The Stirling engine principle of operation, design and configuration.
The Stirling engine is a heat engine in which the working body in the form of gas or liquid moving in a confined volume, a type of external combustion engine. Based on periodic heating and cooling of the working fluid for energy recovery arising from changes in the volume of the working fluid. Can work not only from fuel combustion but also from any source of heat.
The Stirling engine is a heat engine in which the working body in the form of gas or liquid moving in a confined volume, a type of external combustion engine.
Based on periodic heating and cooling of the working fluid with the extraction of energy arising from changes in the volume of the working fluid.
Can work not only from fuel combustion but also from any source of heat.
In the nineteenth century, engineers wanted to create a safe substitution of steam engines of the time, the boilers often exploded due to high pressure steam and unsuitable materials for their construction. A good option appeared with the creation of the Stirling engine, which could convert into work any temperature difference.
The Stirling engine was first patented by the Scottish clergyman Robert Stirling on September 27, 1816 (British patent No. 4081). However, the first basic “engines hot air” was known in the late seventeenth century, long before Stirling. Achievement of Stirling is the addition of a node, which he called “economy.” In modern scientific literature, the host is called a “regenerator”. It increases engine performance, keeping heat in the warm part of the engine, while the working fluid is cooled. This process greatly increases the efficiency of the system. Most often, the exchanger is a chamber filled wire, granules, corrugated foil (corrugations run along the direction of gas flow).
The basic principle of operation of the engine Stirling is constantly alternated heating and cooling the working fluid, e.g., gas in a closed cylinder.
It is known that when heating a gas its volume increases, and by cooling decreases. This property of gases is the basis of operation of the engine is Stirling.
The Stirling engine uses the Stirling cycle, which thermodynamic efficiency is inferior to the Carnot cycle, and even has the advantage. The fact that the Carnot cycle consists of little different between isotherms and adiabats. The practical implementation of this cycle is not very promising. The Stirling cycle has allowed to obtain workable engine to a reasonable size.
The Stirling cycle consists of four phases separated by two transition phases:
– the transition to the cold source,
– and the transition to the heat source.
Thus, the transition from the warm source to the cold source, the expansion and compression of gasin the cylinder. This changes the pressure, whereby it is possible to obtain useful work.
Heating and cooling of a working body (sections 4 and 2) produced by the propellant. Ideally, the amount of heat given to the selected propellant, the same. Useful work is produced only through isotherms, that is, depends on the temperature difference between heater and cooler, as in a Carnot cycle.
Working cycle engine Stirling beta-type (most common) as follows:
where: a — displacing piston; b — the working piston; with flywheel; d — fire (area heating); e — cooling fins (cooling area).
1. The external heat source heats the gas in the lower part of the heat exchange cylinder. Pressure pushing the working piston up (please note that displacing the piston tight against the wall).
2. Flywheel pressure pushes the piston down, thereby moving heated air from the lower part into the cooling chamber.
3. The air cools down and shrinks, the working piston goes down.
4. Displacing the piston rises, thereby moving the cooled air in the lower part. And the cycle repeats.
In the car Stirling movement of the working piston is shifted by 90° relative to the movement of the piston of the displacer. Depending on the sign of this shift, the machine can be an engine or a heat pump. Shear 0° machine not producing any work (except for friction losses) and does not produce it.
– “omnivorous” engine. Engine the Stirling can work from nearly any temperature difference: for example, between different water layers in the ocean, from the sun, from nuclear or isotope heater, coal or wood stoves,etc.
– simplicity of design — the engine design is very simple, it does not require additional systems such as a gas distribution mechanism. It runs independently and does not require a starter,
– long service life — simple design, the absence of many “soft” nodes allows the Stirling engine to provide unprecedented for the other engines performance margin in the tens and hundreds of thousands of hours of continuous operation
– efficiency — for recycling of certain types of thermal energy, especially at low temperature difference, the Stirling engines are frequently the most effective types of engines. For example, in the case of conversion to electricity of solar energy “Stirling” sometimes give greater efficiency (31,25 %) than heat engines,pair
– environmentally friendly — “Stirling” has no exhaust, so its level of noise is much less than that of reciprocating internal combustion engines. Beta rhombic Stirling mechanism is perfectly balanced device and, if a sufficiently high manufacturing quality, has a very low level of vibration (vibration amplitude is less 0,0038 mm). By itself, “Stirling” does not have any parts or processes that can contribute to environmental pollution. It does not consume the working fluid. Environmental friendliness of the engine is primarily due to the environmentally friendly heat source
– The efficiency of the Stirling engine is up to 45 %.
There are several configurations of the Stirling engine:
alpha Stirling contains two separate power piston in separate cylinders, one hot the other cold. The cylinder with the hot piston is located in the heat exchanger with a higher temperature, from cold to colder.
In this type of engine the power-to-volume is large enough, but, unfortunately, the high temperature of the “hot” piston creates certain technical difficulties. The regenerator is between the hot part of the connecting pipe and the cold,
– beta-Stirling — only one cylinder, hot at one end and cold on the other. Inside the cylinder moving the piston (which removes the power) and the displacer separates the hot and cold cavity.
Gas is pumped from the cold end to the hot cylinder through the regenerator. The regenerator may be external, as part of the heat exchanger, or can be combined with piston propellant,
gamma-Stirling — also has a piston and a displacer, but two cylinders — one cold (it moves the piston is removed from power), and a second hot at one end and cold on the other (it moves the displacer).
The regenerator may be external, in this case it connects the hot side of the second cylinder and cold at the same time with the first (cold) cylinder. The internal regenerator is part of the propellant.
The Stirling engine is useful in cases when you need a small Converter of thermal energy, easy on the device, or when the efficiency of other heat engines is lower, for example, if the temperature difference is not enough for a steam or gas turbine:
– universal power supply,
– heat pumps
– refrigeration appliances.
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