OSMOTIC MOISTURE TRANSFER IN WOOD EXPOSED TO INFRARED RADIATION

The drying process of wood exposed to infrared radiation is discussed in this paper. A test pilot-plant was developed using infrared heat radiators. Thick, rectangular Norway spruce (Picea abies [L.] Karst.) timbers of 200 +/- 10mm were irradiated in a closed system. The mechanism of the drying process was discussed based on measured moisture distributions. The change of the moisture profiles was followed up in different stages of the infrared irradiation process. Furthermore, the change of the moisture content was measured continuously in time at certain distances from the sample surface. Due to the infrared radiation, thermal energy is continuously absorbed by the liquid or gaseous moisture phase of the timber. An evaporation front is expected to be formed at the beginning of the infrared process in the surface region. As the evaporation front progresses into the core, a concentration difference is formed among the wood cells producing osmosis through the cell wall. The most intensive moisture gradient in the wood was formed parallel to the heating surfaces without any accordance with the position of the growth rings. The moisture transfer rate was maintained at an approximately uniform value through the whole cross-section of the wood.