I designed this Stirling engine (photos below) to be powered by my
Fresnel lens, basically using concentrated solar power. My Fresnel lens
doesn't focus very well so I needed a big cylinder to capture all the
concentrated sunlight. And since it's for outdoor use, I decided
to try air cooling by giving it a large top plate that acts as
a heat sink. I also wanted my Stirling engine to be sitting upright
so I could spray water onto the top plate so, as diagrammed below,
I reflected the sunlight from the Fresnel lens onto the Stirling
engine's cylinder using a mirror.
How the Stirling engine was made
Cooling the Stirling engine
In the photos below I'm running it inside using an alcohol lamp as
the heat source.
The problem with this is that the hot fumes flow up on the outside
of the top plate, heating it. This is a problem since a Stirling engine
needs heat at one end and cold at the other end. So I poured water
over the top plate and that made it rotate faster. You can see
happening in the first video below.
Top plate being heated by fumes.
Pouring water over the top plate for cooling.
Another method of cooling I tried was to make a fan out of cardboard
and have the fan blow air over the top plate (see photos below.)
Notice that the fan is powered by the Stirling engine. When used
indoors it allowed the Stirling engine to run for longer, since
the top plate was taking longer to heat up. In the photo on the
right you can see the airflow pushing on the tissue paper.
Cooling fan for Stirling engine.
Tissue paper showing airflow.
When it's outdoors, I sprayed water on the top plate but found it
wasn't really necessary (see photos below.) Even a light breeze
flowing over the top plate is enough to keep it cool.
Spraying water on the top plate.
Outdoor airflow over the top plate.
I ran it with the fan outdoors, but it wasn't needed. Instead it
was just a good test of the Stirling engine running with a load,
especially since the breeze was flowing in a direction that countered
the rotation. But as you can see in
the second video below
the fan turned quite well.
Cooling fan outdoors.
This video starts with an explanation of how this Stirling engine
works. Then it shows my first runs of this Stirling engine indoors as I
gradually made improvements and experimented with it.
This video explains how the Fresnel lens and mirror concentrate sunlight
onto the big cylinder of the Stirling engine and then shows it working.
It also shows a little about how the airflow cooling works.
Below are some photos of one Stirling engine made by someone in Germany
using the above one as a guide. It works very well.
The big metal plate that acts as structural support and as a heat sink
is made from a computer case. For the diaphragm casing he's using a
small, flat can-like plumbing part. It's 4cm in diameter and about 2cm
high. He simply wrapped the orange colored balloon around it.
The big cylinder is 8cm in diameter and 8cm tall. The displacer is
3cm high. That way it can move up and down 4cm.
Stirling engine running.
Heating the displacer chamber.
View while not running.
Diaphragm and displacer parts.
Crank shaft while running.
Crank shaft while still.