The water potential concept and generalized Darcy's law for unsaturated flow were proposed as a basis for the study of the energy state and flow of water in wood at high moisture contents. A series of experiments was conducted to investigate wood properties that are crucial to the application of these theories. Much attention was devoted
to the measurement of the moisture content-matric potential (M-Ψm)
relationship by the porous plate methods. Both the boundary drainage
and imbibition curves and the drainage curve starting from the green
condition were determined. In addition, independent Ψm measurements
were made in some of the specimens equilibrated on the porous plates
using Wescor PT51-10 thermocouple psychrometers (TCP). The osmotic
potential was then assumed to be negligible. Transient flow experiments
were also conducted for determining the water conductivity (K) as a
function of both M and Ψm, and the water diffusivity (D) as a function
of M using an instantaneous profile method and the one-step method. The boundary drainage and imbibition curves for the longitudinal direction of flow were thus obtained. The saturated conductivity had to be measured separately. Western hemlock sapwood was used for all determinations which were made at a temperature of 21°C.
The results of the porous plate tests confirmed the presence of
a considerable hysteresis in the M-Ψm relationship at high moisture
contents, with M at a given Ψm greater in drainage than in imbibition. The ink-bottle effect appears to be the primary cause of this phenomenon.
Both types of drainage curves obtained showed a tendency to exhibit a plateau at intermediate M's and were found highly dependent on the initial moisture content.
A fairly good agreement was found between the Ψm values imposed
on the specimens on the porous plates and those measured by the TCP's for
the Ψm range from -1 to -7 bars in drainage. These two types of data
differed markedly at lower Ψm 's in drainage and in imbibition. However,
the differences observed in imbibition were readily explainable and the
results of the TCP tests clearly demonstrated the strong hysteretic
behavior of the M-Ψm relationship in the wet state. The reproducibility
of the TCP method during the Ψm measurements in wood was rather poor.
The K-M, K- Ψm, and D-M curves obtained by the two transient
methods used were very similar in shape. The K(M) function exhibited a
considerable hysteresis with K at a given M greater in imbibition than in
drainage. A change in K of several orders of magnitude was recorded near
full saturation. The K(Ψm) and D(M) functions displayed only a partial
hysteresis. Disproportionality between flux and gradient was observed in imbibition above 75% M. The non-uniqueness of the M- Ψm relationship with respect to the state of flow was apparently the main cause of this anomaly. / Land and Food Systems, Faculty of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/22404 |
| Date | January 1980 |
| Creators | Fortin, Yves |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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