It is important to measure the volume solid concentration and solid concentration distribution of solids-liquid two-phase flow in pipes, since measuring these parameters contributes to make the mechanism of the flow clear and to control the condition of the flow. A review of the state of measuring techniques for the concentration and the distribution is presented in this paper. This report focuses on the typical conventional methods, probe method and image processing concerning the concentration and the distribution.
Three-phase flows are encountered in air-lift pumps, preheaters and reactors, and other industrial plants. It is necessary to clarify not only macroscopic characteristics such as pressure drops and volume fractions of each phase but also local characteristics such as spatial distnbutions of local volume fractions and local velocities of each phase. In the present review, measurement techniques of volumetric fluxes and volumetric fractions of each phase, radial distributions of gas and solid volume fractions and liquid velocities were described for the three-phase bubbly flow. Those of length and velocities of large bubble liquid slug and film thickness of large bubble were also described for the three-phase slug flow Furthermore, application of measurement techniques for two-phase flows to three-phase flows were examined.
Flow patterns of settling slurry flow in a horizontal pipe can be represented graphically on the pressure drop-flow rate relation at a constant concentration, because the mechanism of pressure drop depends makedly on the flow regimes: stationary bed, sliding bed or moving bed, saltation flow, heterogeneous flow, and pseudo-homogeneous flow. Although it is difficult to clarify the sharp boundaries between these categories, the criterion based on concentration distributions may be one of the most effective parameters that depend on the degree of homogeneity. The main objective of this paper is, therefore, to discuss criteria for determining flow patterns and an analytical method of concentration distributions, introducing an interesting method of displaying solids flow behavior on a monitoring screen.
Solid-Liquid two-phase flows are frequently encountered in both industrial and global environmental fields such as chemical engineering, mechanical engineering, civil engineering, drift ice, icebergs and so on. Importance of the flows is growing in the above both fields. Measuring velocities of dispersed solid phase is essential for deep understanding of the flows. In this report, first, summary of measuring methods of the velocities is described.Second, simple and easy methods, namely probe method, and visualization of the flow fields and digital image processing, are discussed.
Upward flows of air-water two-phase mixture formed in 24mm and 64mm dia., long vertical pipes were observed to obtain further knowledge of development process from a bubbly flow to a slugflow. The vertical pipes had 13m length in height and were made of transparent acrylic resin. Ascending motions of the air bubbles in the pipe were tracked by a CCD camera, which was able to move along the vertical pipe. Flow pattern maps were described on a z-jG plane, here z is a height measured from thebottom of the pipe and jG is a superficial air velocity. Bubbly flows including bubble clusters wereobserved in both 24mm and 64mm pipes. However, slug formation processes were much different between 24mm and 64mm pipes, even if the air entrance conditions were same. By coalescence of bubbles in the 24mm pipe, large Taylor type bubbles were formed from the bubble clusters. However, thebubble clusters in the 64mm pipe did not grow up directly to the Taylor type bubbles. They grew up to large bubbles when the relatively large cap type bubbles were formed from the air nozzle set at the bottom of the pipe.
A subchannel analysis code based on a two-fluid model has been proposed and used to calculate two-phase gas-liquid flow redistribution due to void drift between subchannels.In the code, Lahey et al.'s void settling model was incorporated with usual conservation equations of mass and momentum.And then, in order to refine the code, constitutive equations of wall friction, FW, and interfacial friction, F1, needed in the two-fluid model were examined against the redistribution data in our previous experiments.From the examination, it was proved that the FW should be calculated from a separated flow model, and FI from a correlation depending upon the void fraction, α: Tomiyama et al.'s correlation for 0.4<α<0.7, interpolation equation with Tomiyama et al.'s and Fukano & Furukawa's correlation for 0.7<α<0.8, Fukano & Furukawa's correlation for 0.8<α<0.9, and Wallis' correlation incorporated with liquid entrainment effects in the gas core in annular flow for α>0.9.
This paper deals with a method of discriminating microbubbles from images of bubbly water taken by one CCD camera and of determining their diameter and number density. The diameters of nearly spherical microbubbles and the ratio of the shortest semi-axis to the longest one are determined from bubble images, and the ratio is used to separate the defocused bubbles far from the measuring domain. The ratio of the minimum and the maximum gray level of microbubble in the focal field of the CCD camera is used to discriminate bubbles inside an observation field. It is shown that the effective depth of the observation field is 200μm in the present experimental set-up. It is concluded that the method can be applied to determine diameter and number density of microbubbles.