15-11-2012, 11:28 AM
STERLING ENGINE
[attachment=39537]
What is Stirling Engine ?
A Stirling engine is a heatengine 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 energy to mechanical work Like the steam engine, the Stirling engine is traditionally classified as an external combustion engine, as all heat transfers to and from the working fluid take place through the engine wall. This contrasts with an internal combustion engine where heat input is by combustion of a fuel within the body of the working fluid.
Why is it named Sterling Engine ?
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 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-
1. Rider's air engine
2. Robinson's air engine
3. Heinrici's (hot) air engine
4. In 1940s, the Philips company named 'air engine‘
5. In April 1945, the Philips company again named 'Stirling engine' in April 1945.
Definition
"Stirling engine is an external combustion engine 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 Stirling engine is a mechanical device which operates on a closed regenerative thermodynamic cycle, with cyclic compression and expansion of the working fluid at different temperature levels."
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. An internal Regenerative heat exchanger increases the Stirling engine's thermal efficiency compared to simpler hot air engines lacking this feature.
Configurations
There are two major types of Stirling engines that are distinguished by the way they move the air between the hot and cold sides of the cylinder:
1. The two piston alpha type design has pistons in independent cylinders, and gas is driven between the hot and cold spaces.
2. The displacement type Stirling engines, known as beta and gamma types, use an insulated mechanical displacer to push the working gas between the hot and cold sides of the cylinder. The displacer is large enough to insulate the hot and cold sides of the cylinder thermally and to displace a large quantity of gas. It must have enough of a gap between the displacer and the cylinder wall to allow gas to flow around the displacer easily.
Types of Sterling Engine
A beta Stirling has a single power piston arranged within the same cylinder on the same shaft as a displacer piston. The displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas from the hot heat exchanger to the cold heat exchanger. When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston. When it is pushed to the cold end of the cylinder it contracts and the momentum of the machine, usually enhanced by a flywheel, pushes the power piston the other way to compress the gas. Unlike the alpha type, the beta type avoids the technical problems of hot moving seals.
How is Sterling Cycle Worked ?
1.Isothermal Expansion-The expansion-space and associated heat exchanger are maintained at a constant high temperature, and the gas undergoes near-isothermal expansion absorbing heat from the hot source.
2.Constant-Volume heat-removal. The gas is passed through the regenerator, where it cools transferring heat to the regenerator for use in the next cycle.
3.Isothermal Compression-The compression space and associated heat exchanger are maintained at a constant low temperature so the gas undergoes near-isothermal compression rejecting heat to the cold sink
4.Constant-Volume heat-addition. The gas passes back through the regenerator where it recovers much of the heat transferred in 2, heating up on its way to the expansion space.
Advantages
Stirling engines can run directly on any available heat source, not just one produced by combustion, so they can run on heat from solar, geothermal, biological, nuclear sources or waste heat from industrial processes.
Most types of Stirling engines have the bearing and seals on the cool side of the engine, and they require less lubricant and last longer than other reciprocating engine types.
A Stirling engine uses a single-phase working fluid which maintains an internal pressure close to the design pressure
In some cases, low operating pressure allows the use of lightweight cylinders.
They can be built to run quietly and without an air supply, for air-independent propulsion use in submarines.
They are extremely flexible. They can be used as CHP (combined heat and power) in the winter and as coolers in summer.
DisAdvantages
Size and cost issues
Cost for a high temperature heat exchanger accounts for 40% of the engine cost.
Ship propulsion and stationary Microgeneration systems using combined heat and power high power density is not required.
Power and torque issues
Heat exchanger surface for 1 kW output grows with second power of 1/delta-T, so specific cost of very low temperature difference engines is very high.
A Stirling engine cannot start instantly; it literally needs to "warm up".
Power output of a Stirling tends to be constant and to adjust it can sometimes require careful design and additional mechanisms.
Gas choice issues
The used gas should have a low heat capacity, so that a given amount of transferred heat leads to a large increase in pressure.
