Preliminary study on method of vacuum drying

Chinese fir was taken as specimen in this paper. Firstly, specimens were preheated to 80°C, and then the pressure in the drying box was vacuumized to the needed vacuum degree (absolute pressures were 0.06, 0.04 and 0.02MPa respectively), finally, pressure in the drying box was recovered to the atmospheric pressure by vapor from wood during drying period. The results indicated that the drying rates increased along with the decrease of the absolute pressure and the drying rates were 2.19, 2.39, 2.46 (%/h) when the absolute pressures were 0.06, 0.04, 0.02MPa respectively. Then, the drying rates equations under the conditions of temperature being 80°C and absolute pressures being 0.06, 0.04, 0.02MPa respectively were regressed and the results also showed that it was better to use low pressure when wood moisture content was high while better to use high pressure during drying wood with low moisture content.