Question

If $\Delta h_m$ and $\Delta h_f$ are the enthalpy drops across the moving and fixed blades of a turbine stage, then the degree of reaction is

• A. $\dfrac{\Delta h_m}{\Delta h_f}$
• B. $\dfrac{\Delta h_f}{\Delta h_m}$
• C. $\dfrac{\Delta h_m}{\Delta h_m + \Delta h_f}$
• D. $\dfrac{\Delta h_f}{\Delta h_m + \Delta h_f}$

Hint:

Degree of reaction $R$ always measures how much of the total energy conversion happens in the rotor blades.

Answer 1

The Correct Option is C

The degree of reaction $R$ of a turbine stage represents the fraction of total stage enthalpy drop occurring in the moving blades.
By definition:
\[ R = \frac{\text{Enthalpy drop in rotor}}{\text{Total enthalpy drop per stage}} \]
Here,
Rotor enthalpy drop $= \Delta h_m$
Fixed blade enthalpy drop $= \Delta h_f$
Total enthalpy drop $= \Delta h_m + \Delta h_f$
Thus:
\[ R = \frac{\Delta h_m}{\Delta h_m + \Delta h_f} \]
This matches Option (C).