DRYINC RATES DURING HIGH TEMPERATURE DRYING OF YELLOW POPLAR

Experimental drying rates during high temperature drying of Yellow Poplar is analyzed to determine types of drying mechanism. Drying rate during the constant rate period and effective diffusivity during the falling rate periods were obtained at dryer temperatures ranging from 100°C to 150°C.

The drying curve shows three drying regimes: a constant-rate period, and two falling rate periods. The constant rate period, where the drying rate is a linear function of time, is controlled by the rate of heat transfer to the wood surface. Both falling rate periods show a drying rate which is a linear function of the square root of time. Floisture migration during the first falling rate is by simultaneous capillary action and liquid diffusion. while moisture'migration takes place by vapor diffusion during the second falling rate period. This occurs when the moisture content of the wood falls below the fiber saturation point. The effective diffusion coefficient during both periods is found to be constant.