Ultrasound-Assisted Vacuum Drying of Wood: Effects on Drying Time and Product Quality

Ultrasonic energy was applied to assist the wood vacuum drying process. At a drying temperature of 60°C, the absolute pressure was either 0.05 MPa or 0.08 MPa; the ultrasonic power and frequency were 100 W and 28 kHz, respectively. The results showed that the effective water diffusivity of the specimens dried by the ultrasonic assisted vacuum drying at 0.05 MPa or 0.08 MPa were higher than that of the samples dried without ultrasound. The ultrasound-vacuum drying rate was much faster than that of drying without ultrasound, especially for wood with a moisture content above the fiber saturation point. Drying at the absolute pressure of 0.05 MPa was faster than that of 0.08 MPa. Ultrasound-assisted drying was especially more beneficial when removing free water. The ultrasound-vacuum drying method could be applied in the wood drying industry as a means of saving energy and minimizing product quality damage.