Portland State University. Department of Mechanical Engineering
Date of Award
Master of Science (M.S.) in Mechanical Engineering
1 online resource (202 p.)
Wood -- Permeability, Wood -- Moisture, Longleaf pine
One of the major processes in lumber industry is wood drying. This process consumes large amounts of energy and capital, and due to the length of time it takes, it acts as a governing factor in lumber production levels. Development of improvements in processes and equipment used in wood drying can be expedited through computer simulation of various drying procedures. These numerical simulations depend on the accuracy of numerical models representing wood transport properties, including functional dependency of liquid permeability through wood with respect to local saturation level. Data available in the literature mainly represent wood permeability properties at fully saturated levels. This is an indication of steady state flow methods used in determining these values which are based on wide spread use of similar methods utilized in studies on fluid flow through soil. This research determines unsaturated wood permeability using transient liquid flow methods that are more representative of actual drying process. Initially saturated wood samples are spun in a low speed centrifuge to induce liquid migration through the cell structures. Transient local moisture profiles along the sample are measured using a scanning gamma ray densitometer. Numerical integration and curve fitting procedures are used to process these data. Finally, utilizing liquid continuity equation the functional dependency of permeability with respect to saturation is calculated. Some permeability results appear to be reasonable when compared with actual wood behavior during drying. Measurement procedures prove to yield accurate results for moisture content and saturation levels in wood with less than 5% relative error in average saturation level of .75. However, due to natural inhomogeneities in wood cellular structure, the final calculated results for unsaturated permeability show high levels of uncertainty (up to 112% relative error).
Piroozmandi, Farid, "Transient flow inverse study calculation of unsaturated permeability of wood" (1985). Dissertations and Theses. Paper 3573.