A FIRST-ORDER RELAXATION MODEL FOR THE PREDICTION OF THE LOCAL INTERFACIAL AREA DENSITY IN 2-PHASE FLOWS

Many energy production and chemical processes involve vapor/liquid two -phase flows. Mass and energy are often exchanged between the vapor an d the liquid phases, and the fluid mechanics of the two-phase system i s strongly influenced by the exchange of momentum between each phase. Significantly, the transport of mass, energy and momentum between the phases takes place across interfaces. Therefore the interfacial area d ensity (i.e. the interfacial area per unit volume) has to be accuratel y known in order to make reliable predictions of the interfacial trans fers. Indeed, the interfacial area density must be known for both stea dy and transient two-phase flows. It is the purpose of this paper to p resent a first order relaxation model which is derived from the Boltzm ann transport equation, and which accurately describes the evolution o f interfacial area density for bubbly flows. In particular, the local, instantaneous interfacial area densities and volume fractions are pre dicted for vertical dow of a vapor/liquid bubbly how involving both bu bble clusters and individual bubbles. Copyright (C) 1996 Elsevier Scie nce Ltd.