An approach for indirect monitoring of moisture content in rubberwood (Hevea brasiliensis) during hot air drying

Abstract

This study aimed to determine the equilibrium moisture content and to develop an indirect measurement technique for the moisture content (MC) by observing temperature and vapor pressure during hot air drying. The temperature and gas pressure were recorded during hot air drying at several points within wood sample specimens conforming to ASTM D 143 and AOAC, 1990. The moisture content was estimated from measured temperature and pressure. The accuracy of MC estimates was validated by oven-drying method. For validation, nine experiments at different temperatures of hot air drying were run and the indirect measurement was found to provide a good accuracy. The obtained statistics were R² = 82.5%, standard error (SE) ranging from 0.15 to 0.43, root mean square error (RMSE) ranging from 0.16 to 0.38 and mean absolute error (MAE) ranging from 0.4 to 1.1 respectively. It can be concluded that the air in wood was removed completely, especially when the MC was below the fiber saturation point. We have demonstrated an alternative moisture content monitoring method for potential adoption by the rubberwood industries.

Keywords:

• Hot air drying
• moisture content
• real-time measurement
• rubberwood
• vapor pressure

Acknowledgments

The authors are very grateful to Graduate School of Prince of Songkla University and Rubberwood technology and management research group for their financial support. The author would also like to thank A.P.K. Furnishing Parawood Co., Ltd for supplying the wood specimens and Assoc. Prof. Seppo Karrila for editing the manuscript via the Research and Development Office of Prince of Songkla University.

Disclosure statement

The authors declare that they have no conflict of interest.