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Turbomachinery
Lecture 1
- Pumps, Turbines
- Subcomponents
- Units, Constants, Parameters- Thermodynamics
www.engr.uconn.edu/barbertj~
- ME3295 / ME6160
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Turbomachinery
Turbomachine: A device in which energy is transferred to
or from a continuously flowing fluid through a casing bythe dynamic action of a rotor.
Rotor or impellor: Changes stagnation enthalpy of fluidmoving through it by either doing positive or negativework.
Works on fluid to produce either power or flow
Turbomachine categories:
Those which absorb power to increase fluid pressureor head [compressor, pump].
Fan: pressure rise up to 1 lbf/in2
Blower: pressure between 1 - 40 lbf/in2
Compressor: pressure rise above 40 lbf/in2
Those which produce power by expanding fluid to
lower pressure or head [turbine].
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Brayton Thermodynamic Cycle for Single Spool Turbojet Engine
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Meridional Projection of Axial & Centrifugal Compressor Stages
Essentially constant radius Substantial change in radius
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Turbomachinery - Pumps
Positive Displacement: moving boundary forces fluidalong by volume changes. Reciprocating, rotary: piston, screw, ...
Dynamic: momentum change by means of moving
blades or vanes (No closed volume). Axial, centrifugal, mixed
Fluid increases momentum while moving through openpassages and then converts high velocity to pressure rise indiffuser section
In radial machines doughnut-shaped diffuser is called ascroll
Through a casing...........Not wind mills, water wheels orpropellers
Flow conditioning..........Stators, scrolls
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Turbomachinery - Turbines
Extracts energy from a fluid with high head[pump run backwards].
Reaction turbine: fluid fills blade passagesand pressure drop occurs within theimpeller.
Low-head, high-flow devices
V across rotor increases, p decreases
Stators merely alter direction of flow
Impulse turbine: converts high head to highvelocity using a nozzle; then strikes bladesas they pass by.
The impeller passages are not fluid filled,and the jet flow past the blades isessentially at constant pressure.
Discharge velocity relative inlet velocityacross rotor
no net change in p across rotor
stators shaped to increase V, decrease p
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Gas Generator
Purpose: Supply High-Temperature and
High-Pressure Gas
compressor, combustor, turbine
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Turbojet
Purpose: Provide High-Velocity Thrust
inlet, compressor, combustor, turbine, nozzle
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Turbofan Purpose: Produce Lower-Velocity Thrust
Through the Addition of a Fan
inlet, fan, compressor, combustor, turbine, nozzle
Stations0=1=Upstream
2 =compressor inlet
2.5=low-to-high comp
3 =combustor inlet
4 =turbine inlet4.5=high-to-low turb.
5 =nozzle inlet
8 =exit
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Turboprop
Purpose: Produce Low-Velocity Thrust Through
Addition of a Propeller
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Turboshaft
Purpose: Produce Shaft Power for Rotating
Component [Not for Thrust] - helicopter
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Low BPR
BPR= mass flow through bypass/mass flow through core
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High BPR
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Gas Turbine Components
Main Flow-Path
Components of a Gas
Turbine Engine:
inlet
compressor combustor
turbine
nozzle
Secondary Flow-PathComponents:
disk cavities
cooling flow bleed ducts
bearing compartments
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Fan/Compressor
Axial-Flow Fan Axial-Flow Compressor
Low-Pressure
High-Pressure
Centrifugal Compressor Mixed Axial/Radial Flow Fan
Low-Pressure
Compressor
High-PressureCompressor
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Turbine
Extracts Kinetic Energy formExpanding Gases and
Converts to Shaft
Horsepower to Drive the
Compressor/Fan Axial Flow Turbine
High Flow Rates
Low-Moderate Pressure
Ratios
Centrifugal Turbine
Lower Flow Rates
Higher Pressure Ratio
High-Pressure
Turbine
Low-PressureTurbine
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Nozzle Increase the Velocity of the Exhaust Gas Before
Discharge from the Nozzle and Straighten Gas
Flow From the Turbine
Convergent Nozzle Used When Nozzle Pr < 2
(Subsonic Flow) Convergent-Divergent Nozzle Used When Nozzle Pr > 2
Often incorporate variable geometry to control throat areaNozzle
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Favorable [Turbine] & Unfavorable [Compressor] Pressure Gradients
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Units and Key Constants
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Conventional Units
Parameter English Units SI Units
Distance Feet, Inches Meters, M
Time Seconds Seconds, s
Force Pounds (force), lbf 4.448 Newton, N Pressure psf, psi Pascal, Pa (1N/1m2)
bar (105Pa)
1 ft H2O 2.989 kPa
Mass Pounds (mass), lbm 0.4536 kilogram
Energy Btu Joule, J Power 1 Hp 0.7457 kWatt
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System Force Mass Length time
English Eng. lbf lbm ft s
English Gravitational lbf slug ft s
Metric kgf kg m sMetric dyne gm cm s
International System (SI) Newton kg m s
Equivalent Systems of Units
1 Newton = 1 kg-m/sec21 Joule = 1 N-m/sec
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Useful Equivalents
Quantity Original Unit Equivalent
Flow 1.0 cfs [ft3/sec] 448. gal/min
Specific Energy 1.0 ft2
/s2
1.0 ft-lbf/slugMass 1.0 slug 32.174 lbm
Rotational speed 1.0 rad/s 9.549 rev/min
Kinematic viscosity 1.0 ft2/s 92,903 centistokes
Pressue 1.0 in. H2O 5.2 lbf/ft2
Atmospheric pressure
1 in Hg = 0.49116 psi
2116 psf = 14.7 psi = 1.013 Bar = 101,325 Pascals
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For Liquid Water :
U.S. Standard Atmosphere - 1976
3/4.62 ftlbm
2696.14 in
lbf
pressure
Retemperatur 67.518
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Standard Atmosphere
Stratosphere
>65,000 ft
59 F
Temperature
Altitude
3.202 psia
14.696 psia
Pressure
36,089 ft
Altitude
36,089 ft
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Thermodynamics Review
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Thermodynamics Review
Thermodynamic views microscopic: collection of particles in random motion.
