Subkritischen

Subkritischen (subkritisch) is an adjective used in German to describe something that lies below a defined critical threshold in a given system. The term appears across disciplines such as physics, engineering, and chemistry, where criticality or critical points determine behavior, stability, or phase.

In nuclear engineering, a subcritical state is one in which the effective neutron multiplication factor k_eff is less than one, so a nuclear chain reaction cannot sustain itself without an external neutron source. Subcritical configurations are studied for safety and for certain reactor concepts, such as accelerator-driven systems (ADS), where an external driver maintains the reaction.

In fluid dynamics and hydraulic engineering, subkritische Strömung refers to open-channel flow with a Froude number Fr less than one. In this regime, disturbances can propagate upstream, and the flow is typically slower and deeper. This is contrasted with superkritische (Fr > 1) and critical (Fr ≈ 1) conditions, which have different wave and bed-roughness characteristics.

In chemistry and process engineering, subcritical conditions describe states below the substance’s critical point, such as subcritical water or subcritical drying. Subcritical water (below its critical temperature and pressure) serves as a solvent with altered polarity, while subcritical drying removes liquid without reaching the supercritical region, influencing material structure and porosity.

Etymology derives from sub- (under) and criticalis (critical). Related terms include kritisch, superkritisch (supercritical), and Kritikalität. See also subcritical fluids, criticality, and related engineering and scientific contexts.