Air entrainment in vertical central jet dropshafts: complete working conditions and experimental control

In last decades, air entrainment by plunging liquid jets has been studied in international literature pointing out the various aspects of the phenomenon, in particular the involved variables and mechanisms. An accurate experimental observation and a deep theoretical analysis of air entrainment in dropshafts allowed the authors to propose, also on the ground of the existing theories, a complete innovative model, that represents the phenomenon even in working conditions of the dropshaft not previously taken into consideration. This model accepts, as input values, two characteristic experimental lengths of the plant (suitably made nondimensional ones) and returns, as output value, the ratio  between entrained air and falling water volumetric flow-rates. This model holds four experimentally obtainable parameters. The model has been tested and its parameters have been estimated by least squares method through a wide series of experimental tests (159) performed on a physical model on a big scale, organised in order to eliminate secondary effects due to viscosity and surface tension of the liquid, and also to the generally existing jet turbulence.