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In a Rankine cycle, the maximum pressure of steam supplied is 6 bar the dryness fraction is 0.9 the exhaust pressure is 0.7 bar. Find the theoretical work done and rankine effieciency

Mumbai university > Mechanical Engineering > Sem 3 > Thermodynamics

Marks: 12M

Year: May 2016

1 Answer
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Pressure and condition of steam , at inlet to the turbine,

p1=6bar,x=0.9

Exhaust pressure, p2=0.7bar

From steam table at 6 bar: h1=hf1+xhgf1=670.38+0.9×2085.8=2547.6KJ/Kg,

s1=1.9308+.9×4.8785=6.32145 KJ/kgK

From steam table at 0.7 bar:

hf=377.04kJ/kg,hfg=2282.5kJ/kg,vf=0.001036m3kg

sf=1.1929kj/kgk,s_fg=6.2853 kj/kgk

Pump work:

work=(p4p3)vf=(6.7)×0.001036×105

=549.08 W

Turbine work:

s1=s2=sf2+x2sfg2

6.32145=1.1929+6.2853x

x=0.816

h2=hf2+x2hfg2=377.04+0.816×2282.5=2239.56KJ/Kg

Therefore turbine work:

=m(h1h2 )

=2547.6-2239.56

=308.04 kW

The rankine efficiency:

ηrankine=(h1h2)(h1hf2)

=308.042547.6377.04

=0.142

=14.2%

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