Superheating

Superheating is the process by which a liquid is heated above its boiling point at a given pressure without undergoing vaporization. This creates a metastable state in which the liquid remains liquid despite being above the saturation temperature for that pressure. Boiling usually begins when nucleation sites—tiny bubbles or impurities—allow vapor to form, but their absence can suppress bubble formation.

The occurrence of superheating depends on several factors. Purity and surface quality matter: a very smooth, clean container with few nucleation sites can support superheating. Low agitation and uniform heating, such as in some microwave or rapid heat transfer situations, also promote it. Disturbances—such as stirring, adding a seed bubble, or shaking the container—can trigger rapid boiling once nucleation begins, sometimes violently.

Superheating carries safety implications. A liquid that has been superheated can boil explosively when disturbed, posing burn risks or splattering. In household and laboratory settings, this can occur with water in smooth containers or in microwave heating. In industrial contexts, careful control is used to avoid unintended superheating or to harness it in controlled ways.

In steam technology, the term is also used for steam that is heated beyond its saturation temperature at the operating pressure. Superheated steam is common in power generation and processing industries because it has higher thermal energy and lower moisture content, improving turbine efficiency and heat transfer. Generators and boilers use superheaters to produce steam at higher temperatures while maintaining system safety and control.