HIGH-FREQUENCY HATING OF WOOD WITH MOISTURE-CONTENT GRADIENT

The influence af moisture content (MC) gradient on the development of a temperature gradient in wood heated in a high-frequency (HF) electro magnetic field was investigated. Fifteen layers of 1.6-mm-thick beech veneer (Fagus sylvatica L.), with dimension 400 x 400 mm, were used to simulate a moisture content (MC) gradient. A uniform MC of 5, 10, 15, and 20%, and two MC gradient schemes ranging from 20% to 5%, were use d in the experiment. The dielectric constant and loss tangent were mea sured before HF heating at 6.3 MHz. During HF heating of wood, the mag nitude of the MC, the shape of the MC gradient, and the potential for thermal losses influence the development of the temperature gradient. An MC gradient in a laminated composite could be used to control the s hape and severity of the temperature gradient during HF heating.