What are the two main turbine stage types, and how do they differ?

• A. Impulse stages rely on phase change of steam to generate energy.
• B. Reaction stages convert energy by heating the gas to higher temperature.
• C. Impulse stages convert steam velocity into work via nozzles and blades; reaction stages derive work from pressure changes across blades and nozzles.
• D. There are multiple stage types beyond these two, but their energy transfer mechanism is the same.

Answer: (C)

Two main turbine stage types are impulse and reaction. In an impulse stage, steam expands mainly in stationary nozzles, gaining high velocity. The rotor blades then convert that jet’s momentum into shaft work by deflecting the steam, while the static pressure across the stage stays essentially constant. In a reaction stage, energy transfer comes from a pressure drop across blade rows; the blades are shaped to accelerate the flow as it passes through both stationary and moving blades, so the pressure decreases across the stage and part of the work comes from that pressure energy being converted to kinetic energy and then to mechanical work. In practice, turbines often combine both types along their length, but the core difference is whether energy transfer is dominated by nozzle-velocity (impulse) or by pressure changes across the blades (reaction).