Microwave drying kinetics of Gmelina arborea wood

Drying is one of the most important processes for improving wood properties. Several methods are followed to dry wood; however, kiln drying is mainly used at industrial scales. The conventional method of kiln drying is very time-consuming and labour- and energy-intensive. Microwave heating has emerged as an effective technology for accelerating the drying process while minimising defects. This study focuses on the microwave drying characteristics of Gmelina arborea wood, a highly sought-after material in various industries. Drying experiments were conducted in a microwave oven operating at a frequency of 2.45 GHz, using two different power levels (540 W and 900 W). The samples were dried from an initial moisture content of about 130% to 12%. The drying cycles involved continuous exposure to microwave for 1 minute, followed by a 3-minute cooling period, repeated until the desired moisture content was achieved. The temperature profile of wood samples during the drying experiments was measured using an infrared camera. The results indicate that the drying rate was significantly higher in the MW drying experiments carried out at 900 W compared to those at 540 W. Additionally, the drying rate above the fibre saturation point (FSP) was higher than that below the FSP for both power levels. Notably, the total drying time for samples irradiated at 900 W (99 minutes) was nearly half, compared to samples dried at 540 W (213 minutes). However, out of the total drying time, the effective microwave time incurred in drying wood samples at 900 W and 540 W was 25 and 53 minutes, respectively. The moisture distribution between the core and surface was very uniform, and the quality of the dried wood was good, with only slight internal checks. This study demonstrates that microwave heating can be effectively utilized for the rapid and high-quality drying of Gmelina arborea wood.