Pulp consistency profiles and a method for estimating the flow of fluid through apertures within a pressure screen are presented. Unsteady flow fields in a complex geometry and non-uniform feed materials combine to make measurement of flow and consistency difficult inside a pressure screen. Using simplified experimental screening studies performed with narrow bands of screen length and a full-length screen the flow and consistency changes in a pressure screen are determined. Results show that not all of the screen length is used in the same way for fibre and fluid passage. At the front of the screen the stock is of lowest consistency and has the highest fibre passage ratio. Further along the screen the stock is of higher consistency and has the lowest fibre passage ratio. Rotor type significantly affects the consistency profile even with the same level of rejects thickening. Fluid passage is not always constant along the length of the screen as assumed in the literature for screen modelling, but can have forward and reverse flow in different position on the screen depending on the rotor type.
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