Abstract
Ultrasonic pre-treatment of small and pressure saturated Douglas-fir heartwood specimens at 20 kHz fixed frequency with an acoustic horn resulted in increased specific permeability coefficient in both radial and tangential directions. Statistical analysis revealed that there was a high correlation between ultrasonic treatment time and specific permeability coefficient. Improvement rate of permeability in both radial and tangential directions was nearly the same regardless of treatment time.
Highlights
Wood permeability is a measure of the ease with which fluids flow through the wood under a static or dynamic pressure differential
The average K value of non-treated radial specimens was about 1.86×10-18 m2 whereas the one with water immersion for 72 hours was about 1.80×10-18 m2
After ultrasonic treatment, K values in the radial direction increased in a direct fashion
Summary
Wood permeability is a measure of the ease with which fluids flow through the wood under a static or dynamic pressure differential. Bulk flow in wood, such as impregnation of wood with stabilizers, preservatives and pulping agents, and diffusion, such as drying or fumigation, are interrelated to wood permeability levels (Siau 1995). Improved permeability in wood may lead to faster, cheaper and high-quality drying, easier chemical treatment, and effective manufacturing of wood-polymer composites. Transverse permeability, which is much more important than longitudinal permeability in relation to bulk flow and diffusion in timber, is much smaller than that of the longitudinal direction due to the anisotropic structure of wood. Permeability ratios of longitudinal/transverse are 15 to 500,000 in several softwood species in North America (Comstock 1970). Differences between radial and tangential direction (normally a ratio of 2:1 between the two) can cause problems in processing that can result in incomplete and/or significantly variable treatments between and within timbers or logs in a treatment facility
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