Unformatted text preview: puted separately; i.e., the bend length should be added to the pipe length.
As shown in Fig. 6.21, entrance losses are highly dependent upon entrance geometry, but exit losses are not. Sharp edges or protrusions in the entrance cause large zones
of flow separation and large losses. A little rounding goes a long way, and a wellrounded entrance (r 0.2d) has a nearly negligible loss K 0.05. At a submerged exit,
on the other hand, the flow simply passes out of the pipe into the large downstream
reservoir and loses all its velocity head due to viscous dissipation. Therefore K 1.0
for all submerged exits, no matter how well rounded.
If the entrance is from a finite reservoir, it is termed a sudden contraction (SC) between two sizes of pipe. If the exit is to finite-sized pipe, it is termed a sudden expansion (SE). The losses for both are graphed in Fig. 6.22. For the sudden expansion,
the shear stress in the corner separated flow, or deadwater region, is negligible, so that
a control-volume analysis betwe...
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- Spring '08
- Fluid Dynamics, e-Text Main Menu, Osborne Reynolds