Drying timber controls

The elements that eontrol the drying rate are the relative humidity of the air, the air temperature, and the airflow aeross the timber surfaees. In a kiln the temperature and (paradoxieally) relative humidity are maintained at higher levels than in the open air, while powerful fans eontrol the air velocity. In air-drying the same elements eannot be controlled or manipulated nearly as effectively. 

Even with a permeable wood diffusion assumes increasing importance as the average moisture content approaches the irreducible moisture content indeed, in every part of the board where the moisture eontent approaehes this value drying is diffusion controlled. Permeable and impermeable timbers of similar densities should dry from fibre saturation at about the same rate. The behaviour of mixed heart/sapwood boards is eomplieated sinee, at first, there is both an evaporative interface near the sapwood surfaee and one in the interior at the zonal boundary between heart and sapwood. For a board with only a slither of heartwood along one face, mass flow can only move to the sapwood faee so in effeet the board appears to be twice the width than it aetually is. Pang et al. (1994) predieted that such a 50 mm thick board would dry from green to 6% moisture eontent using a 140°C/90°C schedule in 14 hours, compared to 10 hours for sapwood and 11 hours for heartwood. 

Traditional schedules result in a drying rate that decreases with time, only partly countered by increases in the dry-bulb temperature and the wet-bulb depression as the schedule proceeds. Modem automatic process control means that the kiln schedule can be adjusted continuously so ensuring a more constant rate of heat transfer and evaporation. Also this avoids any shock that an abrapt change in the schedule imposes on the timber. 

Black Sea. This meant the Trojans controlled trade in gold, silver, iron, cinnabar, ship s timber, linen, hemp, dried fish, oil and Chinese jade. With the Trojan War lost in 1185BCE, the Trojan Confederacy disintegrated and its people dispersed. 

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