Modelling of Fibre-Mat Build-Up at Jet Impingement on a Permeable Fabric, 2001 Engineering / Finishing & Converting Conference Proceedings

B. Dalpke, S. I. Green, R. J. Kerekes--Jet impingement in a twin-wire paper machine is believed to have a significant influence on paper qualities such as formation, fines distribution and two-sidedness. A fluid mechanics model of jet impingement in roll formers is therefore being developed with the long term goal of simulating the effects of jet impingement on paper properties.

In a previous study, we used the CFD software FLUENT to obtain a two-dimensional initial model of jet impingement on a single fabric. In this work, we extend the previous study to the computation of fibre-mat build-up for the single fabric case. Fibre-mat build-up was computed for typical values of fibre-mat resistance of different furnishes. From the initial assumption of a constant basis weight, drainage profiles can be computed and used to calculate a new basis weight profile and drainage resistance profile. Using this as a new input, the final basis weight profile can be computed by iteration. It was found that relative drainage at jet impingement was influenced by the furnish properties as well as the drainage resistance of the fabric. For fabrics with high resistance, the drainage is around 13% for a slow draining furnish (Eucalyptus) up to 18% for a fast draining furnish (Kraft). For fabrics with lower resistance, the drainage ranges between 14% (Eucalyptus) and 23% (Kraft). The influence of fibre-mat build- up is therefore more pronounced for lower resistance fabrics. The influence of impingement on integrated pressure of different furnishes was found to be small.

In addition to these predictions using CFD, an experimental validation was carried out for a round jet impinging perpendicular to a forming fabric at different jet velocities (initial model, no fibre-mat build-up). Measured drainage rates as a function of jet velocity showed good agreement with the computed drainage rates for this case.