Fluid Flow
CENTRIFUGAL PUMPS
CENTRIFUGAL PUMPS
Centrifugal pumps are one of the most common components found in
fluid systems. In order to understand how a fluid system containing
a centrifugal pump operates, it is necessary to understand the head
and flow relationships for a centrifugal pump.
EO 1.37
DEFINE the terms net positive suction head and
cavitation.
EO 1.38
CALCULATE the new volumetric flow rate, head, or
power for a variable speed centrifugal pump using the
pump laws.
EO 1.39
DESCRIBE the effect on system flow and pump head
for the following changes:
a.
Changing pump speeds
b.
Adding pumps in parallel
c.
Adding pumps in series
Energy Conversion in a Centrifugal Pump
Fluid entering a centrifugal pump is immediately directed to the low pressure area at the center
or eye of the impeller. As the impeller and blading rotate, they transfer momentum to incoming
fluid. A transfer of momentum to the moving fluid increases the fluid’s velocity. As the fluid’s
velocity increases its kinetic energy increases. Fluid of high kinetic energy is forced out of the
impeller area and enters the volute.
The volute is a region of continuously increasing cross-sectional area designed to convert the
kinetic energy of the fluid into fluid pressure. The mechanism of this energy conversion is the
same as that for subsonic flow through the diverging section of a nozzle. The mathematical
analysis of flow through the volute is based on the general energy equation, the continuity
equation, and the equation relating the internal properties of a system. The key parameters
influencing the energy conversion are the expanding cross-sectional area of the volute, the higher
system back pressure at the discharge of the volute, and the incompressible, subsonic flow of the
fluid. As a result of the interdependence of these parameters, the fluid flow in the volute, similar
to subsonic flow in a diverging nozzle, experiences a velocity decrease and a pressure increase.
Rev. 0
Page 47
HT-03
