摘要

In the past 25 years, significant developments in the two-phase flow formulation have been accomplished by the introduction of the drift flux model and the two-fluid model. In the present state of the art, the two-fluid model is the most detailed and accurate macroscopic formulation of the thermo-fluid dynamics of two-phase systems. In the two-fluid model, the field equations are expressed by the six conservation equations consisting of mass, momentum, and energy equations for each phase. Inasmuch as these field equations are obtained from an appropriate averaging of local instantenous balance equations, the phasic interaction term appears in each of the averaged balance equations. These terms represent the mass, momentum, and energy transfers through the interface between the phases. The existence of the interfacial transfer terms is one of the most important characteristics of the two-fluid model formulation. These terms determine the rate of phase changes and the degree of mechanical and thermal nonequilibrium between phases, thus they are the essential closure relations that should be modeled accurately. However, because of considerable difficulties in terms of measurements and modeling, reliable and accurate closure relations for the interfacial transfer terms are not fully developed.
A detailed mathematical analysis as well as physical insight indicate that the interfacial terms are proportional to the interfacial area concentration and driving force for that particular transfer. The interfacial area concentration is the available interfacial area per unit volume of a mixture, and, therefore represents the geometrical effects of the interfacial structure, whereas the driving force represents the physical force that induces that transfer. The interfacial area concentration is unique to two-phase flow and requires special attention. In view of its importance to two-fluid model, the interfacial area concentration has been studied intensively in the last 10 years. One of the most important aspects is the development of the measurement techniques of the local interfacial area concentration.
In what follows, the interfacial transfer terms, interfacial area concentration, and measurement methods for the local interfacial area concentration are reviewed in detail.