Comparison of Vacuum Drying Characteristics of Radiata Pine Timber Using Different Heating Methods

Abstract

Timber logs 14 × 14 × 240 cm long were dried in a vacuum kiln to compare vacuum drying characteristics using contact heating, radiofrequency heating, and the combination of both. Relationships between moisture content (MC) and time for vacuum conductive drying (VCD), RF/vacuum drying (RFVD), and hybrid vacuum drying (HVD) were close to linear. The hybrid vacuum drying offered the higher moisture removal rate than VCD and RFVD. Specific energy consumption curves as a function of MC comprised three sections; rapidly increasing, slightly decreasing, and moderately increasing. Average specific energy (kWh/kg of water removal) for VCD, RFVD, and HVD was 0.352, 0.520, and 0.461 kWh/kg, respectively. Transverse MC distribution represented the convex profile for VCD, the fluctuating profile for RFVD, and the flat profile for HVD. Transverse and longitudinal moisture gradient of HVD was much lower than those of VCD and RFVD. HVD has a very beneficial effect on preventing of surface checks. There were no end- and internal checks of dried timber in three vacuum drying methods.

Keywords:

• Drying rate
• Hybrid vacuum drying
• Moisture profile
• Radio frequency/vacuum drying
• Specific energy
• Vacuum conductive drying

Acknowledgment

Bum-Joon So and Chang-Deuk Eom are grateful for the graduate fellowship provided through the Ministry of Education through Brain Korea 21 Project.