Heat and mass transfer rates associated with the drying of Southern pine and Douglas fir veneer in air and in steam at various temperatures and angles of impingement

Graduation date: 1970Southern pine and Douglas fir veneer samples were dried in air\ud under the following conditions: air temperatures were 350, 600, and\ud 750°F; air velocities were 50, 100, and 150 feet per second, and\ud angles of impingement of air against the veneer surfaces were 0°,\ud 45°, and 90°. The resulting drying curves were compared with drying\ud curves obtained under similar conditions using steam as the drying\ud medium.\ud Statistical analyses were performed to estimate magnitudes of\ud differences in veneer drying times associated with the two drying\ud media, the three angles of impingement, and the two species of wood.\ud Air was found to be more effective than steam as a drying medium at\ud the 350°F operating temperature. For the 600°F and higher operating\ud temperatures, steam was found to be more effective than air. Under\ud all drying conditions, Southern pine dried faster than Douglas fir.\ud Effective heat transfer coefficients representing the convective\ud effects of both heat and mass transfer associated with drying veneer\ud were computed in two ways: based on the experimental data, and\ud based on theoretical considerations. Experimental internal diffusion\ud coefficients were also computed.\ud Diffusion of water from the interior of the veneer to the veneer\ud surfaces was found to be the controlling factor on the rate of veneer\ud drying during all but a brief period in the initial stage of the drying\ud process