Fundamental Understanding of Bound Water Removal in Paper Drying Process: Microscopic Approach

摘要

In the fabrication of paper, a slurry with cellulose fibers and other matter is pressed and dried, which requires a significant expense in energy. In the structure of paper, there are two different types of water: free water and bound water. Free water can be removed relatively efficiently, but removing bound water, which consists of both fluid regions dominated by capillarity, along with water which is inside the fibers, consumes a large portion of energy during the process. This paper strives to understand the different possible physical mechanisms in fiber scale for bound water removal in a paper drying process. Therefore, a thin liquid film upon a solid substrate, which represents the cellulose fibers, is considered. The film is assumed to be incompressible, viscous, and subject to evaporation, thermocapillarity, and surface tension. By using volume of fluid (VOF) model, the effect of above mentioned parameters on drying behavior of the thin film, as bound water, are investigated. Hence, using the results of this research and by controlling the studied parameters on the evaporation of the thin liquid film, the related industries will be able to control the drying of bound water in the final stages of drying processes in order to increase the efficiency of paper-making.