In microwave drying equipment, the heat of wood does not need to undergo a “long” process of convective heat transfer and heat conduction. Microwave energy penetrates directly into the wood in the form of electromagnetic waves. Through the direct interaction between electromagnetic fields and water molecules, wood polarization molecules (mainly hydroxyl groups), the electromagnetic energy can be instantaneously transferred. Heat is changed into heat, and the temperature of wet wood rises rapidly, and the moisture moves rapidly and evaporates.
Therefore, the proportion of the accelerating stage in the drying process is small, and the proportion of the constant-speed stage in the whole drying process is very large, which is in sharp contrast to the conventional drying in the proportion of the constant-speed stage is small, or even does not exist in the characteristics of the constant-speed drying section. In the late stage of drying, most of the free water in the wood has been removed, at this time, the radiation of microwave energy in addition to a small part of the evaporation of residual water in the wood, most of the energy is used to increase the temperature of the wood, drying rate gradually decreased.
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