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Abstract: The possible transport of fibers by fluid flow in fractures is investigatedexperimentally in transparent models using flexible polyester thread meandiameter $280 \mu\mathrm{m}$ and Newtonian and shear thinning fluids.
In thecase of smooth parallel walls, fibers of finite length $\ell = 20-150\mathrm{mm}$ move at a constant velocity of the order of the maximum fluidvelocity in the aperture.
In contrast, for fibers lying initially at the inletside of the model and dragged by the flow inside it, the velocity increaseswith the depth of penetration this results from the lower velocity - and drag- in the inlet part.
In both cases, the friction of the fiber with the smoothwalls is weak.
For rough self-affine walls and a continuous gradient of thelocal mean aperture transverse to the flow, transport of the fibers by a waterflow is only possible in the region of larger aperture $\bar{a} \gtrsim 1.1\mathrm{mm}$ and is of -stop and go- type at low velocities.
Time dependentdistorsions of the fiber are also often observed.
When water is replaced by ashear thinning polymer solution, the fibers move faster and continuously inhigh aperture regions and their friction with the walls is reduced.
Fibertransport becomes also possible in narrower regions where irreversible pinningoccurred for water.
In a third rough model with no global aperture gradient butwith rough walls and a channelization parallel to the mean flow, fibertransport was only possible in shear-thinning flows and pinning andentanglement effects were studied.



Author: Maria Veronica D'Angelo FAST, Harold Auradou FAST, Guillemette Picard, Martin E.
Poitzsch, Jean-Pierre Hulin FAST


Source: https://arxiv.org/



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