Does it make sense yet?
There are several things that make this hard to understand
even when you are looking at an engine. First, the piston assembly is made
of about eight tiny parts that don't look like a piston at all. It looks
more like a grey synthetic rubber diaphragm. Next, the canary yellow foam
that moves back and forth inside the cylinder looks like a piston but it
really isn't. The yellow foam "displaces" the air (moves it) between the
hot and cold sides of the engine. So the foam is called a displacer. The
foam is also warmed and cooled very quickly as the air flows through and
around it.
Why are Stirling engines so efficient?
When air flows from the bottom to the top of the engine
it must flow through and around the foam air filter material. Since the
air is a little bit hotter than the foam, thermal energy flows from the air into
the foam and is "saved" for the next part of the cycle.
This allows the air to cool much faster and means that
less thermal energy will be wasted into the room. As the cycle continues, the foam
moves through the air again giving the air back some of the thermal energy stored
in the foam. This means that less thermal energy has to be absorbed from the cup
of coffee to make the engine run.
Regeneration...
The process of saving some waste thermal energy from one cycle
so it can be used in the next cycle is called regeneration. In the Coffee
Cup engine the regenerator is a piece of yellow foam. In full power Stirling
engines regenerators are often made of stainless steel wool. Regeneration
is what makes the Stirling cycle the most efficient engine cycle in the
world.
If allowed, thermal energy naturally flows from a hotter object to a colder
one. For example, If you put your hand in a bucket of ice water thermal energy flows
from your hand into the water, and your hand feels cold. But if you put
your hand in a bucket of hot water, thermal energy flows from the water into your
hand and your hand feels warm. |