An Aeoli- What?!?
by Katie Crisalli
The purpose of my science project was to demonstrate an ancient experiment that resulted in the first steam engine.
So, just what is an aeolipile (ee-ah-luh-pile) anyway? It doesn't look like much, that's for sure. So steam shoots out of it and a little doohickey on top spins around. So what? That's what people thought when it was first invented almost two thousand years ago. However, the significance of the aeolipile, as meager as you might think it is from looking at this little machine, has actually been enormous. The modern steam turbine came into being during the Industrial Revolution, and went on to power most of the world's ships and power plants. Related to steam turbines are gas and water turbines. Gas turbines power jet aircraft, rocket turbo pumps, ships and stationary power plants, while water turbines produce much of our hydroelectric power. Without the turbine, today's jet airplanes, that many of us ride in so frequently, would never have been possible, and ships might still be at the point of sailing vessels. Turbines have shaped a large and important part of our world today, and it all started with this little machine.
Heron (or Hero), the man who invented the aeolipile around 75A.D., was from Alexandria. He was a Greek mathematician, engineer, and inventor, among other things. Heron was noted for his practical rather than his theoretical work, unlike many inventors of his day. He was knowledgeable on many subjects and wrote on the theory of hydraulic devices, simple machines, and center of gravity, surveying and its instruments. Heron also created the formula for the area of a triangle, which is sometimes attributed to Archimedes. The name aeolipile was derived from the Latin "aeoli pila," which means "ball (or cap) of the god Aeolus". Aeolus was the Greek god of the wind, and since the machine functions by shooting out pressurized steam, the name is an apt one.
By definition, the turbine is "a rotary machine which converts the kinetic energy of a steam of gas or liquid into mechanical energy." In general, there are two types of turbines. The first is an impulse turbine, which is driven by the force of a fluid striking it. The second form, a reaction turbine, is the same as the aeolipile. In this type of turbine, the nozzles are mounted on and, consequently, revolve with the rotor.
The aeolipile is a single-stage turbine, but later American and English designs were multiple stage ones, with several bladed rotors connected to a single shaft and each stage becoming progressively larger. Multiple stage turbines are made in this fashion to extract all the available energy from the steam, water, etc., which is driving it. A steam turbine is a rotary machine that converts the heat energy and pressure of steam into mechanical energy.
In a typical steam turbine, the steam strikes curved or angular blades connected to the main shaft, which causes the rotor to spin. Then the steam is directed outward and meets the stationary blades fastened to the shell of the turbine. These blades redirect the steam into the next set of spinning blades, and the process is repeated for the length of the turbine until all the steam's energy has been converted into mechanical motion.
Some examples of other turbines are windmills and pinwheels, which are fairly simplistic air turbines. Used to grind grain or pump water, windmills were the first type of useful turbines. However, they were slow and immobile.
The water wheel is an example of a water turbine. An example of a water turbine is an old and traditional German candlestick, with a decorative rotating figurine, powered by warm air rising from candles though a wooden turbine.
Actually, though, the aeolipile was considered little more than a toy for centuries. Its principles were unused until the Industrial Revolution in the nineteenth century. People began using steam to drive turbines. This made these mechanisms faster, more effective, and able to generate more power. In addition to this, these new steam turbines could be built small enough and powerful enough to propel themselves. By World War II, most of the ships in the world were powered by steam turbines.
Around the same timeframe, in 1940, a young aeronautical engineer in England named Sir Frank Whittle invented the first jet engine. This device was a very light-weight and incredibly powerful turbine. The jet engine, however, did not use steam. It was powered by burning hydrocarbon fuel and air.
Today, the main uses of steam turbines are in ships and power plants. Gas turbines have a few more uses. As well as being used in power plants and ships, gas turbines are widely used in jet aircraft and turbopumps for rocket engines.
It's amazing, isn't it? Sometimes the most brilliant inventions, the ones that often change the world, are also often ignored and dismissed for years, decades, or sometimes centuries! And then, when the technology is right, they are rediscovered and begin to change people's lives as the steam turbine did in the Industrial Revolution. And then everyone wonders "why we didn't think of that years ago?"
Principles
The aeolipile, both at the time it was originally built and when I reconstructed it, is designed based on a variety of scientific laws and principles. Perhaps most obvious of these is Newton's third law of motion. This law states that for every action there is an equal and opposite reaction. The aeolipile demonstrates this by ejecting steam under pressure from the nozzles, which causes the sphere, or turbine, to spin.
Another principle demonstrated was the conversion of energy by burning fuel to make water into steam. The aeolipile also demonstrates the relationship between temperature and pressure of a gas. Water is heated to generate steam, and the heated steam drives the turbine.
A fourth principle demonstrated was the principle of a force couple. This is the principle of two forces that act over a distance. Specifically, the perpendicular elbow fittings that guide the steam out of the machine create a couple and result in the rotation of the turbine. In this particular instance, the pivot points are holding the center of the turbine stationary while the steam is pushing on it in opposite directions, causing the sphere to spin.
Another aspect of this project which is not, in a technical sense, a principle, but is worth mentioning, is why I used the materials I did. For instance, I used the solder in this aeolipile because I knew it would join the various pieces easily and withstand the level of heat it was going to be subjected to. I used the brass for its durability and resiliency, and I used the copper for its malleability (especially when hammer-forming the boiler lid).
