Have you ever wondered what other methods exist besides the generator that we know and we have previously discussed. What were the “other “ ways of making an engine work? If so,then you are in luck, because on this blogs I will talk about two devices that are not so common, yet they will make an engine run or generate electricity by just taking the temperature difference. The first situation is related to the stirling engine; the second one refers to the Peltier device.
The Stirling engine was invented by Robert Stirling in 1816. This engine is very different from the internal combustion engine that occurs on a regular car[1]. This engine uses what is known as the Stirling cycle; this is how it work:
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Heat, from an external source, is added to the gas inside the heated cylinder, causing pressure to build. This pressure causes the piston to move down.
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The right piston moves up while the right piston moves down. This pushes the hot gas in the cooled cylinder, which quickly cools the gas to the temperature of the cooling source , lowering its pressure.
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The piston in the cooled cylinder starts to compress the gas. Heat generated by this compression is removed by the cooling source.
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The right piston moves up while the left piston moved down. This forces the gas into the heated cylinder, where it quickly heats up , building pressure and restarting the cycle.
You can see a dynamic representation of these steps below :
Stirling Engine Animation
Even though this type of engine seems to be really useful its dependency on an external heat source make it less efficient. Depending on an another heat source means that the engine will require some time to warm up before it can produce useful power [1]. It also means that the engine can not change its power quickly. [1] However, we can still find some uses for this type of engine such as [2]:
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Heats homes in The Netherlands with 50-75 hp engine.
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Provides basic power to remote African villages by burning wood (1-5 hp Van Arsdell-Howard University engine).
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Power oceanographic exploration submarine for Jacques Costeau, the Saga, so his team can quietly sneak up on the fishies and the whalies.
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Power the quietest military submarines in the world—a 1300 hp Stirling engine drives subs in the Swedish and Danish fleets (but not in the American fleet).
On the other hand, we have another very interesting device that is capable of taking the electricity as an input and convert it into two different temperatures. This device is known as the Peltier device (see picture below) and its based on the Peltier effect. This effect is the cooling of one junction (or side) and the heating of the other when electric current is maintained in a circuit of materials consisting of two dissimilar conductors; the effect is even stronger in circuits containing dissimilar semiconductors [3]. “A typical peltier heat pump device involves multiple junctions in series, through which a current is driven . Some of the junctions lose heat due to the Peltier effect, while others gain heat”[4].
Image 1: Real life Peltier Device
Image 2 : Inside structure and components of a Peltier Device
Today, Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. Among some different applications for thermoelectric cooling we have: Calorimetry, Infrared detectors, night vision equipments , Water and Beverage Coolers ,among others.[5]
After covering the basics for the stirling engine and the peltier devices; I believe it its fair to say that even though they are not as broadly used; they still play an important role in people’s lives.
References:
[1] http://auto.howstuffworks.com/stirling-engine.htm
[2] http://www.discoverthis.com/article-stirling-engine-top10.html
[3] http://www.britannica.com/EBchecked/topic/449424/Peltier-effect
[4] http://en.wikipedia.org/wiki/Peltier_effect#Peltier_effect
[5] https://www.ferrotec.com/technology/thermoelectric/thermalRef03