cbe 150a – transport spring semester 2014 pumps. cbe 150a – transport spring semester 2014 goals...
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CBE 150A – Transport Spring Semester 2014
Pumps
CBE 150A – Transport Spring Semester 2014
Goals• Describe how centrifugal and positive-displacement pumps operate Describe how centrifugal and positive-displacement pumps operate
and common applications.and common applications.
• Calculate system head requirements.Calculate system head requirements.
• Determine head, pump efficiency, and pump. horsepower from a Determine head, pump efficiency, and pump. horsepower from a typical centrifugal pump curve.typical centrifugal pump curve.
• Define net positive suction head (NPSH) and understand how it relates Define net positive suction head (NPSH) and understand how it relates to cavitation.to cavitation.
• Compute NPSH required by a pump.Compute NPSH required by a pump.
• Determine an appropriate pump (impeller diameter, efficiency, etc.) for Determine an appropriate pump (impeller diameter, efficiency, etc.) for a given required head.a given required head.
• Describe how to modify system to operate on the appropriate pump Describe how to modify system to operate on the appropriate pump curve.curve.
CBE 150A – Transport Spring Semester 2014
Background
Fluid Moving Equipment
Fluids are moved through flow systems using pumps, fans, blowers, and compressors. Such devices increase the mechanical energy of the fluid. The additional energy can be used to increase
• Velocity (flow rate)• Pressure• Elevation
CBE 150A – Transport Spring Semester 2014
Background
Pump, fan, blower, and compressor are terms that do not have precise meaning. Generally pumps move liquids while fans, blowers and compressors add energy to gasses.
Pumps and fans do not appreciably affect the density of the fluids that they move and thus incompressible flow theory is applicable.
CBE 150A – Transport Spring Semester 2014
Centrifugal Pumps
Most common type of pumping machinery. There are many types, sizes, and designs from various manufacturers who also publish operating characteristics of each pump in the form of performance (pump) curves. The device pictured on the cover page is a centrifugal pump.
Pump curves describe head delivered, pump efficiency, and net positive suction head (NPSH) for a properly operating specific model pump.
Centrifugal pumps are generally used where high flow rates and moderate head increases are required.
CBE 150A – Transport Spring Semester 2014
Centrifugal Pumps
CBE 150A – Transport Spring Semester 2014
Impeller
CBE 150A – Transport Spring Semester 2014
Positive Displacement Pump
CBE 150A – Transport Spring Semester 2014
Positive Displacement PumpsTo move fluids positive displacement pumps admit a fixed volume of liquid from the inlet into a chamber and eject it into the discharge. Positive displacement pumps are used when higher head increases are required. Generally they do not increase velocity.
CBE 150A – Transport Spring Semester 2014
LVAD Application
CBE 150A – Transport Spring Semester 2014
Pump HeadWhat happens if the MEB is multiplied through by g (gc/g)?
2
42
1ˆ 22 VK
D
Lf
pzg
V
gg
Wi
What are the units (SI)?2
2
m
s
kg
mN 2
2
2
3
m
s
skg
mkg
m
PumpHead
System Head
CBE 150A – Transport Spring Semester 2014
Pump Cavitation Net (above the vapor pressure) Positive Suction Head (NPSH))
AvailableHead2
2
c
b
g
VPb
Pa
Zahfs
RequiredHead
vap
CurvePump
PNPSH
Pb
CBE 150A – Transport Spring Semester 2014
Pump Curve Example
What pump horsepower is required to pump 150 GPMof water at a total head of 225 ft using a Goulds Model 3196 operating at 3540 RPM ?
What is the required NPSH ?
What is the pump efficiency ?
Pump Curves (Resources Section)
CBE 150A – Transport Spring Semester 2014
Pump Curves
CBE 150A – Transport Spring Semester 2014
System Response
What happens when flow control valve is closed?• Resistance (f) increases• Flow rate decreases• Need more head to recover flow rate
Tank A
2
Tank B
13
CBE 150A – Transport Spring Semester 2014
System Response
Valve Open
ConstantHead Response
ConstantFlow Response
Valve Closed
CBE 150A – Transport Spring Semester 2014
10 Minute Problem
Tank A
Tank B
A centrifugal pump (Goulds Model: 3196 - 1770 RPM - CDS 3832) with an 11 inch impeller is used to transport water at 350 GPM through the system show below. The system head with the control valve completely open is 90 ft lbf / lbm. For the desired flow rate, it is necessary to partially close the control valve. What pressure drop across
the valve is required ?