Effects of Ultrasound on Mass Transfer within the Boundary Layer during Wood Vacuum Drying

• Main Authors: Zhengbin He, Zhenyu Wang, Huan Lv, Zhenyu Zhang, Songlin Yi
• Format: Article
• Language: English
• Published: North Carolina State University 2015-07-01
• Series: BioResources
• Subjects: Vacuum drying; Ultrasound; Boundary layer; Mass transfer coefficients; Water migration rates
• Online Access: http://ojs.cnr.ncsu.edu/index.php/BioRes/article/view/BioRes_10_3_5267_He_Ultrasound_Mass_Transfer_Wood_Drying

Ultrasound was applied to enhance mass transfer within the boundary layer during wood vacuum drying. Fast growing poplar (Populus tomentosa) was used as the specimen in this work. The water migration rates and the mass transfer coefficients were studied at temperatures of 35 and 50 °C, absolute pressures of 0.03, 0.06, and 0.1 MPa, and ultrasound power-frequency groups of 60 W-28 kHz, 100 W-28 kHz, and 100 W-20 kHz, respectively. The results indicated that ultrasound could markedly increase the water migration rates within the boundary layer. The water migration rates increased with increasing ultrasound power and frequency. The mass transfer coefficients within the boundary layer for specimens treated with ultrasound were much higher than those of the control group, and the mass transfer coefficients increased with decreasing absolute pressure. Ultrasound could be applied in the wood drying industry as a means of saving time and energy.