MATHEMATICAL MODELS FOR PREDICTING KILN-DRYING TIME AND MODIFYING KILN SCHEDULES FOR SOME PHILIPPINE HARDWOOD SPECIES

Abstract

Three models based on Bramhall's drying-effort method for calculating kiln-schedule modifications were developed to determine the reliability of the method to the kiln drying of some Philippine hardwood lumber species. The general form of the models is based on Bramhall's vapor-pressure gradient concept of bound-water diffusion, and is basically dependent on empirically determined relationships between the resistance-to-drying (R) and the average charge moisture content (M). Functional R-M relations were established for three species-thickness combinations of Philippine hardwoods using simple linear regression techniques. In all cases, an exponential relationship of the form R A exp(-bM) was observed. Chi-square tests on several comparisons between predicted and observed drying times showed that the models are sufficiently valid and accurate at 5% level of significance. The models are best fitted to the species-thickness combinations tested but it appears that they are also applicable to the kiln drying of mixed kiln charges involving other lumber species of comparable wood density.