Aeolipile, Hero's engine

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 Aeolipile, Hero's engine

As it can sound interesting, the Chinese Han Dynasty that prevailed around 200 BC is well known for developing rockets which were used for fireworks at that time. However, very early invention of the basic principle for a jet engine goes already back to the Hero of Alexandria (around AD 67). Hero of Alexandria was an Egyptian mathematician and inventor who had invented several machines utilizing water, air, and steam.

An illustration of Hero's aeolipile, source: Wiki

In Figure, you can see schematic illustration of Hero's aeolipile. The Aeolipile, also known as Hero's engine, is a simple, bladeless reaction steam turbine invented by Hero of Alexandria in the 1st century AD. This is considered as first device, based on reactive thrust principle way before Newton's laws, especially the third law of motion. 

The name aeolipile is derived from the Greek name Aeolus, the Greek god of the wind, and word pila, meaning ball. The name basically means "the ball of Aeolus".

This device consists of a metal boiler, a connecting pipe, and rotating sphere with two bended opposing nozzles. It spins due to jets of steam escaping from bent tubes, on similar principle to a jet engine, and it is considered the first recorded steam-powered device. It is simple device which can simply demonstrate the principle of reactive thrust as a basis of rocket propulsion. 

A Hero's engine, or Aeolipile, demonstrates the physics of energy transformation and Newton's third law of motion (action-reaction). When heat is applied, heat from the burner is transferred to the water, causing it to boil and turn into steam. The change in phase from liquid water to gaseous steam increases the internal pressure of the container. This thermal energy is then converted into the kinetic energy of the jet nozzles, as this pressurized steam then shoots out of bended jet nozzles, and for each jet nozzle of steam expelled in one direction (the action), a reaction force propels the device in the opposite direction, causing it to spin. 

The called basis is the action-reaction principle. Action means that the steam is forced out of the nozzles in one direction, and reaction is that the device experiences an equal and opposite force, pushing it in the reverse direction and creating torque. This torque causes the entire apparatus to rotate. 

And finally, momentum and thrust principle tells us that the steam jet nozzles carry momentum. The ejection of these jets generates a reaction force, or thrust, that propels the device, much like a rocket engine. 

Hero's engine, or aeolipile, does not have any real practical applications. It has rather historical and educational purpose to show device illustrating Newton's Third Lad and principles of propulsion, transforming thermal energy into mechanical motion. 

Many people studied the possibility whether the Hero's engine is able to do useful work. It was found that it could but very little. Check this link of Evan Lewis and his project on the topic: https://www.modelengineeringwebsite.com/Heros_engine_1.html That is really good article and I don't want to copy from there. 

Hero's engine has a very ineffective energy transfer, with theoretical efficiencies as low as 1% and practical efficiencies in models measured as low as 0.0128%, due to significant friction and air resistance. 

Main factors affecting efficiency:

1. Friction: Friction in the bearings of the rotating sphere is a major source of energy loss. 

2. Air Resistance: The resistance of the sphere and its arms moving through the air also decreases efficiency. 

3. Low Steam Pressure: Lower steam pressures limit the thrust generated by the escaping steam, as thrust is proportional to steam density and velocity. 

4. Lack of Inertia: The sphere has insufficient inertia, which would be needed for a smooth power output under varying loads, making it difficult to use for practical work. 

What I can say in the end? Even it was not used originally to do any work and it was rather party thing, still the legacy of Hero's engine endures. 

If you want to make your own Hero's engine, check this NASA link: Make an Aeolipile (Hero Engine).


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