Reliability of One Dimensional Model of Moisture Diffusion in Wood

Abstract

A model of the moisture diffusion in wood under isothermal conditions taking into con- sideration coating of the surface of a specimen is presented in a 2-D-in-space formulation. A re- liability of a corresponding 1-D model is investigated for a simulation of moisture movement in 2-D medium. This paper presents a technique to determine the width as well as the degree of edges coating of the specimen making the 1-D model relevant for 2-D medium. This technique bases on the computer simulation of 2-D moisture diffusion to estimate the reliability of the corresponding 1-D model. In the technique, approximate coefficients of the diffusion and surface emission may be employed if accurate values of these coefficients are unknown. Wood drying is a highly energy intensive process of some industrial significance. It is a process whereby the moisture moves from an area of higher moisture content to an area of lower moisture content within the medium. When the surface moisture evaporates from the sides or ends, moisture moves from interior toward these locations. This process continues until the wood reaches its equilibrium moisture content with the ambient air climate (Skaar, 1988; Siau, 1984). Mathematical modelling is gaining an increasing acceptance within the timber dry- ing industry and the use of mathematical simulators, which describe the complex heat and mass transfer phenomena at a fundamental level, can provide important information which could be used in both the design and optimisation of the kiln (Rosen, 1987; Siau, 1984; Turner and Mujumdar, 1997). From a mathematical point of view, the moisture transport process can be treated as a diffusion problem based on the Fick's second law. A model of the wood drying, under ∗ This research was partially supported by Lithuanian State Science and Studies Foundation Grant