An Ottoman engineer used a steam turbine to turn a roasting spit in 1551
Steam turbines generated about 42 percent of American electricity in 2022, yet the idea is ancient. Hero of Alexandria described a spinning steam toy in the first century, and in 1551 Taqi al-Din put steam to work rotating a spit. The practical machine arrived only in 1884, and it still powers much of the world.
Before it was an industry, the steam turbine was a curiosity. Hero's aeolipile, a spinning vessel pushed by escaping steam, was little more than a toy. Taqi al-Din in Ottoman Egypt and later John Wilkins in England described steam jacks for turning meat over a fire, Giovanni Branca sketched a turbine in 1629, and in 1672 the Jesuit Ferdinand Verbiest designed a small turbine-driven toy car. Charles Parsons built the first modern version in 1884; its initial dynamo produced a modest 7.5 kilowatts, but the design scaled up so readily that George Westinghouse licensed it and power station units soon reached 50,000 kilowatts.
Its efficiency comes from expanding steam gradually over many stages, bringing the process closer to the ideal reversible expansion. Designers use two kinds of blade rows. In impulse stages, fixed nozzles speed up the steam, and moving blades are pushed by its impact with little drop in pressure; Gustaf de Laval's simpler impulse turbine, and later versions by Auguste Rateau and the Brown-Curtis partnership, used this principle. In reaction stages, the moving blades are shaped as nozzles themselves, so they are driven both by the incoming steam and by the recoil of steam leaving them. By around 1905 engineers had learned to put impulse wheels at the high-pressure end followed by reaction stages, cutting leakage around the rotor.
Heat is the enemy. At high temperature and stress, blades slowly deform through creep. Modern blades are nickel superalloys strengthened with aluminium and titanium, sometimes with rhenium or ruthenium, and coated with zirconia-based ceramics to shield them from heat and oxidation. Other challenges include rotor imbalance, vibration, bearing wear and thermal shock.
Turbines range from units under 0.75 kilowatts driving pumps to giants for power grids; the largest yet, the Arabelle, is rated at 1,770 megawatts. Condensing turbines in power plants exhaust partly condensed steam into a vacuum-like condenser, while non-condensing ones pass steam on to refineries, paper mills or district heating. Whether the heat comes from coal, uranium, geothermal wells or concentrated sunlight, the spinning shaft is often the same kind of machine.
Source: Steam turbine
