Studies of the Entrainmnt Behavior in Steady and Transient Two-Phase Annular Flow

摘要

Experimental and theoretical studies of the proportion of droplets in two-phase flow with high vapor content are discussed. This proportion of droplets is called the ''entrainment.'' It is first the influence of various hydrodynamic and thermodynamic parameters on the entrainment behavior of steady, heated two-phase flows which is studied, and for reasons of simpler and cost-saving experimental technique, the experiments are carried out with the model fluid R12 (CF sub 2 Cl sub 2 -difluorodichloromethane). It can be established that the flow vapor content and the total mass flux are the decisive influencing parameters on the entrainment mass flow in the vapor core of the flow. The system pressure and the heat transfer surface load are only of subordinate significance with respect to the quantity of entrainment. Finally, the experimental studies were expanded to transient flow, and in addition, the influence of the acceleration on the transient behavior and on the entrainment of droplets was studied. In addition to these measurements, based on the fundamental conservation theorems for mass, energy, and momentum, a theoretical calculation procedure for calculation of the proportion of entrainment in two-phase flow was developed. This equation system permits the determination of the entrainment mass flow both in steady and quite transient flow. The comparison between measurement and calculation gives satisfactory agreement. In the second section of the theoretical part, similarity laws relative to the entrainment behavior between the model and the original fluid were worked out, which permit a transfer of the model experiments to original conditions in practice. (ERA citation 04:008754)