How does a steam turbine use the enthalpy drop of steam to produce work?

A steam turbine converts the enthalpy of steam into mechanical energy by allowing the steam to expand through a series of stationary and rotating passages. Enthalpy represents the sum of the steam's internal thermal energy and the product of its pressure and volume; as steam expands, this energy is released to perform work.1

The process of extracting this energy depends on the turbine's blading design:

• Impulse Blading: Steam expands in stationary nozzles, converting enthalpy into kinetic energy by increasing velocity. This high-velocity steam is then directed onto rotor blades, where the kinetic energy is extracted as the steam changes velocity, exerting a force on the blades.2
• Reaction Blading: The enthalpy drop is distributed between the stationary and rotating passages. As the steam expands through both, the resulting pressure drop and velocity changes exert a tangential force on the rotor, turning it.2

By maximizing the expansion of steam—often by condensing it at pressures well below atmospheric—turbines achieve a larger enthalpy drop, resulting in higher work output and greater efficiency.3