====== Nitinol Windmill ======

{{tag> heat_engine thermodynamics shape_memory_effect nitinol unlocated}}

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===== Description =====

A chassis connects two wheels of equal size. Around them is a loop of nitinol- a shape memory alloy- that has been 'trained' to straighten when heated up. The top wheel has a propeller attached. 

===== Purpose =====

Illustrate another example of the huge variety of heat engines. Demonstrate the action of a much simpler heat engine, and show what unites all heat engines: a heat differential.

===== Apparatus =====

  * Nitinol windmill
  * Cup of nearly boiling water

===== Setup =====

This works off a temperature gradient across the Nitinol wire, and boiling water (or close to, ~90ºC) is usually good enough for a room temperature environment. Submerge the bottom wheel into the boiling water (just enough to cover the wire) and give the blades a small flick to start it.  

===== Notes =====

The one with tape on its supporting beam doesn't work as well. There is also a cup near the windmills that has tearing to indicate the maximum filling line.

This simple engine works using a more complicated principle: the [[wp>Shape-memory_alloy|shape memory effect]]. When the wire is bent around a wheel and heated, it will exert a force attempting to straighten itself out. Once the wheel is given a spin, a temperature asymmetry will cause more force to be exerted on one side of the thermobile, so it continues to spin. 

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| **Location** | ---- |
| **Maker** | Unknown |
| **Current State** | Working |
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