Abstract:

The study was conducted to investigate the variety of inner temperature,
vapor pressure and both relations during the progress of intermittent and continuous microwave drying. Results obtained are summarized as follows: during continuous microwave drying, there are three stages in the change of temperature(rapid temperature increasing stage, constant temperature stage and later temperature increasing stage). The higher the power is, the quicker the temperature increases. In the period of constant temperature stage, the higher the temperature is, the shorter the time is. As the high power was continuously applied to heat wood with high moisture content, inner cracking was found, which can be avoided by decreasing the power supply or using intermittent power supply after the temperature increased to 100 ℃. Charring of wood was mainly found in final stage of drying, and the phenomenon of charring may be avoided by the methods of controlling and avoiding too low moisture contents of wood in the last stage, decreasing the power supply or using intermittent power supply.

Key words: drying defects, energy, evaporation, drying rate