“Can we harness or control thermal expansion to solve the problem?”


Older mechanical home thermostats control furnaces and air conditioners allowing a coiled bimetallic strip to expand in heat. This expansion causes the strip to uncoil and the bulb at the end holding mercury then makes a contact that sends a signal to the furnace or air conditioner.

Turn signal blinkers

Now replaced by electronic switchers, old turn signal blinkers relied on thermal expansion to operate. A bimetallic strip closed the circuit lighting the signal light. This flow of electricity heated the strip which caused it to expand more on one side than the other, disconnecting the circuit. This caused a cycle of cool-connect, heat-disconnect that created the characteristic blinking light.

Shrink fitting

Fit a tight joint together by cooling the inner part to contract, heating the outer part to expand, putting the joint together, and returning to equilibrium.

High pressure turbines

Jet engine’s turbine sections undergo tremendous centrifugal and heat stresses that tend to make the turbine blades expand. Ideally a turbine’s blades will come very close to the shroud they spin within, so that there is little loss of power due to bypass. However, if the blades expand too much, they can rub against the shroud and destroy the engine. To combat this, engines channel cool air into the flow of combustion air over the blades to control their temperature and ensure they remain at the correct length.

More examples

As I stumble across real world examples of this Inventive Principle in action I add them here.

Your turn

What problems do you face that this inventive principle could help solve? Have you used this principle before?