Water Movement And Heat Transfer During High Temperature Drying Of Masson's Pine

Wood drying procedure essentially is a course of energy transfer and mass transfer, especially water state changing taking place during wood drying reflects directly drying rates and the law of drying stress changing in the wood. But so far there is not a good theory to quantitatively describe it. There is almost no one doing about developing heat and mass transfer model during wood high temperature drying in our country. A mathematical model was developed to simulate moisture movement and heat transfer in lumber of Masson's pine during high temperature drying. It is based on the characteristics of water transports of softwood during high temperature drying. In solving the model of water movement using numerical method, it was divided into two parts: When moisture content above F.S.P., water movements are mainly gas permeability for water vapor flow and liquid permeability for free water flow. When moisture content below F.S.P., water movements are mainly diffusions of bound-water and vapor. The model of water movement during high temperature drying of Masson's pine lumber was verified in the thesis, it shows that the water movement model basically can reflect the movement law of profile of moisture content and average moisture content during high temperature drying. The permeability was studied and result was concluded in this thesis. Radial and tangential gas permeability and liquid permeability of Masson's pine lumber both are increasing with moisture content decreasing of wood. Gas permeability is bigger than liquid permeability both in radial direction and tangential direction. Radial permeability of gas and liquid of Masson's pine wood is greater than tangential permeability of that. Whether gas or liquid, radial or tangential, the permeability of Masson's pine wood is increasing from heartwood to sap wood. Moisture unsteady-state diffusion in radial and tangential direction during high temperature drying of Masson's pine lumber was tested and researched. The conclusions follows: When moisture content above F.S.P., the moisture diffusion coefficients of Masson's pine lumber are increasing with moisture content decreasing; When moisture content below F.S.P., the moisture diffusion coefficients of Masson's pine lumber are decreasing with moisture content decreasing. Radial moisture diffusion coefficients are greater then tangential moisture diffusion coefficients. Moisture diffusion coefficients across grain direction increase with medium temperature increasing and humidity decreasing.