Other possible lighter-than-air gases include: methane, and ammonia.
[attachment=39537]
What is Stirling Engine ?
A Stirling engine is a heatengine 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 energy to mechanical work Like the steam engine, the Stirling engine is traditionally classified as an external combustion engine, as all heat transfers to and from the working fluid take place through the engine wall. This contrasts with an internal combustion engine where heat input is by combustion of a fuel within the body of the working fluid.
Why is it named Sterling Engine ?
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 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-
1. Rider's air engine
2. Robinson's air engine
3. Heinrici's (hot) air engine
4. In 1940s, the Philips company named 'air engine‘
5. In April 1945, the Philips company again named 'Stirling engine' in April 1945.
Definition
"Stirling engine is an external combustion engine 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 Stirling engine is a mechanical device which operates on a closed regenerative thermodynamic cycle, with cyclic compression and expansion of the working fluid at different temperature levels."
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. An internal Regenerative heat exchanger increases the Stirling engine's thermal efficiency compared to simpler hot air engines lacking this feature.
Configurations
There are two major types of Stirling engines that are distinguished by the way they move the air between the hot and cold sides of the cylinder:
1. The two piston alpha type design has pistons in independent cylinders, and gas is driven between the hot and cold spaces.
2. The displacement type Stirling engines, known as beta and gamma types, use an insulated mechanical displacer to push the working gas between the hot and cold sides of the cylinder. The displacer is large enough to insulate the hot and cold sides of the cylinder thermally and to displace a large quantity of gas. It must have enough of a gap between the displacer and the cylinder wall to allow gas to flow around the displacer easily.
Types of Sterling Engine
A beta Stirling has a single power piston arranged within the same cylinder on the same shaft as a displacer piston. The displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas from the hot heat exchanger to the cold heat exchanger. When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston. When it is pushed to the cold end of the cylinder it contracts and the momentum of the machine, usually enhanced by a flywheel, pushes the power piston the other way to compress the gas. Unlike the alpha type, the beta type avoids the technical problems of hot moving seals.
How is Sterling Cycle Worked ?
1.Isothermal Expansion-The expansion-space and associated heat exchanger are maintained at a constant high temperature, and the gas undergoes near-isothermal expansion absorbing heat from the hot source.
2.Constant-Volume heat-removal. The gas is passed through the regenerator, where it cools transferring heat to the regenerator for use in the next cycle.
3.Isothermal Compression-The compression space and associated heat exchanger are maintained at a constant low temperature so the gas undergoes near-isothermal compression rejecting heat to the cold sink
4.Constant-Volume heat-addition. The gas passes back through the regenerator where it recovers much of the heat transferred in 2, heating up on its way to the expansion space.
Advantages
Stirling engines can run directly on any available heat source, not just one produced by combustion, so they can run on heat from solar, geothermal, biological, nuclear sources or waste heat from industrial processes.
Most types of Stirling engines have the bearing and seals on the cool side of the engine, and they require less lubricant and last longer than other reciprocating engine types.
A Stirling engine uses a single-phase working fluid which maintains an internal pressure close to the design pressure
In some cases, low operating pressure allows the use of lightweight cylinders.
They can be built to run quietly and without an air supply, for air-independent propulsion use in submarines.
They are extremely flexible. They can be used as CHP (combined heat and power) in the winter and as coolers in summer.
DisAdvantages
Size and cost issues
Cost for a high temperature heat exchanger accounts for 40% of the engine cost.
Ship propulsion and stationary Microgeneration systems using combined heat and power high power density is not required.
Power and torque issues
Heat exchanger surface for 1 kW output grows with second power of 1/delta-T, so specific cost of very low temperature difference engines is very high.
A Stirling engine cannot start instantly; it literally needs to "warm up".
Power output of a Stirling tends to be constant and to adjust it can sometimes require careful design and additional mechanisms.
Gas choice issues
The used gas should have a low heat capacity, so that a given amount of transferred heat leads to a large increase in pressure.
Other possible lighter-than-air gases include: methane, and ammonia.