EQUILIBRIUM MOISTURE CONTENT UNDER VACUUM CONDITIONS

Abstract

The equilibrium moisture content (EMC) of three species was measured under vacuum conditions. Temperature, RH, and ambient pressure in a chamber were controlled during the experiments to obtain accurate EMC measurement under vacuum. Based on the experimental results and on the Hailwood–Horrobin model for EMC, the desorption isotherms of wood under vacuum were analyzed.
EMC charts and a database under vacuum conditions were also built. Results showed that the desorption isotherms of wood under vacuum conditions also presented a typical sigmoid shape similar to the one at atmospheric conditions. The effect of ambient pressure on EMC was small at high RH ranges and became obvious with decreasing RH. Also, the EMC of ambient pressure from 53.3 to 101.3 kPa was not obvious because the difference in EMC was only 0.1-0.4%. Conversely, the effect of pressure became greater from 53.3 to 13.3 kPa and the difference in EMC was 1.2-1.9%. EMC corresponding to temperature, RH, and ambient pressure at vacuum conditions was built with the chart and equations based on experimental results from the real-time MC measurement for vacuum drying and serves as an aid in wood research and drying control under vacuum conditions.