Fluid Dynamics Model of the Film-Fed Rolling Nip with a Porous Web, 1998 Coating Conference Proceedings

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A model is proposed to describe the flow field in the nip of a metered size press. The model accounts for the penetration of the fluid phase into the web and the subsequent possible formation of a filtercake. The model is unique from past calculations in that the pressure field and the penetration are calculated simultaneously; the pressure field is not assumed a priori. The model compares well with finite element results when there is no penetration. The results indicate that the pressure field generated in the nip s linked to the amount of penetration in the nip.

The influence of various process parameters on the amount of penetration and the film transfer ratio are reported. As industrial experience reveals, increased amount of coating fed to the nip results in a thicker fluid layer leaving the nip. The model results are compared with pilot scale trials: the transfer ratios are well predicted with no adjustable parameters when misting is not an issue. The model can be used to predict the operational limits, the potential for misting, and the transfer ratio for the metered size press.