PASCO SE-8576A User manual

Instruction Sheet
012-06870B
Low Delta T Stirling Engine
SE-8576A
800-772-8700 [email protected] www.pasco.com
®
Introduction
The PASCO SE-8576A Low Delta T Stirling Engine is a
jewel-like engine. Because of its precision components and
careful construction, it can operate on temperature differ-
ences as small as four degrees celsius (4 °C).
For example, when the room temperature is 22.2 °C (72 °F)
or cooler, the heat from a warm hand is enough to power the
engine.
Stirling engines can be very efficient with some designs
attaining efficiencies up to 50% of the Carnot Cycle effi-
ciency. The Carnot Cycle determines the maximum theoreti-
cal efficiency of a heat engine according to the formula:
where the temperature is measured in absolute degrees
(kelvin (K) or rankine).
Operation
The Low Delta T Stirling Engine operates as follows:
The bottom plate of the engine along with the clear acrylic
cylinder, the top plate, and the graphite power piston make
up a sealed system. When the air inside this system changes
temperature, so does the pressure.
Inside the clear acrylic cylinder is a large white foam dis-
placer. This displacer looks like a piston, but it has a
3.125 mm (1/8” inch) gap around its outer edge. Air never
pushes on the displacer; it flows around the displacer.
The engine can begin working when either the bottom plate
or the top plate is heated or cooled to a temperature at least
4 °C warmer or cooler than the other plate. A gentle spin on
the flywheel is needed to start the engine.
As the foam displacer moves away from the warm side of the
engine, air flows around the edge of the displacer toward the
warm side and is heated. When the air is heated, it expands,
which increases the pressure inside the entire engine. This
increase in air pressure pushes up on the graphite power pis-
ton.
Next, the energy stored in the flywheel moves the displacer
closer to the warm side of the engine, and the air once again
flows around the edge of the displacer toward the cool side
of the engine.
When the air is cooled, it contracts, and the pressure drops
throughout the engine. The pressure inside the engine
becomes less than the pressure outside, and the graphite
power piston is pushed down. The displacer moves back
toward the cool side, the air is displaced toward the warm
side, and the cycle starts all over again.
The foam displacer only moves the air back and forth from
the warm side to the cool side of the engine. It does not do
any work on the crankshaft. In other words, the connecting
temp hot - temp cold
temp hot
--------------------------------------------------% efficiency=
Flywheel
Crankshaft
Graphite
power piston
Foam
displacer
Connecting
rod
Connecting
rod
IMPORTANT:
Do Not Oil

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Low Delta T Stirling Engine SE-8576A
2
rod to the displacer could be a string and the engine would
still work.
Usage
Place the Low Delta T Stirling Engine on the palm of your
ward hand with the label toward you. After the engine has
warmed up for a couple of minutes, gently spin the flywheel
in a clockwise direction to get it started.
NOTE: Hand temperatures vary widely. Not everyone has
warm enough hands to make this engine run. If your hands
are cool, find someone with warm hands to try this.
You can also run the engine in the opposite direction by plac-
ing the bottom plate on a cold object, letting it cool down,
and then gently spinning the flywheel in the counterclock-
wise direction.
Maintenance
• Dust is the number one enemy of this engine. Cover it
when it is not in use.
• It is a good idea to store it in a plastic case.
• Never oil the engine.
• Do not store the engine where it will be exposed to
bright sunlight or the colors will fade.
• Handle with care. The Low Delta T Stirling Engine is a
delicately balanced precision engine and it is very frag-
ile.
Troubleshooting
Generally there are three reasons why Stirling engines fail to
run: too much friction, air leaks, or inadequate thermal trans-
fer. The most likely reason for the Low Delta T Stirling
Engine to fail to run is inadequate thermal transfer.
If the engine will not run, try the following:
Put 2.5 cm (1 inch) of water in the bottom of a coffee mug.
Heat the water until the water is boiling vigorously. Care-
fully remove the mug from the heat source, and place the
engine on top of the mug. Wait for 15 seconds, and then gen-
tly spin the flywheel. Try spinning the flywheel in both
directions if it fails to start in a minute or so.
If the engine will not run when you try this test, it needs to be
returned for maintenance.
A Brief History of the Stirling Engine
The Reverend Robert Stirling, a minister of the Church of
Scotland, was troubled by some of the dangerous engines
that were used at the beginning of the industrial revolution.
Steam engines would often explode with tragic effects to
anyone unfortunate enough to be standing nearby. So in 1816
he invented and patented “A New Type of Air Engine with
Economizer”.
Robert Stirling realized that the engines he built would be
more efficient if some of the heat that was used to warm the
air for one cycle was saved and used again in the next cycle.
He called the device that saved the heat an “economizer”.
Today, this is usually called a “regenerator”, and is probably
Robert Stirling’s most important invention.
“Hot air engines”, as they were initially called, couldn’t
explode and often produced more power than the steam
engines of their day. The problem was that the only readily
available metal in the early 1800s was cast iron, which oxi-
dizes rapidly when left in a very hot flame.
Despite this difficulty, Stirling engines were widely used as
water pumping engines at the turn of the century. They
required little service, never exploded, were fairly quiet, and
the water provided a good cooling source for the cool side of
the engine. Thousands of these engines were sold
The Low Delta T Stirling Engine
.In 1983, Ivo Kolin, a professor at the University of Zagreb
(in what was then Yugoslavia) demonstrated the first Stirling
engine that would run on small temperature differences.
After he published his work, Dr. James Senft, a mathematics
professor at the University of Wisconsin - River Falls
(United States), built the first engines similar to the PASCO
Low Delta T Stirling Engine.
The Carnot Energy Cycle
In the mid 1800s, a Frenchman named Sadi Carnot figured
out the maximum limits of efficiency. His formula is an
accepted standard for determining the maximum possible
HEATING
EXPANSION
COOLING
CONTRACTION
REVOLUTION
COLD AIR
HOT AIR
Foam displacer
Graphite
power
piston
Operation of a displacer type Stirling Engine

