How does a steam engine convert heat into mechanical work?
The ingenuity people used in harnessing waterpower can be seen in this medieval-style mill. The waterwheel is turned by a stream and is connected to a shaft that leads into the building. At the other end of the shaft is a gear. The connection of a series of gears translates the power from the stream to a shaft that drives a millstone, which grinds flour from grain.
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A steam engine converts heat into mechanical work by utilizing the expansive power of steam, typically generated in a boiler.1
In a reciprocating steam engine, this process involves the following steps:
- Admission: Steam under pressure is admitted into a cylinder via a valve mechanism.1
- Expansion: As the steam expands, it exerts pressure against a piston, forcing it to move within the cylinder.21
- Work: The movement of the piston is transferred through a rod to a crank on a flywheel, converting the linear motion into rotary motion.1
- Exhaust/Condensation: To maximize efficiency, the steam is often exhausted or condensed in a separate condenser at a lower temperature and pressure, allowing the steam to fall through a wide temperature range.1
Alternatively, in a steam turbine, high-velocity steam is discharged through nozzles onto a series of moving blades, causing a rotor to spin at high speeds to generate power. This process is governed by the Rankine cycle, which describes the sequence of pressure and temperature changes required to transform thermal energy into mechanical work.13