Experimental evaluation and modeling of high temperature drying of sub-alpine fir |
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| Authors: | Liping Cai Luiz C Oliveira |
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| Institution: | (1) FPInnovations – Forintek Division, 2665 East Mall, Vancouver, BC, V6T 1W5, Canada |
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| Abstract: | Sub-alpine fir is characterized by its high proportion of wet pockets making it difficult to dry. Since it takes longer to
dry, mills experience reduced kiln productivity and increased energy consumption. High temperature drying (HTD) can be an
effective approach to accelerate the drying process. In this study, three drying schedules, namely, conservative (control),
HTD, and HTD and conservative combined (HTD/Cons), were evaluated when drying green sub-alpine fir 2″ × 4″ dimension lumber.
The results indicated that: (1) the drying rates in the HTD and HTD/Cons schedules were increased by 31–150% in comparison
to the drying rates obtained for the conservative schedule; (2) although drying stresses observed for the HTD schedule were
higher than those that were measured for the conservative schedule, no significant difference in drying stresses was found
between the HTD/Cons and conservative schedules; (3) warp was reduced in both HTD and HTD/Cons schedules; (4) neither the
HTD nor HTD/Cons schedule showed any significant reduction in modulus of rupture (MOR) and modulus of elasticity (MOE) when
compared to the values obtained for the conservative schedule. Diffusion coefficients during HTD for sub-alpine fir were determined
and it was found that diffusivity increases with temperature. A mathematical model describing the processes of heating and
drying under high temperatures was developed. The results of drying tests showed that the predicted drying curves by the model
satisfactorily agree with the experimental data. |
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