核磁共振技术在分析木材微波干燥过程中水分移动的应用

在马尾松木材微波干燥水分迁移试验中,利用核磁共振技术测量微波干燥过程中T2弛豫时间和MRI成像图,以及各干燥阶段温度和压力分布,分析了水分含量变化和迁移动力。结果表明,木材含水率在纤维饱和点以上时,水分移动的主要驱动力应该是温度引起的水蒸汽压力梯度,它使木材中水分以蒸汽的形式排出,相对来讲含水率梯度则影响较小,干燥过程呈现等速干燥。在纤维饱和点以下时,微波干燥过程水分移动的主要驱动力为水蒸汽压力梯度,木材内含水率浓度梯度对水分移动也具有一定的影响。

Analysis of the moisture movement during microwave drying of lumber using NMR technology

In order to analyze the moisture changes and migration, the nuclear magnetic resonance (NMR) technology was used to measure T₂ relaxation time, MRI imaging figure, the drying temperature, and the pressure distribution in the process of microwave drying of lumber. Results showed that when the moisture content was above FSP, the active force of moisture movement was the water vapor pressure gradient caused by the temperature gradient rather than the moisture content gradient, which made the water loss as evaporation. When the moisture content was below FSP, the main driving force of water movement was the water vapor pressure gradient and the water content gradient also showed the effect on water movement in lumber.