Modeling and simulation of the hot-pressing process in the production of medium density fiberboard (MDF)

A mathematical model is presented that describes heat and moisture transfer during the hot-pressing of MDF. The model includes conduction of heat betw een the press platens and the central layer of the mattress, phase change o f water from the adsorbed to the vapor state and the convective heal and ma ss transfer through the edges of the mattress. This approach results in a t hree-dimensional unsteady-state problem in which the properties of the wood fibers, water and the wood-water system are dependent on temperature, matt ress moisture content and steam pressure. For solving this problem, a finit e difference scheme is used for the discretization of spatial variables and the resulting set of ordinary differential equations is solved using an ap propriated ODE solver. This theoretical model is used to predict the evolution of temperature, moi sture content, steam pressure and relative humidity with time at a given po sition in the mattress under typical operating conditions. Several plots ar e shown displaying the profiles of these four dependent variables along the three axes of the panel. The effects of temperature, moisture content and vapor pressure gradients on the physical properties of the system are also analyzed. These simulation results are useful to identify the controlling f actors of hot-pressing operation in order to improve the quantitative under standing of the complex mechanisms involved in panel formation.