It is well known that the friction or the drag of the turbulent flow is reduced by adding certain additives into liquids or gas. This phenomenon is called drag reduction, and the industrial application of the phenomenon connects directly with economizing energy in the hydraulic transport process. The effect of polymers has attracted the attention of many researchers, and there are many experimental and theoretical studies about it. However, there are very few experimental studies of drag reduction in two phase flows. It is very important to understand drag reduction clearly, because it is a subject of wide interest from the points of view of studying the turbulent structure of the flow in the fluid mechanics field. In this review, some experimental results on drag reduction in two phase flows are showed, and subjects for future study on drag reduction in liquid-solid two phase flows are described.
Turbo-pumps have recently been utilized in various industrial fields for reasons of high efficiency and easy maintenance, in place of positive displacement pumps. A pump head degradation due to a two-phase flow comes up as an important engineering problem with the diversification of applications and operating fluids. The objectives of this paper, consisting of this report and the other, are first to review the past research on gas-liquid two-phase flow pump performance, secondly to discuss two-phase flow dynamics in the rotating flow passages and to describe a conceptual view and the present situation for designing two-phase flow pumps. In this report, the transition of two-phase flow problems in pumps are briefly reviewed and the head degradations, associated with various gas phase behaviors in a centrifugal pump, are illustrated to deepen the reader's understanding. Then, the existing methods based on some analytical models for predicting pump performance are described.
In this study, image processing techniques were used to observe the movement of air containing asbestos-like fibrous materials which acted as tracers for visualization. Because of the varying shapes of the fibers, the shapes of the path-lines visualized were normalized by an image processing technique. Two-dimensional diagrams of velocity vectors were obtained using the path-lines. A blind alley zone model with an outlet and an inlet on the same wall was selected as the experimental model for both discharge and circulation. The flow patterns in the model of air containing fibrous materials were examined experimentally. Then the influences of both height and length of the model zone and the size of the inlet on the flow patterns were examined. The dimensions of the model zone in which the materials were unable to stay were obtained from the results.
The mass of gas and that of liquid are conserved in a gas-liquid two-phase flow. In addition, their sum and difference are also conserved quantities. When we conduct a numerical analysis of the two-phase flow, we must select two masses from the aforementioned four conserved masses. Hence six different combinations are available for analysis. These six combinations are mathematically identical in the form of partial differential equations. However, each of them may have different numerical characteristics in the form of finite difference equations. In the present study, this difference was clarified by a mathematical analysis based on condition numbers of matrices constructed by the finite difference method. A method of selecting an effective combination to get an accurate numerical solution was obtained by the present analysis. Furthermore, the validity of the present analysis was confirmed by a numerical experiment.