an introduction to brayton cycle

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AN INTRODUCTION TO

BRAYTON CYCLE

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TECHNOLOGY

Submitted by: Sayantan Dutta(ME) Roll:87040387

By 

Sayantan Dutta 

Roll:87040387 Exam Roll:08125007051

Branch:Mech Engg.

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Brayton Cycles:

The basic gas turbine cycle is named for the Bostonengineer, George Brayton, who first proposed the Braytoncycle around 1870.

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Open Cycle(Generally used in aircraft propulsion.)

Closed Cycle(Electric power generation)

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Brayton Open Cycle 

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Brayton Closed Cycle 

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P-v AND T-s DIAGRAMS OF AN IDEAL BRAYTON CYCLE:

BRAYTON CYCLE CONSISTS OF:

Reversible isentropic

compression.(Process 1-2)

Reversible isobaric heat

addition.(Process 2-3)

Reversible isentropic

expansion.(Process 3-4)

Reversible isobaric heat

rejection.(Process 4-1)

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Theory Of Brayton Cycle:

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Heat addition Q in=mcp(T3-T2)

Heat rejection Q out=mcp(T4-T1)

Then the thermal efficiency of the ideal Brayton cycle becomes

ηth,Brayton =Wnet/Q in = 1-Q out/Q in =1-(T4-T1)/(T3-T2) 

P1V1 P2V2

T1 T2= and

We know,

P1V1k=P2V2

k

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Therefore, from the above equations

we get:

T2/T1=(P2/P1)(k-1)/k =(P3/P4)(k-1)/k=T3/T4 

(Since Processes 1-2 and 3-4

are isentropic, and P2 = P3

 and P4 = P1.)

Substituting these equations into the thermal efficiency relation

and simplifying them

ηth,Brayton =1-1/rp(k-1)/k

Where r  p=P 2 /P 1,is known as Pressure Ratio. 

Theory Of Brayton Cycle:

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Effect Of Pressure Ratio On Brayton Cycle:

The efficiency of the BraytonCycle is a function of  pressure

ratio(r  p ) as given by the

following equation.

ηth,Brayton =1-1/rp(k-1)/k

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Effect Of Pressure Ratio on Brayton Cycle Efficiency:

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rp(rp)max

ηcarnot

η 

10

With the increase in pressureratio(rp) the efficiency also

increases and tends to reach

carnot efficiency(ηcarnot). 

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Effect Of Pressure Ratio On Net Work Output:

(Wnet)max

   W   n   e   t

(rp)opt

(rp)maxrp

10

With the increase in pressure ratiothe net work increases and reaches

a maximum value then reaches to

zero at maximum value of the

pressure ratio.

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The Brayton Cycle with Regeneration:In gas-turbine engines, the temperature of the exhaust gas leaving the turbine is often

considerably higher than the temperature of the air leaving the compressor. Therefore, the

high-pressure air leaving the compressor can be heated by transferring heat to it from the

hot exhaust gases in a counter-flow heat exchanger, which is also known as a regenerator or

recuperator.

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Types of Recuperator:

1.Vertical Recuperator 2.Horizontal Recuperator

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T-s diagram of a Brayton cycle with regeneration:

Here heat rejected from the process

the process 4-6 is used to increase

the inlet temperature from T2 to T5,in the process 2-5.

Effect of Regeneration on Brayton Cycle Efficiency:

•It increases the mean temperature of heat addition.

•It decreases the mean temperature of heat rejection.

•It increases the efficiency of the cycle.

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Intercooling in Brayton Cycle:

The efficiency of Brayton Cycle may often be increased by using staged

compression with Intercooling.

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The work output of the Brayton Cycle can be increased by using staged heat

supply called reheat.

Reheating on Brayton Cycle:

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Brayton Cycle with Intercooling, Reheating, and Regeneration: Regeneration may be used along with intercooling and reheating to increase the cycle

efficiency.

A gas turbine engine with two-stage compression intercooling, two-stage expansion with reheating, and gas-turbine regeneration

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T-s diagram of an ideal gas-turbine with intercooling, regenerationreheating, and regeneration:

Wreheat

Wintercool

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Use of Brayton Cycle:

It is used in gas power plants.

All gas turbine engines.

Air breathing jet engine.

If the number of compression and expansion stages is increased, the ideal gas-

turbine cycle with intercooling, reheating, and regeneration will approach the

Ericsson cycle and the thermal efficiency will approach the theoretical limit

(the Carnot efficiency). That is, the thermal efficiency almost doubles as aresult of regeneration, intercooling, and reheating.

Conclusion:

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References:

Engineering Thermodynamics, P.K.Nag

Wikipedia

Learnthermo.com

Oxfordjournals.org