Application of an alternating drying schedule for high-quality oak

The drying of high-quality hardwoods is an energy and time demanding practice. A reduction in drying time and energy input while keeping up with quality requirements by the industry is still a major research topic. To tackle this problem a novel drying program with alternating cycles of active and passive phases was applied and tested on oak boards (Quercus spp.) with a thickness of app. 50 mm. During the active phases, the wood is dried according to standard process parameters, in the passive phase heating and irrigation are turned off and air movement through the wood pile is reduced. Three drying experiments with different initial moisture contents were conducted with the novel schedule. The drying regime was controlled and operated by a computer-aided process control by regulating temperature and equilibrium moisture content. Moisture content and moisture movement in the boards were measured through resistive measurements and temperature changes inside the boards were recorded with thermocouples positioned in different depths. After the experiments, the moisture distribution and case hardening were determined for quality control of the drying process. The applied schedule shows promising results for future investigations into the intermittent drying of oak as quality defining aspects were excellent and the drying time was in the range of a standard schedule.