Flow visualization experiments of Newtonian laminar flow through branching tubes have been performed to identify the shape of the separation surface or flow divider. The influences of Reynolds number, flow fraction into the side branch, and branch geometry on the separation surface shape have been considered. The shapes presented in this paper are formed by the intersection of the separation surface with the cross section of the parent tube. At low Re the separation surfaces are curved in a convex manner, bulging away from the opening of the side branch. Increasing Re causes the surface to become concave. At Re > 194 the surfaces can become closed for Q* > 0.3. The branch angle has no noticeable effect on the separation surface shape. The side to parent branch diameter ratio, Db/Dp, has a strong influence at low Re. As Re increases the diameter effect diminishes. Previous studies have shown no difference between the separation surfaces of T and Y type junctions at low Re. At Re = 194 there is a marked difference between the separation surfaces of T and Y bifurcations.

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