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-Introduction-

(Hyung Hee Cho)

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GE 9 0 En g i n e GE 9 0 En g i n e

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Assumptions for the basic gas turbine cycle:

Air, as an ideal gas, is the working fluid throughout

Combustion is replaced with heat transfer from an external source

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P C l (H t E i )

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Power Cycles (Heat Engines)

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where:

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Steady-State Flow:

One-Dimensional Flow:

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Recall:

Energy Rate Balance:

Steady State Flow:

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Conservation of Mass

m1 = m2

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Common Form of 1st Law:

Heat transfer is often small enough relative to

the power and enthalpy terms

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Common Form of 1st Law:

Heat transfer is often small enough relative to

the power and enthalpy terms

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Rotating compressors

Reciprocating compressor

Common Form of 1st Law:

Heat transfer is often small enough relative tothe power and enthalpy terms

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A System Property

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y p y

Selecting the symbol S to denote this property, which is called entropy,

its change is given by

Definition of entropy change:

On a differential basis:

Entropy is an extensive property.

Entropy:

1.Since entropy is a property, the change in entropy of a system in going

from one state to another is the same for all processes, both internally

reversible and irreversible, between these two states.

2.Entropy is defined and evaluated in terms of a particular integral for which

no accompanying physical picture is given.

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Internally Reversible Processes of Closed Systems

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y y

Carnot Power Cycle

Carnot Refrigeration and

heat pump Cycle

Cycle1-2 and 3-4 : isentropic process.

Carnot Cycle application

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Ideal Thermal Efficiency

= W/qin = (qin qout)/qin =1 - qout/qin

=

Ideal Thermal Efficiency

= W/qin = (qin qout)/qin =1 - qout/qin

=

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Ideal Thermal EfficiencyIdeal Thermal Efficiency

1-2: COMPRESSOR

3-4: TURBINE

4-1: HEAT REJECT

2-3: COMBUSTER

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Maximum Work

T2 = ?

Maximum Work

T2 = ?

Maximum Thermal Efficiency

T2 = ?Maximum Thermal Efficiency

T2 = ?

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Using Constant Specific Heats, the cycle thermal efficiency is:

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Effect of Pressure Ratio on Performance

(constant k) k= 1.4

Ideal Brayton cycle with different pressure

ratios and the same turbine inlet temperature.

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Maximum workMaximum work

Turbine inlettemperature

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Comparison of actual and isentropic compressions.

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Compressors and Pumps:

Pumps, assuming incompressible model:

Isentropic Turbine Efficiency

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Comparison of actual and

isentropic expansions through a turbine.

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Regenerator Effectiveness :

Heat added per unit mass :

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Compressor Turbine

Combustor

RecuperatorExhaust

AirIntercooled/Recuperated Engine systemIntercooled/Recuperated Engine system

Recuperator

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Reheat, regeneration, and intercooling are most effective when used in

combination with one another. However, weight limitations (e.g. aircraft

applications) often limit their usage.

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Ericsson cycle

Stirling cycle

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