Bejan number

Named after Adrian Bejan.

Bejan number (plural Bejan numbers)

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

• Bejan number on Wikipedia.Wikipedia