Lumber moisture content and temperature changes with kiln conditions

Lumber driers need more information regarding the use of electronic lumber moisture content (MC) and temperature sensors for monitoring and controlling kiln conditions. The goal of this study was to show the quantity and quality of information that users could expect from these sensors. We inserted thermocouples and resistance MC sensors into hem-fir 2 by 4’s and 2 by 6’s in a commercial kiln. On both sides of the lumber load, thermocouples were attached to dry and wet bulbs, and placed in sticker slots (spaces, created by the stickers, through which air passes). The temperature of the air entering and leaving the load, and the internal and surface MCs and temperatures of the lumber, were measured every 15 minutes. The lumber’s surface temperature changed directly with air temperature; its internal temperature did not. The lumber’s MCs were not reliably detectable above about 30 percent, nor below about 8 percent, levels not reached for 10 to 20 hours on the surface and up to 91 hours internally. The data show how the entering- and leaving-air temperatures were related to dry- and wet-bulb temperatures, and how that relationship changed as the wood dried and when the fans were reversed.

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