Equilibrium refers to maximum state of disorder
macroscopic: gas as a continuum. Equilibrium isevidenced by no gradients
0thLaw of Thermo [thermodynamic definition oftemperature]:
When any two bodies are in thermal equilibrium with
a third, they are also in thermal equilibrium with eachother.
Correspondingly, when two bodies are in thermalequilibrium with one another they are said to be atthe same temperature.
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Thermodynamics Review
1st
Law of Thermo [Conservation of energy]: Total workis same in all adiabatic processes between any twoequilibrium states having same kinetic and potentialenergy. Introduces idea of stored or internal energy E
dE = dQ - dW dW = Work done by system [+]=dWout= - pdV
Some books have dE=dQ+dW [where dW is work done ONsystem]
dQ = Heat added to system [+]=dQin
Heat and work are mutually convertible. Ratio of conversion iscalled mechanical equivalent of heat J = joule
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Review of Thermodynamics
Stored energy E components Internal energy (U), kinetic energy (mV2/2), potential energy,
chemical energy
Energy definitions
Introduces e = internal energy = e(T, p)
e = e(T) de = Cv(T) dT thermally perfect e = Cv T calorically perfect
2ndlaw of Thermo
Introduces idea of entropy S
Production of s must be positive
Every natural system, if left undisturbed, will changespontaneously and approach a state of equilibrium or rest. Theproperty associated with the capability of systems for change iscalled entropy.
revQdS TdS dE dW
T
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Review of Thermodynamics
Extensive variables
depend on total mass of the system, e.g. M, E,S, V
Intensive variables do not depend on total mass of the system, e.g.p, T, s, (1/v)
Equilibrium (state of maximum disorder) bodies that are at the sametemperature are called in thermal equilibrium.
Reversible process from one state to another state during which thewhole process is in equilibrium
Irreversible all natural or spontaneous processes are irreversible,e.g. effects of viscosity, conduction, etc.
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Thermodynamic Properties
Extensive Intensive Extensive Intensive
Mass M Density - Energy Eo Specific energy eo
- Pressure p Kinetic energyEk Sp. kin. energy V2/2
- Temperature T Potential energy Ep Sp. pot. energy gz
Volume - V Specific volume - Internal energy - E Sp. int. energy - e
Primitive Derived
2
0 0
0
2k p
T
VE E E E or e e gz
Total or stagnation state
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1st Law of Thermodynamics
For steady flow, defining:
We can write:
and
2
2
0
/ 2 specific kinetic energy
specific potential energy
specific internal energy
= + + specific enthalpy
e total2
V
gz
e
ph e pv e
Ve gz
specific energy
2
0e2
Vpv e gz pv
0 0h e pv and h e pv
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Equation of State
The relation between the thermodynamic properties of a puresubstance is referred to as the equation of state for that substance, i.e.
F(p, v, T) = 0
Ideal (Perfect) Gas
Intermolecular forces are neglected
The ratio pV/T in limit as p 0 is known as the universal gasconstant (R).
p /TR = 8.3143e3
At sufficiently low pressures, for all gases
p/T = R
or
Real gas: intermolecular forces are important
p RT
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Real Gas
1150 R
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Real Gas
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1st& 2ndLaw of Thermodynamics
Gibbs Eqn. relates 2ndlaw properties to 1stlaw properties:
Tds pdv de
h e pv
dh de pdv vdp
dpTds dh
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Gibbs Equation
Isentropic form of Gibbs equation:
and using specific heat at constant pressure:
dp
dh
p
p
RTc dT dP P
dT R dP
T c P
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Mollier Chart for Air
500
1,000
1,500
2,000
2,500
3,000
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
Entropy - BTU/Lbm/deg R
Temperatur
eDegR
P=50Atm
20
10
5
2
1
Isobars are not parallel
Mollier for Static / Total States
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Mollier for Static / Total States
450
650
850
1,050
1,250
1,450
1,650
T
IdealReal
P in
P out
s
Poin
Poout
V2/2
h02i
h02
h01
2
02
Vh h
We will soon see