If a moderately dense suspension (say 0.4 particle fraction) of spherical particles is pushed through a syringe with a constriction, what causes the suspending liquid in the system to squeeze/strain out and the particle fraction to rise? Also are there any simple ways maybe like applying a gradually decreasing diameter to prevent this?
We need more information to a answer properly. I do not think that you would observe this phenomenon for a hard sphere fluid. If there is attraction between the particles, then it could happen. So, without more details, I am guessing that the situation will be improved by adjusting the interaction forces between the particles - adding dispersant, for example.
Hi Sameer,
I agree completely with Alan, but would add a couple of further points. If the diameter of the constriction is
Firstly clear attractive (Van der Waals, electrostatic, chemical) particle-particle and particle-wall material interactions.
Secondly depending on particle size, particle/fluid density difference and fluid rheology investigate the secondary flow vortex formation in the abrupt contraction entrance zone of the syringe under various outflow rates. From this you could derive possible impact of inertia driven flow induced separation forces acting on the particles.
In case of particle fraction increase supported by such secondary entrance flow effects, you could go for a modified entrance flow geometry (e.g. gradually converging) to reduce or fully suppress secondary flow effects.
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