Microwave treatment accelerates solar timber drying

Abstract

Drying is essential before wood can be used. The tortuosity of the moisture transport path in wood profoundly affects drying speed and timber quality. Solar drying can reduce drying costs and energy consumption while producing high quality timber. Unfortunately, solar drying is much slower than many other kiln systems. Intense microwave heating rapidly generates steam inside moist wood. The resulting internal pressure selectively ruptures the wood structure creating radial pathways through which moisture may readily move. This modification process does not dry the wood, but vastly increases its permeability allowing the wood to dry faster with minimal degradation of the timber quality. Subsequent experimentation in a solar kiln resulted in a 17% reduction in drying time for microwave treated Populus alba samples, compared with untreated samples dried in the kiln at the same time. In a second experiment, microwave treated Eucalyptus regnans samples dried in 33 % less time than untreated samples, dried in the solar kiln at the same time. There was no difference in timber quality between treated or control samples during ether experiment. These reductions in drying time are attributable to a combination of wood modification and the initial moisture loss associated with microwave treatment. The energy requirements for microwave treatment were approximately 104 kW-h m-3.