The last principle I used was not a part of the original aeolipile, but was an outgrowth of my science project, "Land Rockets," from last year. In that project, I built a rocket-powered go-cart and tested different types of nozzles to see which one would create the most thrust and, therefore, speed. I found that the DeLaval nozzle worked the best, and so, to make the aeolipile work more effectively, I added this type of nozzle to the steam escape apertures. The DeLaval nozzle works with a converging/diverging orifice, and so increases the gas velocity as the nozzle narrows. When it widens again, the gas accelerates even more and, therefore, the nozzle maximizes velocity.
1) The first thing I did was to gather the necessary materials. I purchased the copper floats used for the main boiler and the rotating sphere, as well as several assorted parts from a local plumbing shop (including elbow fittings, brass tubing, a copper pipe cap, etc.). With everything ready, the next task was to separate the larger copper float down the middle, since I only needed half of it for the boiler. It was soldered together in two halves, so I heated the solder with a torch and pulled the two halves apart. Then I cut a 4 1/2" circle out of sheet copper on the bandsaw, and hammer-formed a 1/2" strip around the edge to form a lip. This was done by hand on a steel mandrel mounted in the lathe.
2) After the lid had been formed, I drilled three holes in it - one for the pivot support arm, one for the steam supply pipe, and one for the waterfill port (I did this drilling first to avoid the pressure that would have been created if I had soldered the lid onto the boiler first). Then I soldered the half-sphere to the boiler lid.
3) The next part I created was the brass stand. I cut a 5" circle out of brass sheeting with the bandsaw, and then cut a 4" circle (just slightly smaller than the lip of the main boiler) out of the center of that with the lathe and a circle saw drill bit, leaving a 1/2" wide ring. Then I used the drill press to drill 3 small holes for screws at equal intervals around the ring. To form legs for the stand, I cut 1/4" hexagonal brass barstock into 4" pieces, made a few decorative cuts, and then drilled and threaded a hole in one end of each. Then I attached these legs to the stand using three small brass screws.
4) Then, I put the water fill port and cap into the third hole drilled in the lid (the water fill port was made from a fitting purchased at a plumbing shop) and soldered it in place. Above the boiler, two pipes support the spinner ball (or turbine). One pipe is only a pivot arm and the other brings steam from the boiler up into the turbine. The next step was to cut the required pipelines to the approximate length (approx. 3 1/4"). I used the lathe to make the little brass pivot piece, and cut some copper tubing on the bandsaw for the steam supply slip-fit.
5) Attached to the turbine on my aeolipile are a pair of elbow fittings which lead the steam out through the tiny DeLaval nozzles. These demonstrate the principle of couples - each elbow fitting forms a couple with the pivot or steam supply points. The principle is this: The steam flowing from the elbow fittings, which are perpendicular with the surface of the turbine, is pushing in opposite directions, while the pivot/steam supply points hold the center of the turbine stationary, and this causes the sphere to spin.
So the next step was to solder the elbow fittings onto the ball, and then machine the tiny DeLaval nozzles, which I soldered into the fittings by cutting tiny holes where they flared out slightly and pushing the solder through those holes where the hot metal melted it. Then I attached both pipes, including slip-fit and pivot piece, with the copper ball in the center. I used some blocks of wood and C-clamps to keep everything square but had some difficulty in keeping the pipes perfectly vertical while I soldered them, and from slipping down through the holes into the main boiler. To fix this problem I machined some little brass fittings out of 1/2" round barstock, designed to help keep the pipelines erect. (I later learned that this didn't keep them exactly squared because the hammer-formed lid wasn't perfectly flat, but it did keep them from falling into the boiler).
6) When the automaton was assembled, I found out it didn't work at all. This was due to the fact that the hole I had made in the turbine for the steam wasn't perfectly aligned with the pivot. Therefore, the pipelines were pressing against opposite sides of the ball and inhibiting free motion. (The turbine had to be able to spin at the slightest provocation because, with the size of the machine, there wasn't the capacity to create lots of pressure and, therefore, the sphere had to spin easily, without much exertion).
7) To fix this, I had to make the hole in the sphere where the steam came in slightly larger and off to one side so it would be centered with the pivot. This made the hole too large for the pipe, so I machined another brass adapter fitting that accommodated the different sizes on opposite ends. I pulled the pipes apart and squeezed the ball back on, and it (phew) was able to spin freely.
8) Testing! I lighted the alcohol pan under the aeolipile and, after awhile, steam shot out of the nozzles (a good sign - that meant that the solder hadn't blocked up any pipelines and that the slip-fit wasn't leaking). But there wasn't enough velocity to make the ball spin. I tried adding more heat by using a torch in addition to the alcohol flame. This generated much more steam and the turbine engine began to spin!!!
No matter how much turbines have changed over the centuries, it was fun and interesting to build a working model of the very first one, the aeolipile, and find out why and how it works. And no matter how many years go by and how much technology changes, it will always be fun to hold a pinwheel (another toy turbine) out of the car window.
Images of Making the Aeolipile
- Katie Cutting Boiler Lid
- Katie Drilling Boiler Lid
- Katie Forming the Boiler
- Katie Making the Aeolipile Legs
- Katie Assembling the Aeolipile
- Katie Soldering the Steam Elbows
- Successful Operation of the Aeolipile
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