Yoshinobu Morikawa

LDV measurements of an air-solid two-phase flow in a vertical pipe

Measurements of air and solid-particle velocities were made in a vertical pipe two-phase flow by the use of a laser-Doppler velocimeter (LDV). Five kinds of plastic particles, diameters of which ranged from about 3 mm to 200 μm, were transported in a vertical pipe of 30 mm inner diameter. It was found that, the smaller the particle size, the flatter was the mean air velocity distribution for the same mass flow ratio of solids to air. Large particles increased air turbulence throughout the pipe section, while small particles reduced it. Both effects of promotion and suppression of turbulence were observed at the same time in the presence of particles of medium size, that is, the turbulence was increased around the pipe centre and reduced near the wall. The frequency spectrum of air turbulence normalized by the turbulence intensity was not changed by the large particles. In the presence of the small particles, the higher-frequency parts of the spectrum increased.

LDV measurements of an air–-solid two-phase flow in a horizontal pipe

Measurements of air and solid velocities were made in an air-solid two-phase flow in a horizontal pipe by the use of a laser-Doppler velocimeter (LDV). The pipe was 30 mm inner diameter, and two kinds of plastic particles, 0.2 and 3.4 mm in diameter, were conveyed in addition to fine particles (ammonium chloride) for air-flow detection. The air velocities averaged over the pipe cross section ranged from 6 to 20m/s and the solid-to-air mass-flow ratio was up to 6. Simultaneous measurements of both air and 0.2 mm particle velocities were found possible by setting threshold values against the pedestal and Doppler components of the photomultiplier signal. As the loading ratio increased and the air velocity decreased, mean-velocity distributions of both phases increased asymmetrical tendency. I n the presence of 0.2mm particles, a flattening of the velocity profile was remarkable. The effects of the solid particles on air-flow turbulence varied greatly with particle size. That is, 3.4 mm particles increased the turbulence markedly, while 0-2 mm ones reduced it. The probability-density function of the air flow deviated from the normal distribution (Gaussian) in the presence of particles. Finally, the frequency spectra of air-flow turbulence were obtained in the presence of 0.2 mm particles by using a fast Fourier transform (FFT). As a result, it was found that t,he higher-frequency components increased with increasing loading ratio.

Numerical simulation of gas-solid two-phase flow in a two-dimensional horizontal channel

Abstract A numerical simulation was made to determine the motion of particles and fluid in a horizontal channel. The simulation was based on the Lagrangian method for the solid phase, where trajectories of many particles are calculated by integrating the equations of motion of a single particle. The fluid motion was solved using a finite-difference method simultaneously with the particle motion. The present simulation requires some empirical parameters concerning the collision of the particles with the wall. These parameters were determined by comparisons between calculated results and measurements.

Fluid-dynamic interaction between two spheres

Abstract Experiment of fluid-dynamic interaction between two spheres was conducted to obtain basic information concerning the two-phase flow, especially in dense phase. Two or three spheres were set up in a water tunnel in the longitudinal or transverse direction with Reynolds numbers less than 10 3 . The flow behind the sphere was visualized by the use of condense milk and change in vortex structure due to the interaction was observed in detail. Additionally, drag force on the sphere was measured by a pendulum method which was developed to detect small drag, and the range of distance in which the drag is affected by the interaction was shown.

Measurement of an axisymmetric jet laden with coarse particles

Abstract Axisymmetric particle-laden jets were measured using three different devices: a Pitot tube, an LDV (laser Doppler velocimeter) and a specially designed optical fiber probe. Particle sizes in the present experiment ranged from 170 to 1400 μm, which is larger than in most previous works. Results are presented for particle and air velocities, particle concentration and air turbulence. Particle diffusion was unexpectedly large. A delay in the decrease of the centerline air velocity and a reduction in the jet width were observed, as in jets laden with fine particles, but the magnitude of such particle effects on the air flow is less with large particles than with small particles for the same loading ratio.

Flow pattern and pressure fluctuation in air-solid two-phase flow in a pipe at low air velocities

Abstract An experiment was made on an air-solid two-phase flow in a horizontal pipe. The main concern was the relation between flow patterns and pressure fluctuation at low air velocities. First, the flow patterns were classified into five different types depending on the air and particle flow rates. Next, it was shown how the properties of pressure fluctuation change as the air velocity decreases. Further, fluctuation signals were analyzed in detail and differences due to the flow patterns and particle size were discussed.

Pressure drops due to pipe bends in air-solids two phase flows; circular and elliptical bends

Since the design of pneumatic transport equipment requires a correct estimate of the pressure drop at pipe bends, many investigations have been made of this configuration. This work deals with the case of a bend having a form of a quarter ellipse as shown in figure 1. When the elliptical bend replaces a circular bend with a long sweep at the upstream and a short radius at the downstream end, one expects that erosion per unit surface is reduced (Zenz & Othmer 1960). The reason is that impact points of particles against the pipe wall are distributed over a wider area compared with the circular bend. However, information about the pressure drop due to the elliptical bend are unavailable, not only in two-phase flows but also in single phase flows. Therefore, the pressure drops due to the elliptical bends of different sizes and shapes were measured in the present work. To investigate the relationship between the elliptical and circular bends, measurements were made also for the circular bend. From those measurements, an empirical formula predicting the pressure drop is proposed. 2. EXPERIMENTAL ARRANGEMENT A suction type of pneumatic conveying system, shown in figure 2, was used. A blower 7, installed after a cyclone separator 6, drew the air-solids mixture through the pipe line. The internal diameter of the test pipe, D, was 40 ram. The bend 4 is made of vinyl chloride. Table 1 shows the dimensions of the bends used in this experiment. The straight pipes in the upstream

PIPE FLOW WITH SOLID PARTICLES FIXED IN SPACE

Abstract A group of solid particles were hung by slender rods in a pipe to make a model of two-phase flow of coarse particles. Pressure gradient and velocities were measured for different types of the models. The drag on the particles (spheres) were obtained from measurements of pressure gradient with some assumptions. The results are summarized as follows. (1) Mean velocities of fluid are lower in the central part of the pipe than in the circumferential part. Turbulence is remarkably increased by particles. The spectrum distribution of turbulent velocity becomes flatter. These results are similar to the gas-solid flow of coarse particles in a vertical pipe. (2) At a large Reynolds number, the drag coefficient per one sphere in the group is larger than that of a single isolated sphere in a uniform flow. When the spheres are arranged along the same line in the longitudinal direction, the drag coefficient becomes smaller as the longitudinal distance between the spheres is shortened.

Pressure drop and solids distribution of air-solids mixture in horizontal unsymmetric branches

Abstract From the experimental results obtained under various combinations of branch angles the effects of branch angles, discharge ratios Of air into the branehed pipe and solid-air loading ratios on the pressure drop due to branching was considered. It was shown that the coefficients of additional pressure drop due to the solids, is proportional to solid-air loading ratios in the branched pipe and independent of branch angle of another branched pipe. The mass flow rate of coarse particles into the branched pipe is not controlled by the discharge ratios of air, and approximately determined by the ratio of the projected area of branched pipe on the plane vertical to the axis of the main pipe to the cross-sectional area of the main pipe.

Measurements of a Solid-Liquid Turbulent Boundary Layer

The structure of turbulence was investigated experimentally in a particle laden turbulent boundary layer flowing vertically. Measurements were made on motions of particles and fluid. Also, spectra of fluid turbulence were obtained. It was found that instability occurring in the outer-layer causes large fluctuations in fluid and particle motions and that spectrum components at high wave numbers become larger due to the presence of particles.