DRYING THICK WESTERN HEMLOCK IN A LABORATORY RADIOFREQUENCY VACUUM DRYER WITH CONSTANT AND VARIABLE ELECTRODE VOLTAGE

Drying experiments with western hemlock lumber, 91 mm square in cross section, were carried out in a laboratory radio-frequency/vacuum dryer with two different electrode voltage methods (constant and variable). During drying, the average moisture content of the lumber load, the temperature and pressure at two locations within the piece of lumber located in the center of the load, and the ambient temperature and pressure inside the vacuum chamber were monitored on a continuous basts. the results demonstrated that the variable electrode voltage heating method resulted in increased drying rates without causing additional lumber degrade when compared to the constant electrode voltage method. The measured moisture content variation in the longitudinal direction of the lumber did not exhibit significant variation in both heating methods. Internal drying stresses in the longitudinal and transverse direction were also absent.