Modeling of the technological process of convective drying of lumber

Abstract

A calculation of the technological process of lumber drying in convection drying chamber of periodic action is presented. For this purpose, a three-dimensional geometric model of a drying chamber with a lumber pile is developed. A physico-mathematical model describing the processes of heat and mass transfer both in the drying agent and in the stack is presented. The three-dimensional geometry of the problem was taken into account by using the Ansys Fluent package. The process of mass transfer in wood was described on the basis of User-Defined Function and User-Defined Scalar. The result of calculation of a specific technological regime of drying of stack from pine sawn timber is given, which allowed finding detailed spatial distributions and temporary changes of the temperature and humidity fields for the drying agent and wood. On their basis, graphs of the time variation of the mean values are plotted. The nonlinearity and interrelationship of the processes of heat and mass transfer in a convective drying chamber leads to unsteadiness of the drying process. So, during the warm-up stage, it is not possible to avoid moisture removal from the lumber. At the drying stages, the unsteadiness leads to an oscillatory character of changes of the temperature, the mass fraction of vapour and the relative humidity of air in the gaps between the wood boards at the intensive heat input. Therefore, it is necessary to take additional procedures to keep the drying agent parameters constant at the drying stages. The obtained results can be used for the design of drying chambers and the development of drying regimes of lumber based on the mathematical modeling and computational experiment.