Question

For two cycles coupled in series, the topping cycle has an efficiency of $30$% and the bottoming cycle has an efficiency of $20$%. The overall combined cycle efficiency is

• A. $38$%
• B. $44$%
• C. $55$%
• D. $50$%

Answer 1

The correct option is B $44$%

${\eta }_{overall}={\eta }_1+{\eta }_2-{\eta }_1{\eta }_2$
$0.3+0.2-0.3\times 0.2$
$0.5-0.06=0.44=44$%
Formula for overall thermal efficiency is calculated as,
Overall efficiency = $\frac{Workoutput}{Heatinput}$
$=\frac{{\eta }_{1}Q+{\eta }_2(1-{\eta }_2)Q}{Q}$
$={\eta }_1+{\eta }_2(1-{\eta }_2)$
$={\eta }_1+{\eta }_2-{\eta }_1{\eta }_2$
Diagram