Dielectric characteristics of two BC coastal species during radio frequency heating

• Main Author: Zhou, Bingning
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/6368

The purpose of this study was to evaluate the dielectric properties (loss factor) of two British Columbian softwoods (western hemlock [Tsuga heterophylla (Raf.) Sarg.] and western red cedar [Thuja plicata Donn]) at different moisture content, temperature, and electric field strength levels. This study is expected to provide useful information for the development of a mathematical model to describe heat and moisture transfer mechanisms in wood during radio frequency/vacuum (RF/V) drying. Such a model would predict and optimise the RF/V drying behaviour of wood on a commercial scale without the requirement of experimentation. In this study, the radial direction loss factor of full-sized western hemlock sapwood and heartwood, and western red cedar heartwood timbers was measured using the direct calorimetric data method with a laboratory-scale RF/V dryer at the frequency of 13.56 MHz, moisture content range between 10 and 80%, temperature range between 25 and 55 °C, and root mean square (rms) electrode voltages 0.8 and 1.1 kV, respectively. The results indicated that the moisture content, temperature, electric field strength and species significantly affected the loss factor. Empirical regression equations were derived based on the experimental data, that made possible the calculation of the loss factor and power density within the wood mass during RF heating.