Abstract:
Southern pine and Douglas fir veneer samples were dried in air
under the following conditions: air temperatures were 350, 600, and
750°F; air velocities were 50, 100, and 150 feet per second, and
angles of impingement of air against the veneer surfaces were 0°,
45°, and 90°. The resulting drying curves were compared with drying
curves obtained under similar conditions using steam as the drying
medium.
Statistical analyses were performed to estimate magnitudes of
differences in veneer drying times associated with the two drying
media, the three angles of impingement, and the two species of wood.
Air was found to be more effective than steam as a drying medium at
the 350°F operating temperature. For the 600°F and higher operating
temperatures, steam was found to be more effective than air. Under
all drying conditions, Southern pine dried faster than Douglas fir.
Effective heat transfer coefficients representing the convective
effects of both heat and mass transfer associated with drying veneer
were computed in two ways: based on the experimental data, and
based on theoretical considerations. Experimental internal diffusion
coefficients were also computed.
Diffusion of water from the interior of the veneer to the veneer
surfaces was found to be the controlling factor on the rate of veneer
drying during all but a brief period in the initial stage of the drying
process.
