Vacuum Drying of Wood Flour and Wafers At Low Temperatures

Drying wood flour disks in vacuum at subfreezing temperatures revealed that the material attains a final equilibrium moisture content between 0 and 3 percent depending upon ambient temperature. Because of the insulating character of the shell of dry wood that forms, the center of the mass dries slowly. Below -10?C, the rate of drying of material thicker than 4-5mm is extremely slow. Affording a conductive heat source with a steel plug partly immersed in mercury increased drying rate. The minimum temperatures produced by evaporation were -22?C with 100 percent moisture content (MC), -18?C with 27 percent MC, and -2?C with 9 percent MC. The temperature rises above freezing when MC falls below half of fiber saturation; thus, the later stages of drying are not really freeze drying. Reducing ambient to -18?C did not drop specimen temperature below ambient. The final EMC in desorption was 2.8 percent at -19?C and decreased curvilinearly with increasing temperature until it was near zero at 25?C. At each equilibrium, the MC could be reduced to a new lower equilibrium by raising ambient temperature.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member