an introduction to brayton cycle
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8/3/2019 An Introduction to Brayton Cycle
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AN INTRODUCTION TO
BRAYTON CYCLE
BENGAL COLLEGE OF ENGI NEERING AND
TECHNOLOGY
Submitted by: Sayantan Dutta(ME) Roll:87040387
By
Sayantan Dutta
Roll:87040387 Exam Roll:08125007051
Branch:Mech Engg.
8/3/2019 An Introduction to Brayton Cycle
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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