Investigation on moisture transfer mechanism in porous media during rapid drying process

In this work, moisture transfer mechanism in wet porous media during rapid drying process is investigated experimentally and analytically. By use of scanning electron microscopic device, the rapid drying processes for potato, carrot, and, radish species were observed and recorded. The microscopic drying experiments show that during high intense and rapid drying process, the mechanism of moisture migration in materials is mainly considered as a displacement flow driven by pressure gradient along a capillary passage. A simplified displacement flow model during,rapid drying process is proposed and the time needed for moisture transfer in porous media is calculated. To examine this drying mechanism, one-dimensional displacement flow test device is built up and a set of experiments under different pressure gradients and temperatures are conducted. Glass beads of 0.8 mm in diameter are used as the porous material. The experimental results show that when pressure gradient is getting greater at constant temperature, the moisture removal time is getting smaller. On the other hand, under the same pressure gradient, when liquid temperature increases, the time for moisture transfer from the internal to the external surface decreases. The calculated moisture removal times are well agreed with the experimental data.