Three-dimensional heat and mass transfer during oriented strandboard hot-pressing.

摘要

This thesis constitutes an empirical and theoretical study of the effects of mat structure on three-dimensional heat and mass transfer during oriented strandboard hot-pressing. The empirical experimentation programme examined the effects of different flake-alignments on lateral and transverse heat and gas flow through the mat. It involved measuring internal mat temperatures and gas pressures in robot formed, single layer, flake mats with varying degrees of flake-alignment. Flake-alignment was seen to impede heat transfer to the core, and to improve lateral gas flow and escape. Increasing the mat density reduced the flake-alignment effects, as did increasing the mat size. Theoretical heat and mass transfer modelling reinforced these experimental conclusions.; Modelling observations indicated that the effects on heat and mass transfer of flake-alignment and lateral permeability are analogous, as are the relative effects of increased mat size versus decreased lateral permeability. Based on mass and energy conservation equations, the modelling involved numerically solving a coupled system of partial differential equations for the rates of change of temperature, gas pressure and moisture content. This yielded dynamic predictions of three-dimensional temperature, gas pressure and moisture content distributions. The resulting predictions followed trends and behaviours consistent with hot-pressing heat and mass transfer theory, and the temperatures closely matched the experimental measurements. In this regard, the model could therefore be of significance in preliminary qualitative comparisons and investigations of other flake-mat structures and pressing conditions.; In addition, this thesis also includes the formulation of a high-temperature moisture sorption isotherm equation, and the formulation of a regression equation for horizontal temperature and gas pressure distributions. These equations were developed for analysing experimental data and modelling heat and mass transfer. On their own, the two equations constitute significant contributions to hot-pressing research. The sorption isotherm equation could also be of significance to high-temperature drying and other high-temperature wood applications.