The Role of Nonuniformity in Convective Heat and Mass Transfer through Porous Media, Part 1

Abstract

Through-air drying is commonly used in the drying of high-quality tissue and towel products. A representative elementary volume method was used to model the fluid flow and heat and mass transfer during through drying in heterogeneous porous biobased materials such as tissue and towel products. Results of flow both upstream and downstream of a modeled porous sheet allowed visualization of the effects of mixing at the top and bottom of the porous medium. The effect of initial nonuniformity on fluid flow and convective heat and mass transfer in heterogeneous porous media was studied. The effect of material nonhomogeneity and associated transport properties on moisture content of the porous material as a function of drying time was studied. Modeling results indicate that for the first time it is possible to simulate the effect of nonuniformity on fluid flow and convective heat and mass transfer in porous media during through-air drying of paper. Moisture and structural nonuniformity contributing to nonuniformity in air flow might contribute significantly to drying nonuniformity. Depending on the moisture regimes and degree of saturation of the convective medium, heat and mass transfer coefficients may have varying effects on the overall drying.

Keywords:

• CFD
• Convection
• Heat and mass transfer
• Nonuniformity
• Paper drying

ACKNOWLEDGMENTS

The authors express their sincere gratitude to Professor Terrence Simon from the Department of Mechanical Engineering, University of Minnesota, and Dr. G. Worry of Georgia Pacific Corporation for research project support and funding. We also acknowledge the Minnesota Supercomputer Institute (MSI) at the University of Minnesota for making available the supercomputing resources and FLUENT/ANSYS Inc.