Junichi Ohta

PIV measurement of particle motion in spiral gas-solid two-phase flow

Abstract With a concise review on some basic and novel algorithms and methods for the techniques of particle-imaging velocimetry (PIV), the paper reports an application of the PIV techniques to the investigation of particle motion in a gas–solid two-phase spiral flow in a horizontal tube. Axial velocities of the transported particles are obtained. Some important features of particle motion governing high transportation efficiency of the spiral flow are revealed by investigating probability density distribution of particle locations in a pipe cross-section.

An appraisal method of exergy cost minimisation for co-generation systems

This study introduces an exergy cost-minimisation appraisal method for a simple gas turbine co-generation system. Optimisation of a gas turbine co-generation system of the electric output class of 17 MW is examined for a variety of turbine inlet temperatures of 950–1,300°C. An optimum value of the turbine inlet temperature exists for exergy cost minimisation and is estimated to be 1,200°C since the manufacturing price of the gas turbine increases greatly above 1,300°C. This fact shows that the rising manufacturing cost of the gas turbine constitutes an important effect for future development of higher temperature systems.

Distribution Characteristics of a Solid-Liquid Two-Phase Flow by using a T-Junction (2nd Report, Bifurcating from Vertical to Horizontal Direction)

A solid-liquid two-phase mixture (water and aluminum particles) was vertically led to a T-junction. Particle number densities (number of particles per volume) at the outlets were measured at inlet concentrations of (1.7-9.2) ×10-3%, Reynolds number ranging from 12000 to 19000, and Stokes number of 0.45 to 4.3. As a result, we found a velocity ratio (branch velocity/inlet velocity) range where solid particles did not enter the branch of the T-junction with the vertical orientation. The present data at lower inlet concentrations was compared with those obtained by Nasr-El-Din at higher inlet concentrations, i.e., 3 to 26%. We found that dimensionless concentrations at the branch (the present data) were higher than those obtained by Nasr-El-Din. Our dimensionless particle number density at the branch for the T-junction with the vertical orientation was found to be higher than those with the horizontal T-junction at similar inlet concentrations.

Distribution Characteristics of a Solid-liquid Two-phase Flow by Using a T-junction : 1st Report, Horizontal Inlet Tube with a Vertical Branch

A solid-liquid two-phase mixture (water and aluminum particles) is horizontally led to a T-junction. The particle number densities (number of particles per volume) at the outlets are measured in the inlet concentration of (0.9-16.8) ×10-3%, at the velocity ratio of the outlet to the inlet as the parameter. The diameter of tube in the T-junction is 10 mm, Stokes number ranges with 0.14 to 6.6, and liquid Reynolds number ranges with 9300 to 13000. The relationship between the particle number densities in the two outlets is obtained by a one-dimensional model. We compare the measured particle number density in the branch with the concentration obtained by Nasr-El-Din whose inlet concentration is 3 to 26%. The followings are obtained. The one-dimensional model can express the relationship between the concentrations of the two outlets. The present distribution characteristics of the T-junction show the same tendency as Nasr-El-Dins. However, the gradient of particle number density with respect to velocity ratio for the low concentration at the inlet is greater than that for high concentration data.

Measurement of Particle Location using Holography

The objective of this study is to apply holography to three-dimensional location measurement of particles. We made experiments using the behind scattering beam type ofF-axis holography with an Ar-Ion Laser. We measured three-dimensional coordinates of particles as follows: Centers of gravity for the particles in a 3-D space were measured by the moment method using a stack of x-y cross-section(slice in the depth direction), y-z cross-section, and x-z cross-section images. The present method is verified. Furthermore, a reconstructed image is showed in a 3-D space.

Bubble Behavior in a Horizontal Narrow Divergent Passage (One-Dimensional Approximate Analysis)

This paper investigates the behavior of a bubble which bridges the gap in a cross section of a horizontal narrow divergent passage under Earths gravity conditions ( 1 G) analytically. In a narrow passage, inertia forces are known to be small compared with viscous forces. Also, gravity force is not dominant for bubble behavior in a horizontal narrow passage. In this sense, the bubble behavior in the passage is similar to that under microgravity conditions. It is important to understand the bubble behavior in relation to separating gas from a gas-liquid two-phase flow and controlling a gas-liquid interface under microgravity conditions. A one-dimensional momentum equation for the bubble behavior is derived. The equation is arranged as an ordinary differential equation with respect to the upstream interfacial location and is solved. Analytical results are compared with experimental ones. As a result, the effects of gap size, bubble projected area, and divergent angle on bubble behavior are explained qualitatively.

