36 Drying of Wood

More documents

Recommendations

Info

(a) Norway spruce (Picea abies) (b) Pedunculate oak (Quercus rubra) (c) European beech (Fagus sylvatica)FIGURE 36.5 Typical anatomical patterns encountered in temperate species: (a) softwood, (b) ring-porous species, and (c)diffuse-porous species. The height of these images represents about 2 mm. (Microphotographs: J.C. Mosnier, LERMAB–ENGREF.)After some years, an intense biological activity ofthese parenchyma cells gives rise to heartwood formation.Metabolites are deposited in the heartwoodand the tree uses the heartwood as a place to storewaste products that are collectively known as extractives.These include resins, gums, oils, and tanninsthat stop up the vessels (or the tracheids in softwood)and clog the wood. In heartwood, all the cells aredead and inactive; they do not function in eitherwater conduction or food storage. The heartwood isoften darker, slightly denser, and more durable (resistanceto fungi or insect attack) than the sapwoodand plays an important role in supporting the tree.However, numerous species do not have dark heartwood(e.g., spruce, fir, and beech) and no correlationexists between heartwood color and durability.In some species, such as certain oaks, the vesselsbecome plugged with the development of cellularmembranes known as tyloses, which enter the vesselsfrom adjacent parenchyma cells (Figure 36.6).36.1.2 CHEMICAL C OMPOSITIONWood is a typical organic material made up of threemain elements: carbon, oxygen, and hydrogen. Becausevery small variations between different wood speciesare observed, the numbers depicted in Table 36.1 arebroadly general but can be higher for some tropicalspecies. Nitrogen as well as some additional inorganicelements (sodium, potassium, calcium, magnesium, andsilicon) are also essential compounds, which are mostlyinvolved in the metabolism of living cells during woodFibersRay cellsTyloses invesselsRTTLFIGURE 36.6 Example of tyloses development in the heartwood of Pedunculate oak (Quercus rubra L.). (ESEM photographs:Patrick Perré and Riad Bakour, LERMAB–ENGREF.)ß 2006 by Taylor & Francis Group, LLC.
TABLE 36.1Elementary Composition of WoodElement Content (%)Carbon 49–50Hydrogen 6Oxygen 43–44Nitrogen
Page 1 and 2: 36Drying of Wood: Principlesand Pra
Page 3 and 4: Primary growthSecondannual ringFirs
Page 5: FIGURE 36.4 Wood is formed by cell
Page 9 and 10: FIGURE 36.8 Tension wood in Peduncu
Page 11 and 12: 36.2.1.3 Bound WaterBound moisture
Page 13 and 14: TABLE 36.6Order of Magnitude of Shr
Page 15 and 16: The transverse permeability and the
Page 17 and 18: FIGURE 36.14 Relative permeability
Page 19 and 20: Low moisture contentHigh moisture c
Page 21 and 22: Boundary layersExternal flowTP vHea
Page 23 and 24: HeatVaporVessel ortracheidLiquidPit
Page 25 and 26: Moisture content (%)15010050Sapwood
Page 27 and 28: to the history of that point (« me
Page 29 and 30: ConstantmoisturecontentTime t = 0 +
Page 31 and 32: Element 1 Element 2 Element NElemen
Page 33 and 34: Averaged moisture content (%)907560
Page 35 and 36: Moisture content (%)12010080604020A
Page 37: Second drying periodTensionParamete
Page 42 and 43: eaction wood produced by environmen
Page 44 and 45: where the boards butt up due to shr
Page 46 and 47: 1.2Normalized moisture content (Φ)
Page 48 and 49: set at a constant value at constant
Page 50 and 51: oards by conduction whereas the vac
Page 52 and 53: KilnSolarcollectorCondenserControlv
Page 54 and 55: Doe, P.E., Oliver, A.R., and Booker
Page 56 and 57:
Perré P., 1992. Transferts couplé
show all

36 Drying of Wood

Create successful ePaper yourself

Delete template?

Save as template?