Hartmann number

The Hartmann number (Ha) is the ratio of electromagnetic force to the viscous force, first introduced by Julius Hartmann (1881 – 1951) of Denmark. It is frequently encountered in fluid flows through magnetic fields. It is defined by:


 * $$\mathrm{Ha} = B L\sqrt{\frac{\sigma} {\mu}}$$

where
 * B is the magnetic field intensity
 * L is the characteristic length scale
 * &sigma; is the electrical conductivity
 * &mu; is the dynamic viscosity