Finite Element Model for the Heating of Frozen Wood

Authors

  • Perry N. Peralta
  • Audimar P. Bangi

Keywords:

Unsteady-state heat transfer, thermal conductivity, heat capacity, thermal diffusivity, latent heat of fusion, thawing

Abstract

A finite element method for calculating the transient heating of frozen log and lumber subject to different initial and boundary conditions is described. The governing equation used in the study accounts for thawing by incorporating the latent heat of fusion into the heat capacity term. The heat capacity and thermal conductivity values for wood in the radial direction for temperatures below and above 0°C were obtained from Steinhagen and Lee (1988). For two- and three-dimensional modeling, it was assumed that the thermal conductivity in the tangential direction is equal to, while that in the longitudinal direction is 2.5 times, the thermal conductivity in the radial direction. The finite element model was validated successfully using the experimental results of Steinhagen (1977) for frozen logs. The model was applied to one-, two-, and three-dimensional heating of lumber and to cases where surface resistance to heat transfer was significant. The thawing of frozen free water in the cell lumina involves the consumption of heat and therefore must be considered in the heating of frozen wood; otherwise the heating time so calculated will be underestimated. A table showing the times needed to heat the center of lumber with different cross-sectional dimensions, green specific gravities, and moisture contents to a temperature of 56.1°C is presented.

References

COMSOL, 2004a. FEMLAB 3 User's Guide. COMSOL AB, Burlington, MA, 406 pp.nCOMSOL, 2004b. Phase Transition with Latent Heat. COMSOL AB, Burlington, MA, 6 pp.nFeihl, O. 1972. Heating frozen and nonfrozen logs. Forest Prod. J.22(10):41-50.nSimpson, W. T. 2001. Heating times for round and rectangular cross section of wood in steam. Gen. Tech. Rep. FPL-GTR-130. USDA, Forest Serv., Forest Prod. Lab. Madison, WI, 103 pp.nSteinhagen, H. P. 1977. Heating times for frozen veneer logs—New experimental data. Forest Prod. J.27(6):24-28.nSteinhagen, H. P. 1991. Heat transfer computation for a long, frozen log heated in agitated water or steam—a practical recipe. Holz Roh-Werkst.49:287-290.nSteinhagen, H. P., and H. W. Lee. 1988. Enthalpy method to compute radial heating and thawing of logs. Wood Fiber Sci.20(4):415-421.n

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Published

2007-06-05

Issue

Number 2 / April 2006

Section

Research Contributions

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