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Heat Engines

Nitinol material is well-suited for constructing heat engines as it can efficiently convert heat into mechanical energy. Several inventors have created working nitinol heat engine designs, including the Thermobile engine which uses a nitinol wire loop placed on two rotating wheels to generate power from a temperature differential between hot water and cool air. Another example is using a nitinol wire loop to power the movement of a small toy boat, with a top ice compartment cooling one side of the wire and warm water below powering the other side and the boat's movement. General Motors is working on a prototype engine that would use shape memory alloys to capture heat from engine exhaust and transfer it to recharge vehicle batteries.

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537 views4 pages

Heat Engines

Nitinol material is well-suited for constructing heat engines as it can efficiently convert heat into mechanical energy. Several inventors have created working nitinol heat engine designs, including the Thermobile engine which uses a nitinol wire loop placed on two rotating wheels to generate power from a temperature differential between hot water and cool air. Another example is using a nitinol wire loop to power the movement of a small toy boat, with a top ice compartment cooling one side of the wire and warm water below powering the other side and the boat's movement. General Motors is working on a prototype engine that would use shape memory alloys to capture heat from engine exhaust and transfer it to recharge vehicle batteries.

Uploaded by

vinus87
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Heat Engines:

Nitinol material makes an excellent material to construct heat engines.

Ti-Ni made it easy to convert heat to mechanical energy where significant sources
of waste heat are available.
Over the years a number of experimenters and companies have created nitinol heat
engines. Several inventors produced working heat engines. A patent search on the
Internet using the key words nitinol and engine turned up several heat engine
designs.
 Thermobile:

The Thermobile, uses a loop of Nitinol wire to generate power.


The Nitinol loop is place on two free rotating wheels, this device uses only hot
water (hot side) and cool ambient air (cool side).
The smaller brass wheel of the Thermobile is immersed in a hot liquid.

In the Thermobile the Nitinol loop wire has been trained to remember a straight
shape. When the loop travels into the hot water it is brought above its transition
temperature and attempts to straighten out.

Thermobile
 At position 1 the Nitinol wire is relatively straight and cool.
 As the wire moves from position 1 to 2, it is bent around the small brass
wheel and enters the hot water.
 As the wire moves from position 2 to 3, the hot water brings the nitinol wire
above its transition temperature and it tries to straighten out.
 When attempting to straighten out the Nitinol wire takes a form depicted by
the dotted lines.
 In doing so, the wire generates a tugging force, F, along the loop. As the
wire segment moves from position 3 to 4 it straightens out. As the wire
travels from position 4 to position 1, through the air and around the large
wheel it has sufficient time to cool below its transition temperature and is
ready for another cycle.

In some cases it is necessary to jump start the engine by rotating the larger wheel.
Interestingly, the Thermobile hasn't a set rotational direction. Whichever way it is
started it will continue to rotate.
The Thermobile can also be solar powered; a magnifying lens focusing sunlight on
the brass wheel also supplies sufficient heat to power the engine.

The current uses:

Using of the loop of nitinol wire to power a small plastic boat.

The nitinol loop is place on two free rotating wheels; see approximate cross section
of Cool-Craft boat in the figure. The smaller bottom wheel has paddles that move
the boat when it rotates.

The boat is made with a small ice compartment on top. The top ice compartment
chills one side of the nitinol loop. The other side of the nitinol loop travels through
warm water where the toy boat is placed. The heat differential between the warm
water and ice is enough to activate the nitinol wire loop and power the craft.
 Working prototype engine using Shape Memory Alloys (SMA):

General Motors has been awarded $2.7 million by the Department of Energy to create a
working prototype engine using Shape Memory Alloys (SMA).

The idea is for the prototype to use SMA tech to capture heat energy from engine exhaust
gasses via an electric generator and transfer that energy to recharge batteries for hybrids or
electric vehicles.

"When you heat up a stretched SMA wire, it shrinks back to its pre-stretched length, and
when it cools back down it becomes less stiff and can revert to the original shape" said Jan
Aase, director of GM's Vehicle Development Research Laboratory. "A loop of this wire
could be used to drive an electric generator to charge a battery."
SMA tech can also theoretically power electronic devices like:

 Power seats.
 Windows in a standard.
 Gas- or diesel-powered car.
 Replacing the power-sapping alternator.

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