Experiments on Bubble Behavior in a Horizontal Narrow Divergent Passage

We investigate a bubble, placed so that it bridges the cross section of a horizontal narrow divergent passage under Earth gravity (1-G). In a narrow passage, inertial forces are known to be small in comparison with viscous forces. Gravitational force is not dominant in bubble behavior in a horizontal narrow passage under the 1-G condition. In this sense, the bubble behavior in the passage is similar to that under a low-gravity condition. Understanding bubble behavior is important in relation to separating a gas from a two-phase gas-liquid flow and controlling a gas-liquid interface under low-gravity conditions. Thus, a single bubble is placed under the 1-G condition. The bubble geometry and its behavior are studied experimentally for gap sizes ranging from 0.5 mm to 2 mm and divergent angles from 1° to 5° using ethyl alcohol as the working fluid. The following results were obtained: (1) the bubble was found to move to the greater cross-sectional area; (2) the gas-liquid interface geometry in a top view can be expressed as a contact circle model that takes the maximum radius in the passage; and (3) the effects of gap size and the projected bubble area on bubble behavior are clarified

Bubble Behavior in a Horizontal Narrow Divergent Passage. One Dimensional Approximate Analysis.

The authors investigate the behavior of a bubble which bridges a gap in a cross section of a horizontal narrow divergent passage under the Earths gravity condition (1G). In a narrow passage, inertia forces are known to be small compared with viscous forces. Also, gravity force is not dominant for bubble behavior in a horizontal narrow passage. In this sense, the bubble behavior in the passage is similar to that under a microgravity condition. It is important to understand the bubble behavior in relation to separating gas from a gas-liquid two-phase flow and controlling a gas-liquid interface under a microgravity condition. A one-dimensional momentum equation for the bubble behavior was derived. The equation was converted into an ordinary differential equation with respect to the upstream interface and was solved. Analytical results were compared with experimental data. As a result, effects of gap size, bubble projected area, and divergent angle on the bubble behavior were explained qualitatively.

Particle Motion in the Linear Shear Duct Flow

The present study is concerned with particle motion in the linear shear flows with constant velocity gradient in a duct. Effects of the velocity gradients at a high Reynolds number on lift acted on a spherical particle are investigated by photographing trajectories of particles suspending in the shear flows using a high speed video and numerical simulation of particle distribution in the duct using the method of Direct Simulation Monte Carlo. The Reynolds number (relative air velocity×particle diameter/kinematic viscosity of air) is ranging from 950 to 2700. The characteristics of the duct flows are discussed after measuring the velocity, and turbulence intensity, or auto-correlation and cross-correlation using hot-wire anemometer and FFT digital spectrum analyzer in order to make clear that the test duct is suitable to the experiments. In the numerical simulation by DSMC the particle-particle and particle-duct wall collisions are taken into account. From the results of numerical simulation, it is shown that particles move from the higher velocity side to the lower velocity side of the shear flows, and this result agrees with the high speed video picture of particle trajectories in the near part downstream of the particle supply part. But, in the far part, particles are scattered randomly due to the particle collisions. In conclusion, It is made clear that lift is applied on a sphere from the higher velocity side to the lower velocity side on the linear shear flows at high Reynolds number.The present study is concerned with particle motion in the linear shear flows with constant velocity gradient in a duct. Effects of the velocity gradients at a high Reynolds number on lift acted on a spherical particle are investigated by photographing trajectories of particles suspending in the shear flows using a high speed video and numerical simulation of particle distribution in the duct using the method of Direct Simulation Monte Carlo. The Reynolds number (relative air velocity×particle diameter/kinematic viscosity of air) is ranging from 950 to 2700. The characteristics of the duct flows are discussed after measuring the velocity, and turbulence intensity, or auto-correlation and cross-correlation using hot-wire anemometer and FFT digital spectrum analyzer in order to make clear that the test duct is suitable to the experiments. In the numerical simulation by DSMC the particle-particle and particle-duct wall collisions are taken into account. From the results of numerical simulation, it is shown that particles move from the higher velocity side to the lower velocity side of the shear flows, and this result agrees with the high speed video picture of particle trajectories in the near part downstream of the particle supply part. But, in the far part, particles are scattered randomly due to the particle collisions. In conclusion, It is made clear that lift is applied on a sphere from the higher velocity side to the lower velocity side on the linear shear flows at high Reynolds number.

2D PTV Based on Binary Correlation Method and Its Application to Fluctuating Flows

A two-dimensional particle tracking velocimetry (2D-PTV) based on binary correlation method which has been proposed by the authors before is applied to measure fluctuating flows around two circular cylinders. The experiments are carried out in the three types of tow cylinder arrangements: (a) tandem, (b) side by side, and (c) staggered. Analyzing the pictures of the flows visualized by the hydrogen bubble technique, instantaneous velocity distribution, root mean square (RMS) values of the fluctuating parts of the flows, streamlines and vorticity contours are obtained. From these experimental data the flow mechanism are discussed.