nearboiling

Nearboiling is the condition of a liquid heated to a temperature very close to its boiling point under the current pressure, in which vaporization is limited and discrete bubbles are few or not yet sustained. The exact temperature range depends on the liquid and the surrounding pressure; at standard atmospheric pressure, water’s boiling point is 100°C, so nearboiling would be temperatures in the high 90s Celsius where the liquid is hot but not vigorously boiling.

Boiling and nearboiling are distinct. Boiling involves rapid, sustained vaporization with rising bubbles and a turbulent surface. Nearboiling may show intermittent bubble formation and an essentially calm surface, approaching the onset of boiling. The term is informal and the transition to boiling can be abrupt if a disturbance or nucleation site is introduced. Nearboiling is also different from superheating, where a liquid is heated above its boiling point without actually boiling, often due to the absence of nucleation sites or rapid energy input.

Several factors influence nearboiling. Pressure is primary: higher pressure raises the boiling point, while lower pressure lowers it. Surface properties, impurities, and the presence of dissolved gases affect nucleation and bubble formation. Container geometry and agitation can either suppress or trigger bubble development as temperature rises.

In practice, nearboiling has implications for heat transfer, cooking, and chemical processing. It can be desirable when gentle heating is needed without vigorous vaporization, but it also carries the risk that a small disturbance will trigger sudden boiling. The term remains informal; specifying the temperature and pressure is preferred for precision.