closeboiling

Closeboiling is a term encountered in the study of boiling heat transfer to describe a regime in which a liquid is heated toward its boiling point and maintains a temperature near the saturation temperature during most of the process. In this regime the bulk liquid temperature stays close to the boiling point of the vapor phase, and vapor generation occurs with only a small amount of superheating. The exact definition of closeboiling can vary between sources, and it is not a universally standardized term.

The physical basis of closeboiling lies in achieving high heat flux while keeping conditions favorable for rapid bubble nucleation at or near the heated surface. Under these conditions, bubbles form readily and detach frequently, allowing substantial vapor production without large temperature rises in the liquid. Factors such as surface characteristics, pressure, fluid purity, and flow dynamics influence whether a system enters a closeboiling state. The result is a high rate of phase change with a relatively small temperature difference between the liquid and its saturation temperature.

Closeboiling is discussed in relation to other boiling regimes, such as subcooled boiling and saturated nucleate boiling. In some contexts it is considered a near-saturation state that emphasizes efficient heat transfer with minimal thermal lag. It is of interest in industrial applications where controlling temperature while maximizing vapor generation is desirable, such as in evaporators, distillation steps, and thermal management systems.

Practical considerations include the sensitivity of closeboiling behavior to pressure changes, impurities, and flow conditions, which can trigger transitions to other boiling regimes. Monitoring ΔT, pressure, and heat flux helps characterize and control the regime.