Project
Hydrodynamics of plane liquid jets.
Project DescriptionIn modern paper manufacturing, a plane liquid jet is used to distribute the fibre suspension in a paper machine. It is believed that the homogeneity of the jet flow is of vital importance to obtain a good quality paper. Theoretical and experimental investigations of the behaviour of plane water jet have been performed. The numerical solution of the basic flow field and stability equations have been compared to experimental results. The experiments show the presence of two-dimensional spanwise homogenous waves, travelling in the streamwise direction of the jet. In connection with these waves, a strong break-up of the jet could be observed. These waves could only be observed with a channel nozzle, which gives a flow dominated by viscosity. A stability investigation of the basic flow field gave results which correlated well with the experimental results. In January and November 1998 visualisations of an industrial headbox jet were performed at STFI using high-speed video. In the first test three different configurations of the headbox were tested, two with separation vanes and one without. The visualisations were performed with both water and a fibre suspension. The visualisations showed waves similar to the instability waves found in the channel flow jet. In the second experimental series visualizations of a multilayered headbox jet were performed using layers with different colours. This allows for an insight in the degree of mixing between different layers. The visualizations were complemented by forming actual paper sheets. By comparing the images captured at the headbox and the final paper sheets, it is possible to determine the overall influence of the headbox flow.
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