Compression Drying of Sapwood


  • R. Wingate-Hill
  • R. B. Cunningham


Pinus radiata, Araucaria cunninghamii, Eucalyptus regnans, E. obliqua, sapwood, compression, drying, moisture loss, energy input, moisture content, compression rate, orientation, specimen thickness


A compression drying experiment carried out on small blocks of sapwood from Pinus radiata, Araucaria cunninghamii. Eucalyptus regnans, and E. obliqua is described. Effects of initial moisture content, speed of compression, specimen thickness and orientation on moisture loss and energy input were studied. All specimens were compressed perpendicular to the grain to the same stress in either a radial or tangential direction in a jig that prevented lateral expansion. Force and deformation changes of the specimens were recorded during compression, and water loss at the end of the process was measured. From these data, volumetric compressions, moisture losses, energy inputs, and energy efficiencies of water removal were calculated.

The analyses of variance confirmed that initial moisture content, species and wood specific gravity, amount of volumetric strain, rate of compression, and specimen orientation all affected unit water removal; specimen thickness did not. The lower density softwoods deformed to a greater extent than the hardwoods and lost more water. More water was removed from wetter specimens than drier ones at the same stress, and a slow compression rate caused a greater water loss than a more rapid rate. Specimens compressed tangentially lost more water than those compressed radially. Energy efficiency of water removal was greatest in the relatively low specific gravity Pinus radiata specimens with high moisture contents which were compressed tangentially at a slow rate.


Bodig, J. 1965. The effect of anatomy on the initial stress-strain relationship in transverse compression. For. Prod. J. 15(5):197-202.nBolza, E., and N. H. Kloot. 1963. The mechanical properties of 174 Australian timbers. CSIRO Div. For. Prod. Tech. Paper No. 25.nDadswell, H. E. 1972. The anatomy of eucalypt woods. CSIRO Div. Applied Chem. Tech. Paper No. 66.nHaygreen, J. G. 1981. Potential for compression drying of green wood chip fuel. For. Prod. J. 31(8):43-54.nHaygreen, J. G. 1982. Mechanics of compression drying solid wood cubes and chip mats. For. Prod. J. 32(10):30-38.nLiu, Z., and J. G. Haygreen. 1985. Drying rates of wood chips during compression drying. Wood Fiber Sci. 17(2):214-227.nKay, J. M. 1968. Fluid mechanics and heat transfer, 2nd ed. Chapter 6. Cambridge Univ. Press.nMack, J. J. 1979. Australian methods for mechanially testing small clear specimens of timber. CSIRO Div. Building Res. Tech. Paper (second series), No. 31.nSiau, J. F. 1984. Transport processes in wood. Chapter 3. Springer-Verlag, New York.nWingate-Hill, R. 1983a. A review of processes which involve compressing wood perpendicular to the grain. Aust. For. Res. 13(2):151-164.nWingate-Hill, R. 1983b. A process for reducing pulpwood transport costs. CSIRO Div. For. Res. Tech. Paper No. 1.nWingate-Hill, R., and R. B. Cunningham. 1984a. Preparation of wood specimens for compression tests parallel to the grain. J. Inst. Wood Sci. 10(2):91-93.nWingate-Hill, R., and R. B. Cunningham. 1984b. Removal of moisture from green sapwood by compression. J. Inst. Wood Sci. 10(2):66-75.n






Research Contributions