summary - philadelphia university
TRANSCRIPT
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CHAPTER (14)
TURBOMACHINARY
Dr. MUNZER EBAID
SUMMARY
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Types of Fluid Machines
1. Positive Displacement Machines.
2. Turbo-Machines.
They operates by forcing fluid into or out of a chamber. Ex. ( Automotive Engines, Gear Pumps(
They involve the flow of fluid through rotating blades or rotors that Added Energy to the fluid, ( Ex. Pumps (Liquids), Fan, blowers and compressors (Gases).
OR Remove Energy from the fluid. ( Ex. Wind turbines, Gas turbines and Hydraulic turbines)
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Hub
Blade
PROPELLER
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Thrust (T) of a propeller is a function of:
Reynolds Number Advance Ratio Thrust Coefficient
n=revolution per seconds
42)( DnCTThrust T
nD
VfCT
0
53DnCPPower P Power (P) of a propeller
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Fig. (14.2)
Coefficient of Thrust Coefficient of Power
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Blade Specifications
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EFFICIENCY
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Axial flow pumps are best suited for Low Heads and High Flow Rates
AXIAL FLOW PUMPS
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AXIAL FLOW PUMPS
Head and Discharge Coefficient for Pumps
Thrust Coefficient of a Pump =
Head Coefficient of a Pump = gnD
HCC TH 22
4
Discharge Coefficient of a Pump =
Power Coefficient of a Pump =
22
2
24242424 44
)(
nD
HgD
nD
Hg
nD
HA
nD
Ap
nD
FC TT
QH
QP
CfC
CfC
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09/10/2019 Dr. Munzer Ebaid 10 Dimensionless performance curves for a typical Axial-Flow Pump
QH
QP
CfC
CfC
Fig.
(14.6) Efficiency Curve
0.72
1.55
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Performance curves for a typical axial-flow pump
Fig.
(14.7)
cm
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Radial - FLOW MACHINES
Centrifugal Pumps
Axial
Radial
Casing with varying area
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Performance curves for a typical centrifugal pump; D = 37.1 cm
Fig.
(14.9)
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Dimensionless performance curves for a typical centrifugal pump from data given in Fig. 14.9
Fig.
(14.10)
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SPECIFIC SPEED
The specific speed is a parameter used to pick a type of a pump or a turbine that is best used for a given application and is obtained as shown below
1. Axial Pump or Turbine used for Low Head, High Discharge
2. Radial Pump or Turbine used for High Head, Low Discharge
Specific speed is obtained by combining both both
To eliminate the diameter (D) QC HC
3
22
nD
QC
gDn
HC
Q
H
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Used in USA
Fig.
(14.14)
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Suction Limitation of Pumps
The pressure at the suction side of the pump is most significant to avoid Cavitation
Cavitation usually occurs when the pressure of a flowing liquid equal the vapour
pressure of the liquid at a given temperature.
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4343
21
NPSHg
NQN SS
)(),(),( feetNPSHgpmQrpmNWhere
Critical value for Cavitation to occur
)8500( SSN
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Centrifugal pump performance curve
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Centrifugal Compressors
For an Ideal gas and Isentropic Compression process (Adiabatic and reversible)
)()( 21 ptopfromgasthecompresstorequiredpowerThe
theoP is called the Theoretical Adiabatic Power with no cooling
Efficiency of a compressor with no water cooling=
SHAFTactual
theo
CompP
P
)(
Is called the Theoretical Isothermal Power with cooling theoP
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Turbines
A turbine is defined as a machine that extracts energy from a flowing
fluid.
(a) Types of Turbines
1. Impulse Turbines.
2. Reaction Turbines.
3. Wind Turbines.
(b) Types of Turbines in relation to the direction of flow
1. Axial Kaplan Turbine. ( Flow is axial).
2. Axial Pelton Turbine. (Flow is axial).
3. Radial Francis Turbine. (Flow is radial).
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TTurbine QhP
g
Vh
j
T2
2
0LosshIf
g
VQP J
Turbine2
2
Apply energy equation between (1) & (2), we have:
Pelton Wheel
Loss
partMech
T
partMech
P hg
Vz
g
ph
g
Vz
g
ph
.
2
222
2
.
2
111
1
22
JVV 1
1 2
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Torque applied on the turbine shaft
Applying momentum Eqn. to a control volume
It is assumed that the exiting velocity has a negligible momentum, then
+Ve
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The mass flow rate across the control volume is , so the torque is Q
For Max. Power, JWheel VV )( 21
Then: Max. Power of the Turbine 2
2
JVQP
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Reaction Turbine
1. The vanes of the reaction turbine are under pressure unlike the Impulse
turbine where the pressure is atmospheric.
2. The flow fills the chamber in which the impeller is located.
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The Torque and the power produced at the shaft is given below
Eqn. (14.25)
Eqn. (14.25) is a function of the flow velocities directions 21 ,
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Wind Turbines: Extracts energy from the wind to produce Power
The max. theoretical power produced by a wind turbine
U: Wind speed
A: Area captured by the wind turbine
Wind Turbines
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END OF CHAPTER (14)