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.
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.