MODELING OF STEADY-STATE 2-PHASE BUBBLY FLOW-THROUGH A SUDDEN ENLARGEMENT

A global formulation of the conservation laws (mass, momentum and ener gy) is applied to a two-phase, two-component flow through a sudden enl argement. The assumption of thermal equilibrium of the phases is accep table. However, due to the difference in the mechanical inertia of the phases, the kinematic non-equilibrium effect has to be taken into acc ount. In order to determine the role of mechanical non-equilibrium two assumptions are made, which can be considered as two limited cases. F irstly, an infinite momentum transfer coefficient (mechanical equilibr ium model) is assumed: an analytical solution can be obtained when the gas is ideal. Secondly, no momentum transfer can occur between phases (mechanical frozen model) : an approximate analytical solution is obt ained in this case. The comparison in terms of singular pressure varia tions between the results of these two models and the experimental dat a of other authors for air-water mixtures shows clearly that both mode ls indeed simulate two extreme conditions. New experimental data were obtained for two-phase air-water bubbly flow through an axisymmetric a nd horizontal sudden enlargement. A new physical model approximately t aking into account the effects of the interfacial drag of the bubbles is developed, and compared favourably with the data in the literature and the new data. This model shows a rather limited dependence with re spect to the reduced bubble diameter. (C) 1997 Elsevier Science Ltd.