摘要:
该研究利用T型聚四氟乙烯连接装置将温度传感器和压力传感器与被干材内部的待测点相连,实现了微波干燥过程中对木材内部同一点温度、蒸汽压力的同步测定.主要分析了木材内温度、蒸汽压力在微波场中的变化特性及其相互关系,并对温度、蒸汽压力的变化与微波干燥中出现的内裂、炭化等干燥缺陷的相关性进行了初步探讨.研究结果表明,木材在微波干燥过程中,温度的变化大致分为3个阶段快速升温段,恒温段和后期升温段;微波辐射功率增高,升温速度加快,恒温段温度提高,恒温段时间缩短;微波辐射功率提高,木材内部蒸汽压力上升速度相应加快,压力峰值也相应变大,最大压力值保持的时间变短.压力上升速度伴随着温升速度的加快而加快,当温度升高到恒温段时,压力也同时达到最大值.内裂通常出现在木材干燥恒温段初期,主要由于高含水率木材内部过高的蒸汽压力造成;炭化通常出现在木材干燥后期,主要由于低含水率木材高温点的介电特性造成.
Abstract:
In this research, the measured point in the dried wood was connected with temperature sensor and pressure sensor by taking advantage of a polyfluortetraethylene T-bridge piece so that the measurement of both temperature and pressure could be available simultaneously during microwave drying. The experiment was mainly conducted to investigate the variations of the inner temperature, steam pressure and both relations, and the correlation between the variations and some drying defects such as inner cracking and charring were discussed as well.Resultsare as the followings: during microwave drying of wood, there are three stages of temperature changing: rapid temperature-increasing stage, constant temperature stage and later temperature-increasing stage; the higher the power is, the quicker the temperature increases. In the period of constant temperature stage, the higher the temperature is, the shorter the duration is. If the power of microwave radiation increases, the steam pressure increases quickly in wood, its peak value becomes higher and the holding time of maximal pressure becomes shorter. If temperature increases quickly, the speed of pressure will increase quickly. When the temperature reaches the constant value, the pressure will reach the maximum meanwhile. Inner cracking usually appears in the initial stage of the drying on account of the excessive steam pressure in high moisture wood; charring usually appears in the final stage of the drying on account of the dielectric characteristics of high temperature point in low moisture wood.
百度学术
下载:
