| Frederick A. Kamke, Chairman
A numerical model based on fundamental engineering principles was developed and validated to establish a relationship between process parameters and the final properties of wood-based
composite boards. The model simulates the mat formation, then compresses the
reconstituted mat to its final thickness in a virtual press. The number of interacting variables
during the hot-compression process is prohibitively large to assess a wide variety of data by
experimental means. Therefore, the main advantage of the model based approach that the effect
of the hot-compression parameters on the final properties of wood-based composite boards can
be monitored without extensive experimentation.
The mat formation part of the model is based on the Monte Carlo simulation technique
to reproduce the spatial structure of the mat. The dimensions and the density of each flake are
considered as random variables in the model, which follow certain probability density
distributions. The parameters of these distributions are derived from data collected on industrial
flakes by using an image analysis technique. The model can simulate the structure of a three-layer
oriented strandboard (OSB) mat as well as the structure of random fiber networks. A grid
is superimposed on the simulated mat and the number of flakes, the thickness, and the density of
the mat at each grid point are computed. Additionally, the model predicts the change in several
void volume fractions within the mat and the contact area between the flakes during
consolidation. The void volume fractions are directly related to the physical properties of the
mat, such as thermal conductivity, diffusivity, and permeability, and the contact area is an
indicator of the effectively bonded area within the mat.
The heat and mass transfer part of the model predicts the change of air content, moisture
content, and temperature at designated mesh points in the cross section of the mat during the hot-compression.
The water content is subdivided into vapor and bound water components. The free
water component is not considered in the model due to the low (typically 6-7 %) initial moisture
content of the flakes. The gas phase (air and vapor) moves by bulk flow and diffusion, while the | 