Heat and Mass Transfer Coefficients in Computer Simulation of Paper Drying

The development of a mathematical model and a computer program to facilitate the study of the multi-cylinder paper drying process is presented. Experimentally determined values far different heat and mass transfer coefficients are used to ensure the physical validity of the model. A unique feature of the model is its inclusion of a mass transfer coefficient for the dryer fabric. Thus far, the mass transfer mechanisms in the web have not been included. Two heat transfer coefficients are used to tune the model to actual mill data. They are assigned values that are consistent with experimental data. The agreement between predicted and experimental data, obtained from nine industrial paper dryers, is generally very good. The investigated basis weights range from 48 to 240 g/m(2). Calculations indicate that the condensate and contact heat transfer coefficients have a major influence on the drying process. The thermal conductivity of the paper and cylinder shell, respectively, are relatively important, whereas the influence of the fabric mass transfer coefficient and the cylinder-fabric-paper heat transfer coefficient are less pronounced. Some guidelines on how to obtain correct values are discussed.