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Factors Affecting the Temperature Increasing Rate in Wood during Radio-Frequency Heating

Radio-frequency (RF) heating has been widely used in the wood industriesand it is essential to understand the factors affecting the heating rates. In this article, Chinese fir (Cunning hamialanceolata) was heated with RF energy intermittently at 2 min per cycle to study the effect of wood moisture content (MC), sample thickness, and RF power level on heating rates. The study revealed that wood MC significantly affected the RF heating rate (p < 0.01). The heating rate was the highest (5.0°C/cycle) at an MC around the wood fiber saturation point (FSP). The heating rates were lower with a lower MC of 15% (0.89°C/cycle) and a higher MC of 70% (1.2°C/cycle). Lumber thickness did not have a significant effect on the RF heating rate at the center of the lumber; however, the heating rates at various locations along the thickness direction were significantly different. The temperature at the lumber center was 20°C higher than the temperature at 10 mm below the surface during heating. The heating rate for lower RF power level was initially greater than the rate at higher power RF level and then rapidly decreased. However, the heating rate at the higher RF power level remained constant during the whole heating process. RF power levels had a significant effect on the internal heating rate of wood (p < 0.01).