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Published on Mar 16, 2011
This Shape Memory Metal (Nitinol) engine is driven by hot water!
You may recall the famous Thermobile, created in 1985 by Frederick Wang. The Heatmobile is a similar design, although offered as a simple self-assembly kit. It is essentially a heat engine that demonstrates the conversion of heat into mechanical energy. It uses the unique property of Nitinol alloy called the "memory effect". Once Nitinol has been formed into shape at high temperature (about 600º C) and allowed to cool to room temperature, it can be easily deformed. However, when heated above a transition temperature (in this case about 70ºC to 80º C) the Nitinol object abruptly returns to its high-temperature shape with substantially more force than that required to deform it when cold.
Heatmobile uses a Nitinol wire formed into a closed loop that drives the two connected wheels. However the high temperature shape of the wire is straight. So when the bottom part of the wire loop is heated by the water, it tries to deform into a straight shape. This action provides a torque at the bottom wheel, and causes it to rotate. As the wire goes up around the top wheel, it is cooled by the air.