In an impulse turbine, energy transfer occurs primarily due to

• A. Kinetic energy conversion
• B. Steam expansion along the blade surface
• C. High pressure creating unbalanced forces
• D. Momentum change of steam hitting the blades

Answer: (D)

In an impulse turbine, energy transfer happens mainly through the momentum change of the steam as it hits and deflects off the blades. The nozzle first accelerates the steam to a high speed, converting part of the steam’s enthalpy into kinetic energy. When this high-velocity steam strikes the rotor blades and is redirected, it undergoes a large change in velocity (and thus momentum). That momentum change exerts an impulse on the blades, and this impulse is what transfers energy to the rotor, producing torque and power. Because the blades move much more slowly than the steam, most of the energy transfer comes from this momentum exchange rather than from pressure acting along the blade surfaces.