Goichi Matsui

Identification of flow regimes in vertical gas-liquid two-phase flow using differential pressure fluctuations

Abstract Differential pressure fluctuations are used to estimate flow regimes of nitrogen gas-water mixtures in a vertical pipe because the fluctuations seem to be closely connected with the flow configuration. The regimes of vertical two-phase flow are classified by the peculiar features of statistical properties of the fluctuations, which are calculated from the data of static pressures measured at four locations along the flow direction. The results show that it is possible to identify the flow pattern from the configuration of probability density functions, the order of variance and the average value of differential pressures because these statistical properties depend on a flow pattern.

Automatic identification of flow regimes in vertical two-phase flow using differential pressure fluctuations

Abstract Differential pressure fluctuations are used to identify the flow regimes of nitrogen gas-water mixtures in a vertical pipe because the fluctuations are determined to be closely connected with the flow configuration. The regimes of vertical two-phase flow are classified by the characteristic features of the statistical properties of differential pressure fluctuations measured at two kinds of rational intervals. The results have shown that it is possible to identify the flow pattern based not on visual observations but on the shape of frequency distributions, the order of variance and the average value of differential pressures, because these statistical properties depend on the flow regimes. Furthermore, to identify the flow patterns automatically, the configuration of frequency distribution is approximated by use of the Gram-Charlier series. Then it is shown that the configuration of fitted frequency curves can be discriminated by the statistical parameters associated with the coefficients of the Gram-Charlier series, such as the mean, standard deviation, coefficient of skewness, and coefficient of excess. On the basis of these data, a flow chart is constructed and an objective and automatic identification technique of flow pattern is proposed.

New measurement method for very low liquid flow rates using ultrasound

Abstract A very small ultrasonic flowmeter for liquids with measuring pipe diameter down to 0.5 mm was developed using disk ultrasonic transducers. The transducer has a hole in the center and the measuring pipe passes through the hole. The vibration mode in the radial direction of the transducer was used, and ultrasound was transmitted and received from outside the pipe wall. The flowmeter can measure a liquid flow rate below 1 ml/min, which corresponds to a Reynolds number of about 40 based on the measuring pipe diameter. The standard deviation of flow rate measurement was 0.01 ml/min (1%) at the flow rate of 1 ml/min.

Measurement of particle/bubble motion and turbulence around it by hybrid PIV

Abstract Characteristics of bubble flow are influenced by bubble motion, liquid flow and interactions between bubbles, and between a bubble and liquid phase. Thus because behavior of a single bubble and liquid around it is regarded as one of the basic elements characterizing bubble flow, the single bubble motion in stagnant water was investigated experimentally by using flow visualization and image processing methods. The bubble motion is influenced by several factors, that is, bubble size, density difference between gas and liquid, bubble shape and deformation in motion. In order to separate the effect of each factor, some solid particles with different size, shape and/or density were also measured and the characteristic of each factor was discussed. Two-dimensional water velocity field and the motion of a rising particle/bubble in the water were simultaneously measured by PIV (Particle Image Velocimetry) and PTV (Particle Tracking Velocimetry), respectively (Hybrid PIV). The experimental results showed that the large density difference between a particle and water caused high relative velocity and induced zigzag motion of the particle. Furthermore, the turbulence intensity of a bubble was about twice in the case of the spherical solid particle of similar diameter.

Visualization of bubble-fluid interaction by a moving object flow image analyzer system.

Abstract: This paper deals with interaction between a bubble and fluid around it, visualized by a moving object flow image analyzer (MOFIA) consisting of a three‐dimensional (3D) moving object image analyzer (MOIA) and two‐dimensional particle image velocimetry (PIV). The experiments were carried out for rising bubbles of various sizes and shapes in stagnant water in a vertical pipe. In the MOFIA employed, 3D‐MOIA was used to measure bubble motion and PIV to measure fluid flow. The 3D position and shape of a bubble and the velocity field were measured simultaneously. The experimental results showed that the interaction was characterized by the shape, size and density of a bubble. Concretely, they showed the characteristics of bubble motion, wake shedding, and flow field.

Effect of Interfacial Area on Flow Characteristics in Bubble Flow

Bubble flow is one of familiar patterns of two-phase flow which we encounter or use frequently in various energy conversion systems and industrial plant such as nuclear reactors, boilers, chemical plant, and air-lift pumps. But bubble flow exhibits inherent properties in the internal flow structures namely distributions of gas phase, phase velocities, and their fluctuations depending on the flow conditions and/or complex interactions between bubbles and liquid or a channel wall. Therefore, in order to improve the efficiency of the systems or apparatus using bubble flows and to guarantee their safe opertions, it is essential to know not only the global flow characteristics but also the local flow charcteristics. However, the mechanism of bubble flows has not been perfectly clear yet.

Visualization and Measurement of Mixing Process of Particles Into Water Jet

A mixing process of catalyst particles into a fluid jet is a key part in a chemical reactor because the efficiency of chemical reaction depends on the particle catalyst distribution. Therefore, a mixing process of polystyrene particles into a water jet was investigated experimentally as a basic study of flow with catalysts in the chemical reactor. The velocity fields of both water and particles were measured by image processing. The main results obtained are as follows. The particle velocity approached to the water velocity at the mixing process, when the particles were entrained into the water jet. Because the particle concentration was very low, the velocity distributions were not changed by the addition of the particles. However, the turbulent intensity of the water increased comparing with the case of the water single phase jet.Copyright

Characteristics of Main Flow Patterns on Statisitcal Parameter Space in Gas-Liquid Two-Phase Flow.

Flow pattern identification using gas-phase fluctuations is studied analytically. The fundamental waveform of periodic gas-phase or void fraction fluctuations for steady two-phase flow is assumed based on the real waveform of gas-phase fluctuations. The structure of the fundamental wave includes some main flow patterns. Thus the statistical parameter characteristics are directly related to flow structure. That is, the parameter characteristics on the parameter space are revealed, because the parameters of the assumed fluctuations can be calculated for given flow patterns. The results show that for slug or plug flow the relationship between the mean and the standard deviation is described by an equation of a half circle, and that the relationship between the coefficients skewness and excess is described by a quadratic equation in those flows. For bubble, annular or separated flow, the coefficient of skewness is larger than zero, because the flow has a flat or direct-current-like part in the fundamental waveform.

A Theoretical Study of Turbulent Energy Spectra in Stably Stratified Shear Flow.

Turbulent energy spectra in stably stratified shear flow were studied theoretically based on the turbulent spectral equation and the experimental results. A theoretical expression of the turbulent energy spectra was derived for the inertial subrange. According to this expression, the energy spectra of the stably stratified shear flow approached those of isothermal shear flow as the wave number increased, and the difference in energy spectra between stratified and isothermal flows was directly proportional to the -3rd power of the wave number. The one-dimensional energy spectrum obtained experimentally conformed to the expression.