A Numerical Model for Heat Transfer and Moisture Evaporation Processes in Hot-Press Drying—An Integral Approach

Authors

  • Yifu Tang
  • Ronald G. Pearson
  • C. Arthur Hart
  • William T. Simpson

Keywords:

Drying, wood drying, press drying, drying model, numerical model, heat transfer, moisture evaporation, southern pine

Abstract

A numerical model, which was based on the energy principle that the rate of water evaporation from the interface (or wet line) at a given time during hot-press drying was controlled by the rate of heat energy reaching the interface at that time, has been developed. The model treated the drying as a process in which the retreat of the interface and free water flow to the interface occur simultaneously. After all parameters were determined according to the available literature and experiments, the numerical model worked well in predicting the drying curves from process and material variables. The model, which has a sound theoretical base but is numerically simple, has a good potential to be expanded for general high temperature drying and to be adopted in a production line to presort the lumber for good drying practice.

References

Barrer, R. M. 1941. Diffusion in and through solids. The Cambridge University Press, Cambridge, England.nBramhall, G. 1979. Mathematical model for lumber drying. Wood Sci. 12(1):14-31.nBrooklyser, B. B., and D. W. Pierson. 1980. Veneer drying and handling. U.S. Patent No. 4. 192,079. March 11, 1980.nChen, P. Y. S. 1978. Press drying black walnut wood: Continuous drying vs. step drying. Forest Prod. J. 28(1):23-25.nChen, P. Y. S. 1980. Press conditions affecting drying rate and shrinkage of hardwood boards. Forest Prod. J. 30(7):43-47.nForest Products Lab. 1987. Wood handbook. USDA Agric. Handb. 72. Washington, D.C.nHann, R. A. 1964. Drying yellow poplar at temperatures above 100 C. Forest Prod. J. 14(5):215-220.nHann, R. A. 1966. Theoretical considerations in the drying of wood at pressures above atmospheric. Forest Prod. J. 16(4):25-32.nHart, C. A. 1988. FORTRAN program to calculate equilibrium moisture content. Personal communication.nHittmeier, M. E., G. L. Comstock, and R. A. Hann. 1968. Press drying nine species of wood. Forest Prod. J. 18(9):91-96.nJames, W. L. 1988. Research needs in wood physics: A broad overview. Wood Fiber Sci. 20(2):277-294.nKoch, P. 1964. Techniques for drying thick southern pine veneer. Forest Prod. J. 14(9):382-386.nKollmann, F. F. P., and W. A. Côté Jr. 1968. Principles of wood science and technology: I. Solid wood. Chapter 6: Physics of wood. Springer-Verlag, New York, NY.nLoehnertz, S. P. 1988. A continuous press dryer for veneer. Forest Prod. J. 38(9):61-63.nMcMillin, C. W. 1969. Specific heat of ovendry loblolly pine wood. Wood Sci. 2:107-111.nMustakallio, K., and M. Paaki. 1977. Finns leading way in eliminating hot-air methods in veneer drying. World Wood 18(12):F18-19.nOkoh, I. A. 1984. Variables affecting press drying of SIPO. J. Inst. Wood Sci. 10(2):76-78.nQuarles, S. L., and L. Nagoda. 1990. Performance of perforated and non-perforated cauls in press drying. Forest Prod. J. 40(11/12):57-60.nRosen, H. N. 1983. Recent advances in the theory of drying lumber. Proceedings of the Wood Drying Working Party at the International Union of Forestry Research Organizations Division 5 Conference, Madison, WI.nSchmidt, J. 1967. Press drying of beechwood. Forest Prod. J. 17(9):107-113.nSimpson, W. T. 1982. Predrying before press drying to reduce defects in hardwoods. Forest Prod. J. 32(11/12):77-80.nSimpson, W. T. 1984a. Maintaining lumber quality in press drying by manipulating sawing patterns. Wood Fiber Sci. 16(3):411-426.nSimpson, W. T. 1984b. Maximum safe initial moisture content for press drying oak lumber without honeycomb. Forest Prod. J. 34(5):47-50.nSimpson, W. T., and Y. Tang. 1990. Empirical model to correlate press drying time of lumber to process and material variables. Wood Fiber Sci. 22(1):39-53.nSimpson, W. T., J. D. Danielson, and R. S. Boone. 1988. Press drying plantation 2 by 4's to reduce warp. Forest Prod. J. 38(11/12):41-48.nSkaar, C. 1972. Water in wood. Syracuse University Press, Syracuse, NY.nSpolek, G. A., and O. A. Plumb. 1980. A numerical model of heat and mass transport during drying. In Drying '80, Proceedings of the Second International Drying Symposium, Montreal. Hemisphere Publishing Co., New York, NY.nStamm, A. J., and R. M. Nelson. 1961. Comparison between measured and theoretical drying diffusion coefficients for southern pine. Forest Prod. J. 11(11):536-543nSteinhagen, H. P. 1977. Thermal conductivity properties of wood, green or dry, from -40° to 100°C: A literature review. USDA For. Serv. Gen. Tech. Rep. FPL-9, 10 pp.nTang, Y. 1992. Modelling hot-press drying of southern pine lumber. Ph.D. dissertation, North Carolina State University, Raleigh, NC.nTschernitz, J. L. 1985. Empirical equations for estimating drying times of thin rotary cut veneer in press and jet dryers. USDA Forest Service, Res. Paper. FPL 453, FPL, Madison, WI.nWang, A. T., and F. C. Beall. 1975. Laboratory press-drying of red oak. Wood Sci. 8(2):131-140.nZiegler, G. A., W. K. Murphy, and F. C. Beall. 1971. Operational variables in press drying eastern hemlock. Forest Prod. J. 21(10):32-34.n

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Published

2007-06-22

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Research Contributions