Evaluation of drying performance and property changes in Grevillea robusta wood under radio frequency vacuum heating

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Abstract

Drying is a critical step in wood processing, affecting its quality and end use application. Kiln drying is widely used, however it is energy intensive and time consuming, often taking several days for drying. Radio-frequency (RF) heating presents an alternative, offering potential benefits such as faster drying rates and more uniform moisture removal. The present study explored the drying performance of silver oak (Grevillea robusta) using an indigenously developed RF vacuum (RFV) dryer. Two drying protocols were tested: Run 1 (8 min heating, 2 min idle-time) and Run 2 (16 min heating, 4 min idle-time). Both protocols achieved comparable drying rates, 7.63%/h for Run 1 and 7.48%/h for Run 2, reaching target moisture levels in just 5–10 h indicating rapid moisture removal. Moisture distribution in the wood was uniform, although case hardening was observed in a few planks. Microscopic analysis showed cell wall ruptures due to internal pressure, which improved preservative absorption. RFV-dried wood showed no significant changes in density or modulus of elasticity compared to air-dried samples. However, reductions were observed in modulus of rupture and compressive strength. Overall, RFV drying proved to be a fast and effective method, suitable for moderately refractory hardwoods like silver oak.

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