2018年10月24日星期三

Mechanism of moisture movement in wood during microwave drying

Abstract: By measuring the internal temperature, pressure and stratified moisture content of wood during microwave drying, the distribution and variation of temperature, vapor pressure and moisture in wood during microwave drying were studied. During the drying process, the temperature distribution in the wood is more uniform, but in the later stage of drying, the non-uniformity of temperature distribution in the wood tends to increase; with the drying process, the moisture content gradient in the wood decreases gradually, and the moisture content distribution becomes more uniform; in the early stage of wood drying, there is moisture accumulation on the surface of the wood; in the power of 10. Under the condition of 00 W, the internal pressure of 300 mm 100 mm 65
Key words:
water movement mechanism, vapor pressure difference, Masson Pine
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In conventional drying, wood microwave drying medium transfers heat to wood, and then water is exchanged to drying medium. Because heat transfer and water transfer are slow processes, the temperature of water (including free water and water vapor) in wood cell cavity increases slowly with limited energy supply, and the evaporation of free water and water vapor occur. In addition, wood cells are semi-enclosed structures, which drain part of the water through the pits on the cell wall, and to a certain extent play a “pressure relief” role. Therefore, it is generally believed that there is no total pressure difference inside and outside the wood in the conventional chamber trunk, and the water content in the wood is in the role of water content gradient (or concentration gradient). In the process of microwave drying, energy permeates directly into the interior of wood in the form of electromagnetic wave. Under the action of microwave electromagnetic field, the sharpened water molecules in wood rotate rapidly, rub against each other, produce heat, heat and dry wood. It is precisely because the energy in the process of microwave drying is in The uniqueness of generation and transfer in wood leads to the different mechanism of moisture movement between wood and conventional drying, resulting in the high speed of wood microwave drying.

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