Engines 1 Knkkkk

8/2/2019 Engines 1 Knkkkk

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Comparison of actual andtheoretical cycles

Presented by Batch 1

Akilesh Khanna(09A202)Anish Kumar.V(10A205)Jothi Raj.P(10A217)Kishore.H(10A220)Nandha Kumar.K(10A226)

Thiyagaprabhu.S.S(11A448)

23-03-2012 Department of automobile engineering 1


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BRAYTON CYCLE

Brayton cycle is a closed gas turbine cycle in whichthe compression and expansion processes remain thesame.

Comparing the power cycles combustion bis replacedby a constant-pressure heat-addition process from anexternal source

The exhaust process is replaced by a constant

pressure heat-rejection process to the ambient air.



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Open cycle gas turbineengine

Closed cycle gas turbineengine


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Efficiency


rp

pressure ratio=

K specific heat ratio.

Under the cold-air-standard assumptions, the thermalefficiency of an ideal Brayton cycle depends on thepressureratio of the gas turbine and the specific heatratio of the working fluid.


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Actual vs Ideal


where states 2a

and 4a

are the actual exitstates of the compressor and theturbine, respectively, and 2sand 4sare thecorresponding states for the isentropiccase


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The deviation of actual compressor and

turbine behaviour from the idealized

isentropic behaviour can be accurately

accounted for by utilizing the isentropic

efficiencies of the turbine and compressor as,



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RANKINE CYCLE

Rankine cycle is the ideal cycle for vapor powerplants.

The ideal Rankine cycle does not involve anyinternal irreversibilities

process:

1-2 Isentropic compression in a pump

2-3 Constant pressure heat addition in a boiler

3-4 Isentropic expansion in a turbine 4-1 Constant pressure heat rejection in a

condenser



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RANKINE CYCLE



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Efficiency



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Actual vs Ideal



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Actual vs Ideal

The actual vapor power cycle differs from the idealRankine cycle as a result of irreversibilities in variouscomponents.

Fluid friction and heat loss to the surroundings are the

two common sources of irreversibilities. Fluid friction causes pressure drops in the boiler, the

condenser. Steam leaves the boiler at a somewhat lower

pressure.

The pressure at the turbine inlet is somewhat lowerthan that at the boiler exit due to the pressure drop inthe connecting pipes.

So, larger work input must be given to the pump.



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Actual vs Ideal

A pump requires a greater work input, and a

turbine produces a smaller work output.

The deviation of actual pumps and turbines

from the isentropic ones can be accounted for

by utilizing isentropic efficiencies.



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THANK YOU


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