“Can a phase change between solid, liquid or gas solve the problem?”


Ice is often considerably colder than the beverage it is placed in but that’s not responsible for the majority of its cooling effect. There is “latent heat of melting”, the amount of heat that it needs to absorb to transition from solid phase to liquid phase. Not only does this mean that ice “stores cold” better, it means you can use less and dilute your drink less.


Cooks are advised to ensure steak is dry before frying, as the moisture interferes with the application of high heat.  In fact, as long as moisture is present, due to the latent heat of evaporation, the pan can’t get hotter than 100C until the moisture is boiled away.

Water expands when turned to steam, and the pressure generated can be used to perform work, such as in a steam engine locomotive.

Steam radiators also use the latent heat of condensation to transfer substantial amounts of heat from steam, returning water to the boiler for another cycle.

Refrigeration and heat pumps

Refrigerant will heat up considerably when compressed to a liquid. This hot liquid can be cooled in ambient air temperatures, and then returned to a gas which becomes very cold. This cold refrigerant is run through a heat exchanger which cools indoor air.

Heat pumps work in the opposite manner, gathering heat from the cold exterior and transferring into a warm interior.


A standard coffee maker works by boiling water so it expands. This expansion pushes liquid water up into the grounds. A check valve only permits water to move from the boiling chamber up into the filter, not back into the water reservoir.

A stove top espresso maker boils the water in the reservoir at the bottom. The pressure of the steam forces the hot water up through grounds.

Both systems rely on the expansion of water into steam to drive the brew process.

Sprinkler heads

Sprinkler heads typically use a small glass bulb to hold back the blow of water until the liquid in the bulb is boiled to a sufficient temperature and pressure to burst.

Automotive thermostats

Wax expands considerably when it melts. In a car thermostat this allows it to open a valve when the coolant in the radiator gets hot, permitting the flow of coolant to the engine.

Related to…

This principle is closely related to Inventive Principle 37 – Thermal Expansion. The distinction is that while phase transitions occur during heating (or cooling), thermal expansion can occur without a phase transition, e.g. a thermostat doesn’t need the dialectic strip to melt to work, just to warm up as a solid.

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?