(278c) Modeling of Paper Drying Under Convective and Radiofrequency (RF) Energy Applications

Radiofrequency (RF) drying has the potential to be an efficient method for drying paper and similar pulp-based products, offering several advantages over traditional drying techniques. Extensively explored in the food industry, RF drying has significantly reduced drying time through volumetric heating. Unlike conventional drying methods that rely on surface heating and can result in uneven moisture removal, RF drying ensures more homogeneous heat penetration, reducing issues like warping, cracking, or degradation of the paper. However, despite its promising potential, there remains a lack of in-depth understanding of the fundamental physics behind RF-assisted drying in paper applications. This study aims to bridge these knowledge gaps by developing a comprehensive computational model to simulate pure convective and RF-assisted drying. The model, created using COMSOL Multiphysics, first simulates the hot air drying process, incorporating convection for moisture evaporation and temperature distribution. Unlike most studies in paper drying simulations, the model utilizes a 2D geometry to highlight the fluxes along and across the thickness of the material. Convection is carried out by supplying ambient air with 50% relative humidity and preheating it to 100°C. Air velocity is set at 5 m/s to represent industrial paper machine speeds. A stray-field RF applicator is included in the model, and RF heating is obtained by solving the quasistatic approximation of Maxwell’s equations at 27.12 MHz. A detailed representation of the coupled heat and mass transfer phenomena occurring during drying is provided, incorporating physics such as bound water removal and capillary action. A comparative analysis of drying rates, liquid saturation, and temperature, both for conventional convective drying and RF-enhanced drying, is presented. The modeling results are further compared with experimental data to evaluate the accuracy of the simulation and analyze the loss mechanisms inherent in both convective and RF-based drying setups.