A Two-Phase Flow Study of Steam Condensation and Condensate Removal via Siphon in a 3D Rotational Paper Dryer

In paper industries, superheated steam has been commonly used to dry paper webs through cylindrical dryers. The superheated steam condenses into saturated water inside a rotating dryer by vaporizing the extra moisture from the wet paper wrapping outside the dryer, which is removed via stationary or rotary siphons. The behavior of the accumulated condensate under the influence of rotation can be categorized into puddling, cascading, or rimming, which significantly affects heat transfer, torque, power requirements, and siphon performance. However, flashing occurs during the condensate siphoning process, which can cause backflow or discontinuity in the siphoning process. A thorough investigation into the thermal-fluid dynamics of rotational dryers is essential for enhancing drying efficiency and achieving significant energy savings. This study aimed to investigate the process of ejecting superheated steam into a three-dimensional rotating paper dryer cylinder, allowing the steam to condense, and subsequently removing the condensed saturated water through a stationary siphon. The Eulerian-Eulerian (E-E) model was used to explore the condensation process and flashing during the uplifting siphoning process. The wall of the paper dryer was kept at a constant temperature as the superheated steam condensed through a layer of rimming condensate. Initially, a 3-D steady state case was first simulated for a stationary cylinder, focusing on developing the appropriate submodels to simulate the two-phase condensation and flashing processes. Later, the transient model was simulated in a 3-D rotational cylindrical dryer. The results of this study are expected to contribute to a broader and deeper understanding of the fundamental multiphase physics involved in the paper drying process and have paved the way for finding innovative methods to save energy.