Mass transfer during convective drying of larch lumber

Abstract

Drying of wood refers to complex technological processes. Therefore, various approaches to the mechanism of water emission from wood during convective drying are possible. To date, there has not been any unambiguous understanding of the mechanism of moisture from such a wood species as larch. The paper proposes the main provisions of the mechanism of water removal during convective drying based on the baromembrane process. Any transfer process is based on the presence of two main components: a mobile substance, a force to move the substance. During the growth of the tree, an aqueous solution of extractive substances is formed. The basis of this group of substances in larch wood is arabinogalactan. Arabinogalactan macromolecules have a relatively low molecular weight. Arabinogalactan, when interacting with water, forms an ion of an energetically rational form, which determines abnormally low viscosity values of aqueous solutions. An increase in temperature puts the larch wood in a chemically active state. As a result, the formed vapor-gas mixture in the micro-cavity of the larch wood cell creates excessive pressure. The direct transfer of an aqueous solution of extractive substances is observed in those areas where a pressure gradient is observed this is primarily at the boundary of the media (surface layers of the board). During the initial drying period, there is an intense emission of an aqueous solution of extractive substances. At the same time, the higher the temperature of the wood, the higher the emission rate. Therefore, the higher the temperature during the initial drying period, the faster the transfer of membranes from the group of non-selective to selective is observed, thereby reducing the productivity of the membrane system. Thus, the drying time interval decreases, at which an increased rate of emission of solution and, accordingly, water is observed. Therefore, it is possible to control the rate of water emission from larch wood by the temperature level in the initial drying period.