I have an application where I would like to keep a bubble flowing freely within a pipe. Assume a single small, spherical, non-deforming gas bubble in a viscous, laminar fluid flowing in a vertical pipe.

Would the sliding shear stress with the pipe wall and fluid layers keep the bubble centered in the pipe?

What about a horizontal pipe? Could shear stress also balance the buoyant forces keeping the bubble away from the top pipe surface?

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    $\begingroup$ Use a bubble that is slightly smaller than the pipe diameter, and it will likely remain centered in a vertical pipe. For the horizontal pipe, the shear stress will not balance the buoyant forces. For an example of a horizontal bubble, look at the bubble in any common carpenter's level. $\endgroup$ – David White May 5 at 18:43

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