2003 Volume 36 Issue 6 Pages 655-662
The drying characteristics of porous materials immersed in the fluidized bed of fluidizing particles with superheated steam were examined. A B-1 brick ball, in which the gas diffusion was governed by Knudsen diffusion, was used as the drying sample and the glass beads (0.12 mm in diameter) were used as the fluidizing particles. N2 gas was also used as the drying gas for the comparison. N2 gas was the substitute of air. The temperature of the fluidized bed and the mass velocity of drying gas were changed, respectively. The theoretical analysis including the convective gas transfer in the sample and condensation of the steam in the sample was also preformed.
There is a period when the temperature of the sample center is almost constant in the fluidized bed drying with superheated steam and with hot air. The temperature of the sample center in superheated steam is higher than that in hot air. In the case of superheated steam, the temperature during the period when the temperature of the sample center is almost constant is equal to the boiling point of water. When the mass transfer resistance in a sample is large, the temperature in the sample increases because of the increment of the pressure in the sample. This phenomenon was confirmed by the calculated pressure in the sample. The effect of the bed temperature on the drying characteristics is significant, while that of the mass velocity of drying gas is very slight.