Bond number

The Bond number (symbol: Bo) is a measure of fluid mechanics. They can be physically interpreted as the ratio of the volume of force acting on the liquid, the force due to surface tension.

Similar to the Reynolds number, the Bond number is suitable for comparison of systems, which differ in certain parameters such as density, size, or surface tension. In contrast to the Reynolds number, which is applied to flow, the bonding number characterizes static systems. A smaller value indicates that the system is determined by the surface tension. A large value means that the surface tension can be ignored for the estimation of the behavior.

Special case: Gravitation as a volume force

If the volume force given by the gravity, the Bond number is calculated as follows:

Where H describes the vertical height and R is the radius of the capillary pressure responsible for eg a drop. Both need not be identical so often two length scales in the Bond number received ( such as vertical capillary: filling height H, radius R). Further, the density and the acceleration of gravity.

For the special case of the lift, the bonding number is transferred into the Eötvös number.

Example: A drop

When a drop of liquid on a flat, horizontal surface, the Bond number allows a prediction of the form which it takes. In this case, the Bond number from the density, the acceleration of gravity, the characteristic radius and the surface tension provides:

The radius is maximum in this case twice the gravitational force, and is responsible for the capillary. If it is much smaller than 1, the gravity does not matter and the droplet is in a good approximation, a sphere section.

• Code ( Fluid Mechanics )