A new formula for the rotational velocity of magnetically driven arcs

A new, more precise and simple semi-empirical formula has been obtained for the prediction of the rotational velocity of magnetically driven arcs in a ir and nitrogen. The formula is based on the balance between the motive Lor entz force and the aerodynamic drag force and takes into account changes in the gas density value due to the are rotation and the axial gas velocity. The formula enables the calculation of the are velocity in electric are hea ters as a function of current, magnetic field, axial gas velocity and gas d ensity. Experimental results are presented for arcs in air and nitrogen, fo r currents in the range 100-1760 A, magnetic induction values of 0.005-3.9 T and axial gas velocities of 0.2-33 m s(-1). The formula can be useful for the study of cold electrode erosion and engineering calculations of electr ic are heaters.