Bejan number

A dimensionless number: the ratio of heat transfer irreversibility to total irreversibility due to heat transfer and fluid friction: Be=(̇S'_(gen,,ΔT))/(̇S'_(gen,,ΔT)+̇S'_(gen,,Δp)), where ̇S'_(gen,,ΔT) is the entropy generation contributed by heat transfer and ̇S'_(gen,,Δp) is the entropy generation contributed by fluid friction.

A dimensionless number: the pressure drop along the fluid path length in both external flows and internal flows: Be_L=(Δp,L²)/(μν), where μ is the dynamic viscosity, ν is the momentum diffusivity (or Kinematic viscosity) and L is fluid path length.