Drying-Rate Curves for One-Inch Yellow-Poplar Lumber in Low Temperature Forced-Air Dryers

One-inch yellow-poplar sapwood and heartwood can be forced-air dried to 18 percent moisture content within 3.5 days in dryers capable of maintaining 120?F and EMC control of 10 percent. With less heating capacity, drying time will be extended; that is, at 80?F and 10 percent EMC, approximately 8.4 days will be required to reach 18 percent moisture content. The calculated drying-rate curves made reliable estimates of drying time for sapwood and heartwood lumber at temperatures between 80? and 120?F, and EMC conditions of 6, 10, 14, 18, and 21 percent. The accuracy of estimates is dependent on a knowledge of actual drying conditions and initial moisture content. Lumber degrade was considered minor–approximately 1 percent of the total volume. The highest value loss was $1.87 per 1,000 board measure, which occurred at the most severe drying conditions of 120?F and 6 percent EMC. Degrade losses were somewhat less at the 10 percent EMC level. These degrade data are considered inconclusive because of the sample size. They do indicate, however, that 1-inch yellow-poplar lumber can be dried with a minimum loss at temperatures up to 120?F and initial EMC conditions of 10 percent and higher. Moisture content uniformity was good in most tests; however, uniformity tended to be poorer at higher average final moisture content levels. These data also indicate that drying to an average moisture content of 18 percent (constant 10 percent EMC) will bring 97.5 percent of all boards below 30 percent moisture content. Moisture content differences between entering-air and leaving-air samples ranged from 4 to 12 percent at the 10 percent EMC level and 13 to 15 percent at the 14 percent EMC level. These data only relate to moisture content variation across an 8-foot-wide lumber charge with one-way air travel, so moisture content uniformity would be expected to improve with periodic fan reversal.

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