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| A steam engine needs a boiler to boil ] to produce steam under pressure. Any ] source can be used, but the most common is a ] or ] ]. The steam is allowed to expand by pushing against a piston or turbine, whose motion is used to do work. | A steam engine needs a boiler to boil ] to produce steam under pressure. Any ] source can be used, but the most common is a ] or ] ]. The steam is allowed to expand by pushing against a piston or turbine, whose motion is used to do work. | ||
| The first steam device, the ''aeolipile'', was invented by ], a ], in the ] AD, but used only as a toy. | The first steam device, the , was invented by ], a ], in the ] AD, but used only as a toy. | ||
| ], a French physicist, built a working model of a steam engine after observing steam escaping from his ] in about ]. | ], a French physicist, built a working model of a steam engine after observing steam escaping from his ] in about ]. | ||
| Early industrial steam engines were designed by ] (]), ] (]), and ] (]), each of whom added new refinements. | Early industrial steam engines were designed by ] (]), ] (]), and ] (]), each of whom added new refinements. | ||
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| Early engines worked by the ] of condensing steam, whereas later types (such as ]s) used the power of expanding steam. | Early engines worked by the ] of condensing steam, whereas later types (such as ]s) used the power of expanding steam. | ||
| The first industrial applications of the vacuum engines were in the pumping of water from deep mineshafts. The first significant improvement was the replacement of manually operated valves with valves operated by the engine itself. Vacuum (condensing) engines are severely limited in their efficiency. but are relatively safe since the steam is at very low pressure and structural failure of the engine will be by inward collapse rather than an outward explosion.. | |||
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| ⚫ | High pressure steam engines are of various types but most are either ] or ] devices. | ||
| Most reciprocating engines use double acting pistons, with pressurized steam admitted alternately to each side while the other side is exhausted to the atmosphere or to a condenser. Power is removed by a sliding rod, sealed against the escape of steam. This rod in turn drives a connecting rod connected to a crank to convert the reciprocating motion to rotary motion. An additional crank or eccentric is used to drive the valve gear, usually through a reversing mechanism to allow reversal of the rotary motion. | |||
| Steam turbines for high power applications will use a number of rotating disks containing propeller-like blades at their outer edge. These "rotor" disks alternate with "stator" blade rings affixed to the turbine case that serve to redirect the steam flow for the next stage. Owing to the high speed of operation such turbines are usually connected to a reduction gear to drive another mechanism such as a ship's propellor. Steam turbines are more durable, smoother operating, and require far less maintenance than reciprocating engines. | |||
| ] demonstrated the first functional self-propelled steam vehicle, his "steam wagon", in ]. | ] demonstrated the first functional self-propelled steam vehicle, his "steam wagon", in ]. | ||
| Arguably, this was the first ]. While not generally successful as a transportation device, the self propelled steam tractor proved very useful as a self mobile power source to drive other farm machinery such as ] or ]. | |||
| Arguably, this was the first ]. | |||
| Steam engine powered automobiles continued to compete with other motive systems into the early decades of the ]. | Steam engine powered automobiles continued to compete with other motive systems into the early decades of the ]. | ||
| However steam engines are less favored for automobiles, which are generally powered by ]s, because steam requires at least thirty seconds (in a flash boiler) or so to develop pressure. | However steam engines are less favored for automobiles, which are generally powered by ]s, because steam requires at least thirty seconds (in a flash boiler) or so to develop pressure. | ||
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| On ], ] at the ] in ], the first self-propelled ] steam engine or steam locomotive built by ] was demonstrated. | On ], ] at the ] in ], the first self-propelled ] steam engine or steam locomotive built by ] was demonstrated. | ||
| The strength of the steam engine for modern purposes is in its ability to convert |
The strength of the steam engine for modern purposes is in its ability to convert heat from almost any source into mechanical work. Unlike the internal combustion engine, the steam engine is not particular about the source of heat. Most notably, without the use of a steam engine ] could not be harnessed for useful work, as a ] does not directly generate either mechanical work or electrical energy - the reactor itself simply heats water. It is the steam engine which converts the heat energy into useful work. Steam may also be produced without combustion of fuel, through solar concentrators. A demonstration power plant has been build using a central heat collecting tower and a large number of solar tracking mirrors, (alled ]). | ||
| A steam engine exhausting to atmosphere will have an efficiency (including the boiler) of 5% but with the addition of a ] the efficiency is greatly improved to 25% or better. | A steam engine exhausting to atmosphere will have an efficiency (including the boiler) of 5% but with the addition of a ] the efficiency is greatly improved to 25% or better. | ||
Revision as of 23:15, 2 August 2004
A steam engine is a heat engine that makes use of the potential energy that exists as pressure in steam, converting it to mechanical work. Steam engines were used in pumps, locomotive trains and steam ships, and were essential to the Industrial Revolution. They are still used for electrical power generation.
