Drying rate correlation for Douglas-fir lumber

The drying rate of individual pieces of lumber at a certain condition is important to know for modeling the moisture content (MC) and board-to-board moisture variability during kiln-drying. Single pieces of Douglas-fir lumber were dried at the conditions typically used in industry, dry-bulb temperatures from 57 to 99 degrees C (135 to 2 10 degrees F), wet-bulb depressions from 3 to 30 degrees C (5 to 55 degrees F), and air velocities from 2.5 to 5 m/s (500 to 1000 ft/min). One set of conditions was held for the entire drying cycle. The weight of each piece was continuously measured as the wood dried from green to 12 percent MC, and a correlation for the drying rate was developed. The independent variables in the correlation are MC, dry-bulb temperature, equilibrium MC, air velocity, SG, and board thickness. Knot area, ring count, ring angle, initial MC, and heartwood percentage were measured for each board but not included in the final correlation.