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Lecture 3:
September 21, 2014 1
Prepared by:
Engr. AN Tabish
Lecturer
Department of
Chemical Engineering
University of Engineering
& Technology, Lahore -Pakistan
Fluid Dynamics
Fluid Dynamics
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Course Outline:
Fluid Dynamics
1. Introduction to fluid dynamics; Transportation of fluids;
2. Storage tanks, pipes, fittings and valves;
- Selection, design, procedures and cost
3. Pumps, compressors, blowers, fans, turbines and expanders;
- Selection, cavitation, chocking, surging, corrosion
prevention
4. Metering of fluids;
5. Agitation and mixing of fluids; static fluid phenomenon in
static mixers; dynamic mixers;
6. Flow passed immersed bodies; fluidization;
7. Chemical engineering CFD;
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Compressor
Fluid Dynamics
Compressor is a device used to increase the pressure of
compressible fluid.
Modes of Compression:
1. Intermittent (+ve displacement)
2. Continuous (Dynamic)
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Compressor
Fluid Dynamics
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Compressor
Fluid Dynamics
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Compressible flow:
Fluid Dynamics
Compressor Cooling System:
Inter-stage coolers
Mack Number:
As gas moves in the constant diameter suction line of
compressor: It experiences
Pressure drops
Gas volume increases as mass flow rate remains constant
Velocity increase =>in sever cases it approaches sonic
velocity
)(CVelocityAcoustic
)(VVelocityGasNumberMack
s
g
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Compressible flow:
Fluid Dynamics
)(CVelocityAcoustic
)(VVelocityGas
NumberMacks
g
Keep Mack Number as low as practical
Temperature at compressor
suction must be considered.
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Compressible flow:
Fluid Dynamics
Surging and Surge Control:
Compressor surges when the differential pressure-imposed by
process-exceeds the differential pressure which it can develop.
The surging occurs when the compressor back pressure ishigh and the compressor can not pump against this high head,
causing the flow to separate and reverse its direction.
Surging results in changes in direction of the thrust forces on therotor, creating damage to the blades and the thrust bearings.
lower limit of stable operation in a compressor
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Compressible flow:
Fluid Dynamics
Surging and Surge Control:
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Compressible flow:
Fluid Dynamics
Surging and Surge Control:
If Pd
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Compressible flow:
Fluid Dynamics
Surging and Surge Control:
Consequences of Surging
Consequences of surging can include:
1. Rapid flow and pressure oscillations cause process instabilities
2. Rising temperatures inside the compressor
3. Tripping of the compressor
4. Mechanical damage
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Compressible flow:
Fluid Dynamics
Surging and Surge Control:
Mechanical damage can include:
1. Radial bearing load during the initial phase of
surging. A side load is placed on the rotor which acts
perpendicular to the axis.
2. Thrust bearing load due to loading and unloading.
3. Seal rubbing
4. Stationary and rotating part contact if thrust bearing isoverloaded.
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Compressible flow:
Fluid Dynamics
Surging and Surge Control:
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Compressible flow:
Fluid Dynamics
Surge Control:
The surge of centrifugal compressor is controlled by two methods:
1. Discharge flow.
2. Varying the drive speed.
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Thank You