Ridgway Banks -1970s
Twenty Million Revolutions and Still Going Strong

I made a prototype engine in 1973 from loops of nitinol wire. The engine had two pans, one containing cold water, the other hot, and it worked from the start. It's now made over 20 million revolutions and still turns as briskly as ever, just as long as we maintain the temperature differential. This led to my first patent on a nitinol engine.

As the temperature differential between the heat source and the heat sink need only be 20°C, I can use geothermal hot springs, solar-heated water, or even Arctic Ocean water combined with ambient air as sources of energy. I was certain I could build practical, useful nitinol engines, particularly since the country was seriously thinking about energy and environment during the mid-1970s. My engine, after all, produced usable work from diffuse, low-grade heat—the most abundant source of energy on earth. It had few mechanical parts: The wire was boiler, expander and condenser all in one. It had neither valves nor seals, and the materials were cheap. Best of all, the engine was nonpolluting. I confidently predicted I'd have a commercial prototype within a year or two.

https://vimeo.com/45924783