Study On Heat And Mass Transfer Multi-scale Model In The Drying Process Of Pinus Sylvestris

Understanding the theory of heat and mass transfer in wood drying is contributing to improve the process of drying wood and save energy. Pinus sylvestr is used as experimental material and construct a multiscale mathematical model which can be accurately simulated the temperature and moisture content change during the wood drying process. the model is made up of three coupled equations:two water diffusion equations and one energy balance equation in macroscopic level, water transfer balance in single cell equation in microscopic level. Analysis the model and the initial and boundary conditions,the form of the finite element mesh, the discretization of the equation, search the corresponding parameters, solvie programming by matlab. Finally establish the multiscale mathematical model and the model proves correctly, the resulesas below:(1) Comparing the experimental value and analog value by weighed method and density volumetric method at f 80℃.analysis their variances, the results shows:the values P with slice weighing method and model is less than 0.5, the values P with the density volumetric method and analog value is more than 0.5,proved that the density volumetric method is more coincide with model method than the slice weighing method.(2) The average moisture content of sawn timber change experiment was performed by the density volumetric method at 40℃、60℃、80℃,compared the results of experiment and model, the curve were congruence. The multi-scale model could reflect the heat and mass transfer behavior at the wood drying process.(3) Then the experiment which measure the varying layer moisture content of the sample at 80℃ was performed, and compared with the value of multi-scale simulation model and the results, the curves had a certain congruence, multi-scale model could reflect the distribution of moisture content at the wood drying process.(4) Finally, the multi-scale model was theoretical analyzed to predict the distribution and change of temperature in different layers at the drying process, demonstrated the accuracy of the model.Build the heat and mass transfer mathematical model from different scales, can accurately reflect the moisture content changes in the wood and spatial distribution, provided a theoretical basis and reference about the moisture in the drying process and temperature distributions research.