A Stirling engine is a heat engine A heat engine is a physical device that converts thermal energy to mechanical output. The mechanical output is called work, and the thermal energy input is called heat. Heat engines typically run on a specific thermodynamic cycle. Heat engines can be open to the atmospheric air or sealed and closed off to the outside operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat In physics and thermodynamics, heat is the process of energy transfer from one body or system to another due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body energy to mechanical work In physics, mechanical work is the amount of energy transferred by a force acting through a distance. Like energy, it is a scalar quantity, with SI units of joules. The term work was first coined in 1826 by the French mathematician Gaspard-Gustave Coriolis.[1] [2]
The engine resembles a steam engine in having all heat transfer flowing through the engine wall. This is traditionally designated an external combustion engine An external combustion engine is a heat engine where an (internal) working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable work. The fluid is then cooled, compressed and reused (closed cycle), or (less in contrast with an internal combustion engine The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine, such as the where the heat is put in by combustion of fuel Fuel is any material that can be used to generate energy to produce mechanical work in a controlled manner. The processes used to convert fuel into energy include chemical reactions, such as combustion, and nuclear reactions, such as nuclear fission or nuclear fusion. Fuels are also used in the cells of organisms in a process known as metabolism within the body of the working fluid. Unlike the steam engine's usage of water as the working fluid in both its liquid and gaseous phases, the Stirling engine encloses a fixed quantity of permanently gaseous fluid such as air or helium Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among the elements and it exists only as a gas except. Typical of heat engines, the general cycle consists of compressing cool gas, heating the gas, expanding the hot gas, and finally cooling the gas before repeating the cycle.
Originally conceived in 1816 as an industrial prime mover to rival the steam engine A steam engine is a heat engine that performs mechanical work using steam as its working fluid, its practical use was largely confined to low-power domestic applications for over a century.[3] The Stirling engine is noted for its high efficiency (up to 40%[4]), quiet operation, and the ease with which it can use almost any heat source. This compatibility with alternative and renewable energy sources has become increasingly significant as the price of conventional fuels rises, and also in light of concerns such as peak oil Peak oil is the point in time when the maximum rate of global petroleum extraction is reached, after which the rate of production enters terminal decline. This concept is based on the observed production rates of individual oil wells, and the combined production rate of a field of related oil wells. The aggregate production rate from an oil field and climate change Climate change is a change in the statistical distribution of weather over periods of time that range from decades to millions of years. It can be a change in the average weather or a change in the distribution of weather events around an average . Climate change may be limited to a specific region, or may occur across the whole Earth. This engine is currently exciting interest as the core component of micro combined heat and power In the majority of energy applications, energy is required in multiple forms. These energy forms typically include some combination of: heating, ventilation, and air conditioning, mechanical energy and electric power. Often, these additional forms of energy are produced by a heat engine, running on a source of high-temperature heat. A heat engine (CHP) units, in which it is more efficient and safer than a comparable steam engine.[5][6] Stirling engines (especially free-piston types) are also being considered by NASA The National Aeronautics and Space Administration is an Executive Branch agency of the United States government, responsible for the nation's civilian space program and aeronautics and aerospace research. Since February 2006 NASA's self-described mission statement is to "pioneer the future in space exploration, scientific discovery and for use in space exploration Space exploration is the use of astronomy and space technology to explore outer space. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft. While the observation of objects in space, known as astronomy, predates reliable recorded history, it was the development of large liquid-fueled rocket engines.[7]
Name and definition
Robert Stirling was the Scottish inventor of the first practical example of a closed cycle air engine in 1816, and it was suggested by Fleeming Jenkin Henry Charles Fleeming Jenkin was Professor of Engineering at the University of Edinburgh, remarkable for his versatility. Known to the world as the inventor of telpherage, he was an electrician and cable engineer, a lecturer, linguist, critic, actor, dramatist and artist. His descendants include the Tory MPs Patrick, Lord Jenkin of Roding and as early as 1884 that all such engines should therefore generically be called Stirling engines. This naming proposal found little favour, and the various types on the market continued to be known by the name of their individual designers or manufacturers, e.g. Rider's, Robinson's or Heinrici's (hot) air engine. In the 1940s, the Philips Koninklijke Philips Electronics N.V. , most commonly known as Philips, (Euronext: PHIA, NYSE: PHG) is a multinational Dutch electronics corporation company searched after a suitable name for its own version of the 'air engine', which by that time had already been tested with other gases, eventually settling on 'Stirling engine' in April 1945.[8] However, nearly thirty years later Graham Walker was still bemoaning the fact that such terms as 'hot air engine' continued to be used interchangeably with 'Stirling engine' which itself was applied widely and indiscriminately. The situation has now improved somewhat, at least in academic literature, and it is now generally accepted that 'Stirling engine' should refer exclusively to a closed-cycle regenerative heat engine A heat engine is a physical device that converts thermal energy to mechanical output. The mechanical output is called work, and the thermal energy input is called heat. Heat engines typically run on a specific thermodynamic cycle. Heat engines can be open to the atmospheric air or sealed and closed off to the outside with a permanently gaseous Gas is one of four classical states of matter. Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons are so energized that they leave their parent atoms working fluid A fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids, where closed-cycle is defined as a thermodynamic system In thermodynamics, a thermodynamic system, originally called a working substance, is defined as that part of the universe that is under consideration. Anything under consideration is called a system. A hypothetical boundary separates the system from the rest of the universe, which is referred to as the environment, surroundings, or reservoir. A in which the working fluid is permanently contained within the system and regenerative describes the use of a specific type of internal heat exchanger A heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural and thermal store, known as the regenerator. An engine working on the same principle but using a liquid rather than gaseous fluid existed in 1931 and was called the Malone heat engine.[9]
It follows from the closed cycle operation that the Stirling engine is an external combustion engine An external combustion engine is a heat engine where an (internal) working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable work. The fluid is then cooled, compressed and reused (closed cycle), or (less that isolates its working fluid from the energy input supplied by an external heat source. There are many possible implementations of the Stirling engine most of which fall into the category of reciprocating piston engine A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the.
Functional description
The engine is designed so that the working gas is generally compressed in the colder portion of the engine and expanded in the hotter portion resulting in a net conversion of heat into work In thermodynamics, work performed by a system is the quantity of energy transferred by the system to another that is accounted for in a particular way; namely, by changes in the external generalized mechanical constraints on the system.[10] An internal Regenerative heat exchanger increases the Stirling engine's thermal efficiency compared to simpler hot air engines lacking this feature.
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