Fluids- hydrodynamic interactions

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In a system of N suspended particles diffusing through a narrow channel, neglecting hydrodynamic interactions implies that the motion of one particle does not influence its neighbors. Without these interactions, particles can only move due to external flow or other forces, as their individual movements are unaffected by the presence of other particles. The discussion highlights that hydrodynamic interactions create a flow field in the solvent that influences all particles, resulting in collective motion. If no flow field exists, particles lack the necessary forces to move, raising questions about their diffusion. The concept of settling is also mentioned as a relevant phenomenon in this context.
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If we consider a system of N suspended particles diffusing through a narrow channel. What happened if the hydrodynamic interactions are neglected? Is there only flow? How can the particles diffusse without flow?
 
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Are you asking what happens in the limit of dilute particles- in other words, that the motion of one particle does not affect the motion of neighboring particles? That's usually what is meant by 'hydrodynamic interaction'.
 
It is know, that when one consider a suspension of particles. The motion of a given particle induces a flow field in the solvent, which will be felt by all the other particles. As a result these particles experience a force which is said to result from hydrodynamic interaction with the original particle.

Then, in the case that there is not hydrodynamic interactions, then the particles cannot move, or they move due to the flow or due to other effects?
or maybe in other words, if there is not flow field, then there is no hydrodynamic interactions, and then why the particles move?
 
If I understand you, if there is no hydrodynamic interaction, then each particle interacts with a flow field that is unaltered by the addition of other particles. Deiter Langbein has a couple very nice articles showing coupling effects for two spheres moving in a fluid, for various configurations of the spheres (parallel, series, etc).

As for your last sentence, think of settling.
 

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