich. Dies weist darauf hin, dass das Model in der Lage ist, die Aufheizrate von Holz bei unterschiedlicher Holzfeuchte und bei bekannter Leistungsdichteverteilung vorherzusagen.

Notes

Acknowledgements

This work is financially supported by a Strategic Grant from the Natural Sciences and Engineering Research Council of Canada. The input regarding the experimental design technical information about the RF-heating by Dr. Terry Enegren is greatly appreciated.

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Ken Watanabe
    • 1
  • Alhassan Abubakari
    • 1
  • Ciprian Lazarescu
    • 1
  • Stavros Avramidis
    • 1
    Email author
  1. 1.Department of Wood ScienceUniversity of British ColumbiaVancouverCanada

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