Thermodynamics >
Entropy and the Second Law > Heat Cycles
DCS# 4F30.60
NITINOL ENGINE
(AKA THERMOBILE)
APPARATUS
thermobile
202-11-E1
beaker of hot water
(50-60°C is optimal)
101-01-C
tea pot
101-12-D
DESCRIPTION
The thermobile is a nitinol wire
(memory wire) loop around two wheels. Dip the edge of
the brass wheel in hot water and the wheels will turn.
If the wheel does not turn continuously, as may happen if the
water is too hot, remove the thermobile from the water and it
will spin until the brass cools.
When the brass wheel heats up,
the wire in contact with it is heated, and tries to straighten
out. When the wheel is spinning, the wire on one side of
the wheel is hotter than on the other and bows out more.
This results in an unbalanced torque on the wheel, causing it
to turn.
