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I checked in two books about microfluidics, and both of them mention that the only parameters that influence $R_{hyd}$ are related to geometry (width of channel, length, depth...) but it is counterintuitive. I can imagine that if I make channel of the same dimensions but made of different materials (eg. one from glass and one from paper) the resistances would be different.

Or am I wrong? Or maybe there's something else that also influences hydrodynamic resistance?

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    $\begingroup$ Roughness of walls matters. See Moody's chart for example. $\endgroup$ – Deep Feb 5 '18 at 4:52
  • $\begingroup$ To me, it is counterintuitive that the wall material would affect the hydrodynamics. Why is it counterintuitive to you that it wouldn’t? $\endgroup$ – Chet Miller Feb 5 '18 at 5:53
  • $\begingroup$ @Deep is it also valid for microfluidics? $\endgroup$ – user46147 Feb 5 '18 at 8:52
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    $\begingroup$ As per Moody's chart, for low Reynolds number flow, wall roughness does not matter. If wall roughness became too high then it would be considered a macroscopic geometric feature of the channel. But rigidity of the wall is important and this is how material characteristics may matter. Walls made of paper are flexible compared to that of glass which in turn changes the flow; for e.g. flexible walls are known to make the flow turbulent at much lower Reynolds number. $\endgroup$ – Deep Feb 5 '18 at 10:56

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