Page 148 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

Then from equation 4.8

T − T
 carnot = 1 2
T 1

526 2 . − 299 7 .
=
526 2 .

= 0.432 or 43.2 %

Also,

Heat supplied = h1-h4 = hfg at 42 bar = 1698 kJ/kg
Then,

W
 carnot = = . 0 432
Q

 W = 0.432 x 1698
i.e. W = 734 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 Steam Tables,

h1 = 2800 kJ/kg and s1 = s2 = 6.049 kJ/kg K

From the equation

s2 = 6.049 = sf2 + x2sfg2 = 0.391 + x2 8.13

. 6 049 − . 0 391
 x2 = = . 0 696
. 8 13
Then,

h2 = hf2 + x2hfg2 = 112 + 0.696 x 2438

= 1808 kJ/kg

Hence, from equation 11.2,

W12 = (h1 – h2)

= (2800 – 1808)

= 992 kJ/kg

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