Mechanics of Fluids

For systems comprising only short runs of straight pipe together with
other components, the flow is altogether more complicated and the above
approach to the estimation of overall system loss may lead to inaccurate
results. For such designs it is often necessary to resort to model tests to
investigate the system performance.
Example 7.4
(a) Derive an expression for the power P required to pump a volumetric
flow rate Q through a horizontal pipe-line of constant
diameter D, length l and friction factor f . Assume that the friction
in the pipe-line is the only source of dissipation, other than that
within the pump itself.
(b) For the purpose of project calculations the total cost of moving a
fluid over a distance by pipe-line at a steady flow rate, Q, can be
broken down into two items. First, the manufacture, laying and
maintenance of the pipe-line, including interest charges, are represented
by the cost C1, which is proportional to D 3 . The second item,
C2, depends solely upon the energy required to pump the fluid.
A preliminary design study for a particular project showed that the
total cost was a minimum for D = 600 mm. If fuel prices are increased
Total head and pressure lines 275
Fig. 7.19