The flow contraction through sharp-edged short orifices respectively the narrowest flow cross-section or the vena contracta has been measured for water, air and air/water mixture. The results demonstrate that the contraction in the case of subcritical single-phase flow is restricted to values between 0.62 and one, while in the twophase flow it is limited to very narrow ranges of air mass flow qualities where the flow regime is specified as bubbly or spray.

The predictions of a new model for the contraction coefficient of single-and two-phase flows through a sharp-edged short orifice are checked against data recently obtained with water, air, and air/water mixture flows. The model includes all relevant primary design parameters. The predictions are validated for a wide range of conditions and physical properties typically encountered in industrial fluid-dynamic systems. Calculations based on the new model are sufficiently accurate for engineering purposes. Reasonable extrapolations to other test conditions with an acceptable accuracy can be expected.