(41CV) Mathematical Model for Control of High Temperature Drying …

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An extract from Mathematical Model for Control of High Temperature Drying of Southern Yellow Pine Dimension Lumber, Luiz Carlos de S. Oliveira (PhD dissertation), Virginia Polytechnic Institute, August 1985 (199 pgs)

(ABSTRACT)
Although High temperature drying (HTD) of southern yellow pine (SYP) is extensively used, quality problems still exist. Approximately 25 percent of all green lumber (2 x 4, 2 x 6 and 2 x B's) are degraded during HTD. Warp degrade, specifically "crook", is the main cause for the loss of quality of SYP dried at temperatures above the boiling point of water.
One of the major causes of warp degrade is excessive shrinkage that results from overdrying. In industrial practices, average final moisture contents for HTD of SYP
lumber are usually well below the 15% MC maximum permitted by the grading rules. Overdrying the lumber causes not only lumber quality problems, but also
constitutes a waste of energy. In order to improve the overall results of HTD of SYP, it is necessary to perform a better control of the process, so unnecessary extended drying can be prevented.
In this study, a mathematical model based on the temperature drop across the load (TDAL) concept was proposed. The model relates TOAL to drying rates and according to the results, it appears to be an important alternative for controlling purposes during HTD of SYP.
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APPENDIX 3: HP-41 CV computer program for the data acquisition and control system.
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