Abstract: | It is shown from dimensional arguments that the semi-empirical jet break-up formula of Hirsch(1) is consistent with physical models characterized by ideal plasticity (yield stress σ0), the material initial density (?0), strain rate (η0), and jet radius (r0). Similar arguments applied to a one-dimensional jet stretching model yields the existence of a maximum unstable perturbation wavelength, and fixes its value to within a numerical constant. Within the class of physical models considered the plastic velocity appearing in the Hirsch formula, the incremental velocity between successive fragments of a particulated jet, and the velocity (σ0/?0)1/2 are all related, as originally conjectured by Hirsch. |