Measurement System of Bubbly Flow Using Ultrasonic Velocity Profile Monitor and Video Data Processing Unit, (III)

The authors have developed a new measurement system which consisted of an Ultrasonic Velocity Profile Monitor (UVP) and a Video Data Processing Unit (VDP) in order to clarify the two-dimensional flow characteristics in bubbly flows and to offer a data base to validate numerical codes for two-dimensional two-phase flow. In the present paper, the proposed measurement system is applied to fully developed bubbly cocurrent flows in a vertical rectangular channel. At first, both bubble and water velocity profiles and void fraction profiles in the channel were investigated statistically. In addition, the two-phase multiplier profile of turbulence intensity, which was defined as a ratio of the standard deviation of velocity fluctuation in a bubbly flow to that in a water single phase flow, were examined. Next, these flow characteristics were compared with those in bubbly countercurrent flows reported in our previous paper. Finally, concerning the drift flux model, the distribution parameter and drift velocity were obtained directly from both bubble and water velocity profiles and void fraction profiles, and their results were compared with those in bubbly countercurrent flows.     

Measurement System of Bubbly Flow Using Ultrasonic Velocity Profile Monitor and Video Data Processing Unit

The authors have been developing a measurement system for bubbly flow in order to clarify its multi-dimensional flow characteristics and to offer a data base to validate numerical codes for multi-dimensional two-phase flow. In this paper, the measurement system combining an ultrasonic velocity profile monitor with a video data processing unit is proposed, which can measure simultaneously velocity profiles in both gas and liquid phases, a void fraction profile for bubbly flow in a channel, and an average bubble diameter and void fraction. Furthermore, the proposed measurement system is applied to measure flow characteristics of a bubbly countercurrent flow in a vertical rectangular channel to verify its capability.     

New Interfacial Drag Force Model Including Effect of Bubble Wake, (II)

In the previous study, we proposed a new interfacial drag force model based on experimental data of steam-water bubbly flow in a large-diameter pipe. This is because our experimental results had suggested that effect of bubble wake should be included in the interfacial drag force model, although it had not been taken into account in the existing models. A preliminary method for including the effect of bubble wake was hence developed and used in the new model. A new bubble size prediction method was also adopted in the model. In the present study, after improving the measuring equipment and signal processing procedure, another series of experiments was carried out. Using the new experimental data, the methods of predicting bubble size and effect of bubble wake were slightly modified. To test the validity of the new model, predicted results were compared with available experimental data sets of steam-water bubbly two-phase flow in large-diameter pipes. One-dimensional and two-dimensional two-fluid models were used for the calculation. Comparisons showed that the new model is in good agreement with the experimental data, whereas the model which does not take into account the effect of bubble wake overestimated the void fractions.