Étude d'un écoulement mixte air-eau vertical descendant : régimes, évolution de la concentration

Study of a vertical downward mixed water and air flow, Flow and concentration conditions

¹ Maître de Recherches au C.N.R.S.
² Docteur-Ingénieur, Ingénieur au Laboratoire d'Avala (Yougoslavie).

Résumé

The authors consider the emulsion formed by a jet impinging upon a free water surface in an upright cylindrical pipe. Starting out from set initial data, they observe three main types of two-phase flow : (1) flow without air entrainment (2) practically stable air entrainment and (3) air entrainment with unstable pockets. This paper comprises three basic parts, one for each stage to be covered in order to gain an overall view of the question : (i) General equations based on simplifying assumptions but nevertheless closely agreeing with experimental data ; (ii) Air entrainment by the jet, expressed by empirical formulae at this stage ; (iii) The general 'mechanism' of the emulsion, which was first investigated experimentally by recording air-in-water concentration profiles by the gamma-ray method and comparing them with Wallis and Zuber-Findlay diagrams. The first of these is adequate for flow without air entrainment, and the second, which is based on non-uniform velocity and concentration distributions, enables the results of measurements to be interpreted in the entrained air case and a simple relationship to be put forward between mean concentration and the rates of air and water flow.