Moisture transport in birch lumber at low radio-frequency and contact vacuum drying

Results of the dynamic distribution of moisture content, temperature, and internal overpressure at low radio-frequency (LRF), up to 100 kHz, and vacuum contact drying are presented. To minimize structural changes of lumber, low temperature drying (less than 70 A degrees C) was used. Contact vacuum drying with LRF volume heating decreases the moisture gradient compared to conductive vacuum drying and increases moisture removal rate by 25 %. The heat consumption energy and electrical energy for drying were determined. The significant influence of the internal overpressure on the moisture transport in birch lumber was proven.