Assignment 5.1: The Stirling Heat Engine & The Peltier Device

The Stirling Heat engine was invented in 1816 by Robert Stirling. He was trying to create a better, more effective steam engine, which often exploded because of high steam pressure. In essence, the Stirling engine functions like other heat engines in that it converts heat energy into mechanical energy, but unlike other engines, the Stirling is closed cycle, meaning that it uses a fixed amount of air or whatever fluid it is using which never leaves the chamber, and it is heated from the outside. Because of this, the Stirling engine can run on any heat source: solar, wind, fossil fuel, chemical, etc. It can run on a very small difference in temperature, as low as 7 degrees Celsius, so it can even be powered by steam from a cup of coffee or body heat.

(How a Stirling Engine runs. Source: http://www.mpoweruk.com/images/sterling_engine.gif)

Peltier Devices run based on the Peltier Effect, discovered by Jean Peltier in 1834. The Peltier Effect is also sometimes called thermoelectric cooling, which occurs when an electric current goes through a thermocouple, a “junction of two dissimilar conductors” (Source B.). It was known that when this occurred, there was a heat current, Joule heating, but Peltier discovered in his experiments that his current was too hot to be just Joule heating. This process occurs when two conductors are in electric contact, causing electrons to flow from the more electron-bound conductor to the less electron-bound conductor. Then, the change in electrostatic potential caused by the moving of electrons causes a temperature gradient. The right materials have to be chosen, but a perfect Peltier device looks like the one pictured below:

(How a Peltier Device runs. Source: http://www.activecool.com/technotes/images/TEC_JC.jpg)

Both devices have serious modern benefits. Both are much quieter than their common alternatives, making them ideal for situations when silence is of the upmost importance. Peltier Devices are used in submarines, for example, when stealth is required for operations. Both devices are also more energy efficient and greener than others. The Peltier Device, unlike similar products, uses no CFCs, which are harmful to our atmosphere. The Stirling engine can run on solar power, the benefits of which have already been discussed in other posts on this blog. Both devices work to enhance naturally occurring scientific phenomena and create cleaner, safer, and more efficient energy and temperature changes.

Sources:

A. http://www.mpoweruk.com/stirling_engine.htm

B. http://www.activecool.com/technotes/thermoelectric.html

C. http://www.physics.rutgers.edu/ugrad/351/oldslides/Lecture11.pdf