Page 453 - Chemical process engineering design and economics

434 Chapter 8

materials. From this list, a velocity of 6 fl/s (1.83 m/s) for the discharge side of
the pump seems to be a reasonable average value. After specifying the volumetric
flow rate of the liquid and selecting a liquid velocity, calculate the inside diameter
of the pipe. Piping is only available in standard diameters, which does not exactly
correspond to either the inside or outside diameter of a pipe, as shown in Table
8.2A, where the pipe dimensions are in inches. In Table 8.2B the dimensions are
in millimeters. Other technical factors may change the suggested velocity of 6 ft/s
(1.83 m/s). For example, if a liquid contains suspended particles, the liquid veloc-
ity must be reduced to prevent erosion. For clear fluids, expect erosion above 10
ft/s ( 3.05 m/s) [31]. On the other hand, to prevent suspended particles from set-
tling or deposits from forming on the pipe wall requires increasing the liquid ve-
locity. A liquid velocity is selected to balance these opposing factors as deter-
mined by experience.

Pumping Cost

Pipe Diameter

Figure 8.13 Optimum pipe diameter.

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