Investigation of boiling front during vacuum drying of wood.

摘要

The objective of this research was to theoretically and experimentally investigate the boiling phenomenon and the existence of a boiling front inside wood during continuous and cyclic vacuum drying. The vacuum drying model was theoretically developed based on an energy balance. The experimental results supported the hypothesis that there is a boiling front during vacuum drying. From the boiling front to the surface of the wood, the boiling temperature is lower than the wood temperature, so water inthis region boils. From the boiling front to the centre of wood, there is no boiling because the pressure inside the wood is higher than the saturation vapour pressure. The boiling front retreats from the surface to the centre of the wood as drying proceeds. The speed of retreat depends on the heat supply and properties of the wood, such as permeability and conductivity.