A steam engine needs a boiler to boil water to produce steam under pressure. Any heat source can be used, but the most common is a wood or coal fire. The steam is allowed to expand by pushing against a piston or turbine, whose motion is used to do work.
The first steam device, the , was invented by Heron of Alexandria, a Greek, in the 1st century AD, but used only as a toy. Denis Papin, a French physicist, built a working model of a steam engine after observing steam escaping from his pressure cooker in about 1679. Early industrial steam engines were designed by Thomas Savery (1698), Thomas Newcomen (1712), and James Watt (1769), each of whom added new refinements.
Early engines worked by the vacuum of condensing steam, whereas later types (such as steam locomotives) used the power of expanding steam.
The first industrial applications of the vacuum engines were in the pumping of water from deep mineshafts. The first significant improvement was the replacement of manually operated valves with valves operated by the engine itself. Vacuum (condensing) engines are severely limited in their efficiency. but are relatively safe since the steam is at very low pressure and structural failure of the engine will be by inward collapse rather than an outward explosion..
High pressure steam engines are of various types but most are either reciprocal piston or turbine devices.
Most reciprocating engines use double acting pistons, with pressurized steam admitted alternately to each side while the other side is exhausted to the atmosphere or to a condenser. Power is removed by a sliding rod, sealed against the escape of steam. This rod in turn drives a connecting rod connected to a crank to convert the reciprocating motion to rotary motion. An additional crank or eccentric is used to drive the valve gear, usually through a reversing mechanism to allow reversal of the rotary motion.
Steam turbines for high power applications will use a number of rotating disks containing propeller-like blades at their outer edge. These "rotor" disks alternate with "stator" blade rings affixed to the turbine case that serve to redirect the steam flow for the next stage. Owing to the high speed of operation such turbines are usually connected to a reduction gear to drive another mechanism such as a ship's propellor. Steam turbines are more durable, smoother operating, and require far less maintenance than reciprocating engines.
Nicolas-Joseph Cugnot demonstrated the first functional self-propelled steam vehicle, his "steam wagon", in 1769. Arguably, this was the first automobile. While not generally successful as a transportation device, the self propelled steam tractor proved very useful as a self mobile power source to drive other farm machinery such as grain threshers or hay bailers.
Steam engine powered automobiles continued to compete with other motive systems into the early decades of the 20th century. However steam engines are less favored for automobiles, which are generally powered by internal combustion engines, because steam requires at least thirty seconds (in a flash boiler) or so to develop pressure.
On February 21, 1804 at the Pen-y-Darren ironworks in Wales, the first self-propelled railway steam engine or steam locomotive built by Richard Trevithick was demonstrated.
The strength of the steam engine for modern purposes is in its ability to convert heat from almost any source into mechanical work. Unlike the internal combustion engine, the steam engine is not particular about the source of heat. Most notably, without the use of a steam engine nuclear energy could not be harnessed for useful work, as a nuclear reactor does not directly generate either mechanical work or electrical energy - the reactor itself simply heats water. It is the steam engine which converts the heat energy into useful work. Steam may also be produced without combustion of fuel, through solar concentrators. A demonstration power plant has been build using a central heat collecting tower and a large number of solar tracking mirrors, (alled heliostats).
A steam engine exhausting to atmosphere will have an efficiency (including the boiler) of 5% but with the addition of a condenser the efficiency is greatly improved to 25% or better. A power station with exhaust reheat, etc. will achieve 30% efficiency.
One source of inefficiency is that the condenser causes losses by being somewhat hotter than the outside world. Thus any closed-cycle engine will always be somewhat less efficient than any open-cycle engine, because of condenser losses.
See also
- Newcomen steam engine
- Watt steam engine
- Steam Locomotive for details of steam powered railway 'engines'
- Crosshead bearing