class 01- thermo

8/10/2019 Class 01- thermo

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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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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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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

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class 01- thermo

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