A dimensionless group used in analysis of fluid flow that characterizes the ratio of gravitational forces to surface or interfacial tension forces. It is usually denoted Nb in the oil field and Bo in chemical engineering. A value of Nb <<1 implies the flow in question is only weakly dependent on gravitational forces, whereas Nb >>1 implies gravitational forces dominate over interfacial forces.
Bond number equation:
Nb = Bo = (Δρ g b2) / σ,
Nb = Bo = Bond number
Δρ = density difference between the two phases
g = acceleration due to gravity
b = a characteristic length scale of the flow geometry
σ = surface or interfacial tension.