The Minto wheel is a

heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state ...

named after Wally Minto. The engine consists of a set of sealed chambers arranged in a circle, with each chamber connected to the chamber opposite it. One chamber in each connected pair is filled with a liquid with a low boiling point ( propane (''T_B'' = −42 °C) and R-12 (''T_B'' = −29.8 °C) are listed in the Mother Earth News articles). Ideally, the working fluid also has a high

vapor pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phas ...

and density.

Operation

As the lower chamber in each pair is heated, the liquid begins to vaporize, forcing the remaining liquid to travel to the upper chamber. This fluid transfer causes a weight imbalance, which causes the wheel to rotate. Minto's pamphlet also suggests obtaining a pressure differential with a dissolved gas instead of a boiling gas. Soda water or propane dissolved in kerosene are suggested.

Characteristics

The Minto wheel operates on a small temperature gradient, and produces a large amount of torque, but at very low rotational speed. The speed of rotation is directly proportional to the surface area of the containers used, the volume, and the height of the wheel. The higher the ratio of surface area to volume, the greater the rate of revolution.

History

Iske brothers and Israel L. Landis

In 1881, the Iske brothers got two patents granted for a design similar to the Minto wheel. According to the patent, the working fluid is alcohol "or other volatile liquid". Air in the tubes is to be removed and the tubes are sealed (creating a partial vacuum). The patent suggests lamps as heating sources.US243909 - 1881 patent for the device
/ref> The first patent describes glass for the bulbs and tubes. The second patent does not specify materials, but the construction implies metal. A later patent then clearly specify metal. File:US242454-0-colored.png File:US243909-Figure 1.png, Figure 1 File:US243909-Figure 3.png, Figure 3 Later the same year, Israel L. Landis got a patent for a similar engine. Different to the Minto wheel and the Iske brothers' patent, the engine was oscillating, not revolving.US250821
/ref> Landis suggested alcohol or ether as the volatile liquid. Landis suggested heating up the apparatus before removing the air from the bulb/chambers. File:US250821-Figure 1.png, Figure 1 In the following years, the Iske brothers were granted various patents, including some relating to modification and/or improvements on engines similarly to the Minto Wheel and an oscillating engine similarly to Israel L. Landis design. File:US253867-Figure 1.png, Figure 1 - motor which rotates File:US253867-Figure 4.png, Figure 4 - motor which oscillates File:US253868-Figure 1.png, Figure 1 File:US253868-Figure 2 and 3.png, Figure 2 and 3 File:US271639-0-colored.png, Figure 1 File:US271639-1-colored.png, Figure 2 and 3

Drinking bird

The oscillating types by the Iske Brothers and Landis are related to the

drinking bird Drinking birds, also known as insatiable birdies, dunking birds, drinky birds, water birds, dipping birds, and “Sippy Chickens” are toy heat engines that mimic the motions of a bird drinking from a water source. They are sometimes incorrectly ...

toy. The drinking bird is dating back to 1910s~1930s. The drinking bird was patented in the US in 1945 and 1946 by two different inventors. File:US2384168-0.png, Arthur M. Hillery, 1944 File:US2402463-0.png, Miles V. Sullivan, 1945

Wally Minto's contribution

Wally Minto experimented with different working fluids. With the working fluids he used, he got the required temperature difference down, enabling the engine - for example - to run on solar power.http://www.keelynet.com/minto/minto2.htm Based on the working fluid, his improved wheel is also known as "

Freon Freon ( ) is a registered trademark of the Chemours Company and generic descriptor for a number of halocarbon products. They are stable, nonflammable, low toxicity gases or liquids which have generally been used as refrigerants and as aerosol prope ...

Power Wheel". Popular Science reported about in its March 1976 issue.

Examples

A working example of a Minto wheel was first published in a series of articles in The ''

Mother Earth News ''Mother Earth News'' is a bi-monthly American magazine that has a circulation of 500,520 . It is published in Topeka, Kansas. Since its founding, ''Mother Earth News'' has promoted renewable energy, recycling, family farms, good agricultural ...

'', Issues #38 March, #39 May and #40 July 1976. Test units constructed by ''Mother Earth News'' (Issue 40, July 1976) and the MythBusters (Episode 24, December 5, 2004 – "Ming Dynasty Astronaut") did work to convert temperature difference into torque; however not as well as overenthusiastic boosters claimed.