Page 262 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology En006G-249 June 27, 2001 14:7

54 Fluid Dynamics (Chemical Engineering)

FIGURE 3B Roughness factors for selected types of pipe materials. [Adapted from Moody, L. F. (1944). Trans. ASME
66, 671–684.]

equivalent of the energy input to the fluid by a pump in motor and is always less than unity. This is a figure of merit
the system. This is the actual or hydraulic head. In order of the pump that must be determined by experimentation
to obtain the total work that a pump–motor combination and is supplied by the pump manufacturer. As a rule of
performs, one must take into account the efficiency of the thumb, well-designed centrifugal pumps usually operate
pump–motor set. at about 75–80% efficiency, while well-designed positive
The efficiency is the ratio of the useful energy delivered displacement pumps generally operate in the 90–95% effi-
to the fluid as work to the total energy consumed by the ciency range. In the case of positive displacement pumps,