Haruki Madarame

Velocity measurement of both red blood cells and plasma of in vitro blood flow using high-speed micro PIV technique

This paper describes a new high-speed micro PIV technique for measuring both red blood cell velocity and plasma velocity to investigate rheology of blood flow in microcirculation. The measurement system consists of an epi-fluorescent microscope equipped with a high-speed camera with an image intensifier and two sets of colour filters. The technique was applied to in vitro blood flow through a micro round tube of 100 µm diameter. Velocity distributions of dyed red blood cells and plasma seeded with fluorescent particles were obtained separately. The obtained velocity distributions have a high spatial resolution of 9.0 µm × 2.2 µm and high temporal resolution of 6000 Hz.

Measurement of pH field of chemically reacting flow in microfluidic devices by laser-induced fluorescence

The interaction between chemical reactions and the flow field in microfluidic devices is investigated by a laser-induced fluorescence technique refined for use at microscopic spatial resolution. The pH distribution of chemically reacting flow at a Y-junction in a neutralization reaction in a microfluidic device is successfully visualized at a spatial resolution of 0.89 µm × 0.89 µm.

Time-resolved proper orthogonal decomposition of the near-field flow of a round jet measured by dynamic particle image velocimetry

In this study time-resolved proper orthogonal decomposition (POD) is proposed for the new technique of dynamic (digital) particle image velocimetry (DPIV), and applied to study the coherent structures at the near field of a round jet flow. Time-resolved POD is computed in the radial direction, the axial direction and the temporal domain, in which the turbulence can be easily measured by DPIV. As a result, large-scale vortical structures and their spatial and temporal evolution at the round jet mixing layer are uncovered.

The development of PIV–PSP hybrid system using pressure sensitive particles

A method for visualizing the spatial distribution of oxygen using particles coated with pressure-sensitive dye is presented. The proposed technique, called the PSParticle method, is a hybrid system combining the technologies of pressure-sensitive paint (PSP) and particle image velocimetry (PIV) and allows the particle velocity and oxygen distribution to be measured simultaneously. As intensity-based imaging is not applicable in this system, a luminescence lifetime-based imaging technique involving double frame imaging is introduced. The system is calibrated and demonstrated in application to measurement of the oxygen distribution in an air jet.

Gas entrainment inception at the border of a flow-swollen liquid surface

Abstract A rapid liquid flow into a tank may impinge on the free surface, making it swell partially. The returning flow branches off from the free surface and re-submerges at the border of the swollen surface. If the flow velocity along the swollen surface is high enough, gas bubbles are formed at the border and entrained by the liquid flow. The conditions necessary for gas entrainment in a simple system are examined experimentally, using water and air as working fluids. The effect of surface tension is examined by adding a surface active agent to the water. The results show that gas entrainment inception is determined by the flow pattern in the system and the product of the Froude and Weber numbers based on the local velocity at the bubble formation point.

Flow observation in two immiscible liquid layers subject to a horizontal temperature gradient

Abstract Marangoni convection, driven by an interfacial instability due to a surface tension gradient, has become a significant problem in the crystal growth on the ground or in a microgravity environment. To suppress and control the convection is important for material processing. Especially in the crystal growth by liquid encapsulated czochralski or liquid encapsulated floating zone technique, in which the melt is encapsulated with an immiscible medium, Marangoni convection can occur on the liquid–liquid interface and on the gas–liquid free surface. In the present paper, experiments were carried out with a double liquid layer of silicone oil and fluorinert both in an open-boat system and in an enclosed system. Flow in a cavity subject to a horizontal temperature gradient was observed. An interactive flow near the interface was measured by using particle image velocimetry technique. The measured flow field seemed to agree sufficiently with the numerical prediction.

Reconstruction of Transient Three-dimensional Density Distributions Using Digital Speckle Tomography

A form of digital speckle tomography has been proposed for calculating transient three-dimensional density distributions. Multiple CCD images have captured movements of speckles due to the variation in density among three angles of view simultaneously and instantaneously so that asymmetrical and transient flows can be measured. Initially, the variations in density of one-nozzle and two-nozzle test sections have been investigated by the use of a cross-correlation method involving the speckle displacements. The results have been compared with measurements made by Mach-Zehnder interferometry to confirm the accuracy. Then, the speckle movements for downward flow of carbon dioxide from a circular small opening with a vertical partition (CO2-air exchange flow) have been obtained by the cross-correlation tracking method so that those distances can be transformed into deflection angles of laser rays for density gradients. The transient three-dimensional density fields have been reconstructed from the deflection angles by tomography.

Instability of Single-phase Natural Circulation Under Double Loop Systemfn1

Abstract The natural circulation in a single loop system has been studied by many researchers. In a multiple loop system, the instability of natural circulation is more complicated because of the interaction between the loops. In this study, the effects of the multiple loops on the natural circulation instability were investigated numerically. The double loop system with one heating tube and two cooling tubes were evaluated. The one-dimensional energy and momentum equations were solved using the Finite Difference Method. The flow regimes of the instability were evaluated with variations in the heat flux and the initial velocity condition. In a double loop system, the observed flow was classified into five regimes, namely, steady, transient–CS, transient–CS⧹CL, transient–CL and complex chaotic regimes, which were more complicated than those observed in single loop system. The flow regimes were qualitatively explained by the stability of the attractor in the phase space. The complexity of the regime was caused by the coexistence of two attractors.

Numerical analysis of the plasma-material interaction during the thermal quench phase of tokamak disruptions

Plasma disruptions in a next generation tokamak will cause high surface energy deposition on the surface of the plasma facing components. After the onset of the energy deposition a series of complex processes develops which are commonly termed as “vapour shielding”. The vapour shield developing in front of the heated material surface may attenuate a part of the incident energy and cause a reduction in the energy which is actually deposited in the plasma facing material. The present paper describes a numerical model for these processes which includes the thermophysical response of the plasma facing material, the magnetohydrodynamic development of the plasma vapour cloud, and the radiation transfer within the vapour cloud. Results of the calculations for an incident energy of 10 MJ m −2 during 0.1 ms using the local thermodynamic equilibrium model are presented. Compared to a calculation without vapour shield the carbon erosion is reduced by 98.9%.

Effect of impurity content in stainless steel on resolidified surface condition after disruption load

Plasma disruptions in tokamaks may cause melting of the surface layer of first walls. If the layer resolidifies without any movement, the same layer repeatedly melts and protects the rest of the wall. A number of stainless steel samples were irradiated by a neutral beam injector. After irradiation tests with the same condition, some had wavy resolidification surfaces with dents, while some had smooth surfaces. In the former samples, the amplitude of the roughness increased by repetitive heat loads. The melt layer moved to the convex areas, which deepened the dents on each occasion. Sulphur was found to be one of the harmful elements which promotes the formation of the wavy surface. It is recommended to be kept below 0.005 wt% for obtaining a uniform resolidification surface. Even if samples have a low sulphur content, a high oxygen content also makes the surface rough. Other impurities have some effects, but they have not been clarified yet.