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Micro-PIV measurement of flow through forming fabrics

University of British Columbia

This thesis describes an experimental investigation of the flow field upstream of forming fabrics that are typically used in the paper making process. Micro Particle Image Velocimetry was used to measure the velocity distribution upstream of a forming fabric. The velocity upstream of two different types of forming fabrics, namely Monoflex D60TM and IntegraTM, was studied. As expected, the experiments show the existence of a highly variable drainage velocity field upstream of both fabrics. The drainage velocity over the holes can be several times greater than the drainage velocity above the fabric filaments. Since fines and filler tend to follow fluid streamlines, one would therefore expect substantially higher fines and filler concentrations in the holes between the filaments as compared over fabric knuckles. The decay in drainage velocity variations can be represented by the equation Aexp(-Bz/D)+C, where A and B are constant and C is the uncertainty in the experimental setup. D and z represent the fabric’s filament diameter and distance above the fabric surface. It is expected that the response of pulp fibers to the velocity variations caused by the fabric’s weave structure is strongly correlated to their length. The fibers with a length greater than 1.5 mm experience a weighted-average velocity field along their length that is approximately uniform. The deposition of short fibers with length <1500 μm is strongly influenced by the fabric’s weave structure. The experiments also indicate that for fines and filler materials, the different filament diameters and weave patterns among the fabrics are irrelevant since their length scale is smaller than the gap between the fabric filaments. In general, the fabric with finer weave pattern results in more uniform fiber deposition. To study the fiber mat formation, thin layers of fibers were deposited onto the fabric. It was observed that as the grammage increases from 1 g/m² to 5 g/m², the normalized standard variations in drainage velocity field increases from 15% to 61%. The thickness of the boundary region (i.e. the upstream region affected by the disturbance generated by the fabric and fibers) also increases from 1.5D to 3.0D.

Text

2013-12-18

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/45656

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/