Degree of reaction – precise definition for a turbine stage Select the correct expression for the degree of reaction (R) of a turbine stage in terms of enthalpy drops.

Introduction / Context:
The degree of reaction quantifies how a stage divides its total enthalpy drop between rotor and stator. It informs blade design (e.g., Parsons 50% reaction) and affects efficiency, loading, and velocity triangles.

Given Data / Assumptions:

• Total stage enthalpy drop Δh_stage = Δh_stator + Δh_rotor.
• All drops are defined per unit mass of working fluid.
• Steady, adiabatic flow assumed for ideal definition.

Concept / Approach:
By definition, the degree of reaction R is the fraction of the stage enthalpy drop that occurs in the rotor (moving blades): R = Δh_rotor / Δh_stage. With Δh_stage = Δh_stator + Δh_rotor, the denominator is the sum of drops across both blade rows.

Step-by-Step Solution:
State formula: R = Δh_rotor / (Δh_stator + Δh_rotor).Match to options: “heat drop in moving blades to the heat drop in fixed blades plus heat drop in moving blades.”Therefore, option (c) is the correct definition.

Verification / Alternative check:
Special cases: R = 0 → pure impulse; R = 0.5 → Parsons reaction stage; 0 < R < 1 → mixed impulse-reaction behavior with pressure drop in both rows.

Why Other Options Are Wrong:

• (a) and (b) are ratios between blade-row drops, not normalized by the stage total.
• (d) is the reciprocal of the desired form.
• (e) omits the moving-blade drop and is not the standard definition.

Common Pitfalls:
Using energy (power) ratios instead of enthalpy-drop ratios; always use per-kg enthalpy drops for R.

Final Answer:
heat drop in moving blades to the heat drop in fixed blades plus heat drop in moving blades