Stirling Engine

Stirling engine is a simple, practical heat engine using a gas as working substance. Stirling engine contains a fixed amount of gas which is transferred back and forth between a “cold” and a “hot” end of a long cylinder. The “displacer piston” moves the gas between the two ends and the “power piston” changes the internal volume as the gas expands and contracts.

The gases used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and there are no explosions taking place. Because of this, Stirling engines are very quiet. The Stirling cycle uses an external heat source, which could be anything from gasoline to solar energy to the heat produced by decaying plants.

A Stirling engine uses the Stirling cycle,­ which is unlike the cycles used in internal-combustion engines.

• The gasses used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and there are no explosions taking place. Because of this, Stirling engines are very quiet.
• The Stirling cycle uses an external heat source, which could be anything from gasoline to solar energy to the heat produced by decaying plants. No combustion takes place inside the cylinders of the engine.

Stirling Engine Aplications:

• Stirling engines are used in some very specialized applications  where quiet operation is important like in submarines & auxiliary power generators

• Stirling Engines are extensively used in Solar Power Generation
• Stirling engines also works in reverse as a heat pump & find its’ applications as Stirling cryocoolers
• There is a potential for nuclear-powered Stirling engines in electric power generation plants
• Stirling engines are often used in automotive applications even though Stirling Engines have too low a power/weight ratio and too long a starting time.

Sources:

• http://auto.howstuffworks.com/stirling-engine.htm
• http://stirlingshop.com/html/applications_.html
• http://www.bekkoame.ne.jp/~khirata/academic/kiriki/begin/general.htm.

Peltier effect

The Peltier effect is a temperature difference created by applying a voltage between two electrodes connected to a sample of semiconductor material. This phenomenon can be useful when it is necessary to transfer heat from one medium to another on a small scale.

See the figure below:

In a Peltier-effect device, the electrodes are typically made of a metal with excellent electrical conductivity. The semiconductor material between the electrodes creates two junctions between dissimilar materials, which, in turn, creates a pair of thermocouplevoltage   is applied to the electrodes to force electrical  current   through the semiconductor, thermal energy flows in the direction of the charge   carriers.

Aopplication:

• Peltier-effect devices are extensively used in refrigeration applications.
• These kinds of devices are used in semiconductor technology
• Peltier-effect devices are used in Instrumentation to change skin temeperature raidly

Sources:

• http://www.huimao.com/about/show.php?lang=en&id=4
• http://www.eng.fsu.edu/~dommelen/quantum/style_a/semicte.html
• http://www.sciencedirect.com/science/article/pii/0361923084902272