Page 152 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

Also,

Heat supplied = h1-h4 = hfg at 42 bar = 1714 kJ/kg

Then,
W
 carnot = = . 0 419
Q

 W = 0.419 x 1714

i.e. W = 718.2 kJ/kg

To find the gross work of the expansion process it is necessary to calculate h2, using the

fact that s1 = s2.

From the tables,

h1 = 2801 kJ/kg and s1 = s2 = 6.070 kJ/kg K

From the equation

s2 = 6.070 = sf2 + x2sfg2 = 0.451 + x2 7.98

. 6 070 − . 0 451
 x2 = = . 0 704
. 7 98
Then,

h2 = hf2 + x2hfg2 = 130 + 0.704 x 2428

= 1839.3 kJ/kg

Hence, from equation 4.5,

W12 = (h1 – h2)

= (2801 – 1839.3)

= 961.7 kJ/kg

Therefore, using equation 4.10,

net work
Work ratio =
gross work

718 2 .
=
961 7 .

= 0.747

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