Advances in Design of Elastic Guiding Vanes Used in Traditional and Stratified Headboxes, 2008 PAPERCON Conference

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We have studied wake of guiding vanes developing in the contracting zone of headbox. It has been found that self-similar solutions can predict the wake characteristics. These predictions can be used in optimization of guiding vanes to improve the mechanical properties of the finished paper. In order to study the mixing in the wake of separating vanes used in multilayer headboxes, we have measured the flow in a model headbox in a wind-tunnel. To quantify mixing, the airflow above the plate was heated and the temperature stratification in the wake was traced by measuring the temperature field using constant current anemometry (CCA). Using different plate lengths, we found that the degree of mixing, obtained at a given position in the straight channel, was quite sensitive to the distance for which the wake had developed in the contraction. For a plate which does not protrude into the straight channel, we demonstrate the existence of an optimal distance from the plate trailing edge to the contraction outlet that results in the lowest possible degree of mixing at a given downstream position in the straight channel. This finding is also supported by a semi-empirical relationship based on our developed self-similar solution for mixing layers in planar contractions and constant cross-section channels.