Question 2.13: Compare the SSC, work ratio and thermal efficiency of the Ra...
Compare the SSC, work ratio and thermal efficiency of the Rankine and Carnot cycles operating between 100 bar and 0.3 bar.
In the case of the Rankine cycle, the compression work is 10 kJ/kg of water. Using some of the results from the turbine work in the Carnot calculation above:
SSC for Rankine is
1 × 3600/(836 – 10) = 4.891 kg/kWh
Carnot was 6.742 kg/kWh.
r_{W} for Rankine is
\frac{(836 – 10)}{836} = 98.8%
For Carnot it is 64%.
For thermal efficiency, the external heat added is required. For the Rankine cycle it is
h_{g100bar} – (h_{f,0.3bar} + 10) kJ/kg = 2725 – (289 + 10)
= 2426 kJ/kg
Therefore
\eta _{TH,Rankine} = \frac{(836 – 302)}{2426} = 22%
The comparison shows that Rankine is a significant improvement over Carnot for SSC and r_{W}, but that the thermal efficiency is significantly affected.