In "Modeling for Hydraulic Capacity" (Boxall et al, April 2004) the authors'
key finding is that growth of roughness elements in pipes affects pipes in
two ways: it increases the equivalent sand grain roughness; and,
decreases the pipe diameter. As stated by the authors, most methods used
to account for roughness growth adjust the roughness coefficients alone and
do not also decrease the pipe diameter. The authors are indeed correct in stating
that both should be adjusted; however, how this effect is quantified should be
examined. The relationship depends on the type of flow, the flow velocity, and the diameter of the pipe. In general, a 1-mm (0.04-in.) increase in roughness has a much greater effect on head loss than a 2-mm (0.08-in.) decrease in diameter.
Although a relationship between roughness (or Cfactor)
and diameter reduction exists, there are an infinite
number of pairs of roughness and diameter values
that can reproduce observed head loss. It would take a
great deal of testing for a modeler to determine a specific
point in any pipe. Such extra work can only be justified
on rare occasions.
Includes figures.
| Edition : | Vol. 96 - No. 10 |
| File Size : | 1
file
, 190 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 6 |
| Published : | 10/01/2004 |
