THE LABORATORY WOOD DRIER - FROM THEORY TO PRACTICE

Based on the principle of similarity, the wood drying process can be investigated on a scale model, which is the laboratory drier, instead of the full-size industrial drier. Thus, the investigation is simplified and the drying time reduced. The laboratory drying kiln, developed by the research team, is a controlled climate air duct with closed circuit, fitted with a rectangular test section. The air flow is circulated by a centrifugal fan and the air heating is carried out by a set of electric resistances. The selection of the fan and of the heating resistances was performed according to the aerodynamic and thermal calculations, presented in the paper. For the air humidification, in accordance to the drying schedule requirements, the drier has a steam generator that prepares steam which is injected in the air. The wood sample is placed within the drier on a device conceived for both sample support and vertical motion and also, for continuous weighing. By applying the principle of similarity for both, the industrial kiln and the laboratory drier, the required air velocity for the laboratory drier is determined, for constant values of the temperature and relative humidity of air. Different invariants,characteristic to the drying schedule that was applied, have been also calculated.