Investigation of boiling front during vacuum drying of wood

The objective of this research was to theoretically and experimentally inve stigate the boiling phenomenon and the existence of a boiling front inside wood during continuous and cyclic vacuum drying. The vacuum drying model wa s theoretically developed based on an energy balance. The experimental resu lts supported the hypothesis that there is a boiling front during vacuum dr ying, From the boiling front to the surface of the wood, the boiling temper ature is lower than the wood temperature, so water in this region boils. Fr om the boiling front to the center of wood, there is no boiling because the pressure inside the wood is higher than the saturation vapor pressure. The boiling front retreats from the surface to the center of the wood as dryin g proceeds. The speed of retreat depends on the heat supply and properties of the wood, such as permeability and conductivity.