All kind of Rankine or steam engines need a suitable fluid, that reacts to heating with an increase in pressure. The increased pressure of the fluid will be used to drive a piston, a turbine blade, lift a mass … and generate power. In this sense the fluid can be called “power fluid”. The following charts show graphs of the vapor pressure (bar) versus the temperatures (°C) for several fluids. The second chart uses a logarithmic vertical axis. The fluids are:
The solid red curve shows the pressure rise of normal air resulting from isochoric (constant volume) heating. Note: this is only a limited collection and not all of those fluid have been tested for a steam engine application.
1) The Idea: Diodes with control rods
The orientation of the diodes should only change between horizontal and upright orientation with a slope only to the right or only to the left side. So we connect the pivoted diodes b to the end of the spokes with radius r and control the swinging movement via a control rod connected bp to the other end of the diodes.
2) Configurations with 1,2 and 3 spokes and diodes up and down
3) Simulation: Method of virtual displacement
To calculate the driving torque i.e. the tangential force Fr (unkown) resulting from the gravitational force Fm (known) acting downwards on the diodes, we use the method of vitual displacement. Here we choose an numerical attempt: Find the displacement dM of the center of mass of the diode when the spokes are rotated about dAlpha. Energy conservation yields to:
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 …