Microwave drying of wet clay with intermittent heating
Microwave drying of wet clay with intermittent heating
复制标题
DOI：
10.1080/07373937.2018.1547740
复制
发表时间：
2019-04-04
影响因子：
3.3
通讯作者：
Prat, M.
中科院分区：
文献类型：
--
作者：
Vorhauer, N.;Tretau, A.;Prat, M.
在这篇文章中，我们研究了一种基于微波加热和对流干燥相结合的湿粘土保守干燥的替代工艺。这项研究是建立在控制干燥的多孔物质在温度梯度的存在下的过程的实验分析。我们表明，并讨论了过程控制不能可靠地基于温度，因为与微波加热相关联的传质现象决定干燥动力学。基本上，如果微波加热不受控制或具有高功率，则压力建立和液体排出的发生主要取决于粘土的水分含量。因此，如果内部蒸发速率高，则粘土的劣化是有问题的，因此在干燥开始时水分含量也高。在此之后，我们建议间歇微波加热与对流干燥周期相结合，目的是减少总干燥时间（与传统的对流干燥相比），并通过减少材料收缩来提高产品质量。干燥实验表明，整体干燥时间的减少和产品质量取决于间歇加热和对流干燥的两个后续阶段的频率和持续时间。观察结果可以解释与干燥过程中的液体和蒸汽的孔尺度分布的演变。
In this article, we study an alternative process for the conservative drying of wet clay based on combined microwave heating and convective drying. The study is founded on an experimental analysis of the processes that control drying of porous matter in presence of temperature gradients. We show and discuss that process control cannot be reliably based on temperature alone because mass transfer phenomena associated with microwave heating dictate drying kinetics. Essentially, the occurrence of pressure build up and liquid expulsion, dominating mass transfer if microwave heating is uncontrolled or with high power, vitally depend on the moisture content of the clay. As a consequence, the deterioration of clay is problematic if internal evaporation rates are high, thus at the start of drying when also the moisture content is high. Following this, we propose intermittent microwave heating in combination with convective drying periods with the aim to reduce overall drying time (compared to conventional convective drying) and to improve product quality by reduced material shrinkage. Drying experiments indicate that the overall drying time reduction and product quality depend on the frequency and duration of the two subsequent periods of intermittent heating and convective drying. The observations can be explained with the evolution of the pore-scale distribution of liquid and vapor during drying.