Real-Time Moisture Content Measurement of Wood Under Radio-Frequency/Vacuum (RF/V) Drying

Abstract

Hinoki timber was dried under radio-frequency at 6.7 kPa using two drying schedules, schedule A and schedule B. Moisture content (MC) was measured at 58 points in various locations of the timber using a new in-process monitoring concept. This concept uses the relationship between temperature, pressure, and equilibrium moisture content (EMC). Factors affecting the accuracy of MC measurement were also investigated in this study. The results showed that small wood pieces reached equilibrium at constant conditions within 1.5 h of the fiber saturation point (FSP) and that using the mean value of temperature and pressure within 30 min during radio-frequency/vacuum (RF/V) drying for MC measurement was an efficient method. The accuracy of moisture content measurement was the same for both drying schedules A and B. It can be concluded that air in wood was removed completely with drying schedule B and that below the FSP, pressure in the wood was maintained only by water vapor pressure during drying. It was possible to obtain accurate MC measurement. Above or near the FSP, MC cannot be measured using this method, whereas below the FSP, whatever the MC is, it can be measured practically anywhere in the timber.

Keywords:

• Effect factors
• Moisture content measurement
• Radio-frequency/vacuum drying
• Real-time measurement

ACKNOWLEDGMENTS

Special acknowledgement is extended to the Yasujima Company and Francois-Xavier Maquart for their assistance.

Notes

^a Errors: Moisture content measured – Moisture content (by oven drying method).

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