Development of a Schedule for Jet-Drying Yellow-Poplar

Certain nonrefractory wood species can be high-temperature jet-dried faster than in a conventional kiln. Yellow-poplar is a common commercial species which has been dried at high temperatures without excessive degrade. Three types of runs were made with 4/4 yellow-poplar in a prototype jet dryer over a range of dry-bulb temperatures (DB) from 225? to 350?F and wet-bulb temperatures (WB) from 130? to 210?F, respectively. The first set of runs was at constant conditions with boards containing heartwood and sapwood to determine wood quality; the second was also at constant conditions but with boards containing only sapwood to determine the effect of WB on drying time and drying rate; and the third (based on the results of the previous two sets of runs) was made with a two-step drying schedule with boards containing both heartwood and sapwood. Drying yellow-poplar at constant conditions above 225?F DB when heartwood and sapwood were present caused honeycomb and end checks in the heartwood of the boards. The sapwood remained free of defects. When drying boards with only sapwood present, the humidity or WB in the dryer had no effect on drying time above 250?F. The jet dryer, using a two-step, high-temperature schedule (1 hr. at 350?F DB and 180?F WB and 18 hr. at 220?F DB and 195?F WB) followed by conditioning, dried 4/4 yellow-poplar seven times faster than a conventional kiln. The jet-dried wood had less shrinkage, but slightly more degrade, and slightly lower strength than kiln-dried lumber.

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