Q. 4.25 - An Introduction to Thermal Physics

Question

In a real turbine, the entropy of the steam will increase somewhat. How will this affect the percentages of liquid and gas at point $4$ in the cycle? How will the efficiency be affected? 

Step-by-Step Solution

Answer

The efficiency of the cycle is always less than the expected efficiency.

Step 1. Formula of efficiency

Efficiency of cycle is given by

$\text{e=1-}\frac{{\text{H}}_4{\text{-H}}_1}{{\text{H}}_3{\text{-H}}_1}$

Step 2. Explanation

• If the entropy of steam increases in the real turbine then there will be less water and more steam at point $4$ in the cycle. So, the value of ${\text{H}}_4$ will be much bigger which will affect the efficiency of the real turbine directly.
• As, the value of ${\text{H}}_4$ is larger, then the efficiency of real turbine will be smaller. Hence, the cycle will have smaller efficiency.

Step 3. Conclusion

As a large amount of heat and pressure losses involved in the cycle. 

Therefore, the efficiency of the cycle is always less than the expected efficiency.