Page 155 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

Turbine:

The expansion is adiabatic (i.e. Q = 0), and isentropic (i.e. s1 = s2 ), and h2 can be

calculated using this latter fact. Then

h1 + Q12 = h2 + W12
W12 = ( h1 – h2) (4.14)

Condenser:

h2 + Q23 = h3 + W23

Therefore, since W = 0

Q23 = h3 – h2

i.e. Q23 = - ( h2 – h3 )

 Heat rejected in condenser = h2 – h3 (4.15)

Pump:

h3 + Q34 = h4 + W34
The compression is isentropic ( i.e. s3 = s4 ), and adiabatic ( i.e. Q = 0 ).

 W34 = ( h3 – h4 ) = -( h4 – h3 )

i.e. Work input to pump = ( h4 – h3 ) (4.16)

This is the feed pump term, and as the quantity is small as compared to the

turbine work, W12. The feed pump is usually neglected, especially when the

boiler pressures are low.

The net work done in the cycle, W = W12 + W34
i.e. W = ( h1 – h2) – ( h4 – h3 ) (4.17)

Or, if the feed pump work is neglected,
W = ( h1 – h2 ) (4.18)

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