Interfacial passage frequency for two-phase, gas-liquid flows in narrow rectangular ducts

Hydrodynamic and thermal transfer and relaxation phenomena in two-phase gas-liquid are strongly dependent on departure from equilibrium and the interfacial area density available for phase interactions. Such interactions include mass, momentum, and energy exchange for which the transfer coefficient must be known accurately as well as the area available for interactions to occur. The direct measurement of interaction interfacial area density is an exceedingly difficult task in view of today's knowledge. On the other hand, knowledge of the interfacial passage frequencies coupled with information regarding the flow structure would enable a model to predict the area densities reasonably well. Such information has been obtained using a sub-miniature, hot-film anemometer in air-water flows at velocities up to approximately 25 m/s. These data include bubbly slug, annular, and annular mist flows. The method is described, data are presented, and it is shown how certain conclusions regarding the flow structure can be drawn, particularly regarding the nature of roll waves in narrow ducts. (author)