Page 123 - Fluid mechanics, heat transfer, and mass transfer

5

PUMPS, EJECTORS, BLOWERS, AND COMPRESSORS

5.1 Pumps 101 5.1.1 Centrifugal Pumps
5.1.1 Centrifugal Pumps 101
5.1.2 Cavitation 112 . What is the principle of operation of a centrifugal
5.1.3 Centrifugal Pump Performance and pump? How does it work?
Operational Issues 118
& The purpose of a centrifugal pump is to convert the
5.1.4 Positive Displacement Pumps 127
energy of the motor or other prime mover, first into
5.1.5 Miscellaneous Pumps 137
the kinetic energy (velocity) of the fluid being
5.1.6 Vacuum Pumps 141
pumped and then into pressure energy. The velocity
5.2 Ejectors 145
5.3 Fans, Blowers, and Compressors 152 is developed in the rotating impeller, whereas the
conversion to pressure takes place within the station-
ary volute or diffuser.
& The process liquid enters the pump near the impeller
axis, that is, eye of the impeller and the rotating
impeller vanes. As a result of this rotation, impeller
5.1 PUMPS vanes transfer mechanical work to the fluid in the
impeller channel, which is formed by the impeller
. Classify pumps. vanes. The rotating impeller channel sweeps the
& Pumps are divided into two fundamental types based liquid out the ends of the impeller blades at high
on the manner in which they transmit energy to the velocity. As liquid leaves the impeller eye, a low-
pumped media, namely, kinetic displacement or pressure area is created, causing more liquid to flow
positive displacement. toward the inlet. Because the blades are curved, the
fluid is pushed in a tangential and radial direction by
& In kinetic displacement, a centrifugal force of the
the centrifugal force.
rotating element, called an impeller, imparts kinetic
energy to the fluid, moving the fluid from pump & Energy added to the pump by centrifugal force is
suction to the discharge. kinetic energy, which is given to the liquid propor-
tionate to velocity at the edge or vane tip of the
& On the other hand, positive displacement uses the
impeller. The faster the impeller rotates or the bigger
reciprocating action of one or several pistons, or a
the impeller is, the higher will be the velocity of the
squeezing action of meshing gears, lobes, or other
liquid at the vane tip and the greater the energy
moving bodies, to displace the media from one area
imparted to the liquid.
into another (i.e., moving the material from suction to
discharge). . What are the salient features of centrifugal pumps? What
type of applications a centrifugal pump is suitable?
& Figure 5.1 presents a broad classification of pumps.
& Very high capacity and low head.
& Hydraulic Institute classifies pumps by type, not by
application, into two basic types, namely, kinetic & Smooth nonpulsating flow.
types and positive displacement types, which are & No damage on closure of discharge valve, unlike
detailed in Figures 5.2 and 5.3. positive displacement pumps.

Fluid Mechanics, Heat Transfer, and Mass Transfer: Chemical Engineering Practice, By K. S. N. Raju
Copyright Ó 2011 John Wiley & Sons, Inc.
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