A Computational Analysis of a Headbox Flow: a Case Study

摘要

The flow in a hydraulic headbox has been investigated numerically. A new methodology has been developed thatrnallows for the efficient computation of the flow through the complete headbox. That was made possible by therndevelopment of a solution method for the flow in the full headbox including a large number of tubes between thernentrance pipe and the outlet of the slice. Computational results have pointed out that the main source of the outletrnflow profile non-uniformity is in the design of the header, which creates a back to front gradient in the manifoldrntubes that have to be compensated by the slice opening profile at the expense of the cross flows. The recirculationrnrate has some influence on the headbox flow, but cannot fully compensate for the shape of the header manifold. Thernedge flow has a small effect on the machine direction flow out of the slice and a more noticeable effect on the slicerncross flows near the walls. Modifications to the top slice profile can improve the mass flow uniformity across thernslice, but at the cost of a substantial increase of the cross-flows. It is shown that the best way to obtain a uniformrnflow out of the slice is to optimize the shape of the header manifold.