Simulation of vacuum dewatering in papermaking using level-set tracking with discrete bulk variation

Water removal in paper manufacturing is highly energy-intensive and proceeds through gravity drainage, vacuum dewatering, wet pressing, and thermal drying, the latter being the most energy-demanding stage. This study focuses on vacuum dewatering. CFD simulations employing a Level-Set method were used to track free water during different stages of the vacuum dewatering process. Two-dimensional paper sheet models were developed in COMSOL Multiphysics® (v6.4) via the application interface within the MATLAB programming environment, enabling controlled random fiber distributions and the regulation of basis weight and bulk density. Sheets with basis weights of 20 g/m2, 50 g/m2, and 100 g/m2 were analyzed to represent tissue and paperboard grades. Results show increasing solids content with dwell time and fairly good agreement with experimental data, with MAE and RMSE values ranging from 2.0 to 3.5 relative to literature data. The model captures the onset of consolidation and diminishing dewatering rates, while bulk density and thickness remain first-order approximations. As expected, the penetrated airflow varies significantly across different bulk stages. The final consolidation stage tends to underpredict airflow for papers with basis weights of 20 and 50 g/m2, while providing reasonably accurate predictions at higher basis weights. Surface tension introduces capillary resistance at low saturations, slightly limiting solids content build-up at later stages of the dewatering.