The Stirling Heat Engine was invented by Robert Stirling in 1816.  The Stirling Engine was gained a lot of popularity because it was much safer than the steam engine and had endless applications.  This engine is very basic and has the potential for very high efficiency when compared to the internal combustion engine.  These engines are also known for being very quiet.  Today, this engine is still used but in few modern day applications where a quiet engine is important.  For example, they are often used for powering submarines and yachts.

The Stirling engine uses a Stirling cycle to generate power, a unique approach that is different from other engines.  These engines uses external sources of heat to create power.  The interesting thing about these engines is that the heat source can by any resource that provides enough heat to change the temperatures of the gases contained in the cylinders, meaning gas could be used to power the engine or even sun light.   There are four components to the Stirling cycle.  First, heat is used to changes the pressure in the ‘heated’ cylinder.  When the pressure gets high enough this forces the piston down.  Second, the left piston, located in the ‘cooled’ cylinder, moves up while the right piston moves down, pushing the hot gas into the cooled cylinder cooling the hot gas and ultimately lower the pressure back down.  Third, the piston in the cooled cylinder compresses the gas.  The right piston moves up with the left moves down.  This forces the gas into the heated cylinder where it quickly heats up and and builds pressure and the cycle is repeated.    The gases contained in the engine never leave and this engine does not have exhaust valves.  Since the Stirling Heat Engine is very quiet, can run on almost any heat source, and is very efficient innovators are attempting to re-apply this engine to the modern world where efficiency is becoming an important topic.

How the Stirling Heat Engine Works

The Peltier Device can be used for either heating and cooling applications and is classified as a thermoelectric generator.  This device was invented through two important discoveries.  In 1821, a scientist named J. T. Seebeck discovered that dissimilar metals that are connected at two different locations, known as junctions, will generate a small voltage if the two junctions are held at two different temperatures.  This set up is called a thermocouple and the greater the difference in temperatures the greater the charge that is generated.  This is known as the ‘Seebeck Effect’.  About a decade later, another scientist, Peltier, discovered the inverse of the Seebeck effect and called it the ‘Peltier Effect’.  Peltier discovered that if you put a voltage across a thermocouple it will cause a temperature difference at each of the junctions.  Peltier’s discovery allowed for the development of small heating and cooling systems.  This device is often found in water coolers and air conditioning units.Home Video Experiment: Peltier Device