Bejan number

English

Named after Adrian Bejan.

Bejan number (plural Bejan numbers)

(thermodynamics) A dimensionless number: the ratio of heat transfer irreversibility to total irreversibility due to heat transfer and fluid friction: $\mathrm {Be} ={\frac {{\dot {S}}'_{\mathrm {gen} ,\,\Delta T}}{{\dot {S}}'_{\mathrm {gen} ,\,\Delta T}+{\dot {S}}'_{\mathrm {gen} ,\,\Delta p}}}$ , where ${\dot {S}}'_{\mathrm {gen} ,\,\Delta T}$ is the entropy generation contributed by heat transfer and ${\dot {S}}'_{\mathrm {gen} ,\,\Delta p}$ is the entropy generation contributed by fluid friction.
(fluid dynamics) A dimensionless number: the pressure drop along the fluid path length in both external flows and internal flows: $\mathrm {Be_{L}} ={\frac {\Delta p\,L^{2}}{\mu \nu }}$ , where $\mu$ is the dynamic viscosity, $\nu$ is the momentum diffusivity (or Kinematic viscosity) and $L$ is fluid path length.