Small preassembled solar parabolic concentrator. The concentrator mirror is made of 24 Aluminium strips with a high reflective coating. Diameter of the total mirror is 35cm, power in the focal plane with direct sun ~50 W. The unit comes with a small black coated pot. A demonstration unit of big solar cookers.
The Flap Turbine (FT) is a novel type of vertical axis turbine (VAT) where the blades are made of movable flaps. These movable flaps, when combined together, act as a sail or blade for the VAT. This type of turbine is also known as a check valve turbine because of the check valve like behavior of the moving flaps. When the sail is moving in the downwind direction, the flaps are closed and will not allow air (water if the turbine operates in the water) to pass through the sail. However, when the sail is moving in the upwind direction the flaps will be in the open position and allow air (or water) pass through the sail.
The most crucial point to build a Minto wheel – see post Iske Wheel alias Minto Wheel is the working fluid. Adequate fluids that have a boiling point at atmospheric pressure below room temperature are toxic, flammable and not easy to handle. For this reason we started experiments with a ready made device that has a kind of structure like a Minto wheel’s spoke:
The famous “Drinking Bird”
We tried to use the birds as spokes for the wheel. By the way: you can order the bird in exergia’s new energy shop.
Until now we did not achieve a proper working wheel … experiments will be continiued. We would love to get some feedback.
May be you are interested in a kit for own experiments. Don’t hesitate to contact us.
The basic idee of the so called Minto wheel is to build a simple motor, that is driven by a temperature differential between a hot water reservoir and the surrounding cooling air. The spokes of a wheel like structure are made from tubes with a liquid inside, that exist both in a gaseous and a liquid phase in the desired temperature range. The are connected to bulb like reservoirs at both ends in a way, that the ends of the tubes protude into each reservoir a little bit. During operation the warmer gas inside the lower vessel has a higher pressure than the cooled gas in the upper vessel. This pressure pushes the liquid inside the tube and with it the center of mass of the wheel up. This results in a net torque that drives the wheel, brings the next spoke in contact with the hot water and the whole process continues. A cruical thing is to choose the right working fluid. Fluids like Methylen Chloride, Methanol, Butan, Propan, Hexane may work …
The original idea of Anthony and Albert Iske from 1881 has been reinvented or rediscovered – who knows – in the late 1940s by Wally Minto.
Idea: use a Drinking bird like device (“mechanical flow diode”) as spoke like structure of a wheel and build somethinmg similar like a Minto wheel.
Two main entropy sources could drive the process:
1.) Time fluctuating heating and cooling
Heat flows from hot water bassin at a fixed position at the bottom -
2.) Continuously heating and cooling
Water evaporation on one end of the flow diode.
1.) Time fluctuating heating and cooling
During the heating phase – the lower bird part is in contact with the hot water – the symmetrical inclinations of the birds axis towards the water surface normal vector, meaning more or less shifting the center of mass in compensating locations without resulting net torque. So one has to use this unsymmetrical configuration:
The bird does react very slowly, when the hot water is only in contact with the liquid phase of the working fluid. So you have to dip deeper into the hot water …
You need additional force to put the glass bulb under water … Possibly this may be solved by increasing the wheels momentum of inertiat … add additional masses.
Does not work properly … because of the thermal mass of the glass bulb there is a more or less continious heating and no real time fluctuation. Of coures amount of heating power changes during the period in the hot water and outside. But proper operation would need some tricky adjustment of the temperature and amount of fluid inside the bird … don’t know if this would be the right direction to continue …
Take care to include a mechanism to balance the center of mass of the main wheel and the spokes. Otherwise the resulting torque of displaced fluid mass inside the bird may be to small to drive the whole thing … Stef’s new idea – cut the end of the glass tubes with an oblique angle so the problematical phases of counteracting torque may be eliminated … ???
2.) water evaporation on one end of the flow diode – continuously heating and cooling
The above type will not work here. Because of permanent cooling (and heating) there are phases where the rise of the fluid will shift the center of mass to the up right or left side resulting in compensation a the resulting clock- and counterclockwise torques. So we need a new idea …
I have always been drawn to hobbies that spark my curiosity, problem solving, and creativity. For the past several years I have been designing and building small Stirling engines. I was challenged by an engineer to see if it would be possible to design a Stirling engine that would run from the heat of a hand, yet be something that could be built without a machine shop for under $30. I spent the next several years researching and experimenting with different designs. I had a lot of fun working out problems with friction and momentum while keeping things as simple and low tech as possible. The end result is what you see in the first book, “Three LTD (*) Engines You Can Build Without a Machine Shop”. (* Low Temperature Differential)
I threw out the idea of a conventional design and decided to re-think the LTD engine. My goal was to reduce friction and pressure leaks so that the engine would be able to run on a very low temperature differential. This was my approach:
I eliminated the friction of the displacer shaft by eliminating the shaft and using magnets to move the displacer.
This also eliminated the pressure leak caused by the displacer gland.
I added vents to the pressure chamber so I could occasionally vent the pressure, or even replace the working gas with helium when I wanted to.
I eliminated the need to lift the displacer by changing the orientation of the pressure chamber so that the displacer rocked back and forth, rather than being lifted.
I simplified the drive mechanism so that there were fewer moving parts. Fewer moving parts equates to less friction.
I created a horizontal flywheel that rides on a point, like a spinning top.
The end result, the first engine was a reciprocating engine that would run from the heat of my hand when the room temperature was below 70 F. I was able to measure a 10 degree temperature differential when running with air, and 8 or 9 degrees when I filled the motor with helium.
An unintended side effect from this design is the fact that this engine will adjust itself to accommodate for changes in temperature differential as it runs. Low temperature differentials cause a short swing of the drive mechanism to move the displacer. As the differential increases the magnetic drive allows the swing to increase. The magnetic drive works like a spring and stores and releases energy with each cycle.
The second engine was a modification of the same design, this time with the addition of a rotating flywheel. Adding the flywheel brings a more traditional look and feel to the engine. It also means that the travel of the magnetic drive is now in a fixed motion path and must be manually adjusted to match the operation conditions. I built in lots of adjustment points and this is fairly easy to do after you learn what to look for.
The third engine was designed in an effort to build a low temperature differential engine with as few moving parts as possible. The only moving parts on this engine are the displacer, the diaphragm, and the flywheel. It uses a magnetic drive so there is no pushrod for the displacer. This design uses a horizontal drive axle, which causes more friction than the vertical axle. As a result, this engine requires a higher temperature differential to operate, and will only run from the heat of my hand with the addition of a little ice on the cool side.”