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Low Delta T Stirling Engine SE-8576A
3
efficiency of an engine. No engine can exceed the Carnot
efficiency. (The second law of thermodynamics says you
can’t get out more than you put in; you can only break even.)
It takes good engineering and complex machines to achieve
a significant fraction of the Carnot efficiency. Real Stirling
engines can reach 50 percent of the maximum theoretical
value, which is a very high percentage.
Stirling Engines Today
The modern uses of Stirling engines are invisible to almost
everyone. There have been many research engines built in
recent years, but there are only three areas where Stirling
engines have made a dramatic impact. These are Stirling
engines in submarines, in cryocoolers, and in science class-
rooms.
Cryogenics is the science of things that are very cold, and
Stirling engines can be used to produce extremely cold tem-
peratures. It’s not obvious, but a Stirling engine is reversible.
If you warm one side and cool the other, you get mechanical
work out. However, if you mechanical work in, by connect-
ing an electric motor, for example, one side will get hot and
the other will get cold. In a correctly designed Stirling
engine, the cold side will get extremely cold. In fact, Stirling
engines used as cryocoolers have been made that will cool
below 10 kelvin (K). Micro-sized Stirling engines have been
produced in large numbers for cooling infrared chips down
to 80 K for use in night vision goggles and infrared cameras.
Since Stirling engines are so efficient, an obvious question
is: Why doesn’t my car have one?
Although a variety of prototype Stirling engine powered cars
have been developed, they have not gained popularity
because that have to warm up for 30 seconds to a minute
before they will move. Most consumers have not been will-
ing to wait that long to get started. The low gas prices of the
1980s and 1990s did not provide an economic incentive for
consumers to switch to Stirling engines, and automobile
companies have not had the incentive to research and
develop more saleable engine designs.
Stirling Engines in the Future
Future uses of Stirling engines could include applications in
the maritime and aviation industries. Stirling engines would
work exceptionally well for auxiliary power generators on
pleasure boats, where their silence and efficiency would be
value, and cooling water is plentiful. Some research has
already been done in this area: the French research subma-
rine “Saga” is Stirling engine powered. Stirling engines
would also work very well in airplanes where the air gets
cooler as the plane climbs to altitude. Stirling engines would
not lose as much power as they climb as conventional piston
engines or jet engines. Stirling engines would operate with
very low levels of vibration and noise.
Technical Support
For assistance with any PASCO product, contact PASCO at:
For more information about the Low Delta T Stirling Engine
and the latest revision of this Instruction Sheet, go to the
PASCO web site at www.pasco.com and enter SE-8576A in
the Search window.
Limited Warranty For a description of the product warranty, see
the PASCO catalog. Copyright The PASCO scientific
012-06870B Low Delta T Stirling Engine Instruction Sheet is copy-
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