Investigation of Boiling Front During Vacuum Drying of Wood

Authors

  • Zhangjing Chen
  • Fred M. Lamb

Keywords:

Vacuum drying, drying model

Abstract

The objective of this research was to theoretically and experimentally investigate the boiling phenomenon and the existence of a boiling front inside wood during continuous and cyclic vacuum drying. The vacuum drying model was theoretically developed based on an energy balance. The experimental results supported the hypothesis that there is a boiling front during vacuum drying. From the boiling front to the surface of the wood, the boiling temperature is lower than the wood temperature, so water in this region boils. From the boiling front to the center of wood, there is no boiling because the pressure inside the wood is higher than the saturation vapor pressure. The boiling front retreats from the surface to the center of the wood as drying proceeds. The speed of retreat depends on the heat supply and properties of the wood, such as permeability and conductivity.

References

Avramidis, S., M. Liu, and B. J. Neilson. 1994. Radiofrequency/vacuum drying of softwoods: Drying of thick western red cedar with constant electrode voltage. Forest Prod. J.44(1):41-47.nBramhall, G. 1979. Mathematical model for lumber drying. II. The model. Wood Science12(1): 14-21.nChen, Z. 1997. Primary driving force in wood vacuum drying. Ph.D. dissertation, Virginia Tech., Blacksburg, VA. http://scholar.lib.vt.edu/theses/available/etd-02198-185538'>http://scholar.lib.vt.edu/theses/available/etd-02198-185538nChen, Z., and F. M. Lamb. 1995. The concept of boiling front in vacuum drying. Vacuum Drying of Wood '95. Slovakia. Pp. 110-116.nChoong, E. T., F. O. Tesoro, and F. G. Manwiller. 1974. Permeability of twenty-two small diameter hardwoods growing on southern pine sites. Wood Fiber6(1):91-101.nEaton, R. A., and M. D. C. Hale. 1993. Wood: Decay, pests, and protection. Chapman and Hall, New York, NY. 546 pp.nJones, F. E. 1991. Evaporation of water. Lewis Publisher, Chelsea, MI. 188 pp.nKarki, K. C., and S. V. Patankar. 1988. Calculation procedure for viscous impressible flows in complex geometries. Num. Heat Transfer14(3):295-317.nNeumann R., A. Mielke, and G. Böhner. 1992. Comparison of conventional and convective vacuum drying of beech. Understanding the Wood Drying Process: A Synthesis of Theory and Practice. 3rd IUFRO International Wood Drying Conference. Vienna, Austria.nPatankar. S. V. 1991. Computation of conduction and duct flow. Heat Transfer Innovative Research Inc., Maple Grove, MN. 354 pp.nSiau, J. F. 1984. Transport process in wood. Springer-Verlag, New York, NY. 218 pp.nSkaar, C. 1972. Water in wood. Syracuse Univ. Press, Syracuse, NY. 218 pp.nSparrow, E.M., S. V. Patankar, and H. Shahrestani. 1978. Laminar heat transfer in a pipe subjected to a circumferentially varying enteral heat transfer coefficient. Num. Heat Transfer1(1):117-127.nStanish, M. A., G. S. Schajer, and F. Kayihan. 1986. A mathematical model of drying for hygroscopic porous media. AIChE J.32(8): 1301-1311.nVergnaud, J. M. 1982. Drying of polymeric and solid materials. Springer-Verlag, New York, NY. 336 pp.n

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Published

2007-06-05

Issue

Number 4 / October 2001

Section

Research Contributions

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